From c73b0a35a1dfa9bdd51c2856dfa6f543def358b4 Mon Sep 17 00:00:00 2001
From: Andrew Nesbitt <andrewnez@gmail.com>
Date: Mon, 27 Apr 2026 12:04:38 +0100
Subject: [PATCH 01/36] Add direct-serve via presigned storage URLs

When storage.direct_serve is enabled and the backend supports it (S3,
Azure), cached artifact downloads return a 302 redirect to a presigned
URL instead of streaming bytes through the proxy. Falls back to
streaming when the backend can't sign (fileblob, local filesystem) or
signing fails.

Adds the azureblob driver so azblob:// storage URLs work.

Cache-hit accounting already happened before io.Copy so redirects are
counted correctly; the metrics calls are pulled into a helper so both
paths share them.

Closes #96
---
 config.example.yaml                 |   9 ++
 go.mod                              |  16 +++
 go.sum                              |  27 +++++
 internal/config/config.go           |  48 ++++++++-
 internal/config/config_test.go      |  51 +++++++++
 internal/handler/handler.go         |  70 +++++++++----
 internal/handler/handler_test.go    | 157 +++++++++++++++++++++++++++-
 internal/server/server.go           |   2 +
 internal/storage/blob.go            |  17 +++
 internal/storage/blob_test.go       |  13 +++
 internal/storage/filesystem.go      |   5 +
 internal/storage/filesystem_test.go |  10 ++
 internal/storage/storage.go         |   9 ++
 13 files changed, 407 insertions(+), 27 deletions(-)

diff --git a/config.example.yaml b/config.example.yaml
index ea17d15..c272979 100644
--- a/config.example.yaml
+++ b/config.example.yaml
@@ -29,6 +29,15 @@ storage:
   # Empty or "0" means unlimited
   max_size: ""
 
+  # Redirect cached artifact downloads to presigned storage URLs (HTTP 302)
+  # instead of streaming through the proxy. Only effective for S3 and Azure.
+  # Leave disabled if clients reach the proxy through an authenticating gateway,
+  # since presigned URLs bypass it.
+  direct_serve: false
+
+  # How long presigned URLs remain valid (e.g. "5m", "1h"). Default: "15m".
+  direct_serve_ttl: "15m"
+
 # Database configuration
 database:
   # Database driver: "sqlite" (default) or "postgres"
diff --git a/go.mod b/go.mod
index 1067a3a..6226ab6 100644
--- a/go.mod
+++ b/go.mod
@@ -28,6 +28,8 @@ require (
 require (
 	4d63.com/gocheckcompilerdirectives v1.3.0 // indirect
 	4d63.com/gochecknoglobals v0.2.2 // indirect
+	cloud.google.com/go/auth v0.18.2 // indirect
+	cloud.google.com/go/auth/oauth2adapt v0.2.8 // indirect
 	cloud.google.com/go/compute/metadata v0.9.0 // indirect
 	codeberg.org/chavacava/garif v0.2.0 // indirect
 	codeberg.org/polyfloyd/go-errorlint v1.9.0 // indirect
@@ -40,6 +42,13 @@ require (
 	github.com/Antonboom/errname v1.1.1 // indirect
 	github.com/Antonboom/nilnil v1.1.1 // indirect
 	github.com/Antonboom/testifylint v1.6.4 // indirect
+	github.com/Azure/azure-sdk-for-go/sdk/azcore v1.20.0 // indirect
+	github.com/Azure/azure-sdk-for-go/sdk/azidentity v1.13.1 // indirect
+	github.com/Azure/azure-sdk-for-go/sdk/internal v1.11.2 // indirect
+	github.com/Azure/azure-sdk-for-go/sdk/storage/azblob v1.6.3 // indirect
+	github.com/Azure/go-autorest v14.2.0+incompatible // indirect
+	github.com/Azure/go-autorest/autorest/to v0.4.1 // indirect
+	github.com/AzureAD/microsoft-authentication-library-for-go v1.6.0 // indirect
 	github.com/BurntSushi/toml v1.6.0 // indirect
 	github.com/Djarvur/go-err113 v0.1.1 // indirect
 	github.com/KyleBanks/depth v1.2.1 // indirect
@@ -138,6 +147,7 @@ require (
 	github.com/gobwas/glob v0.2.3 // indirect
 	github.com/godoc-lint/godoc-lint v0.11.2 // indirect
 	github.com/gofrs/flock v0.13.0 // indirect
+	github.com/golang-jwt/jwt/v5 v5.3.0 // indirect
 	github.com/golangci/asciicheck v0.5.0 // indirect
 	github.com/golangci/dupl v0.0.0-20250308024227-f665c8d69b32 // indirect
 	github.com/golangci/go-printf-func-name v0.1.1 // indirect
@@ -150,8 +160,10 @@ require (
 	github.com/golangci/swaggoswag v0.0.0-20250504205917-77f2aca3143e // indirect
 	github.com/golangci/unconvert v0.0.0-20250410112200-a129a6e6413e // indirect
 	github.com/google/go-cmp v0.7.0 // indirect
+	github.com/google/s2a-go v0.1.9 // indirect
 	github.com/google/uuid v1.6.0 // indirect
 	github.com/google/wire v0.7.0 // indirect
+	github.com/googleapis/enterprise-certificate-proxy v0.3.12 // indirect
 	github.com/googleapis/gax-go/v2 v2.17.0 // indirect
 	github.com/gordonklaus/ineffassign v0.2.0 // indirect
 	github.com/gostaticanalysis/analysisutil v0.7.1 // indirect
@@ -174,6 +186,7 @@ require (
 	github.com/kkHAIKE/contextcheck v1.1.6 // indirect
 	github.com/kulti/thelper v0.7.1 // indirect
 	github.com/kunwardeep/paralleltest v1.0.15 // indirect
+	github.com/kylelemons/godebug v1.1.0 // indirect
 	github.com/lasiar/canonicalheader v1.1.2 // indirect
 	github.com/ldez/exptostd v0.4.5 // indirect
 	github.com/ldez/gomoddirectives v0.8.0 // indirect
@@ -209,6 +222,7 @@ require (
 	github.com/pandatix/go-cvss v0.6.2 // indirect
 	github.com/pelletier/go-toml v1.9.5 // indirect
 	github.com/pelletier/go-toml/v2 v2.2.4 // indirect
+	github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/prometheus/common v0.67.5 // indirect
 	github.com/prometheus/procfs v0.20.1 // indirect
@@ -277,10 +291,12 @@ require (
 	go.uber.org/zap v1.27.1 // indirect
 	go.yaml.in/yaml/v2 v2.4.3 // indirect
 	go.yaml.in/yaml/v3 v3.0.4 // indirect
+	golang.org/x/crypto v0.48.0 // indirect
 	golang.org/x/exp v0.0.0-20260218203240-3dfff04db8fa // indirect
 	golang.org/x/exp/typeparams v0.0.0-20260209203927-2842357ff358 // indirect
 	golang.org/x/mod v0.33.0 // indirect
 	golang.org/x/net v0.51.0 // indirect
+	golang.org/x/oauth2 v0.35.0 // indirect
 	golang.org/x/sys v0.42.0 // indirect
 	golang.org/x/text v0.34.0 // indirect
 	golang.org/x/tools v0.42.0 // indirect
diff --git a/go.sum b/go.sum
index 49b11f9..26647ed 100644
--- a/go.sum
+++ b/go.sum
@@ -43,6 +43,26 @@ github.com/Antonboom/nilnil v1.1.1 h1:9Mdr6BYd8WHCDngQnNVV0b554xyisFioEKi30sksuf
 github.com/Antonboom/nilnil v1.1.1/go.mod h1:yCyAmSw3doopbOWhJlVci+HuyNRuHJKIv6V2oYQa8II=
 github.com/Antonboom/testifylint v1.6.4 h1:gs9fUEy+egzxkEbq9P4cpcMB6/G0DYdMeiFS87UiqmQ=
 github.com/Antonboom/testifylint v1.6.4/go.mod h1:YO33FROXX2OoUfwjz8g+gUxQXio5i9qpVy7nXGbxDD4=
+github.com/Azure/azure-sdk-for-go/sdk/azcore v1.20.0 h1:JXg2dwJUmPB9JmtVmdEB16APJ7jurfbY5jnfXpJoRMc=
+github.com/Azure/azure-sdk-for-go/sdk/azcore v1.20.0/go.mod h1:YD5h/ldMsG0XiIw7PdyNhLxaM317eFh5yNLccNfGdyw=
+github.com/Azure/azure-sdk-for-go/sdk/azidentity v1.13.1 h1:Hk5QBxZQC1jb2Fwj6mpzme37xbCDdNTxU7O9eb5+LB4=
+github.com/Azure/azure-sdk-for-go/sdk/azidentity v1.13.1/go.mod h1:IYus9qsFobWIc2YVwe/WPjcnyCkPKtnHAqUYeebc8z0=
+github.com/Azure/azure-sdk-for-go/sdk/azidentity/cache v0.3.2 h1:yz1bePFlP5Vws5+8ez6T3HWXPmwOK7Yvq8QxDBD3SKY=
+github.com/Azure/azure-sdk-for-go/sdk/azidentity/cache v0.3.2/go.mod h1:Pa9ZNPuoNu/GztvBSKk9J1cDJW6vk/n0zLtV4mgd8N8=
+github.com/Azure/azure-sdk-for-go/sdk/internal v1.11.2 h1:9iefClla7iYpfYWdzPCRDozdmndjTm8DXdpCzPajMgA=
+github.com/Azure/azure-sdk-for-go/sdk/internal v1.11.2/go.mod h1:XtLgD3ZD34DAaVIIAyG3objl5DynM3CQ/vMcbBNJZGI=
+github.com/Azure/azure-sdk-for-go/sdk/resourcemanager/storage/armstorage v1.8.1 h1:/Zt+cDPnpC3OVDm/JKLOs7M2DKmLRIIp3XIx9pHHiig=
+github.com/Azure/azure-sdk-for-go/sdk/resourcemanager/storage/armstorage v1.8.1/go.mod h1:Ng3urmn6dYe8gnbCMoHHVl5APYz2txho3koEkV2o2HA=
+github.com/Azure/azure-sdk-for-go/sdk/storage/azblob v1.6.3 h1:ZJJNFaQ86GVKQ9ehwqyAFE6pIfyicpuJ8IkVaPBc6/4=
+github.com/Azure/azure-sdk-for-go/sdk/storage/azblob v1.6.3/go.mod h1:URuDvhmATVKqHBH9/0nOiNKk0+YcwfQ3WkK5PqHKxc8=
+github.com/Azure/go-autorest v14.2.0+incompatible h1:V5VMDjClD3GiElqLWO7mz2MxNAK/vTfRHdAubSIPRgs=
+github.com/Azure/go-autorest v14.2.0+incompatible/go.mod h1:r+4oMnoxhatjLLJ6zxSWATqVooLgysK6ZNox3g/xq24=
+github.com/Azure/go-autorest/autorest/to v0.4.1 h1:CxNHBqdzTr7rLtdrtb5CMjJcDut+WNGCVv7OmS5+lTc=
+github.com/Azure/go-autorest/autorest/to v0.4.1/go.mod h1:EtaofgU4zmtvn1zT2ARsjRFdq9vXx0YWtmElwL+GZ9M=
+github.com/AzureAD/microsoft-authentication-extensions-for-go/cache v0.1.1 h1:WJTmL004Abzc5wDB5VtZG2PJk5ndYDgVacGqfirKxjM=
+github.com/AzureAD/microsoft-authentication-extensions-for-go/cache v0.1.1/go.mod h1:tCcJZ0uHAmvjsVYzEFivsRTN00oz5BEsRgQHu5JZ9WE=
+github.com/AzureAD/microsoft-authentication-library-for-go v1.6.0 h1:XRzhVemXdgvJqCH0sFfrBUTnUJSBrBf7++ypk+twtRs=
+github.com/AzureAD/microsoft-authentication-library-for-go v1.6.0/go.mod h1:HKpQxkWaGLJ+D/5H8QRpyQXA1eKjxkFlOMwck5+33Jk=
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
 github.com/BurntSushi/toml v1.6.0 h1:dRaEfpa2VI55EwlIW72hMRHdWouJeRF7TPYhI+AUQjk=
 github.com/BurntSushi/toml v1.6.0/go.mod h1:ukJfTF/6rtPPRCnwkur4qwRxa8vTRFBF0uk2lLoLwho=
@@ -305,6 +325,8 @@ github.com/godoc-lint/godoc-lint v0.11.2 h1:Bp0FkJWoSdNsBikdNgIcgtaoo+xz6I/Y9s5W
 github.com/godoc-lint/godoc-lint v0.11.2/go.mod h1:iVpGdL1JCikNH2gGeAn3Hh+AgN5Gx/I/cxV+91L41jo=
 github.com/gofrs/flock v0.13.0 h1:95JolYOvGMqeH31+FC7D2+uULf6mG61mEZ/A8dRYMzw=
 github.com/gofrs/flock v0.13.0/go.mod h1:jxeyy9R1auM5S6JYDBhDt+E2TCo7DkratH4Pgi8P+Z0=
+github.com/golang-jwt/jwt/v5 v5.3.0 h1:pv4AsKCKKZuqlgs5sUmn4x8UlGa0kEVt/puTpKx9vvo=
+github.com/golang-jwt/jwt/v5 v5.3.0/go.mod h1:fxCRLWMO43lRc8nhHWY6LGqRcf+1gQWArsqaEUEa5bE=
 github.com/golang/protobuf v1.5.4 h1:i7eJL8qZTpSEXOPTxNKhASYpMn+8e5Q6AdndVa1dWek=
 github.com/golang/protobuf v1.5.4/go.mod h1:lnTiLA8Wa4RWRcIUkrtSVa5nRhsEGBg48fD6rSs7xps=
 github.com/golangci/asciicheck v0.5.0 h1:jczN/BorERZwK8oiFBOGvlGPknhvq0bjnysTj4nUfo0=
@@ -396,6 +418,8 @@ github.com/julz/importas v0.2.0 h1:y+MJN/UdL63QbFJHws9BVC5RpA2iq0kpjrFajTGivjQ=
 github.com/julz/importas v0.2.0/go.mod h1:pThlt589EnCYtMnmhmRYY/qn9lCf/frPOK+WMx3xiJY=
 github.com/karamaru-alpha/copyloopvar v1.2.2 h1:yfNQvP9YaGQR7VaWLYcfZUlRP2eo2vhExWKxD/fP6q0=
 github.com/karamaru-alpha/copyloopvar v1.2.2/go.mod h1:oY4rGZqZ879JkJMtX3RRkcXRkmUvH0x35ykgaKgsgJY=
+github.com/keybase/go-keychain v0.0.1 h1:way+bWYa6lDppZoZcgMbYsvC7GxljxrskdNInRtuthU=
+github.com/keybase/go-keychain v0.0.1/go.mod h1:PdEILRW3i9D8JcdM+FmY6RwkHGnhHxXwkPPMeUgOK1k=
 github.com/kisielk/errcheck v1.9.0 h1:9xt1zI9EBfcYBvdU1nVrzMzzUPUtPKs9bVSIM3TAb3M=
 github.com/kisielk/errcheck v1.9.0/go.mod h1:kQxWMMVZgIkDq7U8xtG/n2juOjbLgZtedi0D+/VL/i8=
 github.com/kkHAIKE/contextcheck v1.1.6 h1:7HIyRcnyzxL9Lz06NGhiKvenXq7Zw6Q0UQu/ttjfJCE=
@@ -509,6 +533,8 @@ github.com/pelletier/go-toml/v2 v2.2.4 h1:mye9XuhQ6gvn5h28+VilKrrPoQVanw5PMw/TB0
 github.com/pelletier/go-toml/v2 v2.2.4/go.mod h1:2gIqNv+qfxSVS7cM2xJQKtLSTLUE9V8t9Stt+h56mCY=
 github.com/peterbourgon/g2s v0.0.0-20170223122336-d4e7ad98afea h1:sKwxy1H95npauwu8vtF95vG/syrL0p8fSZo/XlDg5gk=
 github.com/peterbourgon/g2s v0.0.0-20170223122336-d4e7ad98afea/go.mod h1:1VcHEd3ro4QMoHfiNl/j7Jkln9+KQuorp0PItHMJYNg=
+github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c h1:+mdjkGKdHQG3305AYmdv1U2eRNDiU2ErMBj1gwrq8eQ=
+github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c/go.mod h1:7rwL4CYBLnjLxUqIJNnCWiEdr3bn6IUYi15bNlnbCCU=
 github.com/planetscale/vtprotobuf v0.6.1-0.20240319094008-0393e58bdf10 h1:GFCKgmp0tecUJ0sJuv4pzYCqS9+RGSn52M3FUwPs+uo=
 github.com/planetscale/vtprotobuf v0.6.1-0.20240319094008-0393e58bdf10/go.mod h1:t/avpk3KcrXxUnYOhZhMXJlSEyie6gQbtLq5NM3loB8=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
@@ -771,6 +797,7 @@ golang.org/x/sys v0.0.0-20211019181941-9d821ace8654/go.mod h1:oPkhp1MJrh7nUepCBc
 golang.org/x/sys v0.0.0-20211105183446-c75c47738b0c/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.1.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.5.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.8.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
diff --git a/internal/config/config.go b/internal/config/config.go
index ad0acc0..186b395 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -133,6 +133,15 @@ type StorageConfig struct {
 	// When exceeded, least recently used artifacts are evicted.
 	// Empty or "0" means unlimited.
 	MaxSize string `json:"max_size" yaml:"max_size"`
+
+	// DirectServe enables redirecting cached artifact downloads to presigned
+	// storage URLs (HTTP 302) instead of streaming bytes through the proxy.
+	// Only effective for backends that support URL signing (S3, Azure).
+	DirectServe bool `json:"direct_serve" yaml:"direct_serve"`
+
+	// DirectServeTTL is how long presigned URLs remain valid.
+	// Uses Go duration syntax (e.g. "5m", "1h"). Default: "15m".
+	DirectServeTTL string `json:"direct_serve_ttl" yaml:"direct_serve_ttl"`
 }
 
 // DatabaseConfig configures the cache database.
@@ -303,6 +312,12 @@ func (c *Config) LoadFromEnv() {
 	if v := os.Getenv("PROXY_STORAGE_MAX_SIZE"); v != "" {
 		c.Storage.MaxSize = v
 	}
+	if v := os.Getenv("PROXY_STORAGE_DIRECT_SERVE"); v != "" {
+		c.Storage.DirectServe = envBool(v)
+	}
+	if v := os.Getenv("PROXY_STORAGE_DIRECT_SERVE_TTL"); v != "" {
+		c.Storage.DirectServeTTL = v
+	}
 	if v := os.Getenv("PROXY_DATABASE_DRIVER"); v != "" {
 		c.Database.Driver = v
 	}
@@ -322,10 +337,10 @@ func (c *Config) LoadFromEnv() {
 		c.Cooldown.Default = v
 	}
 	if v := os.Getenv("PROXY_CACHE_METADATA"); v != "" {
-		c.CacheMetadata = v == "true" || v == "1"
+		c.CacheMetadata = envBool(v)
 	}
 	if v := os.Getenv("PROXY_MIRROR_API"); v != "" {
-		c.MirrorAPI = v == "true" || v == "1"
+		c.MirrorAPI = envBool(v)
 	}
 	if v := os.Getenv("PROXY_METADATA_TTL"); v != "" {
 		c.MetadataTTL = v
@@ -379,6 +394,13 @@ func (c *Config) Validate() error {
 		}
 	}
 
+	// Validate direct serve TTL if specified
+	if c.Storage.DirectServeTTL != "" {
+		if _, err := time.ParseDuration(c.Storage.DirectServeTTL); err != nil {
+			return fmt.Errorf("invalid storage.direct_serve_ttl %q: %w", c.Storage.DirectServeTTL, err)
+		}
+	}
+
 	// Validate metadata TTL if specified
 	if c.MetadataTTL != "" && c.MetadataTTL != "0" {
 		if _, err := time.ParseDuration(c.MetadataTTL); err != nil {
@@ -389,7 +411,10 @@ func (c *Config) Validate() error {
 	return nil
 }
 
-const defaultMetadataTTL = 5 * time.Minute //nolint:mnd // sensible default
+const (
+	defaultMetadataTTL    = 5 * time.Minute  //nolint:mnd // sensible default
+	defaultDirectServeTTL = 15 * time.Minute //nolint:mnd // sensible default
+)
 
 // ParseMetadataTTL returns the metadata TTL duration.
 // Returns 5 minutes if unset, 0 if explicitly disabled.
@@ -407,6 +432,19 @@ func (c *Config) ParseMetadataTTL() time.Duration {
 	return d
 }
 
+// ParseDirectServeTTL returns the presigned URL expiry duration.
+// Returns 15 minutes if unset.
+func (c *Config) ParseDirectServeTTL() time.Duration {
+	if c.Storage.DirectServeTTL == "" {
+		return defaultDirectServeTTL
+	}
+	d, err := time.ParseDuration(c.Storage.DirectServeTTL)
+	if err != nil {
+		return defaultDirectServeTTL
+	}
+	return d
+}
+
 // ParseSize parses a human-readable size string (e.g., "10GB", "500MB").
 // Returns the size in bytes.
 func ParseSize(s string) (int64, error) {
@@ -487,3 +525,7 @@ func (a *AuthConfig) Header() (name, value string) {
 func expandEnv(s string) string {
 	return os.Expand(s, os.Getenv)
 }
+
+func envBool(v string) bool {
+	return v == "true" || v == "1"
+}
diff --git a/internal/config/config_test.go b/internal/config/config_test.go
index 6e8c3a0..967a4e5 100644
--- a/internal/config/config_test.go
+++ b/internal/config/config_test.go
@@ -355,3 +355,54 @@ func TestLoadMetadataTTLFromEnv(t *testing.T) {
 		t.Errorf("MetadataTTL = %q, want %q", cfg.MetadataTTL, "10m")
 	}
 }
+
+func TestParseDirectServeTTL(t *testing.T) {
+	tests := []struct {
+		name string
+		ttl  string
+		want time.Duration
+	}{
+		{"empty defaults to 15m", "", 15 * time.Minute},
+		{"5 minutes", "5m", 5 * time.Minute},
+		{"1 hour", "1h", 1 * time.Hour},
+		{"invalid defaults to 15m", "not-a-duration", 15 * time.Minute},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			cfg := Default()
+			cfg.Storage.DirectServeTTL = tt.ttl
+			got := cfg.ParseDirectServeTTL()
+			if got != tt.want {
+				t.Errorf("ParseDirectServeTTL() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestValidateDirectServeTTL(t *testing.T) {
+	cfg := Default()
+	cfg.Storage.DirectServeTTL = "invalid"
+	if err := cfg.Validate(); err == nil {
+		t.Error("expected validation error for invalid storage.direct_serve_ttl")
+	}
+
+	cfg.Storage.DirectServeTTL = "5m"
+	if err := cfg.Validate(); err != nil {
+		t.Errorf("unexpected error for valid storage.direct_serve_ttl: %v", err)
+	}
+}
+
+func TestLoadDirectServeFromEnv(t *testing.T) {
+	cfg := Default()
+	t.Setenv("PROXY_STORAGE_DIRECT_SERVE", "true")
+	t.Setenv("PROXY_STORAGE_DIRECT_SERVE_TTL", "30m")
+	cfg.LoadFromEnv()
+
+	if !cfg.Storage.DirectServe {
+		t.Error("Storage.DirectServe should be true")
+	}
+	if cfg.Storage.DirectServeTTL != "30m" {
+		t.Errorf("Storage.DirectServeTTL = %q, want %q", cfg.Storage.DirectServeTTL, "30m")
+	}
+}
diff --git a/internal/handler/handler.go b/internal/handler/handler.go
index d7d79c9..d4609cb 100644
--- a/internal/handler/handler.go
+++ b/internal/handler/handler.go
@@ -61,15 +61,17 @@ func ReadMetadata(r io.Reader) ([]byte, error) {
 
 // Proxy provides shared functionality for protocol handlers.
 type Proxy struct {
-	DB            *database.DB
-	Storage       storage.Storage
-	Fetcher       fetch.FetcherInterface
-	Resolver      *fetch.Resolver
-	Logger        *slog.Logger
-	Cooldown      *cooldown.Config
-	CacheMetadata bool
-	MetadataTTL   time.Duration
-	HTTPClient    *http.Client
+	DB             *database.DB
+	Storage        storage.Storage
+	Fetcher        fetch.FetcherInterface
+	Resolver       *fetch.Resolver
+	Logger         *slog.Logger
+	Cooldown       *cooldown.Config
+	CacheMetadata  bool
+	MetadataTTL    time.Duration
+	DirectServe    bool
+	DirectServeTTL time.Duration
+	HTTPClient     *http.Client
 }
 
 // NewProxy creates a new Proxy with the given dependencies.
@@ -92,6 +94,7 @@ func NewProxy(db *database.DB, store storage.Storage, fetcher fetch.FetcherInter
 // CacheResult contains information about a cached or fetched artifact.
 type CacheResult struct {
 	Reader      io.ReadCloser
+	RedirectURL string
 	Size        int64
 	ContentType string
 	Hash        string
@@ -138,6 +141,26 @@ func (p *Proxy) checkCache(ctx context.Context, pkgPURL, versionPURL, filename s
 		return nil, nil
 	}
 
+	result := &CacheResult{
+		Size:        artifact.Size.Int64,
+		ContentType: artifact.ContentType.String,
+		Hash:        artifact.ContentHash.String,
+		Cached:      true,
+	}
+
+	if p.DirectServe {
+		url, err := p.Storage.SignedURL(ctx, artifact.StoragePath.String, p.DirectServeTTL)
+		if err == nil {
+			result.RedirectURL = url
+			p.recordCacheHit(pkgPURL, versionPURL, filename)
+			return result, nil
+		}
+		if !errors.Is(err, storage.ErrSignedURLUnsupported) {
+			p.Logger.Warn("failed to sign storage URL, falling back to streaming",
+				"path", artifact.StoragePath.String, "error", err)
+		}
+	}
+
 	start := time.Now()
 	reader, err := p.Storage.Open(ctx, artifact.StoragePath.String)
 	metrics.RecordStorageOperation("read", time.Since(start))
@@ -148,20 +171,16 @@ func (p *Proxy) checkCache(ctx context.Context, pkgPURL, versionPURL, filename s
 		return nil, nil
 	}
 
+	result.Reader = reader
+	p.recordCacheHit(pkgPURL, versionPURL, filename)
+	return result, nil
+}
+
+func (p *Proxy) recordCacheHit(pkgPURL, versionPURL, filename string) {
 	_ = p.DB.RecordArtifactHit(versionPURL, filename)
-
-	// Extract ecosystem from pkgPURL for metrics
-	if p, err := purl.Parse(pkgPURL); err == nil {
-		metrics.RecordCacheHit(purl.PURLTypeToEcosystem(p.Type))
+	if parsed, err := purl.Parse(pkgPURL); err == nil {
+		metrics.RecordCacheHit(purl.PURLTypeToEcosystem(parsed.Type))
 	}
-
-	return &CacheResult{
-		Reader:      reader,
-		Size:        artifact.Size.Int64,
-		ContentType: artifact.ContentType.String,
-		Hash:        artifact.ContentHash.String,
-		Cached:      true,
-	}, nil
 }
 
 func (p *Proxy) fetchAndCache(ctx context.Context, ecosystem, name, version, filename, pkgPURL, versionPURL string) (*CacheResult, error) {
@@ -276,6 +295,15 @@ func (p *Proxy) updateCacheDB(ecosystem, name, filename, pkgPURL, versionPURL, u
 
 // ServeArtifact writes a CacheResult to an HTTP response.
 func ServeArtifact(w http.ResponseWriter, result *CacheResult) {
+	if result.RedirectURL != "" {
+		if result.Hash != "" {
+			w.Header().Set("ETag", fmt.Sprintf(`"%s"`, result.Hash))
+		}
+		w.Header().Set("Location", result.RedirectURL)
+		w.WriteHeader(http.StatusFound)
+		return
+	}
+
 	defer func() { _ = result.Reader.Close() }()
 
 	if result.ContentType != "" {
diff --git a/internal/handler/handler_test.go b/internal/handler/handler_test.go
index 78ed415..b544c40 100644
--- a/internal/handler/handler_test.go
+++ b/internal/handler/handler_test.go
@@ -21,9 +21,11 @@ import (
 
 // mockStorage implements storage.Storage for testing.
 type mockStorage struct {
-	files    map[string][]byte
-	storeErr error
-	openErr  error
+	files     map[string][]byte
+	storeErr  error
+	openErr   error
+	signedURL string
+	signErr   error
 }
 
 func newMockStorage() *mockStorage {
@@ -79,6 +81,16 @@ func (s *mockStorage) UsedSpace(_ context.Context) (int64, error) {
 	return total, nil
 }
 
+func (s *mockStorage) SignedURL(_ context.Context, _ string, _ time.Duration) (string, error) {
+	if s.signErr != nil {
+		return "", s.signErr
+	}
+	if s.signedURL == "" {
+		return "", storage.ErrSignedURLUnsupported
+	}
+	return s.signedURL, nil
+}
+
 func (s *mockStorage) URL() string { return "mem://" }
 
 func (s *mockStorage) Close() error { return nil }
@@ -311,6 +323,145 @@ func TestGetOrFetchArtifactFromURL_CacheMiss_StorageMissing(t *testing.T) {
 	}
 }
 
+func TestGetOrFetchArtifact_DirectServe_Redirect(t *testing.T) {
+	proxy, db, store, fetcher := setupTestProxy(t)
+	seedPackage(t, db, store, "npm", "lodash", "4.17.21", "lodash-4.17.21.tgz", "cached content")
+
+	proxy.DirectServe = true
+	proxy.DirectServeTTL = 15 * time.Minute
+	store.signedURL = "https://bucket.s3.amazonaws.com/npm/lodash?X-Amz-Signature=abc"
+
+	result, err := proxy.GetOrFetchArtifact(context.Background(), "npm", "lodash", "4.17.21", "lodash-4.17.21.tgz")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if !result.Cached {
+		t.Error("expected result to be cached")
+	}
+	if result.RedirectURL != store.signedURL {
+		t.Errorf("RedirectURL = %q, want %q", result.RedirectURL, store.signedURL)
+	}
+	if result.Reader != nil {
+		t.Error("Reader should be nil when redirecting")
+	}
+	if fetcher.fetchCalled {
+		t.Error("fetcher should not be called on cache hit")
+	}
+
+	// Hit count should still be recorded on the redirect path.
+	art, _ := db.GetArtifact("pkg:npm/lodash@4.17.21", "lodash-4.17.21.tgz")
+	if art == nil || art.HitCount != 1 {
+		t.Errorf("artifact hit count not recorded: %+v", art)
+	}
+}
+
+func TestGetOrFetchArtifact_DirectServe_FallbackOnUnsupported(t *testing.T) {
+	proxy, db, store, _ := setupTestProxy(t)
+	seedPackage(t, db, store, "npm", "lodash", "4.17.21", "lodash-4.17.21.tgz", "cached content")
+
+	proxy.DirectServe = true
+	// store.signedURL is empty so SignedURL returns ErrSignedURLUnsupported.
+
+	result, err := proxy.GetOrFetchArtifact(context.Background(), "npm", "lodash", "4.17.21", "lodash-4.17.21.tgz")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	defer func() { _ = result.Reader.Close() }()
+
+	if result.RedirectURL != "" {
+		t.Errorf("RedirectURL should be empty, got %q", result.RedirectURL)
+	}
+	if result.Reader == nil {
+		t.Fatal("Reader should be set when signing is unsupported")
+	}
+	body, _ := io.ReadAll(result.Reader)
+	if string(body) != "cached content" {
+		t.Errorf("got body %q, want %q", body, "cached content")
+	}
+}
+
+func TestGetOrFetchArtifact_DirectServe_FallbackOnError(t *testing.T) {
+	proxy, db, store, _ := setupTestProxy(t)
+	seedPackage(t, db, store, "npm", "lodash", "4.17.21", "lodash-4.17.21.tgz", "cached content")
+
+	proxy.DirectServe = true
+	store.signErr = errors.New("signing failed")
+
+	result, err := proxy.GetOrFetchArtifact(context.Background(), "npm", "lodash", "4.17.21", "lodash-4.17.21.tgz")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	defer func() { _ = result.Reader.Close() }()
+
+	if result.RedirectURL != "" {
+		t.Errorf("RedirectURL should be empty on signing error, got %q", result.RedirectURL)
+	}
+	if result.Reader == nil {
+		t.Fatal("Reader should be set when signing fails")
+	}
+}
+
+func TestGetOrFetchArtifact_DirectServe_DisabledIgnoresSigning(t *testing.T) {
+	proxy, db, store, _ := setupTestProxy(t)
+	seedPackage(t, db, store, "npm", "lodash", "4.17.21", "lodash-4.17.21.tgz", "cached content")
+
+	proxy.DirectServe = false
+	store.signedURL = "https://bucket.example/should-not-be-used"
+
+	result, err := proxy.GetOrFetchArtifact(context.Background(), "npm", "lodash", "4.17.21", "lodash-4.17.21.tgz")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	defer func() { _ = result.Reader.Close() }()
+
+	if result.RedirectURL != "" {
+		t.Errorf("RedirectURL should be empty when DirectServe is off, got %q", result.RedirectURL)
+	}
+}
+
+func TestServeArtifact_Redirect(t *testing.T) {
+	w := httptest.NewRecorder()
+	ServeArtifact(w, &CacheResult{
+		RedirectURL: "https://bucket.s3.amazonaws.com/file?sig=abc",
+		Hash:        "abc123",
+		Cached:      true,
+	})
+
+	if w.Code != http.StatusFound {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusFound)
+	}
+	if loc := w.Header().Get("Location"); loc != "https://bucket.s3.amazonaws.com/file?sig=abc" {
+		t.Errorf("Location = %q", loc)
+	}
+	if etag := w.Header().Get("ETag"); etag != `"abc123"` {
+		t.Errorf("ETag = %q, want %q", etag, `"abc123"`)
+	}
+	if cl := w.Header().Get("Content-Length"); cl != "" {
+		t.Errorf("Content-Length should not be set on redirect, got %q", cl)
+	}
+}
+
+func TestServeArtifact_Stream(t *testing.T) {
+	w := httptest.NewRecorder()
+	ServeArtifact(w, &CacheResult{
+		Reader:      io.NopCloser(strings.NewReader("payload")),
+		Size:        7,
+		ContentType: "application/octet-stream",
+		Hash:        "abc123",
+	})
+
+	if w.Code != http.StatusOK {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusOK)
+	}
+	if w.Body.String() != "payload" {
+		t.Errorf("body = %q, want %q", w.Body.String(), "payload")
+	}
+	if ct := w.Header().Get("Content-Type"); ct != "application/octet-stream" {
+		t.Errorf("Content-Type = %q", ct)
+	}
+}
+
 func TestGetOrFetchArtifactFromURL_CacheHit(t *testing.T) {
 	proxy, db, store, fetcher := setupTestProxy(t)
 	seedPackage(t, db, store, "pypi", "requests", "2.28.0", "requests-2.28.0.tar.gz", "pypi content")
diff --git a/internal/server/server.go b/internal/server/server.go
index 5d544a2..445c0db 100644
--- a/internal/server/server.go
+++ b/internal/server/server.go
@@ -148,6 +148,8 @@ func (s *Server) Start() error {
 	proxy.Cooldown = cd
 	proxy.CacheMetadata = s.cfg.CacheMetadata
 	proxy.MetadataTTL = s.cfg.ParseMetadataTTL()
+	proxy.DirectServe = s.cfg.Storage.DirectServe
+	proxy.DirectServeTTL = s.cfg.ParseDirectServeTTL()
 
 	// Create router with Chi
 	r := chi.NewRouter()
diff --git a/internal/storage/blob.go b/internal/storage/blob.go
index 2d6af46..dc41668 100644
--- a/internal/storage/blob.go
+++ b/internal/storage/blob.go
@@ -6,12 +6,15 @@ import (
 	"encoding/hex"
 	"fmt"
 	"io"
+	"net/http"
 	"os"
 	"path/filepath"
 	"runtime"
 	"strings"
+	"time"
 
 	"gocloud.dev/blob"
+	_ "gocloud.dev/blob/azureblob"
 	_ "gocloud.dev/blob/fileblob"
 	_ "gocloud.dev/blob/s3blob"
 	"gocloud.dev/gcerrors"
@@ -138,6 +141,20 @@ func (b *Blob) Delete(ctx context.Context, path string) error {
 	return nil
 }
 
+func (b *Blob) SignedURL(ctx context.Context, path string, expiry time.Duration) (string, error) {
+	url, err := b.bucket.SignedURL(ctx, path, &blob.SignedURLOptions{
+		Method: http.MethodGet,
+		Expiry: expiry,
+	})
+	if err != nil {
+		if gcerrors.Code(err) == gcerrors.Unimplemented {
+			return "", ErrSignedURLUnsupported
+		}
+		return "", fmt.Errorf("signing URL: %w", err)
+	}
+	return url, nil
+}
+
 func (b *Blob) Size(ctx context.Context, path string) (int64, error) {
 	attrs, err := b.bucket.Attributes(ctx, path)
 	if err != nil {
diff --git a/internal/storage/blob_test.go b/internal/storage/blob_test.go
index bb2d089..d80290b 100644
--- a/internal/storage/blob_test.go
+++ b/internal/storage/blob_test.go
@@ -10,6 +10,7 @@ import (
 	"runtime"
 	"strings"
 	"testing"
+	"time"
 )
 
 func TestOpenBucket(t *testing.T) {
@@ -188,6 +189,18 @@ func TestBlobLargeFile(t *testing.T) {
 	assertLargeFileRoundTrip(t, createTestBlob(t))
 }
 
+func TestBlobSignedURLUnsupported(t *testing.T) {
+	b := createTestBlob(t)
+	ctx := context.Background()
+
+	// fileblob has no URL signer configured, so this must surface as
+	// ErrSignedURLUnsupported rather than a generic error.
+	_, err := b.SignedURL(ctx, "test/file.txt", time.Minute)
+	if !errors.Is(err, ErrSignedURLUnsupported) {
+		t.Errorf("SignedURL on fileblob = %v, want ErrSignedURLUnsupported", err)
+	}
+}
+
 func TestBlobOverwrite(t *testing.T) {
 	b := createTestBlob(t)
 	ctx := context.Background()
diff --git a/internal/storage/filesystem.go b/internal/storage/filesystem.go
index cf6a1fe..7a4147a 100644
--- a/internal/storage/filesystem.go
+++ b/internal/storage/filesystem.go
@@ -8,6 +8,7 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+	"time"
 )
 
 // Filesystem implements Storage using the local filesystem.
@@ -129,6 +130,10 @@ func (fs *Filesystem) Delete(ctx context.Context, path string) error {
 	return nil
 }
 
+func (fs *Filesystem) SignedURL(_ context.Context, _ string, _ time.Duration) (string, error) {
+	return "", ErrSignedURLUnsupported
+}
+
 func (fs *Filesystem) Size(ctx context.Context, path string) (int64, error) {
 	fullPath := fs.fullPath(path)
 
diff --git a/internal/storage/filesystem_test.go b/internal/storage/filesystem_test.go
index 7b7828d..cdd7f6b 100644
--- a/internal/storage/filesystem_test.go
+++ b/internal/storage/filesystem_test.go
@@ -10,6 +10,7 @@ import (
 	"path/filepath"
 	"strings"
 	"testing"
+	"time"
 )
 
 func TestNewFilesystem(t *testing.T) {
@@ -236,6 +237,15 @@ func TestFilesystemLargeFile(t *testing.T) {
 	assertLargeFileRoundTrip(t, createTestFilesystem(t))
 }
 
+func TestFilesystemSignedURLUnsupported(t *testing.T) {
+	fs := createTestFilesystem(t)
+
+	_, err := fs.SignedURL(context.Background(), "test/file.txt", time.Minute)
+	if !errors.Is(err, ErrSignedURLUnsupported) {
+		t.Errorf("SignedURL = %v, want ErrSignedURLUnsupported", err)
+	}
+}
+
 func createTestFilesystem(t *testing.T) *Filesystem {
 	t.Helper()
 	dir := t.TempDir()
diff --git a/internal/storage/storage.go b/internal/storage/storage.go
index 8a9026c..0dba46a 100644
--- a/internal/storage/storage.go
+++ b/internal/storage/storage.go
@@ -15,12 +15,17 @@ import (
 	"encoding/hex"
 	"errors"
 	"io"
+	"time"
 )
 
 const dirPermissions = 0755
 
 var (
 	ErrNotFound = errors.New("artifact not found")
+
+	// ErrSignedURLUnsupported is returned by SignedURL when the backend
+	// cannot generate presigned URLs (e.g. local filesystem).
+	ErrSignedURLUnsupported = errors.New("signed URLs not supported by storage backend")
 )
 
 // Storage defines the interface for artifact storage backends.
@@ -45,6 +50,10 @@ type Storage interface {
 	// Returns ErrNotFound if the path does not exist.
 	Size(ctx context.Context, path string) (int64, error)
 
+	// SignedURL returns a presigned URL granting time-limited GET access to path.
+	// Returns ErrSignedURLUnsupported if the backend cannot generate presigned URLs.
+	SignedURL(ctx context.Context, path string, expiry time.Duration) (string, error)
+
 	// UsedSpace returns the total bytes used by all stored content.
 	UsedSpace(ctx context.Context) (int64, error)
 

From 1ad182782de398bbf621a81c9a0bbb5301482210 Mon Sep 17 00:00:00 2001
From: Andrew Nesbitt <andrewnez@gmail.com>
Date: Mon, 27 Apr 2026 12:14:37 +0100
Subject: [PATCH 02/36] Add storage.direct_serve_base_url to override presigned
 URL host

When the proxy reaches storage at an internal address (127.0.0.1, a
Docker service name) the presigned URLs it generates point there too,
which is useless to external clients. This adds an optional base URL
that replaces the scheme and host of signed URLs before they're returned,
keeping the signed path and query intact.
---
 config.example.yaml              |  8 ++++
 internal/config/config.go        | 18 +++++++++
 internal/config/config_test.go   | 23 +++++++++++
 internal/handler/handler.go      | 31 +++++++++++++--
 internal/handler/handler_test.go | 68 ++++++++++++++++++++++++++++++++
 internal/server/server.go        |  1 +
 6 files changed, 146 insertions(+), 3 deletions(-)

diff --git a/config.example.yaml b/config.example.yaml
index c272979..8f37450 100644
--- a/config.example.yaml
+++ b/config.example.yaml
@@ -38,6 +38,14 @@ storage:
   # How long presigned URLs remain valid (e.g. "5m", "1h"). Default: "15m".
   direct_serve_ttl: "15m"
 
+  # Public base URL to substitute into presigned URLs. Set this when the
+  # proxy reaches storage at an internal address (127.0.0.1, a Docker
+  # service name) but clients must use a public hostname. Only scheme and
+  # host are used; the signed path and query are preserved. For S3/MinIO
+  # the reverse proxy at this address must forward requests with the
+  # internal Host header or the SigV4 signature will not validate.
+  # direct_serve_base_url: "https://minio.example.com"
+
 # Database configuration
 database:
   # Database driver: "sqlite" (default) or "postgres"
diff --git a/internal/config/config.go b/internal/config/config.go
index 186b395..7dafab1 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -51,6 +51,7 @@ import (
 	"encoding/base64"
 	"encoding/json"
 	"fmt"
+	"net/url"
 	"os"
 	"path/filepath"
 	"strconv"
@@ -142,6 +143,12 @@ type StorageConfig struct {
 	// DirectServeTTL is how long presigned URLs remain valid.
 	// Uses Go duration syntax (e.g. "5m", "1h"). Default: "15m".
 	DirectServeTTL string `json:"direct_serve_ttl" yaml:"direct_serve_ttl"`
+
+	// DirectServeBaseURL overrides the scheme and host of presigned URLs
+	// before returning them to clients. Useful when the proxy reaches
+	// storage at an internal address (e.g. 127.0.0.1 or a Docker hostname)
+	// but clients must use a public one.
+	DirectServeBaseURL string `json:"direct_serve_base_url" yaml:"direct_serve_base_url"`
 }
 
 // DatabaseConfig configures the cache database.
@@ -318,6 +325,9 @@ func (c *Config) LoadFromEnv() {
 	if v := os.Getenv("PROXY_STORAGE_DIRECT_SERVE_TTL"); v != "" {
 		c.Storage.DirectServeTTL = v
 	}
+	if v := os.Getenv("PROXY_STORAGE_DIRECT_SERVE_BASE_URL"); v != "" {
+		c.Storage.DirectServeBaseURL = v
+	}
 	if v := os.Getenv("PROXY_DATABASE_DRIVER"); v != "" {
 		c.Database.Driver = v
 	}
@@ -401,6 +411,14 @@ func (c *Config) Validate() error {
 		}
 	}
 
+	// Validate direct serve base URL if specified
+	if c.Storage.DirectServeBaseURL != "" {
+		u, err := url.Parse(c.Storage.DirectServeBaseURL)
+		if err != nil || u.Scheme == "" || u.Host == "" {
+			return fmt.Errorf("invalid storage.direct_serve_base_url %q: must be an absolute URL", c.Storage.DirectServeBaseURL)
+		}
+	}
+
 	// Validate metadata TTL if specified
 	if c.MetadataTTL != "" && c.MetadataTTL != "0" {
 		if _, err := time.ParseDuration(c.MetadataTTL); err != nil {
diff --git a/internal/config/config_test.go b/internal/config/config_test.go
index 967a4e5..2d85fd6 100644
--- a/internal/config/config_test.go
+++ b/internal/config/config_test.go
@@ -397,6 +397,7 @@ func TestLoadDirectServeFromEnv(t *testing.T) {
 	cfg := Default()
 	t.Setenv("PROXY_STORAGE_DIRECT_SERVE", "true")
 	t.Setenv("PROXY_STORAGE_DIRECT_SERVE_TTL", "30m")
+	t.Setenv("PROXY_STORAGE_DIRECT_SERVE_BASE_URL", "https://cdn.example.com")
 	cfg.LoadFromEnv()
 
 	if !cfg.Storage.DirectServe {
@@ -405,4 +406,26 @@ func TestLoadDirectServeFromEnv(t *testing.T) {
 	if cfg.Storage.DirectServeTTL != "30m" {
 		t.Errorf("Storage.DirectServeTTL = %q, want %q", cfg.Storage.DirectServeTTL, "30m")
 	}
+	if cfg.Storage.DirectServeBaseURL != "https://cdn.example.com" {
+		t.Errorf("Storage.DirectServeBaseURL = %q, want %q", cfg.Storage.DirectServeBaseURL, "https://cdn.example.com")
+	}
+}
+
+func TestValidateDirectServeBaseURL(t *testing.T) {
+	cfg := Default()
+
+	cfg.Storage.DirectServeBaseURL = "not a url"
+	if err := cfg.Validate(); err == nil {
+		t.Error("expected validation error for relative direct_serve_base_url")
+	}
+
+	cfg.Storage.DirectServeBaseURL = "://bad"
+	if err := cfg.Validate(); err == nil {
+		t.Error("expected validation error for unparseable direct_serve_base_url")
+	}
+
+	cfg.Storage.DirectServeBaseURL = "https://cdn.example.com"
+	if err := cfg.Validate(); err != nil {
+		t.Errorf("unexpected error for valid direct_serve_base_url: %v", err)
+	}
 }
diff --git a/internal/handler/handler.go b/internal/handler/handler.go
index d4609cb..746b9e8 100644
--- a/internal/handler/handler.go
+++ b/internal/handler/handler.go
@@ -10,6 +10,7 @@ import (
 	"io"
 	"log/slog"
 	"net/http"
+	"net/url"
 	"strconv"
 	"strings"
 	"time"
@@ -71,7 +72,11 @@ type Proxy struct {
 	MetadataTTL    time.Duration
 	DirectServe    bool
 	DirectServeTTL time.Duration
-	HTTPClient     *http.Client
+	// DirectServeBaseURL, if set, replaces the scheme and host of presigned
+	// URLs so clients receive a public address even when the proxy reaches
+	// storage at an internal one.
+	DirectServeBaseURL string
+	HTTPClient         *http.Client
 }
 
 // NewProxy creates a new Proxy with the given dependencies.
@@ -149,9 +154,9 @@ func (p *Proxy) checkCache(ctx context.Context, pkgPURL, versionPURL, filename s
 	}
 
 	if p.DirectServe {
-		url, err := p.Storage.SignedURL(ctx, artifact.StoragePath.String, p.DirectServeTTL)
+		signed, err := p.Storage.SignedURL(ctx, artifact.StoragePath.String, p.DirectServeTTL)
 		if err == nil {
-			result.RedirectURL = url
+			result.RedirectURL = rewriteSignedURLHost(signed, p.DirectServeBaseURL)
 			p.recordCacheHit(pkgPURL, versionPURL, filename)
 			return result, nil
 		}
@@ -176,6 +181,26 @@ func (p *Proxy) checkCache(ctx context.Context, pkgPURL, versionPURL, filename s
 	return result, nil
 }
 
+// rewriteSignedURLHost replaces the scheme and host of a signed URL with those
+// from baseURL, preserving the path and query (which carry the signature).
+// Returns signed unchanged if baseURL is empty or either URL fails to parse.
+func rewriteSignedURLHost(signed, baseURL string) string {
+	if baseURL == "" {
+		return signed
+	}
+	s, err := url.Parse(signed)
+	if err != nil {
+		return signed
+	}
+	b, err := url.Parse(baseURL)
+	if err != nil || b.Scheme == "" || b.Host == "" {
+		return signed
+	}
+	s.Scheme = b.Scheme
+	s.Host = b.Host
+	return s.String()
+}
+
 func (p *Proxy) recordCacheHit(pkgPURL, versionPURL, filename string) {
 	_ = p.DB.RecordArtifactHit(versionPURL, filename)
 	if parsed, err := purl.Parse(pkgPURL); err == nil {
diff --git a/internal/handler/handler_test.go b/internal/handler/handler_test.go
index b544c40..3a1d2ab 100644
--- a/internal/handler/handler_test.go
+++ b/internal/handler/handler_test.go
@@ -356,6 +356,74 @@ func TestGetOrFetchArtifact_DirectServe_Redirect(t *testing.T) {
 	}
 }
 
+func TestGetOrFetchArtifact_DirectServe_BaseURLRewrite(t *testing.T) {
+	proxy, db, store, _ := setupTestProxy(t)
+	seedPackage(t, db, store, "npm", "lodash", "4.17.21", "lodash-4.17.21.tgz", "cached content")
+
+	proxy.DirectServe = true
+	proxy.DirectServeBaseURL = "https://cdn.example.com"
+	store.signedURL = "http://127.0.0.1:9000/bucket/npm/lodash?X-Amz-Signature=abc&X-Amz-Expires=900"
+
+	result, err := proxy.GetOrFetchArtifact(context.Background(), "npm", "lodash", "4.17.21", "lodash-4.17.21.tgz")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	want := "https://cdn.example.com/bucket/npm/lodash?X-Amz-Signature=abc&X-Amz-Expires=900"
+	if result.RedirectURL != want {
+		t.Errorf("RedirectURL = %q, want %q", result.RedirectURL, want)
+	}
+}
+
+func TestRewriteSignedURLHost(t *testing.T) {
+	tests := []struct {
+		name    string
+		signed  string
+		baseURL string
+		want    string
+	}{
+		{
+			"empty base url is no-op",
+			"http://127.0.0.1:9000/bucket/key?sig=abc",
+			"",
+			"http://127.0.0.1:9000/bucket/key?sig=abc",
+		},
+		{
+			"replaces scheme and host",
+			"http://127.0.0.1:9000/bucket/key?sig=abc",
+			"https://cdn.example.com",
+			"https://cdn.example.com/bucket/key?sig=abc",
+		},
+		{
+			"preserves path and query",
+			"http://minio:9000/bucket/npm/lodash/4.17.21/lodash.tgz?X-Amz-Signature=abc&X-Amz-Date=20260101",
+			"https://files.example.com",
+			"https://files.example.com/bucket/npm/lodash/4.17.21/lodash.tgz?X-Amz-Signature=abc&X-Amz-Date=20260101",
+		},
+		{
+			"ignores base url path",
+			"http://127.0.0.1:9000/bucket/key?sig=abc",
+			"https://cdn.example.com/ignored",
+			"https://cdn.example.com/bucket/key?sig=abc",
+		},
+		{
+			"invalid base url is no-op",
+			"http://127.0.0.1:9000/bucket/key?sig=abc",
+			"://bad",
+			"http://127.0.0.1:9000/bucket/key?sig=abc",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := rewriteSignedURLHost(tt.signed, tt.baseURL)
+			if got != tt.want {
+				t.Errorf("rewriteSignedURLHost(%q, %q) = %q, want %q", tt.signed, tt.baseURL, got, tt.want)
+			}
+		})
+	}
+}
+
 func TestGetOrFetchArtifact_DirectServe_FallbackOnUnsupported(t *testing.T) {
 	proxy, db, store, _ := setupTestProxy(t)
 	seedPackage(t, db, store, "npm", "lodash", "4.17.21", "lodash-4.17.21.tgz", "cached content")
diff --git a/internal/server/server.go b/internal/server/server.go
index 445c0db..fdfda20 100644
--- a/internal/server/server.go
+++ b/internal/server/server.go
@@ -150,6 +150,7 @@ func (s *Server) Start() error {
 	proxy.MetadataTTL = s.cfg.ParseMetadataTTL()
 	proxy.DirectServe = s.cfg.Storage.DirectServe
 	proxy.DirectServeTTL = s.cfg.ParseDirectServeTTL()
+	proxy.DirectServeBaseURL = s.cfg.Storage.DirectServeBaseURL
 
 	// Create router with Chi
 	r := chi.NewRouter()

From f9f2a6ecd4501c5670fbd0ba97188bd52bf2ccf4 Mon Sep 17 00:00:00 2001
From: Andrew Nesbitt <andrewnez@gmail.com>
Date: Mon, 27 Apr 2026 21:26:23 +0100
Subject: [PATCH 03/36] Use cosign v4 bundle format for release signing

---
 .goreleaser.yaml | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/.goreleaser.yaml b/.goreleaser.yaml
index b6256de..e5881db 100644
--- a/.goreleaser.yaml
+++ b/.goreleaser.yaml
@@ -36,11 +36,10 @@ checksum:
 
 signs:
   - cmd: cosign
-    certificate: "${artifact}.pem"
+    signature: "${artifact}.cosign.bundle"
     args:
       - sign-blob
-      - "--output-certificate=${certificate}"
-      - "--output-signature=${signature}"
+      - "--bundle=${signature}"
       - "${artifact}"
       - "--yes"
     artifacts: checksum

From 3a68ccef3e534919de3a3350c484c08941e3ffcf Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Thu, 30 Apr 2026 15:18:04 +0000
Subject: [PATCH 04/36] Bump modernc.org/sqlite from 1.48.2 to 1.49.1

Bumps [modernc.org/sqlite](https://gitlab.com/cznic/sqlite) from 1.48.2 to 1.49.1.
- [Changelog](https://gitlab.com/cznic/sqlite/blob/master/CHANGELOG.md)
- [Commits](https://gitlab.com/cznic/sqlite/compare/v1.48.2...v1.49.1)

---
updated-dependencies:
- dependency-name: modernc.org/sqlite
  dependency-version: 1.49.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
---
 go.mod |  4 ++--
 go.sum | 16 ++++++++--------
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/go.mod b/go.mod
index 1067a3a..8e76200 100644
--- a/go.mod
+++ b/go.mod
@@ -22,7 +22,7 @@ require (
 	golang.org/x/sync v0.20.0
 	google.golang.org/protobuf v1.36.11
 	gopkg.in/yaml.v3 v3.0.1
-	modernc.org/sqlite v1.48.2
+	modernc.org/sqlite v1.49.1
 )
 
 require (
@@ -291,7 +291,7 @@ require (
 	gopkg.in/ini.v1 v1.67.0 // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect
 	honnef.co/go/tools v0.7.0 // indirect
-	modernc.org/libc v1.70.0 // indirect
+	modernc.org/libc v1.72.0 // indirect
 	modernc.org/mathutil v1.7.1 // indirect
 	modernc.org/memory v1.11.0 // indirect
 	mvdan.cc/gofumpt v0.9.2 // indirect
diff --git a/go.sum b/go.sum
index 49b11f9..19f8695 100644
--- a/go.sum
+++ b/go.sum
@@ -851,10 +851,10 @@ gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
 gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 honnef.co/go/tools v0.7.0 h1:w6WUp1VbkqPEgLz4rkBzH/CSU6HkoqNLp6GstyTx3lU=
 honnef.co/go/tools v0.7.0/go.mod h1:pm29oPxeP3P82ISxZDgIYeOaf9ta6Pi0EWvCFoLG2vc=
-modernc.org/cc/v4 v4.27.1 h1:9W30zRlYrefrDV2JE2O8VDtJ1yPGownxciz5rrbQZis=
-modernc.org/cc/v4 v4.27.1/go.mod h1:uVtb5OGqUKpoLWhqwNQo/8LwvoiEBLvZXIQ/SmO6mL0=
-modernc.org/ccgo/v4 v4.32.0 h1:hjG66bI/kqIPX1b2yT6fr/jt+QedtP2fqojG2VrFuVw=
-modernc.org/ccgo/v4 v4.32.0/go.mod h1:6F08EBCx5uQc38kMGl+0Nm0oWczoo1c7cgpzEry7Uc0=
+modernc.org/cc/v4 v4.27.3 h1:uNCgn37E5U09mTv1XgskEVUJ8ADKpmFMPxzGJ0TSo+U=
+modernc.org/cc/v4 v4.27.3/go.mod h1:3YjcbCqhoTTHPycJDRl2WZKKFj0nwcOIPBfEZK0Hdk8=
+modernc.org/ccgo/v4 v4.32.4 h1:L5OB8rpEX4ZsXEQwGozRfJyJSFHbbNVOoQ59DU9/KuU=
+modernc.org/ccgo/v4 v4.32.4/go.mod h1:lY7f+fiTDHfcv6YlRgSkxYfhs+UvOEEzj49jAn2TOx0=
 modernc.org/fileutil v1.4.0 h1:j6ZzNTftVS054gi281TyLjHPp6CPHr2KCxEXjEbD6SM=
 modernc.org/fileutil v1.4.0/go.mod h1:EqdKFDxiByqxLk8ozOxObDSfcVOv/54xDs/DUHdvCUU=
 modernc.org/gc/v2 v2.6.5 h1:nyqdV8q46KvTpZlsw66kWqwXRHdjIlJOhG6kxiV/9xI=
@@ -863,8 +863,8 @@ modernc.org/gc/v3 v3.1.2 h1:ZtDCnhonXSZexk/AYsegNRV1lJGgaNZJuKjJSWKyEqo=
 modernc.org/gc/v3 v3.1.2/go.mod h1:HFK/6AGESC7Ex+EZJhJ2Gni6cTaYpSMmU/cT9RmlfYY=
 modernc.org/goabi0 v0.2.0 h1:HvEowk7LxcPd0eq6mVOAEMai46V+i7Jrj13t4AzuNks=
 modernc.org/goabi0 v0.2.0/go.mod h1:CEFRnnJhKvWT1c1JTI3Avm+tgOWbkOu5oPA8eH8LnMI=
-modernc.org/libc v1.70.0 h1:U58NawXqXbgpZ/dcdS9kMshu08aiA6b7gusEusqzNkw=
-modernc.org/libc v1.70.0/go.mod h1:OVmxFGP1CI/Z4L3E0Q3Mf1PDE0BucwMkcXjjLntvHJo=
+modernc.org/libc v1.72.0 h1:IEu559v9a0XWjw0DPoVKtXpO2qt5NVLAnFaBbjq+n8c=
+modernc.org/libc v1.72.0/go.mod h1:tTU8DL8A+XLVkEY3x5E/tO7s2Q/q42EtnNWda/L5QhQ=
 modernc.org/mathutil v1.7.1 h1:GCZVGXdaN8gTqB1Mf/usp1Y/hSqgI2vAGGP4jZMCxOU=
 modernc.org/mathutil v1.7.1/go.mod h1:4p5IwJITfppl0G4sUEDtCr4DthTaT47/N3aT6MhfgJg=
 modernc.org/memory v1.11.0 h1:o4QC8aMQzmcwCK3t3Ux/ZHmwFPzE6hf2Y5LbkRs+hbI=
@@ -873,8 +873,8 @@ modernc.org/opt v0.1.4 h1:2kNGMRiUjrp4LcaPuLY2PzUfqM/w9N23quVwhKt5Qm8=
 modernc.org/opt v0.1.4/go.mod h1:03fq9lsNfvkYSfxrfUhZCWPk1lm4cq4N+Bh//bEtgns=
 modernc.org/sortutil v1.2.1 h1:+xyoGf15mM3NMlPDnFqrteY07klSFxLElE2PVuWIJ7w=
 modernc.org/sortutil v1.2.1/go.mod h1:7ZI3a3REbai7gzCLcotuw9AC4VZVpYMjDzETGsSMqJE=
-modernc.org/sqlite v1.48.2 h1:5CnW4uP8joZtA0LedVqLbZV5GD7F/0x91AXeSyjoh5c=
-modernc.org/sqlite v1.48.2/go.mod h1:hWjRO6Tj/5Ik8ieqxQybiEOUXy0NJFNp2tpvVpKlvig=
+modernc.org/sqlite v1.49.1 h1:dYGHTKcX1sJ+EQDnUzvz4TJ5GbuvhNJa8Fg6ElGx73U=
+modernc.org/sqlite v1.49.1/go.mod h1:m0w8xhwYUVY3H6pSDwc3gkJ/irZT/0YEXwBlhaxQEew=
 modernc.org/strutil v1.2.1 h1:UneZBkQA+DX2Rp35KcM69cSsNES9ly8mQWD71HKlOA0=
 modernc.org/strutil v1.2.1/go.mod h1:EHkiggD70koQxjVdSBM3JKM7k6L0FbGE5eymy9i3B9A=
 modernc.org/token v1.1.0 h1:Xl7Ap9dKaEs5kLoOQeQmPWevfnk/DM5qcLcYlA8ys6Y=

From 96049c1f883150db48be3feb9bcd7616ec4eca20 Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Thu, 30 Apr 2026 15:18:13 +0000
Subject: [PATCH 05/36] Bump goreleaser/goreleaser-action from 7.0.0 to 7.1.0

Bumps [goreleaser/goreleaser-action](https://github.com/goreleaser/goreleaser-action) from 7.0.0 to 7.1.0.
- [Release notes](https://github.com/goreleaser/goreleaser-action/releases)
- [Commits](https://github.com/goreleaser/goreleaser-action/compare/ec59f474b9834571250b370d4735c50f8e2d1e29...e24998b8b67b290c2fa8b7c14fcfa7de2c5c9b8c)

---
updated-dependencies:
- dependency-name: goreleaser/goreleaser-action
  dependency-version: 7.1.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
---
 .github/workflows/release.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index f787509..cc79d4a 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -27,7 +27,7 @@ jobs:
           go-version-file: go.mod
           cache: false
 
-      - uses: goreleaser/goreleaser-action@ec59f474b9834571250b370d4735c50f8e2d1e29 # v7.0.0
+      - uses: goreleaser/goreleaser-action@e24998b8b67b290c2fa8b7c14fcfa7de2c5c9b8c # v7.1.0
         with:
           version: "~> v2"
           args: release --clean

From f1ea8b50a114c7fa32574e839b9149aa9aa59daf Mon Sep 17 00:00:00 2001
From: Andrew Nesbitt <andrewnez@gmail.com>
Date: Sat, 2 May 2026 18:00:04 +0100
Subject: [PATCH 06/36] Serve .html, .svg and .xhtml as text/plain in browse
 file handler (#103)

These file types were served with executable content types (text/html,
image/svg+xml) allowing stored XSS via package archive contents.
Also adds Content-Security-Policy: sandbox and X-Content-Type-Options:
nosniff headers to all browse file responses.
---
 internal/server/browse.go      | 10 +++++-----
 internal/server/browse_test.go |  4 ++++
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/internal/server/browse.go b/internal/server/browse.go
index 6f718cd..0442c3d 100644
--- a/internal/server/browse.go
+++ b/internal/server/browse.go
@@ -348,11 +348,11 @@ func (s *Server) browseFile(w http.ResponseWriter, r *http.Request, ecosystem, n
 	}
 	defer func() { _ = fileReader.Close() }()
 
-	// Set content type based on file extension
 	contentType := detectContentType(filePath)
 	w.Header().Set("Content-Type", contentType)
+	w.Header().Set("Content-Security-Policy", "sandbox")
+	w.Header().Set("X-Content-Type-Options", "nosniff")
 
-	// Set filename for download
 	_, filename := path.Split(filePath)
 	w.Header().Set("Content-Disposition", fmt.Sprintf("inline; filename=%q", filename))
 
@@ -368,8 +368,8 @@ func detectContentType(filename string) string {
 	// Text formats
 	case ".txt", ".md", ".markdown":
 		return contentTypePlainText
-	case ".html", ".htm":
-		return "text/html; charset=utf-8"
+	case ".html", ".htm", ".xhtml":
+		return contentTypePlainText
 	case ".css":
 		return "text/css; charset=utf-8"
 	case ".js", ".mjs":
@@ -423,7 +423,7 @@ func detectContentType(filename string) string {
 	case ".gif":
 		return "image/gif"
 	case ".svg":
-		return "image/svg+xml"
+		return contentTypePlainText
 	case ".ico":
 		return "image/x-icon"
 
diff --git a/internal/server/browse_test.go b/internal/server/browse_test.go
index 2706e90..e47bcc9 100644
--- a/internal/server/browse_test.go
+++ b/internal/server/browse_test.go
@@ -179,6 +179,10 @@ func TestDetectContentType(t *testing.T) {
 		{"file.go", "text/x-go; charset=utf-8"},
 		{"file.py", "text/x-python; charset=utf-8"},
 		{"file.rs", "text/x-rust; charset=utf-8"},
+		{"file.html", contentTypePlainText},
+		{"file.htm", contentTypePlainText},
+		{"file.xhtml", contentTypePlainText},
+		{"file.svg", contentTypePlainText},
 		{"file.png", "image/png"},
 		{"file.jpg", "image/jpeg"},
 		{"README", contentTypePlainText},

From cfcf480f692ff91a11f346c293deca560e704e0a Mon Sep 17 00:00:00 2001
From: Andrew Nesbitt <andrewnez@gmail.com>
Date: Sat, 2 May 2026 18:00:22 +0100
Subject: [PATCH 07/36] Limit io.ReadAll in openArchive to 512 MB (#104)

The browse and compare handlers buffer the full artifact into memory for
prefix detection. Without a cap, a single request for a large cached
artifact could exhaust server memory.
---
 internal/server/browse.go      | 12 ++++++++++--
 internal/server/browse_test.go | 16 ++++++++++++++++
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/internal/server/browse.go b/internal/server/browse.go
index 0442c3d..0eef2a4 100644
--- a/internal/server/browse.go
+++ b/internal/server/browse.go
@@ -18,6 +18,11 @@ import (
 
 const contentTypePlainText = "text/plain; charset=utf-8"
 
+// maxBrowseArchiveSize caps how much data openArchive will buffer for
+// prefix detection. Artifacts larger than this are rejected to prevent
+// memory exhaustion from a single request.
+const maxBrowseArchiveSize = 512 << 20 // 512 MB
+
 // archiveFilename returns a filename suitable for archive format detection.
 // Some ecosystems (e.g. composer) store artifacts with bare hash filenames
 // that have no extension. This adds .zip when the original has no extension
@@ -69,11 +74,14 @@ func openArchive(filename string, content io.Reader, ecosystem string) (archives
 		return archives.OpenWithPrefix(fname, content, "package/")
 	}
 
-	// Read content into memory so we can scan then wrap with prefix
-	data, err := io.ReadAll(content)
+	limited := io.LimitReader(content, maxBrowseArchiveSize+1)
+	data, err := io.ReadAll(limited)
 	if err != nil {
 		return nil, fmt.Errorf("reading artifact: %w", err)
 	}
+	if int64(len(data)) > maxBrowseArchiveSize {
+		return nil, fmt.Errorf("artifact too large for browsing (%d bytes)", len(data))
+	}
 
 	// Open once to detect root prefix
 	probe, err := archives.Open(fname, bytes.NewReader(data))
diff --git a/internal/server/browse_test.go b/internal/server/browse_test.go
index e47bcc9..611a319 100644
--- a/internal/server/browse_test.go
+++ b/internal/server/browse_test.go
@@ -202,6 +202,22 @@ func TestDetectContentType(t *testing.T) {
 	}
 }
 
+func TestOpenArchiveSizeLimit(t *testing.T) {
+	huge := bytes.Repeat([]byte("x"), int(maxBrowseArchiveSize)+1)
+	_, err := openArchive("test.tar.gz", bytes.NewReader(huge), "npm")
+	if err != nil {
+		t.Log("npm path streams directly, error is acceptable:", err)
+	}
+
+	_, err = openArchive("test.tar.gz", bytes.NewReader(huge), "go")
+	if err == nil {
+		t.Fatal("expected error for oversized archive, got nil")
+	}
+	if !strings.Contains(err.Error(), "too large") {
+		t.Fatalf("expected 'too large' error, got: %v", err)
+	}
+}
+
 func TestIsLikelyText(t *testing.T) {
 	tests := []struct {
 		filename string

From d6066af230672f838008e543cedd39927188e0f0 Mon Sep 17 00:00:00 2001
From: Andrew Nesbitt <andrewnez@gmail.com>
Date: Sat, 2 May 2026 18:00:25 +0100
Subject: [PATCH 08/36] Add MaxBytesReader to mirror API HandleCreate (#105)

Matches the pattern already used in api.go to prevent unbounded request
body reads.
---
 internal/server/mirror_api.go      |  1 +
 internal/server/mirror_api_test.go | 13 +++++++++++++
 2 files changed, 14 insertions(+)

diff --git a/internal/server/mirror_api.go b/internal/server/mirror_api.go
index 6a6a6ca..1eb6f93 100644
--- a/internal/server/mirror_api.go
+++ b/internal/server/mirror_api.go
@@ -20,6 +20,7 @@ func NewMirrorAPIHandler(jobs *mirror.JobStore) *MirrorAPIHandler {
 
 // HandleCreate starts a new mirror job.
 func (h *MirrorAPIHandler) HandleCreate(w http.ResponseWriter, r *http.Request) {
+	r.Body = http.MaxBytesReader(w, r.Body, maxBodySize)
 	var req mirror.JobRequest
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
 		w.Header().Set("Content-Type", "application/json")
diff --git a/internal/server/mirror_api_test.go b/internal/server/mirror_api_test.go
index 0e84da1..73b8731 100644
--- a/internal/server/mirror_api_test.go
+++ b/internal/server/mirror_api_test.go
@@ -71,6 +71,19 @@ func TestMirrorAPICreateJob(t *testing.T) {
 	}
 }
 
+func TestMirrorAPICreateOversizedBody(t *testing.T) {
+	h := setupMirrorAPI(t)
+
+	body := bytes.Repeat([]byte("x"), int(maxBodySize)+1)
+	req := httptest.NewRequest("POST", "/api/mirror", bytes.NewReader(body))
+	w := httptest.NewRecorder()
+	h.HandleCreate(w, req)
+
+	if w.Code != http.StatusBadRequest {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusBadRequest)
+	}
+}
+
 func TestMirrorAPICreateInvalidBody(t *testing.T) {
 	h := setupMirrorAPI(t)
 

From 71e8d3b9eb751345f9d9a487b8bff7f72355fa55 Mon Sep 17 00:00:00 2001
From: Andrew Nesbitt <andrewnez@gmail.com>
Date: Sat, 2 May 2026 18:00:28 +0100
Subject: [PATCH 09/36] Reject path traversal in filesystem storage (#106)

---
 internal/storage/filesystem.go      | 41 ++++++++++++++++++++++-------
 internal/storage/filesystem_test.go | 26 ++++++++++++++++--
 2 files changed, 55 insertions(+), 12 deletions(-)

diff --git a/internal/storage/filesystem.go b/internal/storage/filesystem.go
index 7a4147a..53cff42 100644
--- a/internal/storage/filesystem.go
+++ b/internal/storage/filesystem.go
@@ -8,6 +8,7 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+	"strings"
 	"time"
 )
 
@@ -31,12 +32,19 @@ func NewFilesystem(root string) (*Filesystem, error) {
 	return &Filesystem{root: absRoot}, nil
 }
 
-func (fs *Filesystem) fullPath(path string) string {
-	return filepath.Join(fs.root, filepath.FromSlash(path))
+func (fs *Filesystem) fullPath(path string) (string, error) {
+	full := filepath.Clean(filepath.Join(fs.root, filepath.FromSlash(path)))
+	if full != fs.root && !strings.HasPrefix(full, fs.root+string(filepath.Separator)) {
+		return "", fmt.Errorf("%w: path escapes storage root", ErrNotFound)
+	}
+	return full, nil
 }
 
 func (fs *Filesystem) Store(ctx context.Context, path string, r io.Reader) (int64, string, error) {
-	fullPath := fs.fullPath(path)
+	fullPath, err := fs.fullPath(path)
+	if err != nil {
+		return 0, "", err
+	}
 
 	dir := filepath.Dir(fullPath)
 	if err := os.MkdirAll(dir, dirPermissions); err != nil {
@@ -83,7 +91,10 @@ func (fs *Filesystem) Store(ctx context.Context, path string, r io.Reader) (int6
 }
 
 func (fs *Filesystem) Open(ctx context.Context, path string) (io.ReadCloser, error) {
-	fullPath := fs.fullPath(path)
+	fullPath, err := fs.fullPath(path)
+	if err != nil {
+		return nil, err
+	}
 
 	f, err := os.Open(fullPath)
 	if err != nil {
@@ -97,9 +108,12 @@ func (fs *Filesystem) Open(ctx context.Context, path string) (io.ReadCloser, err
 }
 
 func (fs *Filesystem) Exists(ctx context.Context, path string) (bool, error) {
-	fullPath := fs.fullPath(path)
+	fullPath, err := fs.fullPath(path)
+	if err != nil {
+		return false, err
+	}
 
-	_, err := os.Stat(fullPath)
+	_, err = os.Stat(fullPath)
 	if err != nil {
 		if os.IsNotExist(err) {
 			return false, nil
@@ -111,9 +125,12 @@ func (fs *Filesystem) Exists(ctx context.Context, path string) (bool, error) {
 }
 
 func (fs *Filesystem) Delete(ctx context.Context, path string) error {
-	fullPath := fs.fullPath(path)
+	fullPath, err := fs.fullPath(path)
+	if err != nil {
+		return err
+	}
 
-	err := os.Remove(fullPath)
+	err = os.Remove(fullPath)
 	if err != nil && !os.IsNotExist(err) {
 		return fmt.Errorf("removing file: %w", err)
 	}
@@ -135,7 +152,10 @@ func (fs *Filesystem) SignedURL(_ context.Context, _ string, _ time.Duration) (s
 }
 
 func (fs *Filesystem) Size(ctx context.Context, path string) (int64, error) {
-	fullPath := fs.fullPath(path)
+	fullPath, err := fs.fullPath(path)
+	if err != nil {
+		return 0, err
+	}
 
 	info, err := os.Stat(fullPath)
 	if err != nil {
@@ -174,7 +194,8 @@ func (fs *Filesystem) Root() string {
 
 // FullPath returns the full filesystem path for a storage path.
 // Useful for serving files directly or debugging.
-func (fs *Filesystem) FullPath(path string) string {
+// Returns an error if the resulting path would escape the storage root.
+func (fs *Filesystem) FullPath(path string) (string, error) {
 	return fs.fullPath(path)
 }
 
diff --git a/internal/storage/filesystem_test.go b/internal/storage/filesystem_test.go
index cdd7f6b..332dfbf 100644
--- a/internal/storage/filesystem_test.go
+++ b/internal/storage/filesystem_test.go
@@ -52,7 +52,10 @@ func TestFilesystemStore(t *testing.T) {
 	}
 
 	// Verify file exists on disk
-	fullPath := fs.FullPath("npm/lodash/4.17.21/lodash.tgz")
+	fullPath, err := fs.FullPath("npm/lodash/4.17.21/lodash.tgz")
+	if err != nil {
+		t.Fatalf("FullPath failed: %v", err)
+	}
 	data, err := os.ReadFile(fullPath)
 	if err != nil {
 		t.Fatalf("reading stored file: %v", err)
@@ -163,7 +166,10 @@ func TestFilesystemDelete(t *testing.T) {
 	}
 
 	// Empty parent directories should be cleaned up
-	nestedDir := fs.FullPath("test/delete/nested")
+	nestedDir, err := fs.FullPath("test/delete/nested")
+	if err != nil {
+		t.Fatalf("FullPath failed: %v", err)
+	}
 	if _, err := os.Stat(nestedDir); !os.IsNotExist(err) {
 		t.Error("empty nested directory not cleaned up")
 	}
@@ -237,6 +243,22 @@ func TestFilesystemLargeFile(t *testing.T) {
 	assertLargeFileRoundTrip(t, createTestFilesystem(t))
 }
 
+func TestFilesystemRejectsTraversal(t *testing.T) {
+	tmp := t.TempDir()
+	fs, err := NewFilesystem(tmp)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, p := range []string{"../etc/passwd", "../../etc/passwd", "a/../../etc/passwd"} {
+		if _, err := fs.Open(context.Background(), p); err == nil {
+			t.Errorf("Open(%q) should reject traversal", p)
+		}
+		if _, _, err := fs.Store(context.Background(), p, strings.NewReader("x")); err == nil {
+			t.Errorf("Store(%q) should reject traversal", p)
+		}
+	}
+}
+
 func TestFilesystemSignedURLUnsupported(t *testing.T) {
 	fs := createTestFilesystem(t)
 

From adca29326904ab72a13e1d55979db0144f19fb36 Mon Sep 17 00:00:00 2001
From: Andrew Nesbitt <andrewnez@gmail.com>
Date: Sat, 2 May 2026 18:01:06 +0100
Subject: [PATCH 10/36] Bump git-pkgs deps to latest patch releases

---
 go.mod | 18 ++++++++++--------
 go.sum | 36 ++++++++++++++++++++----------------
 2 files changed, 30 insertions(+), 24 deletions(-)

diff --git a/go.mod b/go.mod
index 2619970..c9f6ba5 100644
--- a/go.mod
+++ b/go.mod
@@ -4,13 +4,13 @@ go 1.25.6
 
 require (
 	github.com/CycloneDX/cyclonedx-go v0.10.0
-	github.com/git-pkgs/archives v0.2.2
+	github.com/git-pkgs/archives v0.2.3
 	github.com/git-pkgs/enrichment v0.2.2
-	github.com/git-pkgs/purl v0.1.10
-	github.com/git-pkgs/registries v0.4.1
-	github.com/git-pkgs/spdx v0.1.2
-	github.com/git-pkgs/vers v0.2.4
-	github.com/git-pkgs/vulns v0.1.4
+	github.com/git-pkgs/purl v0.1.12
+	github.com/git-pkgs/registries v0.5.1
+	github.com/git-pkgs/spdx v0.1.3
+	github.com/git-pkgs/vers v0.2.5
+	github.com/git-pkgs/vulns v0.1.5
 	github.com/go-chi/chi/v5 v5.2.5
 	github.com/jmoiron/sqlx v1.4.0
 	github.com/lib/pq v1.12.3
@@ -22,7 +22,7 @@ require (
 	golang.org/x/sync v0.20.0
 	google.golang.org/protobuf v1.36.11
 	gopkg.in/yaml.v3 v3.0.1
-	modernc.org/sqlite v1.49.1
+	modernc.org/sqlite v1.50.0
 )
 
 require (
@@ -127,7 +127,8 @@ require (
 	github.com/fzipp/gocyclo v0.6.0 // indirect
 	github.com/ghostiam/protogetter v0.3.20 // indirect
 	github.com/git-pkgs/packageurl-go v0.3.1 // indirect
-	github.com/github/go-spdx/v2 v2.4.0 // indirect
+	github.com/git-pkgs/pom v0.1.4 // indirect
+	github.com/github/go-spdx/v2 v2.6.0 // indirect
 	github.com/go-critic/go-critic v0.14.3 // indirect
 	github.com/go-logr/logr v1.4.3 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
@@ -219,6 +220,7 @@ require (
 	github.com/nishanths/predeclared v0.2.2 // indirect
 	github.com/nunnatsa/ginkgolinter v0.23.0 // indirect
 	github.com/oapi-codegen/runtime v1.2.0 // indirect
+	github.com/package-url/packageurl-go v0.1.6 // indirect
 	github.com/pandatix/go-cvss v0.6.2 // indirect
 	github.com/pelletier/go-toml v1.9.5 // indirect
 	github.com/pelletier/go-toml/v2 v2.2.4 // indirect
diff --git a/go.sum b/go.sum
index f8028ee..dcc385e 100644
--- a/go.sum
+++ b/go.sum
@@ -250,24 +250,26 @@ github.com/fzipp/gocyclo v0.6.0 h1:lsblElZG7d3ALtGMx9fmxeTKZaLLpU8mET09yN4BBLo=
 github.com/fzipp/gocyclo v0.6.0/go.mod h1:rXPyn8fnlpa0R2csP/31uerbiVBugk5whMdlyaLkLoA=
 github.com/ghostiam/protogetter v0.3.20 h1:oW7OPFit2FxZOpmMRPP9FffU4uUpfeE/rEdE1f+MzD0=
 github.com/ghostiam/protogetter v0.3.20/go.mod h1:FjIu5Yfs6FT391m+Fjp3fbAYJ6rkL/J6ySpZBfnODuI=
-github.com/git-pkgs/archives v0.2.2 h1:RxOjrV8RzKicbMVdf2GDKOqIOHZNVjrLY/Pc7KSE/WQ=
-github.com/git-pkgs/archives v0.2.2/go.mod h1:LTJ1iQVFA7otizWMOyiI82NYVmyBWAPRzwu/e30rcXU=
+github.com/git-pkgs/archives v0.2.3 h1:iyKo4CY/KA3HJyshAj2iTVloq4gXSp8vv2+0H+IE4gc=
+github.com/git-pkgs/archives v0.2.3/go.mod h1:LTJ1iQVFA7otizWMOyiI82NYVmyBWAPRzwu/e30rcXU=
 github.com/git-pkgs/enrichment v0.2.2 h1:vaQu5vs3tjQB5JI0gzBrUCynUc9z3l5byPhgKFaNZrc=
 github.com/git-pkgs/enrichment v0.2.2/go.mod h1:5JWGmlHWcv5HQHUrctcpnRUNpEF5VAixD2z4zvqKejs=
 github.com/git-pkgs/packageurl-go v0.3.1 h1:WM3RBABQZLaRBxgKyYughc3cVBE8KyQxbSC6Jt5ak7M=
 github.com/git-pkgs/packageurl-go v0.3.1/go.mod h1:rcIxiG37BlQLB6FZfgdj9Fm7yjhRQd3l+5o7J0QPAk4=
-github.com/git-pkgs/purl v0.1.10 h1:NMjeF10nzFn3tdQlz6rbmHB+i+YkyrFQxho3e33ePTQ=
-github.com/git-pkgs/purl v0.1.10/go.mod h1:C5Vp/kyZ/wGckCLexx4wPVfUxEiToRkdsOPh5Z7ig/I=
-github.com/git-pkgs/registries v0.4.1 h1:4qlKVNhC/6x6Bt87t3wrGJtF3EFrUpHQt9/zKsa5IvU=
-github.com/git-pkgs/registries v0.4.1/go.mod h1:49UCPFWQmwNV7rBEr9TrTDWKR7vYxFcxp3VfdkeFbdE=
-github.com/git-pkgs/spdx v0.1.2 h1:wHSK+CqFsO5N7yDTPvxDmer5LgNEa7vAsiZhi5Aci0A=
-github.com/git-pkgs/spdx v0.1.2/go.mod h1:V98MgZapNgYw54/pdGR82d7RU93qzJoybahbpZqTfw8=
-github.com/git-pkgs/vers v0.2.4 h1:Zr3jR/Xf1i/6cvBaJKPxhCwjzqz7uvYHE0Fhid/GPBk=
-github.com/git-pkgs/vers v0.2.4/go.mod h1:biTbSQK1qdbrsxDEKnqe3Jzclxz8vW6uDcwKjfUGcOo=
-github.com/git-pkgs/vulns v0.1.4 h1:SlnGWHNmtdQgABjfrX/I/pVe+DWLbZ5Yi9xg+/De5r8=
-github.com/git-pkgs/vulns v0.1.4/go.mod h1:34xkR7QncIVfxoi78k3YT6Y9DfTEaL7j6PzCqjsRP9U=
-github.com/github/go-spdx/v2 v2.4.0 h1:+4IwVwJJbm3rzvrQ6P1nI9BDMcy3la4RchRy5uehV/M=
-github.com/github/go-spdx/v2 v2.4.0/go.mod h1:/5rwgS0txhGtRdUZwc02bTglzg6HK3FfuEbECKlK2Sg=
+github.com/git-pkgs/pom v0.1.4 h1:C6st+XSbF75eKuwfdkDZZtYHoTcaWRIEQYar5VtszUo=
+github.com/git-pkgs/pom v0.1.4/go.mod h1:ufdMBe1lKzqOeP9IUb9NPZ458xKV8E8NvuyBMxOfwIk=
+github.com/git-pkgs/purl v0.1.12 h1:qCskrEU1LWQhCkIVZd992W5++Bsxazvx2Cx1/65qCvU=
+github.com/git-pkgs/purl v0.1.12/go.mod h1:ofp4mHsR0cUeVONQaf33n6Wxg2QTEvtUdRfCedI8ouA=
+github.com/git-pkgs/registries v0.5.1 h1:UPE42CyZAsOfqO3N5bDelu28wS4Ifx/aOj0XZS4qYeI=
+github.com/git-pkgs/registries v0.5.1/go.mod h1:BY0YW+V0WDGBMuDR2aSMR3NzOPFK4K+F3j6+ch+cq3M=
+github.com/git-pkgs/spdx v0.1.3 h1:YQou23mLfzbW//6JlHUuc5x1P5VNIIDSku5gvauf86I=
+github.com/git-pkgs/spdx v0.1.3/go.mod h1:4HGGWyC8tg4DjOhrtBTYl4Lu+5i2BFuauGX8zcVcYPg=
+github.com/git-pkgs/vers v0.2.5 h1:tDtUMik9Iw1lyPHdT5V6LXjLo9LsJc0xOawURz7ibQU=
+github.com/git-pkgs/vers v0.2.5/go.mod h1:biTbSQK1qdbrsxDEKnqe3Jzclxz8vW6uDcwKjfUGcOo=
+github.com/git-pkgs/vulns v0.1.5 h1:mtX88/27toFl+B95kaH5QbAdOCQ3YIDGjJrlrrnqQTE=
+github.com/git-pkgs/vulns v0.1.5/go.mod h1:bZFikfrR/5gC0ZMwXh7qcEu2gpKfXMBhVsy4kF12Ae0=
+github.com/github/go-spdx/v2 v2.6.0 h1:Y/Chr7L8oG85Ilbzl11xkUSQFUfG1kGkLP18LyInvhg=
+github.com/github/go-spdx/v2 v2.6.0/go.mod h1:Ftc45YYG1WzpzwEPKRVm9Jv8vDqOrN4gWoCkK+bHer0=
 github.com/go-chi/chi/v5 v5.2.5 h1:Eg4myHZBjyvJmAFjFvWgrqDTXFyOzjj7YIm3L3mu6Ug=
 github.com/go-chi/chi/v5 v5.2.5/go.mod h1:X7Gx4mteadT3eDOMTsXzmI4/rwUpOwBHLpAfupzFJP0=
 github.com/go-critic/go-critic v0.14.3 h1:5R1qH2iFeo4I/RJU8vTezdqs08Egi4u5p6vOESA0pog=
@@ -525,6 +527,8 @@ github.com/otiai10/curr v0.0.0-20150429015615-9b4961190c95/go.mod h1:9qAhocn7zKJ
 github.com/otiai10/curr v1.0.0/go.mod h1:LskTG5wDwr8Rs+nNQ+1LlxRjAtTZZjtJW4rMXl6j4vs=
 github.com/otiai10/mint v1.3.0/go.mod h1:F5AjcsTsWUqX+Na9fpHb52P8pcRX2CI6A3ctIT91xUo=
 github.com/otiai10/mint v1.3.1/go.mod h1:/yxELlJQ0ufhjUwhshSj+wFjZ78CnZ48/1wtmBH1OTc=
+github.com/package-url/packageurl-go v0.1.6 h1:YO3p6u1XmCUliivUg/qWphaY8vI6hxSnnPv7Bfg3m5M=
+github.com/package-url/packageurl-go v0.1.6/go.mod h1:nKAWB8E6uk1MHqiS/lQb9pYBGH2+mdJ2PJc2s50dQY0=
 github.com/pandatix/go-cvss v0.6.2 h1:TFiHlzUkT67s6UkelHmK6s1INKVUG7nlKYiWWDTITGI=
 github.com/pandatix/go-cvss v0.6.2/go.mod h1:jDXYlQBZrc8nvrMUVVvTG8PhmuShOnKrxP53nOFkt8Q=
 github.com/pelletier/go-toml v1.9.5 h1:4yBQzkHv+7BHq2PQUZF3Mx0IYxG7LsP222s7Agd3ve8=
@@ -900,8 +904,8 @@ modernc.org/opt v0.1.4 h1:2kNGMRiUjrp4LcaPuLY2PzUfqM/w9N23quVwhKt5Qm8=
 modernc.org/opt v0.1.4/go.mod h1:03fq9lsNfvkYSfxrfUhZCWPk1lm4cq4N+Bh//bEtgns=
 modernc.org/sortutil v1.2.1 h1:+xyoGf15mM3NMlPDnFqrteY07klSFxLElE2PVuWIJ7w=
 modernc.org/sortutil v1.2.1/go.mod h1:7ZI3a3REbai7gzCLcotuw9AC4VZVpYMjDzETGsSMqJE=
-modernc.org/sqlite v1.49.1 h1:dYGHTKcX1sJ+EQDnUzvz4TJ5GbuvhNJa8Fg6ElGx73U=
-modernc.org/sqlite v1.49.1/go.mod h1:m0w8xhwYUVY3H6pSDwc3gkJ/irZT/0YEXwBlhaxQEew=
+modernc.org/sqlite v1.50.0 h1:eMowQSWLK0MeiQTdmz3lqoF5dqclujdlIKeJA11+7oM=
+modernc.org/sqlite v1.50.0/go.mod h1:m0w8xhwYUVY3H6pSDwc3gkJ/irZT/0YEXwBlhaxQEew=
 modernc.org/strutil v1.2.1 h1:UneZBkQA+DX2Rp35KcM69cSsNES9ly8mQWD71HKlOA0=
 modernc.org/strutil v1.2.1/go.mod h1:EHkiggD70koQxjVdSBM3JKM7k6L0FbGE5eymy9i3B9A=
 modernc.org/token v1.1.0 h1:Xl7Ap9dKaEs5kLoOQeQmPWevfnk/DM5qcLcYlA8ys6Y=

From a4fd333d48e344c7bc936418d5c3752a865e7885 Mon Sep 17 00:00:00 2001
From: Andrew Nesbitt <andrewnez@gmail.com>
Date: Sun, 3 May 2026 09:07:16 +0100
Subject: [PATCH 11/36] Check for path traversal after URL decoding (#108)

containsPathTraversal only checked literal ".." segments separated by
forward slashes. Encoded forms like %2e%2e%2f or backslash separators
would slip past if a caller ever passed a raw or Windows-style path.

The check now URL-decodes the input and treats backslashes as
separators before splitting. Go's stdlib already decodes r.URL.Path so
the encoded case is mostly belt-and-braces for cache keys and other
non-router inputs, but the storage layer guard from #106 makes this
worth locking in with tests.

Fixes #74
---
 internal/handler/handler.go             | 16 ++++++++++++++--
 internal/handler/path_traversal_test.go |  9 +++++++++
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/internal/handler/handler.go b/internal/handler/handler.go
index 746b9e8..bf834ed 100644
--- a/internal/handler/handler.go
+++ b/internal/handler/handler.go
@@ -24,9 +24,21 @@ import (
 )
 
 // containsPathTraversal returns true if the path contains ".." segments
-// that could be used to escape the intended directory.
+// that could be used to escape the intended directory. It checks the path
+// as given and after URL-decoding, and treats backslashes as separators.
 func containsPathTraversal(path string) bool {
-	for _, segment := range strings.Split(path, "/") {
+	if hasDotDotSegment(path) {
+		return true
+	}
+	if decoded, err := url.PathUnescape(path); err == nil && decoded != path {
+		return hasDotDotSegment(decoded)
+	}
+	return false
+}
+
+func hasDotDotSegment(path string) bool {
+	path = strings.ReplaceAll(path, "\\", "/")
+	for segment := range strings.SplitSeq(path, "/") {
 		if segment == ".." {
 			return true
 		}
diff --git a/internal/handler/path_traversal_test.go b/internal/handler/path_traversal_test.go
index 14d2218..5ad68a5 100644
--- a/internal/handler/path_traversal_test.go
+++ b/internal/handler/path_traversal_test.go
@@ -14,6 +14,15 @@ func TestContainsPathTraversal(t *testing.T) {
 		{"pool/main/../../../etc/shadow", true},
 		{"pool/..hidden/file", false}, // ".." as a segment, not "..hidden"
 		{"", false},
+		{"%2e%2e/etc/passwd", true},
+		{"%2e%2e%2fetc%2fpasswd", true},
+		{"pool/%2e%2e/%2e%2e/etc/shadow", true},
+		{"%2E%2E%2Fetc", true},
+		{`..\\etc\\passwd`, true},
+		{`pool\\..\\..\\etc`, true},
+		{"%2e%2e%5cetc%5cpasswd", true},
+		{"pool/%2e%2ehidden/file", false},
+		{"pool/%zz/bad-encoding", false},
 	}
 
 	for _, tt := range tests {

From 522c6f233e3f1cea54dd9ee29ed17daf5a7ac833 Mon Sep 17 00:00:00 2001
From: Andrew Nesbitt <andrewnez@gmail.com>
Date: Sun, 3 May 2026 09:14:18 +0100
Subject: [PATCH 12/36] Validate package paths before database lookups (#109)

The wildcard package routes (/packages/{ecosystem}/*, /api/package/*,
/api/vulns/*, /api/browse/*, /api/compare/*) only checked for an empty
path before passing user input to GetPackageByEcosystemName and the
enrichment service.

Add validatePackagePath as a coarse first-line filter: reject null
bytes, other control characters, and paths over 512 bytes. Wired into
all five entry handlers immediately after the chi wildcard is read.

This is the generic layer; ecosystem-specific name format rules (npm
scoped name shape, Maven coordinate structure, etc.) can be added on
top per #75.

Fixes #75
---
 internal/server/api.go          |  8 ++++++++
 internal/server/api_test.go     | 30 +++++++++++++++++++++++++++++
 internal/server/browse.go       |  8 ++++++++
 internal/server/resolve.go      | 28 +++++++++++++++++++++++++++
 internal/server/resolve_test.go | 34 +++++++++++++++++++++++++++++++++
 internal/server/server.go       |  4 ++++
 6 files changed, 112 insertions(+)

diff --git a/internal/server/api.go b/internal/server/api.go
index 903dc22..052c7ea 100644
--- a/internal/server/api.go
+++ b/internal/server/api.go
@@ -140,6 +140,10 @@ type BulkResponse struct {
 func (h *APIHandler) HandlePackagePath(w http.ResponseWriter, r *http.Request) {
 	ecosystem := chi.URLParam(r, "ecosystem")
 	wildcard := chi.URLParam(r, "*")
+	if err := validatePackagePath(wildcard); err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
 	segments := splitWildcardPath(wildcard)
 
 	if ecosystem == "" || len(segments) == 0 {
@@ -274,6 +278,10 @@ func (h *APIHandler) getVersion(w http.ResponseWriter, r *http.Request, ecosyste
 func (h *APIHandler) HandleVulnsPath(w http.ResponseWriter, r *http.Request) {
 	ecosystem := chi.URLParam(r, "ecosystem")
 	wildcard := chi.URLParam(r, "*")
+	if err := validatePackagePath(wildcard); err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
 	segments := splitWildcardPath(wildcard)
 
 	if ecosystem == "" || len(segments) == 0 {
diff --git a/internal/server/api_test.go b/internal/server/api_test.go
index 548f324..0494b2f 100644
--- a/internal/server/api_test.go
+++ b/internal/server/api_test.go
@@ -9,6 +9,7 @@ import (
 	"net/http/httptest"
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 
 	"github.com/git-pkgs/proxy/internal/database"
@@ -48,6 +49,35 @@ func TestHandlePackagePath_MissingParams(t *testing.T) {
 	}
 }
 
+func TestHandlePackagePath_InvalidName(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	svc := enrichment.New(logger)
+	h := NewAPIHandler(svc, nil)
+
+	r := chi.NewRouter()
+	r.Get("/api/package/{ecosystem}/*", h.HandlePackagePath)
+
+	tests := []struct {
+		name string
+		path string
+	}{
+		{"null byte", "/api/package/npm/lodash%00"},
+		{"too long", "/api/package/npm/" + strings.Repeat("a", maxPackagePathLen+1)},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			req := httptest.NewRequest("GET", tt.path, nil)
+			w := httptest.NewRecorder()
+			r.ServeHTTP(w, req)
+
+			if w.Code != http.StatusBadRequest {
+				t.Errorf("expected status 400, got %d", w.Code)
+			}
+		})
+	}
+}
+
 func TestHandleVulnsPath_MissingParams(t *testing.T) {
 	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
 	svc := enrichment.New(logger)
diff --git a/internal/server/browse.go b/internal/server/browse.go
index 0eef2a4..d0645af 100644
--- a/internal/server/browse.go
+++ b/internal/server/browse.go
@@ -133,6 +133,10 @@ type BrowseFileInfo struct {
 func (s *Server) handleBrowsePath(w http.ResponseWriter, r *http.Request) {
 	ecosystem := chi.URLParam(r, "ecosystem")
 	wildcard := chi.URLParam(r, "*")
+	if err := validatePackagePath(wildcard); err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
 	segments := splitWildcardPath(wildcard)
 
 	if ecosystem == "" || len(segments) < 2 {
@@ -185,6 +189,10 @@ func (s *Server) handleBrowsePath(w http.ResponseWriter, r *http.Request) {
 func (s *Server) handleComparePath(w http.ResponseWriter, r *http.Request) {
 	ecosystem := chi.URLParam(r, "ecosystem")
 	wildcard := chi.URLParam(r, "*")
+	if err := validatePackagePath(wildcard); err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
 	segments := splitWildcardPath(wildcard)
 
 	if ecosystem == "" || len(segments) < 3 {
diff --git a/internal/server/resolve.go b/internal/server/resolve.go
index 479ede6..51f203d 100644
--- a/internal/server/resolve.go
+++ b/internal/server/resolve.go
@@ -1,11 +1,39 @@
 package server
 
 import (
+	"fmt"
 	"strings"
+	"unicode"
 
 	"github.com/git-pkgs/proxy/internal/database"
 )
 
+// maxPackagePathLen bounds the wildcard portion of package routes (name plus
+// version and any suffix). npm caps names at 214 and Maven coordinates can be
+// longer, so 512 leaves room without admitting pathological inputs.
+const maxPackagePathLen = 512
+
+// validatePackagePath rejects wildcard package paths that cannot be valid in
+// any supported ecosystem. It is a coarse filter applied before database or
+// enrichment lookups; ecosystem-specific name rules are layered on top.
+func validatePackagePath(path string) error {
+	if path == "" {
+		return fmt.Errorf("package name required")
+	}
+	if len(path) > maxPackagePathLen {
+		return fmt.Errorf("package path exceeds %d bytes", maxPackagePathLen)
+	}
+	for _, r := range path {
+		if r == 0 {
+			return fmt.Errorf("package path contains null byte")
+		}
+		if unicode.IsControl(r) {
+			return fmt.Errorf("package path contains control character %#U", r)
+		}
+	}
+	return nil
+}
+
 // resolvePackageName determines the package name from a wildcard path by
 // checking the database. This handles namespaced packages like Composer's
 // vendor/name format where the package name contains a slash.
diff --git a/internal/server/resolve_test.go b/internal/server/resolve_test.go
index 427c2cb..dd7d2dc 100644
--- a/internal/server/resolve_test.go
+++ b/internal/server/resolve_test.go
@@ -3,6 +3,7 @@ package server
 import (
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 
 	"github.com/git-pkgs/proxy/internal/database"
@@ -118,3 +119,36 @@ func TestSplitWildcardPath(t *testing.T) {
 		}
 	}
 }
+
+func TestValidatePackagePath(t *testing.T) {
+	tests := []struct {
+		name    string
+		path    string
+		wantErr bool
+	}{
+		{"simple", "lodash", false},
+		{"with version", "lodash/4.17.21", false},
+		{"npm scoped", "@babel/core/7.0.0", false},
+		{"composer namespaced", "symfony/console/6.0.0", false},
+		{"maven coordinates", "org.apache.commons/commons-lang3/3.12.0", false},
+		{"unicode", "café/1.0.0", false},
+		{"empty", "", true},
+		{"null byte", "lodash\x00/4.17.21", true},
+		{"null byte suffix", "lodash\x00", true},
+		{"newline", "lodash\n4.17.21", true},
+		{"carriage return", "lodash\r", true},
+		{"escape", "lodash\x1b[31m", true},
+		{"delete", "lodash\x7f", true},
+		{"too long", strings.Repeat("a", maxPackagePathLen+1), true},
+		{"at limit", strings.Repeat("a", maxPackagePathLen), false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := validatePackagePath(tt.path)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("validatePackagePath(%q) error = %v, wantErr %v", tt.path, err, tt.wantErr)
+			}
+		})
+	}
+}
diff --git a/internal/server/server.go b/internal/server/server.go
index ebf9268..a15985a 100644
--- a/internal/server/server.go
+++ b/internal/server/server.go
@@ -615,6 +615,10 @@ func (s *Server) handlePackagesList(w http.ResponseWriter, r *http.Request) {
 func (s *Server) handlePackagePath(w http.ResponseWriter, r *http.Request) {
 	ecosystem := chi.URLParam(r, "ecosystem")
 	wildcard := chi.URLParam(r, "*")
+	if err := validatePackagePath(wildcard); err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
 	segments := splitWildcardPath(wildcard)
 
 	if ecosystem == "" || len(segments) == 0 {

From e912227e3b82a67b4a406411f9ae51ef8effefef Mon Sep 17 00:00:00 2001
From: Andrew Nesbitt <andrewnez@gmail.com>
Date: Sun, 3 May 2026 09:29:42 +0100
Subject: [PATCH 13/36] Use archives.OpenBytes in browse handler to cut buffer
 copies (#107)

* Use archives.OpenBytes in openArchive to avoid redundant buffer copies

* Bump git-pkgs/archives to v0.3.0
---
 go.mod                               |  2 +-
 go.sum                               |  4 +-
 internal/server/browse.go            | 15 +++-----
 internal/server/browse_bench_test.go | 57 ++++++++++++++++++++++++++++
 internal/server/browse_test.go       | 19 ++++------
 5 files changed, 74 insertions(+), 23 deletions(-)
 create mode 100644 internal/server/browse_bench_test.go

diff --git a/go.mod b/go.mod
index c9f6ba5..87fd2db 100644
--- a/go.mod
+++ b/go.mod
@@ -4,7 +4,7 @@ go 1.25.6
 
 require (
 	github.com/CycloneDX/cyclonedx-go v0.10.0
-	github.com/git-pkgs/archives v0.2.3
+	github.com/git-pkgs/archives v0.3.0
 	github.com/git-pkgs/enrichment v0.2.2
 	github.com/git-pkgs/purl v0.1.12
 	github.com/git-pkgs/registries v0.5.1
diff --git a/go.sum b/go.sum
index dcc385e..80df597 100644
--- a/go.sum
+++ b/go.sum
@@ -250,8 +250,8 @@ github.com/fzipp/gocyclo v0.6.0 h1:lsblElZG7d3ALtGMx9fmxeTKZaLLpU8mET09yN4BBLo=
 github.com/fzipp/gocyclo v0.6.0/go.mod h1:rXPyn8fnlpa0R2csP/31uerbiVBugk5whMdlyaLkLoA=
 github.com/ghostiam/protogetter v0.3.20 h1:oW7OPFit2FxZOpmMRPP9FffU4uUpfeE/rEdE1f+MzD0=
 github.com/ghostiam/protogetter v0.3.20/go.mod h1:FjIu5Yfs6FT391m+Fjp3fbAYJ6rkL/J6ySpZBfnODuI=
-github.com/git-pkgs/archives v0.2.3 h1:iyKo4CY/KA3HJyshAj2iTVloq4gXSp8vv2+0H+IE4gc=
-github.com/git-pkgs/archives v0.2.3/go.mod h1:LTJ1iQVFA7otizWMOyiI82NYVmyBWAPRzwu/e30rcXU=
+github.com/git-pkgs/archives v0.3.0 h1:iXKyO83jEFub1PGEDlHmk2tQ7XeV5LySTc0sEkH3x78=
+github.com/git-pkgs/archives v0.3.0/go.mod h1:LTJ1iQVFA7otizWMOyiI82NYVmyBWAPRzwu/e30rcXU=
 github.com/git-pkgs/enrichment v0.2.2 h1:vaQu5vs3tjQB5JI0gzBrUCynUc9z3l5byPhgKFaNZrc=
 github.com/git-pkgs/enrichment v0.2.2/go.mod h1:5JWGmlHWcv5HQHUrctcpnRUNpEF5VAixD2z4zvqKejs=
 github.com/git-pkgs/packageurl-go v0.3.1 h1:WM3RBABQZLaRBxgKyYughc3cVBE8KyQxbSC6Jt5ak7M=
diff --git a/internal/server/browse.go b/internal/server/browse.go
index d0645af..9396180 100644
--- a/internal/server/browse.go
+++ b/internal/server/browse.go
@@ -1,7 +1,6 @@
 package server
 
 import (
-	"bytes"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -69,11 +68,6 @@ func detectSingleRootDir(reader archives.Reader) string {
 func openArchive(filename string, content io.Reader, ecosystem string) (archives.Reader, error) { //nolint:ireturn // wraps multiple archive implementations
 	fname := archiveFilename(filename)
 
-	// npm always uses package/ prefix
-	if ecosystem == "npm" {
-		return archives.OpenWithPrefix(fname, content, "package/")
-	}
-
 	limited := io.LimitReader(content, maxBrowseArchiveSize+1)
 	data, err := io.ReadAll(limited)
 	if err != nil {
@@ -83,15 +77,18 @@ func openArchive(filename string, content io.Reader, ecosystem string) (archives
 		return nil, fmt.Errorf("artifact too large for browsing (%d bytes)", len(data))
 	}
 
-	// Open once to detect root prefix
-	probe, err := archives.Open(fname, bytes.NewReader(data))
+	if ecosystem == "npm" {
+		return archives.OpenBytesWithPrefix(fname, data, "package/")
+	}
+
+	probe, err := archives.OpenBytes(fname, data)
 	if err != nil {
 		return nil, err
 	}
 	prefix := detectSingleRootDir(probe)
 	_ = probe.Close()
 
-	return archives.OpenWithPrefix(fname, bytes.NewReader(data), prefix)
+	return archives.OpenBytesWithPrefix(fname, data, prefix)
 }
 
 // BrowseListResponse contains the file listing for a directory in an archives.
diff --git a/internal/server/browse_bench_test.go b/internal/server/browse_bench_test.go
new file mode 100644
index 0000000..03f3f02
--- /dev/null
+++ b/internal/server/browse_bench_test.go
@@ -0,0 +1,57 @@
+package server
+
+import (
+	"archive/tar"
+	"bytes"
+	"compress/gzip"
+	"fmt"
+	"math/rand"
+	"testing"
+)
+
+func createBenchTarGz(prefix string, fileCount, fileSize int) []byte {
+	rnd := rand.New(rand.NewSource(1)) //nolint:gosec
+	buf := new(bytes.Buffer)
+	gw := gzip.NewWriter(buf)
+	tw := tar.NewWriter(gw)
+
+	payload := make([]byte, fileSize)
+	for i := range fileCount {
+		rnd.Read(payload)
+		_ = tw.WriteHeader(&tar.Header{
+			Name: fmt.Sprintf("%sfile%04d.dat", prefix, i),
+			Size: int64(fileSize),
+			Mode: 0644,
+		})
+		_, _ = tw.Write(payload)
+	}
+	_ = tw.Close()
+	_ = gw.Close()
+	return buf.Bytes()
+}
+
+func BenchmarkOpenArchive(b *testing.B) {
+	cases := []struct {
+		name      string
+		ecosystem string
+		filename  string
+		data      []byte
+	}{
+		{"npm", "npm", "pkg.tgz", createBenchTarGz("package/", 64, 16*1024)},
+		{"go", "go", "v1.2.3.tar.gz", createBenchTarGz("repo-abc123/", 64, 16*1024)},
+	}
+
+	for _, tc := range cases {
+		b.Run(tc.name, func(b *testing.B) {
+			b.SetBytes(int64(len(tc.data)))
+			b.ReportAllocs()
+			for b.Loop() {
+				r, err := openArchive(tc.filename, bytes.NewReader(tc.data), tc.ecosystem)
+				if err != nil {
+					b.Fatal(err)
+				}
+				_ = r.Close()
+			}
+		})
+	}
+}
diff --git a/internal/server/browse_test.go b/internal/server/browse_test.go
index 611a319..28f08da 100644
--- a/internal/server/browse_test.go
+++ b/internal/server/browse_test.go
@@ -204,17 +204,14 @@ func TestDetectContentType(t *testing.T) {
 
 func TestOpenArchiveSizeLimit(t *testing.T) {
 	huge := bytes.Repeat([]byte("x"), int(maxBrowseArchiveSize)+1)
-	_, err := openArchive("test.tar.gz", bytes.NewReader(huge), "npm")
-	if err != nil {
-		t.Log("npm path streams directly, error is acceptable:", err)
-	}
-
-	_, err = openArchive("test.tar.gz", bytes.NewReader(huge), "go")
-	if err == nil {
-		t.Fatal("expected error for oversized archive, got nil")
-	}
-	if !strings.Contains(err.Error(), "too large") {
-		t.Fatalf("expected 'too large' error, got: %v", err)
+	for _, eco := range []string{"npm", "go"} {
+		_, err := openArchive("test.tar.gz", bytes.NewReader(huge), eco)
+		if err == nil {
+			t.Fatalf("%s: expected error for oversized archive, got nil", eco)
+		}
+		if !strings.Contains(err.Error(), "too large") {
+			t.Fatalf("%s: expected 'too large' error, got: %v", eco, err)
+		}
 	}
 }
 

From 8d2740624fc08f95515f91f6463cbc2494013433 Mon Sep 17 00:00:00 2001
From: Andrew Nesbitt <andrewnez@gmail.com>
Date: Sun, 3 May 2026 09:42:03 +0100
Subject: [PATCH 14/36] Structured JSON error responses for API endpoints
 (#110)

* Structured JSON error responses for API endpoints

API handlers returned errors via http.Error (text/plain) with ad-hoc
strings, while the mirror API used a different {"error": "..."} shape
and leaked internal err.Error() text to clients.

Add ErrorResponse{Code, Message} with stable codes (BAD_REQUEST,
NOT_FOUND, UPSTREAM_ERROR, INTERNAL_ERROR) and writeError/badRequest/
notFound/internalError helpers. Convert all JSON API handlers in
api.go, browse.go, mirror_api.go and the /stats endpoint. Enrichment
failures now report 502 UPSTREAM_ERROR rather than 500.

Protocol handlers in internal/handler/ are deliberately unchanged
since npm/pip/cargo clients expect their own response formats, not
JSON. HTML page handlers in server.go also keep text/plain.

Swagger @Failure annotations updated and docs regenerated.

Fixes #76

* Convert validatePackagePath errors to JSON in API handlers
---
 docs/swagger/docs.go           | 43 ++++++++++------
 docs/swagger/swagger.json      | 43 ++++++++++------
 internal/server/api.go         | 50 +++++++++---------
 internal/server/browse.go      | 70 ++++++++++++-------------
 internal/server/errors.go      | 42 +++++++++++++++
 internal/server/errors_test.go | 93 ++++++++++++++++++++++++++++++++++
 internal/server/mirror_api.go  | 18 ++-----
 internal/server/server.go      |  6 +--
 8 files changed, 256 insertions(+), 109 deletions(-)
 create mode 100644 internal/server/errors.go
 create mode 100644 internal/server/errors_test.go

diff --git a/docs/swagger/docs.go b/docs/swagger/docs.go
index fedf889..34aedbf 100644
--- a/docs/swagger/docs.go
+++ b/docs/swagger/docs.go
@@ -64,13 +64,13 @@ const docTemplate = `{
                     "404": {
                         "description": "Not Found",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     },
                     "500": {
                         "description": "Internal Server Error",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     }
                 }
@@ -126,19 +126,19 @@ const docTemplate = `{
                     "400": {
                         "description": "Bad Request",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     },
                     "404": {
                         "description": "Not Found",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     },
                     "500": {
                         "description": "Internal Server Error",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     }
                 }
@@ -177,13 +177,13 @@ const docTemplate = `{
                     "400": {
                         "description": "Bad Request",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     },
                     "500": {
                         "description": "Internal Server Error",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     }
                 }
@@ -240,13 +240,13 @@ const docTemplate = `{
                     "404": {
                         "description": "Not Found",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     },
                     "500": {
                         "description": "Internal Server Error",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     }
                 }
@@ -285,13 +285,13 @@ const docTemplate = `{
                     "400": {
                         "description": "Bad Request",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     },
                     "500": {
                         "description": "Internal Server Error",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     }
                 }
@@ -338,13 +338,13 @@ const docTemplate = `{
                     "400": {
                         "description": "Bad Request",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     },
                     "500": {
                         "description": "Internal Server Error",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     }
                 }
@@ -384,13 +384,13 @@ const docTemplate = `{
                     "400": {
                         "description": "Bad Request",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     },
                     "500": {
                         "description": "Internal Server Error",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     }
                 }
@@ -440,7 +440,7 @@ const docTemplate = `{
                     "500": {
                         "description": "Internal Server Error",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     }
                 }
@@ -504,6 +504,17 @@ const docTemplate = `{
                 }
             }
         },
+        "server.ErrorResponse": {
+            "type": "object",
+            "properties": {
+                "code": {
+                    "type": "string"
+                },
+                "message": {
+                    "type": "string"
+                }
+            }
+        },
         "server.OutdatedPackage": {
             "type": "object",
             "properties": {
diff --git a/docs/swagger/swagger.json b/docs/swagger/swagger.json
index 88df1e9..b775e63 100644
--- a/docs/swagger/swagger.json
+++ b/docs/swagger/swagger.json
@@ -57,13 +57,13 @@
                     "404": {
                         "description": "Not Found",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     },
                     "500": {
                         "description": "Internal Server Error",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     }
                 }
@@ -119,19 +119,19 @@
                     "400": {
                         "description": "Bad Request",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     },
                     "404": {
                         "description": "Not Found",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     },
                     "500": {
                         "description": "Internal Server Error",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     }
                 }
@@ -170,13 +170,13 @@
                     "400": {
                         "description": "Bad Request",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     },
                     "500": {
                         "description": "Internal Server Error",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     }
                 }
@@ -233,13 +233,13 @@
                     "404": {
                         "description": "Not Found",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     },
                     "500": {
                         "description": "Internal Server Error",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     }
                 }
@@ -278,13 +278,13 @@
                     "400": {
                         "description": "Bad Request",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     },
                     "500": {
                         "description": "Internal Server Error",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     }
                 }
@@ -331,13 +331,13 @@
                     "400": {
                         "description": "Bad Request",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     },
                     "500": {
                         "description": "Internal Server Error",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     }
                 }
@@ -377,13 +377,13 @@
                     "400": {
                         "description": "Bad Request",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     },
                     "500": {
                         "description": "Internal Server Error",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     }
                 }
@@ -433,7 +433,7 @@
                     "500": {
                         "description": "Internal Server Error",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.ErrorResponse"
                         }
                     }
                 }
@@ -497,6 +497,17 @@
                 }
             }
         },
+        "server.ErrorResponse": {
+            "type": "object",
+            "properties": {
+                "code": {
+                    "type": "string"
+                },
+                "message": {
+                    "type": "string"
+                }
+            }
+        },
         "server.OutdatedPackage": {
             "type": "object",
             "properties": {
diff --git a/internal/server/api.go b/internal/server/api.go
index 052c7ea..ddb9ca7 100644
--- a/internal/server/api.go
+++ b/internal/server/api.go
@@ -141,13 +141,13 @@ func (h *APIHandler) HandlePackagePath(w http.ResponseWriter, r *http.Request) {
 	ecosystem := chi.URLParam(r, "ecosystem")
 	wildcard := chi.URLParam(r, "*")
 	if err := validatePackagePath(wildcard); err != nil {
-		http.Error(w, err.Error(), http.StatusBadRequest)
+		badRequest(w, err.Error())
 		return
 	}
 	segments := splitWildcardPath(wildcard)
 
 	if ecosystem == "" || len(segments) == 0 {
-		http.Error(w, "ecosystem and name are required", http.StatusBadRequest)
+		badRequest(w, "ecosystem and name are required")
 		return
 	}
 
@@ -194,12 +194,12 @@ func (h *APIHandler) HandlePackagePath(w http.ResponseWriter, r *http.Request) {
 func (h *APIHandler) getPackage(w http.ResponseWriter, r *http.Request, ecosystem, name string) {
 	info, err := h.enrichment.EnrichPackage(r.Context(), ecosystem, name)
 	if err != nil {
-		http.Error(w, "failed to enrich package", http.StatusInternalServerError)
+		writeError(w, http.StatusBadGateway, ErrCodeUpstream, "failed to enrich package")
 		return
 	}
 
 	if info == nil {
-		http.Error(w, "package not found", http.StatusNotFound)
+		notFound(w, "package not found")
 		return
 	}
 
@@ -221,7 +221,7 @@ func (h *APIHandler) getPackage(w http.ResponseWriter, r *http.Request, ecosyste
 func (h *APIHandler) getVersion(w http.ResponseWriter, r *http.Request, ecosystem, name, version string) {
 	result, err := h.enrichment.EnrichFull(r.Context(), ecosystem, name, version)
 	if err != nil {
-		http.Error(w, "failed to enrich version", http.StatusInternalServerError)
+		writeError(w, http.StatusBadGateway, ErrCodeUpstream, "failed to enrich version")
 		return
 	}
 
@@ -279,13 +279,13 @@ func (h *APIHandler) HandleVulnsPath(w http.ResponseWriter, r *http.Request) {
 	ecosystem := chi.URLParam(r, "ecosystem")
 	wildcard := chi.URLParam(r, "*")
 	if err := validatePackagePath(wildcard); err != nil {
-		http.Error(w, err.Error(), http.StatusBadRequest)
+		badRequest(w, err.Error())
 		return
 	}
 	segments := splitWildcardPath(wildcard)
 
 	if ecosystem == "" || len(segments) == 0 {
-		http.Error(w, "ecosystem and name are required", http.StatusBadRequest)
+		badRequest(w, "ecosystem and name are required")
 		return
 	}
 
@@ -306,7 +306,7 @@ func (h *APIHandler) HandleVulnsPath(w http.ResponseWriter, r *http.Request) {
 
 	vulns, err := h.enrichment.CheckVulnerabilities(r.Context(), ecosystem, name, version)
 	if err != nil {
-		http.Error(w, "failed to check vulnerabilities", http.StatusInternalServerError)
+		writeError(w, http.StatusBadGateway, ErrCodeUpstream, "failed to check vulnerabilities")
 		return
 	}
 
@@ -338,19 +338,19 @@ func (h *APIHandler) HandleVulnsPath(w http.ResponseWriter, r *http.Request) {
 // @Produce json
 // @Param request body OutdatedRequest true "Packages to check"
 // @Success 200 {object} OutdatedResponse
-// @Failure 400 {string} string
-// @Failure 500 {string} string
+// @Failure 400 {object} ErrorResponse
+// @Failure 500 {object} ErrorResponse
 // @Router /api/outdated [post]
 func (h *APIHandler) HandleOutdated(w http.ResponseWriter, r *http.Request) {
 	r.Body = http.MaxBytesReader(w, r.Body, maxBodySize)
 	var req OutdatedRequest
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
-		http.Error(w, "invalid request body", http.StatusBadRequest)
+		badRequest(w, "invalid request body")
 		return
 	}
 
 	if len(req.Packages) == 0 {
-		http.Error(w, "packages list is required", http.StatusBadRequest)
+		badRequest(w, "packages list is required")
 		return
 	}
 
@@ -384,19 +384,19 @@ func (h *APIHandler) HandleOutdated(w http.ResponseWriter, r *http.Request) {
 // @Produce json
 // @Param request body BulkRequest true "PURLs"
 // @Success 200 {object} BulkResponse
-// @Failure 400 {string} string
-// @Failure 500 {string} string
+// @Failure 400 {object} ErrorResponse
+// @Failure 500 {object} ErrorResponse
 // @Router /api/bulk [post]
 func (h *APIHandler) HandleBulkLookup(w http.ResponseWriter, r *http.Request) {
 	r.Body = http.MaxBytesReader(w, r.Body, maxBodySize)
 	var req BulkRequest
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
-		http.Error(w, "invalid request body", http.StatusBadRequest)
+		badRequest(w, "invalid request body")
 		return
 	}
 
 	if len(req.PURLs) == 0 {
-		http.Error(w, "purls list is required", http.StatusBadRequest)
+		badRequest(w, "purls list is required")
 		return
 	}
 
@@ -484,15 +484,15 @@ type SearchPackageResult struct {
 // @Param q query string true "Query"
 // @Param ecosystem query string false "Ecosystem"
 // @Success 200 {object} SearchResponse
-// @Failure 400 {string} string
-// @Failure 500 {string} string
+// @Failure 400 {object} ErrorResponse
+// @Failure 500 {object} ErrorResponse
 // @Router /api/search [get]
 func (h *APIHandler) HandleSearch(w http.ResponseWriter, r *http.Request) {
 	query := r.URL.Query().Get("q")
 	ecosystem := r.URL.Query().Get("ecosystem")
 
 	if query == "" {
-		http.Error(w, "query parameter 'q' is required", http.StatusBadRequest)
+		badRequest(w, "query parameter 'q' is required")
 		return
 	}
 
@@ -502,7 +502,7 @@ func (h *APIHandler) HandleSearch(w http.ResponseWriter, r *http.Request) {
 	// Search in database
 	results, err := h.db.SearchPackages(query, ecosystem, limit, (page-1)*limit)
 	if err != nil {
-		http.Error(w, "search failed", http.StatusInternalServerError)
+		internalError(w, "search failed")
 		return
 	}
 
@@ -546,7 +546,7 @@ func (h *APIHandler) HandleSearch(w http.ResponseWriter, r *http.Request) {
 func writeJSON(w http.ResponseWriter, v any) {
 	w.Header().Set("Content-Type", "application/json")
 	if err := json.NewEncoder(w).Encode(v); err != nil {
-		http.Error(w, "failed to encode response", http.StatusInternalServerError)
+		internalError(w, "failed to encode response")
 	}
 }
 
@@ -581,8 +581,8 @@ type PackageListResult struct {
 // @Param ecosystem query string false "Ecosystem"
 // @Param sort query string false "Sort" Enums(hits,name,size,cached_at,ecosystem,vulns)
 // @Success 200 {object} PackagesListResponse
-// @Failure 400 {string} string
-// @Failure 500 {string} string
+// @Failure 400 {object} ErrorResponse
+// @Failure 500 {object} ErrorResponse
 // @Router /api/packages [get]
 func (h *APIHandler) HandlePackagesList(w http.ResponseWriter, r *http.Request) {
 	ecosystem := r.URL.Query().Get("ecosystem")
@@ -600,7 +600,7 @@ func (h *APIHandler) HandlePackagesList(w http.ResponseWriter, r *http.Request)
 		"vulns":       true,
 	}
 	if !validSorts[sortBy] {
-		http.Error(w, "invalid sort parameter", http.StatusBadRequest)
+		badRequest(w, "invalid sort parameter")
 		return
 	}
 
@@ -609,7 +609,7 @@ func (h *APIHandler) HandlePackagesList(w http.ResponseWriter, r *http.Request)
 
 	packages, err := h.db.ListCachedPackages(ecosystem, sortBy, limit, (page-1)*limit)
 	if err != nil {
-		http.Error(w, "failed to list packages", http.StatusInternalServerError)
+		internalError(w, "failed to list packages")
 		return
 	}
 
diff --git a/internal/server/browse.go b/internal/server/browse.go
index 9396180..be2b04a 100644
--- a/internal/server/browse.go
+++ b/internal/server/browse.go
@@ -117,8 +117,8 @@ type BrowseFileInfo struct {
 // @Param version path string true "Version"
 // @Param path query string false "Directory path inside the archive"
 // @Success 200 {object} BrowseListResponse
-// @Failure 404 {string} string
-// @Failure 500 {string} string
+// @Failure 404 {object} ErrorResponse
+// @Failure 500 {object} ErrorResponse
 // @Router /api/browse/{ecosystem}/{name}/{version} [get]
 // handleBrowsePath dispatches /api/browse/{ecosystem}/* to the appropriate browse handler.
 // It resolves namespaced package names by consulting the database.
@@ -131,13 +131,13 @@ func (s *Server) handleBrowsePath(w http.ResponseWriter, r *http.Request) {
 	ecosystem := chi.URLParam(r, "ecosystem")
 	wildcard := chi.URLParam(r, "*")
 	if err := validatePackagePath(wildcard); err != nil {
-		http.Error(w, err.Error(), http.StatusBadRequest)
+		badRequest(w, err.Error())
 		return
 	}
 	segments := splitWildcardPath(wildcard)
 
 	if ecosystem == "" || len(segments) < 2 {
-		http.Error(w, "ecosystem, name, and version required", http.StatusBadRequest)
+		badRequest(w, "ecosystem, name, and version required")
 		return
 	}
 
@@ -161,7 +161,7 @@ func (s *Server) handleBrowsePath(w http.ResponseWriter, r *http.Request) {
 			rest = nameVersionSegments[len(nameVersionSegments)-1:]
 		}
 		if len(rest) != 1 {
-			http.Error(w, "not found", http.StatusNotFound)
+			notFound(w, "not found")
 			return
 		}
 		s.browseFile(w, r, ecosystem, name, rest[0], filePath)
@@ -175,7 +175,7 @@ func (s *Server) handleBrowsePath(w http.ResponseWriter, r *http.Request) {
 		rest = segments[len(segments)-1:]
 	}
 	if len(rest) != 1 {
-		http.Error(w, "not found", http.StatusNotFound)
+		notFound(w, "not found")
 		return
 	}
 	s.browseList(w, r, ecosystem, name, rest[0])
@@ -187,13 +187,13 @@ func (s *Server) handleComparePath(w http.ResponseWriter, r *http.Request) {
 	ecosystem := chi.URLParam(r, "ecosystem")
 	wildcard := chi.URLParam(r, "*")
 	if err := validatePackagePath(wildcard); err != nil {
-		http.Error(w, err.Error(), http.StatusBadRequest)
+		badRequest(w, err.Error())
 		return
 	}
 	segments := splitWildcardPath(wildcard)
 
 	if ecosystem == "" || len(segments) < 3 {
-		http.Error(w, "ecosystem, name, fromVersion, and toVersion required", http.StatusBadRequest)
+		badRequest(w, "ecosystem, name, fromVersion, and toVersion required")
 		return
 	}
 
@@ -213,12 +213,12 @@ func (s *Server) browseList(w http.ResponseWriter, r *http.Request, ecosystem, n
 	versionPURL := purl.MakePURLString(ecosystem, name, version)
 	artifacts, err := s.db.GetArtifactsByVersionPURL(versionPURL)
 	if err != nil {
-		http.Error(w, "version not found", http.StatusNotFound)
+		notFound(w, "version not found")
 		return
 	}
 
 	if len(artifacts) == 0 {
-		http.Error(w, "no artifacts cached", http.StatusNotFound)
+		notFound(w, "no artifacts cached")
 		return
 	}
 
@@ -232,7 +232,7 @@ func (s *Server) browseList(w http.ResponseWriter, r *http.Request, ecosystem, n
 	}
 
 	if cachedArtifact == nil {
-		http.Error(w, "artifact not cached", http.StatusNotFound)
+		notFound(w, "artifact not cached")
 		return
 	}
 
@@ -240,7 +240,7 @@ func (s *Server) browseList(w http.ResponseWriter, r *http.Request, ecosystem, n
 	artifactReader, err := s.storage.Open(r.Context(), cachedArtifact.StoragePath.String)
 	if err != nil {
 		s.logger.Error("failed to read artifact from storage", "error", err)
-		http.Error(w, "failed to read artifact", http.StatusInternalServerError)
+		internalError(w, "failed to read artifact")
 		return
 	}
 	defer func() { _ = artifactReader.Close() }()
@@ -249,7 +249,7 @@ func (s *Server) browseList(w http.ResponseWriter, r *http.Request, ecosystem, n
 	archiveReader, err := openArchive(cachedArtifact.Filename, artifactReader, ecosystem)
 	if err != nil {
 		s.logger.Error("failed to open archive", "error", err, "filename", cachedArtifact.Filename)
-		http.Error(w, "failed to open archive", http.StatusInternalServerError)
+		internalError(w, "failed to open archive")
 		return
 	}
 	defer func() { _ = archiveReader.Close() }()
@@ -258,7 +258,7 @@ func (s *Server) browseList(w http.ResponseWriter, r *http.Request, ecosystem, n
 	files, err := archiveReader.ListDir(dirPath)
 	if err != nil {
 		s.logger.Error("failed to list directory", "error", err, "path", dirPath)
-		http.Error(w, "failed to list directory", http.StatusInternalServerError)
+		internalError(w, "failed to list directory")
 		return
 	}
 
@@ -293,13 +293,13 @@ func (s *Server) browseList(w http.ResponseWriter, r *http.Request, ecosystem, n
 // @Param version path string true "Version"
 // @Param filepath path string true "File path inside the archive"
 // @Success 200 {file} file
-// @Failure 400 {string} string
-// @Failure 404 {string} string
-// @Failure 500 {string} string
+// @Failure 400 {object} ErrorResponse
+// @Failure 404 {object} ErrorResponse
+// @Failure 500 {object} ErrorResponse
 // @Router /api/browse/{ecosystem}/{name}/{version}/file/{filepath} [get]
 func (s *Server) browseFile(w http.ResponseWriter, r *http.Request, ecosystem, name, version, filePath string) {
 	if filePath == "" {
-		http.Error(w, "file path required", http.StatusBadRequest)
+		badRequest(w, "file path required")
 		return
 	}
 
@@ -307,12 +307,12 @@ func (s *Server) browseFile(w http.ResponseWriter, r *http.Request, ecosystem, n
 	versionPURL := purl.MakePURLString(ecosystem, name, version)
 	artifacts, err := s.db.GetArtifactsByVersionPURL(versionPURL)
 	if err != nil {
-		http.Error(w, "version not found", http.StatusNotFound)
+		notFound(w, "version not found")
 		return
 	}
 
 	if len(artifacts) == 0 {
-		http.Error(w, "no artifacts cached", http.StatusNotFound)
+		notFound(w, "no artifacts cached")
 		return
 	}
 
@@ -326,7 +326,7 @@ func (s *Server) browseFile(w http.ResponseWriter, r *http.Request, ecosystem, n
 	}
 
 	if cachedArtifact == nil {
-		http.Error(w, "artifact not cached", http.StatusNotFound)
+		notFound(w, "artifact not cached")
 		return
 	}
 
@@ -334,7 +334,7 @@ func (s *Server) browseFile(w http.ResponseWriter, r *http.Request, ecosystem, n
 	artifactReader, err := s.storage.Open(r.Context(), cachedArtifact.StoragePath.String)
 	if err != nil {
 		s.logger.Error("failed to read artifact from storage", "error", err)
-		http.Error(w, "failed to read artifact", http.StatusInternalServerError)
+		internalError(w, "failed to read artifact")
 		return
 	}
 	defer func() { _ = artifactReader.Close() }()
@@ -343,7 +343,7 @@ func (s *Server) browseFile(w http.ResponseWriter, r *http.Request, ecosystem, n
 	archiveReader, err := openArchive(cachedArtifact.Filename, artifactReader, ecosystem)
 	if err != nil {
 		s.logger.Error("failed to open archive", "error", err, "filename", cachedArtifact.Filename)
-		http.Error(w, "failed to open archive", http.StatusInternalServerError)
+		internalError(w, "failed to open archive")
 		return
 	}
 	defer func() { _ = archiveReader.Close() }()
@@ -352,11 +352,11 @@ func (s *Server) browseFile(w http.ResponseWriter, r *http.Request, ecosystem, n
 	fileReader, err := archiveReader.Extract(filePath)
 	if err != nil {
 		if strings.Contains(err.Error(), "not found") {
-			http.Error(w, "file not found", http.StatusNotFound)
+			notFound(w, "file not found")
 			return
 		}
 		s.logger.Error("failed to extract file", "error", err, "path", filePath)
-		http.Error(w, "failed to extract file", http.StatusInternalServerError)
+		internalError(w, "failed to extract file")
 		return
 	}
 	defer func() { _ = fileReader.Close() }()
@@ -496,8 +496,8 @@ type BrowseSourceData struct {
 // @Param fromVersion path string true "From version"
 // @Param toVersion path string true "To version"
 // @Success 200 {object} map[string]any
-// @Failure 404 {string} string
-// @Failure 500 {string} string
+// @Failure 404 {object} ErrorResponse
+// @Failure 500 {object} ErrorResponse
 // @Router /api/compare/{ecosystem}/{name}/{fromVersion}/{toVersion} [get]
 func (s *Server) compareDiff(w http.ResponseWriter, r *http.Request, ecosystem, name, fromVersion, toVersion string) {
 	// Get artifacts for both versions
@@ -506,13 +506,13 @@ func (s *Server) compareDiff(w http.ResponseWriter, r *http.Request, ecosystem,
 
 	fromArtifacts, err := s.db.GetArtifactsByVersionPURL(fromPURL)
 	if err != nil || len(fromArtifacts) == 0 {
-		http.Error(w, "from version not found or not cached", http.StatusNotFound)
+		notFound(w, "from version not found or not cached")
 		return
 	}
 
 	toArtifacts, err := s.db.GetArtifactsByVersionPURL(toPURL)
 	if err != nil || len(toArtifacts) == 0 {
-		http.Error(w, "to version not found or not cached", http.StatusNotFound)
+		notFound(w, "to version not found or not cached")
 		return
 	}
 
@@ -532,7 +532,7 @@ func (s *Server) compareDiff(w http.ResponseWriter, r *http.Request, ecosystem,
 	}
 
 	if fromArtifact == nil || toArtifact == nil {
-		http.Error(w, "one or both versions not cached", http.StatusNotFound)
+		notFound(w, "one or both versions not cached")
 		return
 	}
 
@@ -540,7 +540,7 @@ func (s *Server) compareDiff(w http.ResponseWriter, r *http.Request, ecosystem,
 	fromReader, err := s.storage.Open(r.Context(), fromArtifact.StoragePath.String)
 	if err != nil {
 		s.logger.Error("failed to open from artifact", "error", err)
-		http.Error(w, "failed to read from version", http.StatusInternalServerError)
+		internalError(w, "failed to read from version")
 		return
 	}
 	defer func() { _ = fromReader.Close() }()
@@ -548,7 +548,7 @@ func (s *Server) compareDiff(w http.ResponseWriter, r *http.Request, ecosystem,
 	toReader, err := s.storage.Open(r.Context(), toArtifact.StoragePath.String)
 	if err != nil {
 		s.logger.Error("failed to open to artifact", "error", err)
-		http.Error(w, "failed to read to version", http.StatusInternalServerError)
+		internalError(w, "failed to read to version")
 		return
 	}
 	defer func() { _ = toReader.Close() }()
@@ -556,7 +556,7 @@ func (s *Server) compareDiff(w http.ResponseWriter, r *http.Request, ecosystem,
 	fromArchive, err := openArchive(fromArtifact.Filename, fromReader, ecosystem)
 	if err != nil {
 		s.logger.Error("failed to open from archive", "error", err)
-		http.Error(w, "failed to open from archive", http.StatusInternalServerError)
+		internalError(w, "failed to open from archive")
 		return
 	}
 	defer func() { _ = fromArchive.Close() }()
@@ -564,7 +564,7 @@ func (s *Server) compareDiff(w http.ResponseWriter, r *http.Request, ecosystem,
 	toArchive, err := openArchive(toArtifact.Filename, toReader, ecosystem)
 	if err != nil {
 		s.logger.Error("failed to open to archive", "error", err)
-		http.Error(w, "failed to open to archive", http.StatusInternalServerError)
+		internalError(w, "failed to open to archive")
 		return
 	}
 	defer func() { _ = toArchive.Close() }()
@@ -573,7 +573,7 @@ func (s *Server) compareDiff(w http.ResponseWriter, r *http.Request, ecosystem,
 	result, err := diff.Compare(fromArchive, toArchive)
 	if err != nil {
 		s.logger.Error("failed to generate diff", "error", err)
-		http.Error(w, "failed to generate diff", http.StatusInternalServerError)
+		internalError(w, "failed to generate diff")
 		return
 	}
 
diff --git a/internal/server/errors.go b/internal/server/errors.go
new file mode 100644
index 0000000..474ecd7
--- /dev/null
+++ b/internal/server/errors.go
@@ -0,0 +1,42 @@
+package server
+
+import (
+	"encoding/json"
+	"net/http"
+)
+
+// Error codes returned in API error responses. These are stable identifiers
+// that clients can match on; the message text is for humans and may change.
+const (
+	ErrCodeBadRequest = "BAD_REQUEST"
+	ErrCodeNotFound   = "NOT_FOUND"
+	ErrCodeUpstream   = "UPSTREAM_ERROR"
+	ErrCodeInternal   = "INTERNAL_ERROR"
+)
+
+// ErrorResponse is the JSON body returned for API errors.
+type ErrorResponse struct {
+	Code    string `json:"code"`
+	Message string `json:"message"`
+}
+
+// writeError sends a JSON error response with the given status, code and
+// user-facing message. Internal error details should be logged separately
+// by the caller, never passed as the message.
+func writeError(w http.ResponseWriter, status int, code, message string) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(status)
+	_ = json.NewEncoder(w).Encode(ErrorResponse{Code: code, Message: message})
+}
+
+func badRequest(w http.ResponseWriter, message string) {
+	writeError(w, http.StatusBadRequest, ErrCodeBadRequest, message)
+}
+
+func notFound(w http.ResponseWriter, message string) {
+	writeError(w, http.StatusNotFound, ErrCodeNotFound, message)
+}
+
+func internalError(w http.ResponseWriter, message string) {
+	writeError(w, http.StatusInternalServerError, ErrCodeInternal, message)
+}
diff --git a/internal/server/errors_test.go b/internal/server/errors_test.go
new file mode 100644
index 0000000..c660ae2
--- /dev/null
+++ b/internal/server/errors_test.go
@@ -0,0 +1,93 @@
+package server
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestWriteError(t *testing.T) {
+	tests := []struct {
+		name    string
+		fn      func(w http.ResponseWriter)
+		status  int
+		code    string
+		message string
+	}{
+		{
+			name:    "badRequest",
+			fn:      func(w http.ResponseWriter) { badRequest(w, "missing field") },
+			status:  http.StatusBadRequest,
+			code:    ErrCodeBadRequest,
+			message: "missing field",
+		},
+		{
+			name:    "notFound",
+			fn:      func(w http.ResponseWriter) { notFound(w, "package not found") },
+			status:  http.StatusNotFound,
+			code:    ErrCodeNotFound,
+			message: "package not found",
+		},
+		{
+			name:    "internalError",
+			fn:      func(w http.ResponseWriter) { internalError(w, "boom") },
+			status:  http.StatusInternalServerError,
+			code:    ErrCodeInternal,
+			message: "boom",
+		},
+		{
+			name: "upstream",
+			fn: func(w http.ResponseWriter) {
+				writeError(w, http.StatusBadGateway, ErrCodeUpstream, "registry unreachable")
+			},
+			status:  http.StatusBadGateway,
+			code:    ErrCodeUpstream,
+			message: "registry unreachable",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			w := httptest.NewRecorder()
+			tt.fn(w)
+
+			if w.Code != tt.status {
+				t.Errorf("status = %d, want %d", w.Code, tt.status)
+			}
+			if ct := w.Header().Get("Content-Type"); ct != "application/json" {
+				t.Errorf("Content-Type = %q, want application/json", ct)
+			}
+
+			var resp ErrorResponse
+			if err := json.Unmarshal(w.Body.Bytes(), &resp); err != nil {
+				t.Fatalf("response body is not valid JSON: %v (body: %q)", err, w.Body.String())
+			}
+			if resp.Code != tt.code {
+				t.Errorf("code = %q, want %q", resp.Code, tt.code)
+			}
+			if resp.Message != tt.message {
+				t.Errorf("message = %q, want %q", resp.Message, tt.message)
+			}
+		})
+	}
+}
+
+func TestAPIErrorResponseShape(t *testing.T) {
+	w := httptest.NewRecorder()
+	badRequest(w, "x")
+
+	var raw map[string]any
+	if err := json.Unmarshal(w.Body.Bytes(), &raw); err != nil {
+		t.Fatalf("invalid JSON: %v", err)
+	}
+	if _, ok := raw["code"]; !ok {
+		t.Error("response missing 'code' field")
+	}
+	if _, ok := raw["message"]; !ok {
+		t.Error("response missing 'message' field")
+	}
+	if len(raw) != 2 {
+		t.Errorf("response has unexpected fields: %v", raw)
+	}
+}
diff --git a/internal/server/mirror_api.go b/internal/server/mirror_api.go
index 1eb6f93..028d4e0 100644
--- a/internal/server/mirror_api.go
+++ b/internal/server/mirror_api.go
@@ -23,17 +23,13 @@ func (h *MirrorAPIHandler) HandleCreate(w http.ResponseWriter, r *http.Request)
 	r.Body = http.MaxBytesReader(w, r.Body, maxBodySize)
 	var req mirror.JobRequest
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
-		w.Header().Set("Content-Type", "application/json")
-		w.WriteHeader(http.StatusBadRequest)
-		writeJSON(w, map[string]string{"error": "invalid request body"})
+		badRequest(w, "invalid request body")
 		return
 	}
 
 	id, err := h.jobs.Create(req)
 	if err != nil {
-		w.Header().Set("Content-Type", "application/json")
-		w.WriteHeader(http.StatusBadRequest)
-		writeJSON(w, map[string]string{"error": err.Error()})
+		badRequest(w, "invalid mirror job request")
 		return
 	}
 
@@ -47,13 +43,10 @@ func (h *MirrorAPIHandler) HandleGet(w http.ResponseWriter, r *http.Request) {
 	id := chi.URLParam(r, "id")
 	job := h.jobs.Get(id)
 	if job == nil {
-		w.Header().Set("Content-Type", "application/json")
-		w.WriteHeader(http.StatusNotFound)
-		writeJSON(w, map[string]string{"error": "job not found"})
+		notFound(w, "job not found")
 		return
 	}
 
-	w.Header().Set("Content-Type", "application/json")
 	writeJSON(w, job)
 }
 
@@ -61,11 +54,8 @@ func (h *MirrorAPIHandler) HandleGet(w http.ResponseWriter, r *http.Request) {
 func (h *MirrorAPIHandler) HandleCancel(w http.ResponseWriter, r *http.Request) {
 	id := chi.URLParam(r, "id")
 	if h.jobs.Cancel(id) {
-		w.Header().Set("Content-Type", "application/json")
 		writeJSON(w, map[string]string{"status": "canceled"})
 	} else {
-		w.Header().Set("Content-Type", "application/json")
-		w.WriteHeader(http.StatusNotFound)
-		writeJSON(w, map[string]string{"error": "job not found or not running"})
+		notFound(w, "job not found or not running")
 	}
 }
diff --git a/internal/server/server.go b/internal/server/server.go
index a15985a..a168b4a 100644
--- a/internal/server/server.go
+++ b/internal/server/server.go
@@ -826,20 +826,20 @@ type StatsResponse struct {
 // @Tags meta
 // @Produce json
 // @Success 200 {object} StatsResponse
-// @Failure 500 {string} string
+// @Failure 500 {object} ErrorResponse
 // @Router /stats [get]
 func (s *Server) handleStats(w http.ResponseWriter, r *http.Request) {
 	ctx := r.Context()
 
 	count, err := s.db.GetCachedArtifactCount()
 	if err != nil {
-		http.Error(w, "failed to get artifact count", http.StatusInternalServerError)
+		internalError(w, "failed to get artifact count")
 		return
 	}
 
 	size, err := s.db.GetTotalCacheSize()
 	if err != nil {
-		http.Error(w, "failed to get cache size", http.StatusInternalServerError)
+		internalError(w, "failed to get cache size")
 		return
 	}
 

From 61741123bf23255297142632c56df691dd92e261 Mon Sep 17 00:00:00 2001
From: Andrew Nesbitt <andrewnez@gmail.com>
Date: Sun, 3 May 2026 10:36:28 +0100
Subject: [PATCH 15/36] Verify cached artifacts on read (#111)

checkCache opened the storage reader and streamed it to the client
without checking that the bytes still matched what was originally
stored, or what the upstream registry declared. Disk corruption,
accidental overwrites, or local tampering would go unnoticed.

Wrap the storage reader in a verifyingReader that computes SHA256
(against artifact.content_hash) and, when version.integrity holds an
SRI string, the corresponding sha256/384/512 digest as bytes flow
through. At EOF the digests are compared; on mismatch we log at
error level, bump proxy_integrity_failures_total, and clear the
artifact's cache entry so the next request refetches from upstream.

Verification is skipped when the stream was not fully consumed
(client disconnect) to avoid evicting good artifacts on partial
reads. The DirectServe presigned-URL path is unverified since the
proxy never sees those bytes.

Refs #42 (part 1)
---
 internal/handler/handler.go        |  11 ++-
 internal/handler/integrity.go      | 140 +++++++++++++++++++++++++++++
 internal/handler/integrity_test.go | 136 ++++++++++++++++++++++++++++
 internal/metrics/metrics.go        |  14 +++
 4 files changed, 300 insertions(+), 1 deletion(-)
 create mode 100644 internal/handler/integrity.go
 create mode 100644 internal/handler/integrity_test.go

diff --git a/internal/handler/handler.go b/internal/handler/handler.go
index bf834ed..6bcf506 100644
--- a/internal/handler/handler.go
+++ b/internal/handler/handler.go
@@ -188,7 +188,16 @@ func (p *Proxy) checkCache(ctx context.Context, pkgPURL, versionPURL, filename s
 		return nil, nil
 	}
 
-	result.Reader = reader
+	result.Reader = newVerifyingReader(reader, artifact.ContentHash.String, ver.Integrity.String,
+		func(reason string) {
+			p.Logger.Error("cached artifact failed integrity check",
+				"purl", versionPURL, "filename", filename,
+				"path", artifact.StoragePath.String, "reason", reason)
+			metrics.RecordIntegrityFailure(pkg.Ecosystem)
+			if err := p.DB.ClearArtifactCache(versionPURL, filename); err != nil {
+				p.Logger.Warn("failed to clear corrupt artifact from cache", "error", err)
+			}
+		})
 	p.recordCacheHit(pkgPURL, versionPURL, filename)
 	return result, nil
 }
diff --git a/internal/handler/integrity.go b/internal/handler/integrity.go
new file mode 100644
index 0000000..bb29a21
--- /dev/null
+++ b/internal/handler/integrity.go
@@ -0,0 +1,140 @@
+package handler
+
+import (
+	"crypto/sha256"
+	"crypto/sha512"
+	"crypto/subtle"
+	"encoding/base64"
+	"encoding/hex"
+	"fmt"
+	"hash"
+	"io"
+	"strings"
+)
+
+// parseSRI parses a Subresource Integrity string (e.g. "sha512-abc==") into
+// an algorithm name and raw digest bytes. Returns ok=false for empty,
+// malformed, or unsupported entries. Only the first hash in a multi-hash
+// SRI string is considered.
+func parseSRI(s string) (algo string, digest []byte, ok bool) {
+	s = strings.TrimSpace(s)
+	if s == "" {
+		return "", nil, false
+	}
+	if i := strings.IndexByte(s, ' '); i >= 0 {
+		s = s[:i]
+	}
+	algo, b64, found := strings.Cut(s, "-")
+	if !found {
+		return "", nil, false
+	}
+	d, err := base64.StdEncoding.DecodeString(b64)
+	if err != nil {
+		return "", nil, false
+	}
+	switch algo {
+	case "sha256", "sha384", "sha512":
+		return algo, d, true
+	default:
+		return "", nil, false
+	}
+}
+
+func newSRIHash(algo string) hash.Hash {
+	switch algo {
+	case "sha256":
+		return sha256.New()
+	case "sha384":
+		return sha512.New384()
+	case "sha512":
+		return sha512.New()
+	}
+	return nil
+}
+
+// verifyingReader wraps an io.ReadCloser and computes SHA256 (and optionally
+// a second SRI hash) as bytes are read. When the underlying reader reaches
+// EOF it compares the digests against the expected values and calls
+// onMismatch for each failure. Verification is skipped if the stream was
+// not fully consumed (e.g. client disconnect) to avoid false positives.
+type verifyingReader struct {
+	r          io.ReadCloser
+	sha256     hash.Hash
+	wantSHA256 string
+	sri        hash.Hash
+	sriAlgo    string
+	wantSRI    []byte
+	onMismatch func(reason string)
+	eof        bool
+	verified   bool
+}
+
+func newVerifyingReader(r io.ReadCloser, contentHash, sri string, onMismatch func(string)) io.ReadCloser {
+	if contentHash == "" && sri == "" {
+		return r
+	}
+	v := &verifyingReader{
+		r:          r,
+		onMismatch: onMismatch,
+	}
+	if contentHash != "" {
+		v.sha256 = sha256.New()
+		v.wantSHA256 = contentHash
+	}
+	if algo, digest, ok := parseSRI(sri); ok {
+		v.sri = newSRIHash(algo)
+		v.sriAlgo = algo
+		v.wantSRI = digest
+	}
+	if v.sha256 == nil && v.sri == nil {
+		return r
+	}
+	return v
+}
+
+func (v *verifyingReader) Read(p []byte) (int, error) {
+	n, err := v.r.Read(p)
+	if n > 0 {
+		if v.sha256 != nil {
+			v.sha256.Write(p[:n])
+		}
+		if v.sri != nil {
+			v.sri.Write(p[:n])
+		}
+	}
+	if err == io.EOF {
+		v.eof = true
+		v.verify()
+	}
+	return n, err
+}
+
+func (v *verifyingReader) Close() error {
+	if v.eof {
+		v.verify()
+	}
+	return v.r.Close()
+}
+
+func (v *verifyingReader) verify() {
+	if v.verified {
+		return
+	}
+	v.verified = true
+
+	if v.sha256 != nil {
+		got := hex.EncodeToString(v.sha256.Sum(nil))
+		if subtle.ConstantTimeCompare([]byte(got), []byte(v.wantSHA256)) != 1 {
+			v.onMismatch(fmt.Sprintf("content_hash mismatch: stored=%s computed=%s", v.wantSHA256, got))
+		}
+	}
+	if v.sri != nil {
+		got := v.sri.Sum(nil)
+		if subtle.ConstantTimeCompare(got, v.wantSRI) != 1 {
+			v.onMismatch(fmt.Sprintf("integrity mismatch: %s expected=%s computed=%s",
+				v.sriAlgo,
+				base64.StdEncoding.EncodeToString(v.wantSRI),
+				base64.StdEncoding.EncodeToString(got)))
+		}
+	}
+}
diff --git a/internal/handler/integrity_test.go b/internal/handler/integrity_test.go
new file mode 100644
index 0000000..93c448c
--- /dev/null
+++ b/internal/handler/integrity_test.go
@@ -0,0 +1,136 @@
+package handler
+
+import (
+	"crypto/sha256"
+	"crypto/sha512"
+	"encoding/base64"
+	"encoding/hex"
+	"io"
+	"strings"
+	"testing"
+)
+
+func sha256Hex(data string) string {
+	sum := sha256.Sum256([]byte(data))
+	return hex.EncodeToString(sum[:])
+}
+
+func sha512SRI(data string) string {
+	sum := sha512.Sum512([]byte(data))
+	return "sha512-" + base64.StdEncoding.EncodeToString(sum[:])
+}
+
+func TestParseSRI(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		algo  string
+		ok    bool
+	}{
+		{"sha512", sha512SRI("hello"), "sha512", true},
+		{"sha256", "sha256-" + base64.StdEncoding.EncodeToString([]byte("0123456789012345678901234567890123456789")), "sha256", true},
+		{"empty", "", "", false},
+		{"no dash", "sha512abc", "", false},
+		{"bad base64", "sha512-not!base64", "", false},
+		{"unsupported algo", "md5-" + base64.StdEncoding.EncodeToString([]byte("x")), "", false},
+		{"multi hash takes first", sha512SRI("a") + " " + sha512SRI("b"), "sha512", true},
+		{"whitespace", "  " + sha512SRI("x") + "  ", "sha512", true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			algo, digest, ok := parseSRI(tt.input)
+			if ok != tt.ok {
+				t.Fatalf("ok = %v, want %v", ok, tt.ok)
+			}
+			if !tt.ok {
+				return
+			}
+			if algo != tt.algo {
+				t.Errorf("algo = %q, want %q", algo, tt.algo)
+			}
+			if len(digest) == 0 {
+				t.Error("digest is empty")
+			}
+		})
+	}
+}
+
+func TestVerifyingReader(t *testing.T) {
+	const data = "hello world"
+	goodSHA := sha256Hex(data)
+	goodSRI := sha512SRI(data)
+
+	tests := []struct {
+		name      string
+		hash      string
+		sri       string
+		wantCalls int
+	}{
+		{"both match", goodSHA, goodSRI, 0},
+		{"sha256 only match", goodSHA, "", 0},
+		{"sri only match", "", goodSRI, 0},
+		{"sha256 mismatch", sha256Hex("other"), "", 1},
+		{"sri mismatch", "", sha512SRI("other"), 1},
+		{"both mismatch", sha256Hex("other"), sha512SRI("other"), 2},
+		{"no checks", "", "", 0},
+		{"unparseable sri ignored", goodSHA, "garbage", 0},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var calls []string
+			r := newVerifyingReader(io.NopCloser(strings.NewReader(data)), tt.hash, tt.sri,
+				func(reason string) { calls = append(calls, reason) })
+
+			got, err := io.ReadAll(r)
+			if err != nil {
+				t.Fatalf("ReadAll: %v", err)
+			}
+			if string(got) != data {
+				t.Errorf("data corrupted: got %q", got)
+			}
+			if err := r.Close(); err != nil {
+				t.Fatalf("Close: %v", err)
+			}
+
+			if len(calls) != tt.wantCalls {
+				t.Errorf("onMismatch called %d times, want %d: %v", len(calls), tt.wantCalls, calls)
+			}
+		})
+	}
+}
+
+func TestVerifyingReaderPassthrough(t *testing.T) {
+	src := io.NopCloser(strings.NewReader("x"))
+	r := newVerifyingReader(src, "", "", func(string) { t.Fatal("should not be called") })
+	if r != src {
+		t.Error("expected passthrough when no hashes provided")
+	}
+}
+
+func TestVerifyingReaderPartialRead(t *testing.T) {
+	var calls int
+	r := newVerifyingReader(io.NopCloser(strings.NewReader("hello world")),
+		sha256Hex("hello world"), "", func(string) { calls++ })
+
+	buf := make([]byte, 5)
+	_, _ = r.Read(buf)
+	_ = r.Close()
+
+	if calls != 0 {
+		t.Errorf("onMismatch called %d times for partial read, want 0", calls)
+	}
+}
+
+func TestVerifyingReaderVerifyOnce(t *testing.T) {
+	var calls int
+	r := newVerifyingReader(io.NopCloser(strings.NewReader("x")), sha256Hex("y"), "",
+		func(string) { calls++ })
+	_, _ = io.ReadAll(r)
+	_ = r.Close()
+	_ = r.Close()
+	if calls != 1 {
+		t.Errorf("onMismatch called %d times, want 1", calls)
+	}
+}
diff --git a/internal/metrics/metrics.go b/internal/metrics/metrics.go
index da8bde6..18ebe88 100644
--- a/internal/metrics/metrics.go
+++ b/internal/metrics/metrics.go
@@ -120,6 +120,14 @@ var (
 			Help: "Number of currently active requests",
 		},
 	)
+
+	IntegrityFailures = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "proxy_integrity_failures_total",
+			Help: "Cached artifacts that failed hash verification on read",
+		},
+		[]string{"ecosystem"},
+	)
 )
 
 func init() {
@@ -138,6 +146,7 @@ func init() {
 		StorageOperationDuration,
 		StorageErrors,
 		ActiveRequests,
+		IntegrityFailures,
 	)
 }
 
@@ -178,6 +187,11 @@ func RecordStorageOperation(operation string, duration time.Duration) {
 	StorageOperationDuration.WithLabelValues(operation).Observe(duration.Seconds())
 }
 
+// RecordIntegrityFailure increments the integrity failure counter.
+func RecordIntegrityFailure(ecosystem string) {
+	IntegrityFailures.WithLabelValues(ecosystem).Inc()
+}
+
 // RecordStorageError increments storage error counter.
 func RecordStorageError(operation string) {
 	StorageErrors.WithLabelValues(operation).Inc()

From 31a9ca75b21ed931b92d24c9e16eae212c584632 Mon Sep 17 00:00:00 2001
From: Mati Kepa <36644582+matikepa@users.noreply.github.com>
Date: Mon, 4 May 2026 12:15:16 +0200
Subject: [PATCH 16/36] add Gradle Build Cache support with handler and tests
 (#87)

* add Gradle Build Cache support with handler and tests

* linting issue

* MR Suggestions: Add Gradle HTTP Build Cache configuration to README

* implement  minor stuff: Refactor Gradle handler to remove unnecessary URL parameter and update related tests

Co-authored-by: Copilot <copilot@github.com>

* Add Gradle build cache configuration and eviction support

- Introduced configuration options for Gradle build cache in config files and documentation.
- Implemented read-only mode and upload size limits for the Gradle build cache.
- Added cache eviction logic based on age and size, with corresponding tests.
- Enhanced storage interfaces to support listing objects by prefix.

* implement minor stuff: Refactor Gradle handler to remove unnecessary URL parameter and update related tests

* last finding fix

* fix tests and implement PR suggestions

Co-authored-by: Copilot <copilot@github.com>

* unify path

---------

Co-authored-by: Mateusz (Mati) Kepa <m.kepa@sportradar.com>
Co-authored-by: Copilot <copilot@github.com>
---
 README.md                                     |  17 ++
 cmd/proxy/main.go                             |  10 +
 config.example.yaml                           |  20 ++
 docs/configuration.md                         |  24 ++
 internal/config/config.go                     | 146 +++++++++++
 internal/config/config_test.go                |  96 ++++++++
 internal/handler/gradle.go                    | 158 ++++++++++++
 internal/handler/gradle_test.go               | 229 ++++++++++++++++++
 internal/handler/handler.go                   |  22 +-
 internal/server/dashboard.go                  |  14 ++
 internal/server/gradle_cache_eviction.go      | 156 ++++++++++++
 internal/server/gradle_cache_eviction_test.go | 138 +++++++++++
 internal/server/server.go                     |   6 +
 internal/server/server_test.go                |  29 +++
 internal/server/templates_test.go             |   2 +-
 internal/storage/blob.go                      |  29 +++
 internal/storage/filesystem.go                |  49 ++++
 internal/storage/storage.go                   |   7 +
 18 files changed, 1141 insertions(+), 11 deletions(-)
 create mode 100644 internal/handler/gradle.go
 create mode 100644 internal/handler/gradle_test.go
 create mode 100644 internal/server/gradle_cache_eviction.go
 create mode 100644 internal/server/gradle_cache_eviction_test.go

diff --git a/README.md b/README.md
index 411f25c..22beaaf 100644
--- a/README.md
+++ b/README.md
@@ -32,6 +32,7 @@ Resolution order: package override, then ecosystem override, then global default
 | pub.dev | Dart | Yes | ✓ |
 | PyPI | Python | Yes | ✓ |
 | Maven | Java | | ✓ |
+| Gradle Build Cache | Java/Kotlin | | ✓ |
 | NuGet | .NET | Yes | ✓ |
 | Composer | PHP | Yes | ✓ |
 | Conan | C/C++ | | ✓ |
@@ -208,6 +209,22 @@ Add to your `~/.m2/settings.xml`:
 </settings>
 ```
 
+### Gradle HTTP Build Cache
+
+Configure in `settings.gradle(.kts)`:
+
+```kotlin
+buildCache {
+  local {
+    enabled = false
+  }
+  remote<HttpBuildCache> {
+    url = uri("http://localhost:8080/gradle/")
+    push = true
+  }
+}
+```
+
 ### NuGet
 
 Configure in `nuget.config`:
diff --git a/cmd/proxy/main.go b/cmd/proxy/main.go
index 0268e9e..946d12a 100644
--- a/cmd/proxy/main.go
+++ b/cmd/proxy/main.go
@@ -72,6 +72,11 @@
 //	PROXY_DATABASE_URL     - PostgreSQL connection URL
 //	PROXY_LOG_LEVEL        - Log level
 //	PROXY_LOG_FORMAT       - Log format
+//	PROXY_GRADLE_BUILD_CACHE_READ_ONLY       - Disable Gradle PUT uploads
+//	PROXY_GRADLE_BUILD_CACHE_MAX_UPLOAD_SIZE - Max Gradle PUT request body size
+//	PROXY_GRADLE_BUILD_CACHE_MAX_AGE         - Gradle cache max age eviction
+//	PROXY_GRADLE_BUILD_CACHE_MAX_SIZE        - Gradle cache max total size
+//	PROXY_GRADLE_BUILD_CACHE_SWEEP_INTERVAL  - Gradle cache eviction sweep interval
 //
 // Example:
 //
@@ -193,6 +198,11 @@ func runServe() {
 		fmt.Fprintf(os.Stderr, "  PROXY_DATABASE_URL     PostgreSQL connection URL\n")
 		fmt.Fprintf(os.Stderr, "  PROXY_LOG_LEVEL        Log level\n")
 		fmt.Fprintf(os.Stderr, "  PROXY_LOG_FORMAT       Log format\n")
+		fmt.Fprintf(os.Stderr, "  PROXY_GRADLE_BUILD_CACHE_READ_ONLY       Disable Gradle PUT uploads\n")
+		fmt.Fprintf(os.Stderr, "  PROXY_GRADLE_BUILD_CACHE_MAX_UPLOAD_SIZE Max Gradle PUT request body size\n")
+		fmt.Fprintf(os.Stderr, "  PROXY_GRADLE_BUILD_CACHE_MAX_AGE         Gradle cache max age eviction\n")
+		fmt.Fprintf(os.Stderr, "  PROXY_GRADLE_BUILD_CACHE_MAX_SIZE        Gradle cache max total size\n")
+		fmt.Fprintf(os.Stderr, "  PROXY_GRADLE_BUILD_CACHE_SWEEP_INTERVAL  Gradle cache eviction sweep interval\n")
 	}
 
 	_ = fs.Parse(os.Args[1:])
diff --git a/config.example.yaml b/config.example.yaml
index 8f37450..4505849 100644
--- a/config.example.yaml
+++ b/config.example.yaml
@@ -108,6 +108,26 @@ upstream:
     #   header_name: "X-Auth-Token"
     #   header_value: "${MAVEN_TOKEN}"
 
+# Gradle HttpBuildCache configuration
+gradle:
+  build_cache:
+    # Set to true to disable PUT uploads (read-only cache mode)
+    read_only: false
+
+    # Maximum accepted Gradle cache upload body size
+    # Required and must be > 0
+    max_upload_size: "100MB"
+
+    # Evict entries older than this age (set to "0" to disable age-based eviction)
+    max_age: "168h"
+
+    # Cap total Gradle cache size; oldest entries are deleted first
+    # ("0" disables size-based eviction)
+    # max_size: "20GB"
+
+    # How often eviction runs when max_age or max_size is set
+    sweep_interval: "10m"
+
 # Version cooldown configuration
 # Hides package versions published too recently, giving the community time
 # to spot malicious releases before they're pulled into projects.
diff --git a/docs/configuration.md b/docs/configuration.md
index be196de..ac85d54 100644
--- a/docs/configuration.md
+++ b/docs/configuration.md
@@ -184,6 +184,30 @@ upstream:
       token: "${PRIVATE_TOKEN}"
 ```
 
+## Gradle Build Cache
+
+The `/gradle` endpoint supports optional safeguards for upload control and cache retention.
+
+```yaml
+gradle:
+  build_cache:
+    read_only: false
+    max_upload_size: "100MB"
+    max_age: "168h"
+    max_size: "20GB"
+    sweep_interval: "10m"
+```
+
+| Config | Environment | Description |
+|--------|-------------|-------------|
+| `gradle.build_cache.read_only` | `PROXY_GRADLE_BUILD_CACHE_READ_ONLY` | Disable PUT uploads and keep GET/HEAD read-only |
+| `gradle.build_cache.max_upload_size` | `PROXY_GRADLE_BUILD_CACHE_MAX_UPLOAD_SIZE` | Maximum accepted PUT body size (must be > 0) |
+| `gradle.build_cache.max_age` | `PROXY_GRADLE_BUILD_CACHE_MAX_AGE` | Delete entries older than this duration (default `168h`, set `0` to disable) |
+| `gradle.build_cache.max_size` | `PROXY_GRADLE_BUILD_CACHE_MAX_SIZE` | Total size cap for `_gradle/http-build-cache`, deleting oldest first (`0` disables) |
+| `gradle.build_cache.sweep_interval` | `PROXY_GRADLE_BUILD_CACHE_SWEEP_INTERVAL` | Frequency for background eviction sweeps |
+
+`max_age` and `max_size` are independent and can be combined. When both are set, age-based eviction runs first, then size-based eviction trims remaining entries oldest-first.
+
 ## Cooldown
 
 The cooldown feature hides package versions published too recently, giving the community time to spot malicious releases before they reach your projects. When a version is within its cooldown period, it's stripped from metadata responses so package managers won't install it.
diff --git a/internal/config/config.go b/internal/config/config.go
index c69e462..b728f68 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -99,6 +99,9 @@ type Config struct {
 	// MirrorAPI enables the /api/mirror endpoints for starting mirror jobs via HTTP.
 	// Disabled by default to prevent unauthenticated users from triggering downloads.
 	MirrorAPI bool `json:"mirror_api" yaml:"mirror_api"`
+
+	// Gradle configures Gradle HttpBuildCache behavior.
+	Gradle GradleConfig `json:"gradle" yaml:"gradle"`
 }
 
 // CooldownConfig configures version cooldown periods.
@@ -151,6 +154,34 @@ type StorageConfig struct {
 	DirectServeBaseURL string `json:"direct_serve_base_url" yaml:"direct_serve_base_url"`
 }
 
+// GradleConfig configures Gradle-specific features.
+type GradleConfig struct {
+	// BuildCache configures the /gradle HttpBuildCache endpoint.
+	BuildCache GradleBuildCacheConfig `json:"build_cache" yaml:"build_cache"`
+}
+
+// GradleBuildCacheConfig configures Gradle HttpBuildCache safeguards.
+type GradleBuildCacheConfig struct {
+	// ReadOnly disables PUT uploads and keeps cache reads (GET/HEAD) enabled.
+	ReadOnly bool `json:"read_only" yaml:"read_only"`
+
+	// MaxUploadSize caps a single PUT body size (e.g., "100MB"). Must be > 0.
+	// Default: "100MB".
+	MaxUploadSize string `json:"max_upload_size" yaml:"max_upload_size"`
+
+	// MaxAge evicts entries older than this duration (e.g., "24h", "7d").
+	// Empty or "0" disables age-based eviction.
+	MaxAge string `json:"max_age" yaml:"max_age"`
+
+	// MaxSize evicts oldest entries until total Gradle cache size is <= MaxSize.
+	// Empty or "0" disables size-based eviction.
+	MaxSize string `json:"max_size" yaml:"max_size"`
+
+	// SweepInterval controls periodic eviction frequency.
+	// Default: "10m".
+	SweepInterval string `json:"sweep_interval" yaml:"sweep_interval"`
+}
+
 // DatabaseConfig configures the cache database.
 type DatabaseConfig struct {
 	// Driver is the database driver: "sqlite" or "postgres".
@@ -260,6 +291,15 @@ func Default() *Config {
 			Cargo:         "https://index.crates.io",
 			CargoDownload: "https://static.crates.io/crates",
 		},
+		Gradle: GradleConfig{
+			BuildCache: GradleBuildCacheConfig{
+				ReadOnly:      false,
+				MaxUploadSize: "100MB",
+				MaxAge:        "168h",
+				MaxSize:       "",
+				SweepInterval: "10m",
+			},
+		},
 	}
 }
 
@@ -355,6 +395,21 @@ func (c *Config) LoadFromEnv() {
 	if v := os.Getenv("PROXY_METADATA_TTL"); v != "" {
 		c.MetadataTTL = v
 	}
+	if v := os.Getenv("PROXY_GRADLE_BUILD_CACHE_READ_ONLY"); v != "" {
+		c.Gradle.BuildCache.ReadOnly = v == "true" || v == "1"
+	}
+	if v := os.Getenv("PROXY_GRADLE_BUILD_CACHE_MAX_UPLOAD_SIZE"); v != "" {
+		c.Gradle.BuildCache.MaxUploadSize = v
+	}
+	if v := os.Getenv("PROXY_GRADLE_BUILD_CACHE_MAX_AGE"); v != "" {
+		c.Gradle.BuildCache.MaxAge = v
+	}
+	if v := os.Getenv("PROXY_GRADLE_BUILD_CACHE_MAX_SIZE"); v != "" {
+		c.Gradle.BuildCache.MaxSize = v
+	}
+	if v := os.Getenv("PROXY_GRADLE_BUILD_CACHE_SWEEP_INTERVAL"); v != "" {
+		c.Gradle.BuildCache.SweepInterval = v
+	}
 }
 
 // Validate checks the configuration for errors.
@@ -426,9 +481,48 @@ func (c *Config) Validate() error {
 		}
 	}
 
+	// Validate Gradle build cache upload size (always required and must be > 0).
+	if c.Gradle.BuildCache.MaxUploadSize == "" {
+		c.Gradle.BuildCache.MaxUploadSize = "100MB"
+	}
+	uploadSize, err := ParseSize(c.Gradle.BuildCache.MaxUploadSize)
+	if err != nil {
+		return fmt.Errorf("invalid gradle.build_cache.max_upload_size: %w", err)
+	}
+	if uploadSize <= 0 {
+		return fmt.Errorf("invalid gradle.build_cache.max_upload_size %q: must be > 0", c.Gradle.BuildCache.MaxUploadSize)
+	}
+
+	// Validate Gradle max age if specified.
+	if c.Gradle.BuildCache.MaxAge != "" && c.Gradle.BuildCache.MaxAge != "0" {
+		if _, err := time.ParseDuration(c.Gradle.BuildCache.MaxAge); err != nil {
+			return fmt.Errorf("invalid gradle.build_cache.max_age %q: %w", c.Gradle.BuildCache.MaxAge, err)
+		}
+	}
+
+	// Validate Gradle max size if specified.
+	if c.Gradle.BuildCache.MaxSize != "" {
+		if _, err := ParseSize(c.Gradle.BuildCache.MaxSize); err != nil {
+			return fmt.Errorf("invalid gradle.build_cache.max_size: %w", err)
+		}
+	}
+
+	// Validate Gradle sweep interval if specified.
+	if c.Gradle.BuildCache.SweepInterval != "" {
+		d, err := time.ParseDuration(c.Gradle.BuildCache.SweepInterval)
+		if err != nil {
+			return fmt.Errorf("invalid gradle.build_cache.sweep_interval %q: %w", c.Gradle.BuildCache.SweepInterval, err)
+		}
+		if d <= 0 {
+			return fmt.Errorf("invalid gradle.build_cache.sweep_interval %q: must be > 0", c.Gradle.BuildCache.SweepInterval)
+		}
+	}
+
 	return nil
 }
 
+const defaultGradleBuildCacheMaxUploadSize = 100 << 20
+const defaultGradleBuildCacheSweepInterval = 10 * time.Minute
 const (
 	defaultMetadataTTL    = 5 * time.Minute  //nolint:mnd // sensible default
 	defaultDirectServeTTL = 15 * time.Minute //nolint:mnd // sensible default
@@ -463,6 +557,58 @@ func (c *Config) ParseMetadataTTL() time.Duration {
 	return d
 }
 
+// ParseGradleBuildCacheMaxUploadSize returns the max accepted PUT body size.
+// Defaults to 100MB if unset or invalid.
+func (c *Config) ParseGradleBuildCacheMaxUploadSize() int64 {
+	if c.Gradle.BuildCache.MaxUploadSize == "" {
+		return defaultGradleBuildCacheMaxUploadSize
+	}
+	size, err := ParseSize(c.Gradle.BuildCache.MaxUploadSize)
+	if err != nil || size <= 0 {
+		return defaultGradleBuildCacheMaxUploadSize
+	}
+	return size
+}
+
+// ParseGradleBuildCacheMaxAge returns age-based eviction threshold.
+// Returns 0 when disabled or invalid.
+func (c *Config) ParseGradleBuildCacheMaxAge() time.Duration {
+	if c.Gradle.BuildCache.MaxAge == "" || c.Gradle.BuildCache.MaxAge == "0" {
+		return 0
+	}
+	d, err := time.ParseDuration(c.Gradle.BuildCache.MaxAge)
+	if err != nil || d <= 0 {
+		return 0
+	}
+	return d
+}
+
+// ParseGradleBuildCacheMaxSize returns total-size cap in bytes.
+// Returns 0 when disabled or invalid.
+func (c *Config) ParseGradleBuildCacheMaxSize() int64 {
+	if c.Gradle.BuildCache.MaxSize == "" || c.Gradle.BuildCache.MaxSize == "0" {
+		return 0
+	}
+	size, err := ParseSize(c.Gradle.BuildCache.MaxSize)
+	if err != nil || size <= 0 {
+		return 0
+	}
+	return size
+}
+
+// ParseGradleBuildCacheSweepInterval returns eviction sweep cadence.
+// Defaults to 10m if unset or invalid.
+func (c *Config) ParseGradleBuildCacheSweepInterval() time.Duration {
+	if c.Gradle.BuildCache.SweepInterval == "" {
+		return defaultGradleBuildCacheSweepInterval
+	}
+	d, err := time.ParseDuration(c.Gradle.BuildCache.SweepInterval)
+	if err != nil || d <= 0 {
+		return defaultGradleBuildCacheSweepInterval
+	}
+	return d
+}
+
 // ParseDirectServeTTL returns the presigned URL expiry duration.
 // Returns 15 minutes if unset.
 func (c *Config) ParseDirectServeTTL() time.Duration {
diff --git a/internal/config/config_test.go b/internal/config/config_test.go
index de10191..26a0fc6 100644
--- a/internal/config/config_test.go
+++ b/internal/config/config_test.go
@@ -25,6 +25,12 @@ func TestDefault(t *testing.T) {
 	if cfg.Database.Path == "" {
 		t.Error("Database.Path should not be empty")
 	}
+	if cfg.Gradle.BuildCache.MaxUploadSize != "100MB" {
+		t.Errorf("Gradle.BuildCache.MaxUploadSize = %q, want %q", cfg.Gradle.BuildCache.MaxUploadSize, "100MB")
+	}
+	if cfg.Gradle.BuildCache.MaxAge != "168h" {
+		t.Errorf("Gradle.BuildCache.MaxAge = %q, want %q", cfg.Gradle.BuildCache.MaxAge, "168h")
+	}
 }
 
 func TestValidate(t *testing.T) {
@@ -98,6 +104,41 @@ func TestValidate(t *testing.T) {
 			modify:  func(c *Config) { c.Storage.MaxSize = "10GB" },
 			wantErr: false,
 		},
+		{
+			name:    "invalid gradle upload size",
+			modify:  func(c *Config) { c.Gradle.BuildCache.MaxUploadSize = testInvalid },
+			wantErr: true,
+		},
+		{
+			name:    "zero gradle upload size",
+			modify:  func(c *Config) { c.Gradle.BuildCache.MaxUploadSize = "0" },
+			wantErr: true,
+		},
+		{
+			name:    "invalid gradle max age",
+			modify:  func(c *Config) { c.Gradle.BuildCache.MaxAge = testInvalid },
+			wantErr: true,
+		},
+		{
+			name:    "valid gradle max age",
+			modify:  func(c *Config) { c.Gradle.BuildCache.MaxAge = "24h" },
+			wantErr: false,
+		},
+		{
+			name:    "invalid gradle max size",
+			modify:  func(c *Config) { c.Gradle.BuildCache.MaxSize = testInvalid },
+			wantErr: true,
+		},
+		{
+			name:    "invalid gradle sweep interval",
+			modify:  func(c *Config) { c.Gradle.BuildCache.SweepInterval = "0" },
+			wantErr: true,
+		},
+		{
+			name:    "valid gradle sweep interval",
+			modify:  func(c *Config) { c.Gradle.BuildCache.SweepInterval = "30m" },
+			wantErr: false,
+		},
 	}
 
 	for _, tt := range tests {
@@ -223,6 +264,11 @@ func TestLoadFromEnv(t *testing.T) {
 	t.Setenv("PROXY_BASE_URL", "https://env.example.com")
 	t.Setenv("PROXY_STORAGE_PATH", "/env/cache")
 	t.Setenv("PROXY_LOG_LEVEL", testLevelDebug)
+	t.Setenv("PROXY_GRADLE_BUILD_CACHE_READ_ONLY", "true")
+	t.Setenv("PROXY_GRADLE_BUILD_CACHE_MAX_UPLOAD_SIZE", "32MB")
+	t.Setenv("PROXY_GRADLE_BUILD_CACHE_MAX_AGE", "12h")
+	t.Setenv("PROXY_GRADLE_BUILD_CACHE_MAX_SIZE", "10GB")
+	t.Setenv("PROXY_GRADLE_BUILD_CACHE_SWEEP_INTERVAL", "15m")
 
 	cfg.LoadFromEnv()
 
@@ -238,6 +284,21 @@ func TestLoadFromEnv(t *testing.T) {
 	if cfg.Log.Level != testLevelDebug {
 		t.Errorf("Log.Level = %q, want %q", cfg.Log.Level, testLevelDebug)
 	}
+	if !cfg.Gradle.BuildCache.ReadOnly {
+		t.Error("Gradle.BuildCache.ReadOnly = false, want true")
+	}
+	if cfg.Gradle.BuildCache.MaxUploadSize != "32MB" {
+		t.Errorf("Gradle.BuildCache.MaxUploadSize = %q, want %q", cfg.Gradle.BuildCache.MaxUploadSize, "32MB")
+	}
+	if cfg.Gradle.BuildCache.MaxAge != "12h" {
+		t.Errorf("Gradle.BuildCache.MaxAge = %q, want %q", cfg.Gradle.BuildCache.MaxAge, "12h")
+	}
+	if cfg.Gradle.BuildCache.MaxSize != "10GB" {
+		t.Errorf("Gradle.BuildCache.MaxSize = %q, want %q", cfg.Gradle.BuildCache.MaxSize, "10GB")
+	}
+	if cfg.Gradle.BuildCache.SweepInterval != "15m" {
+		t.Errorf("Gradle.BuildCache.SweepInterval = %q, want %q", cfg.Gradle.BuildCache.SweepInterval, "15m")
+	}
 }
 
 func TestLoadCooldownConfig(t *testing.T) {
@@ -381,6 +442,41 @@ func TestLoadMetadataTTLFromEnv(t *testing.T) {
 	}
 }
 
+func TestParseGradleBuildCacheConfig(t *testing.T) {
+	cfg := Default()
+
+	if got := cfg.ParseGradleBuildCacheMaxUploadSize(); got != 100*1024*1024 {
+		t.Errorf("ParseGradleBuildCacheMaxUploadSize() = %d, want %d", got, 100*1024*1024)
+	}
+	if got := cfg.ParseGradleBuildCacheMaxAge(); got != 168*time.Hour {
+		t.Errorf("ParseGradleBuildCacheMaxAge() = %v, want %v", got, 168*time.Hour)
+	}
+	if got := cfg.ParseGradleBuildCacheMaxSize(); got != 0 {
+		t.Errorf("ParseGradleBuildCacheMaxSize() = %d, want 0", got)
+	}
+	if got := cfg.ParseGradleBuildCacheSweepInterval(); got != 10*time.Minute {
+		t.Errorf("ParseGradleBuildCacheSweepInterval() = %v, want %v", got, 10*time.Minute)
+	}
+
+	cfg.Gradle.BuildCache.MaxUploadSize = "64MB"
+	cfg.Gradle.BuildCache.MaxAge = "48h"
+	cfg.Gradle.BuildCache.MaxSize = "2GB"
+	cfg.Gradle.BuildCache.SweepInterval = "20m"
+
+	if got := cfg.ParseGradleBuildCacheMaxUploadSize(); got != 64*1024*1024 {
+		t.Errorf("ParseGradleBuildCacheMaxUploadSize() = %d, want %d", got, 64*1024*1024)
+	}
+	if got := cfg.ParseGradleBuildCacheMaxAge(); got != 48*time.Hour {
+		t.Errorf("ParseGradleBuildCacheMaxAge() = %v, want %v", got, 48*time.Hour)
+	}
+	if got := cfg.ParseGradleBuildCacheMaxSize(); got != 2*1024*1024*1024 {
+		t.Errorf("ParseGradleBuildCacheMaxSize() = %d, want %d", got, 2*1024*1024*1024)
+	}
+	if got := cfg.ParseGradleBuildCacheSweepInterval(); got != 20*time.Minute {
+		t.Errorf("ParseGradleBuildCacheSweepInterval() = %v, want %v", got, 20*time.Minute)
+	}
+}
+
 func TestParseDirectServeTTL(t *testing.T) {
 	tests := []struct {
 		name string
diff --git a/internal/handler/gradle.go b/internal/handler/gradle.go
new file mode 100644
index 0000000..41c9f76
--- /dev/null
+++ b/internal/handler/gradle.go
@@ -0,0 +1,158 @@
+package handler
+
+import (
+	"errors"
+	"io"
+	"net/http"
+	"regexp"
+	"strconv"
+	"strings"
+
+	"github.com/git-pkgs/proxy/internal/storage"
+)
+
+const (
+	gradleBuildCacheContentType = "application/vnd.gradle.build-cache-artifact.v2"
+	gradleBuildCacheStorageRoot = "_gradle/http-build-cache"
+	defaultGradleMaxUploadSize  = 100 << 20
+)
+
+var gradleBuildCacheKeyPattern = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9._-]*$`)
+
+// GradleBuildCacheHandler handles Gradle HttpBuildCache GET/HEAD/PUT requests.
+//
+// This handler accepts /{key} when mounted under a base URL.
+type GradleBuildCacheHandler struct {
+	proxy *Proxy
+}
+
+// NewGradleBuildCacheHandler creates a Gradle HttpBuildCache handler.
+func NewGradleBuildCacheHandler(proxy *Proxy) *GradleBuildCacheHandler {
+	return &GradleBuildCacheHandler{proxy: proxy}
+}
+
+// Routes returns the HTTP handler for Gradle HttpBuildCache requests.
+func (h *GradleBuildCacheHandler) Routes() http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		switch r.Method {
+		case http.MethodGet, http.MethodHead, http.MethodPut:
+		default:
+			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+			return
+		}
+
+		key, statusCode := h.parseCacheKey(r.URL.Path)
+		if statusCode != http.StatusOK {
+			if statusCode == http.StatusNotFound {
+				http.NotFound(w, r)
+				return
+			}
+			http.Error(w, "invalid cache key", statusCode)
+			return
+		}
+
+		if r.Method == http.MethodPut {
+			if h.proxy.GradleReadOnly {
+				http.Error(w, "gradle build cache is read-only", http.StatusMethodNotAllowed)
+				return
+			}
+			h.handlePut(w, r, key)
+			return
+		}
+
+		h.handleGetOrHead(w, r, key)
+	})
+}
+
+func (h *GradleBuildCacheHandler) parseCacheKey(urlPath string) (string, int) {
+	keyPath := strings.TrimPrefix(urlPath, "/")
+	if keyPath == "" {
+		return "", http.StatusNotFound
+	}
+
+	if containsPathTraversal(keyPath) {
+		return "", http.StatusBadRequest
+	}
+
+	if keyPath == "" || strings.Contains(keyPath, "/") {
+		return "", http.StatusNotFound
+	}
+
+	if !gradleBuildCacheKeyPattern.MatchString(keyPath) {
+		return "", http.StatusBadRequest
+	}
+
+	return keyPath, http.StatusOK
+}
+
+func (h *GradleBuildCacheHandler) cacheStoragePath(key string) string {
+	return gradleBuildCacheStorageRoot + "/" + key
+}
+
+func (h *GradleBuildCacheHandler) handleGetOrHead(w http.ResponseWriter, r *http.Request, key string) {
+	storagePath := h.cacheStoragePath(key)
+	w.Header().Set("Content-Type", gradleBuildCacheContentType)
+
+	if r.Method == http.MethodHead {
+		exists, err := h.proxy.Storage.Exists(r.Context(), storagePath)
+		if err != nil {
+			h.proxy.Logger.Error("failed to check gradle build cache entry", "key", key, "error", err)
+			http.Error(w, "failed to read cache entry", http.StatusInternalServerError)
+			return
+		}
+		if !exists {
+			http.NotFound(w, r)
+			return
+		}
+
+		if size, err := h.proxy.Storage.Size(r.Context(), storagePath); err == nil && size >= 0 {
+			w.Header().Set("Content-Length", strconv.FormatInt(size, 10))
+		}
+
+		w.WriteHeader(http.StatusOK)
+		return
+	}
+
+	reader, err := h.proxy.Storage.Open(r.Context(), storagePath)
+	if err != nil {
+		if errors.Is(err, storage.ErrNotFound) {
+			http.NotFound(w, r)
+			return
+		}
+		h.proxy.Logger.Error("failed to open gradle build cache entry", "key", key, "error", err)
+		http.Error(w, "failed to read cache entry", http.StatusInternalServerError)
+		return
+	}
+	defer func() { _ = reader.Close() }()
+
+	w.WriteHeader(http.StatusOK)
+	_, _ = io.Copy(w, reader)
+}
+
+func (h *GradleBuildCacheHandler) handlePut(w http.ResponseWriter, r *http.Request, key string) {
+	storagePath := h.cacheStoragePath(key)
+	maxUploadSize := h.proxy.GradleMaxUploadSize
+	if maxUploadSize <= 0 {
+		maxUploadSize = defaultGradleMaxUploadSize
+	}
+
+	r.Body = http.MaxBytesReader(w, r.Body, maxUploadSize)
+
+	_, hash, err := h.proxy.Storage.Store(r.Context(), storagePath, r.Body)
+	if err != nil {
+		var maxBytesErr *http.MaxBytesError
+		if errors.As(err, &maxBytesErr) {
+			http.Error(w, "cache entry too large", http.StatusRequestEntityTooLarge)
+			return
+		}
+
+		h.proxy.Logger.Error("failed to store gradle build cache entry", "key", key, "error", err)
+		http.Error(w, "failed to write cache entry", http.StatusInternalServerError)
+		return
+	}
+
+	w.Header().Set("Content-Length", "0")
+	w.Header().Set("ETag", `"`+hash+`"`)
+
+	w.WriteHeader(http.StatusCreated)
+}
diff --git a/internal/handler/gradle_test.go b/internal/handler/gradle_test.go
new file mode 100644
index 0000000..f002a51
--- /dev/null
+++ b/internal/handler/gradle_test.go
@@ -0,0 +1,229 @@
+package handler
+
+import (
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+func TestGradleBuildCacheHandler_PutGetHead(t *testing.T) {
+	proxy, _, _, _ := setupTestProxy(t)
+	h := NewGradleBuildCacheHandler(proxy)
+	srv := httptest.NewServer(h.Routes())
+	defer srv.Close()
+
+	key := "a1b2c3d4e5f6"
+	payload := "cache entry content"
+
+	putReq, err := http.NewRequest(http.MethodPut, srv.URL+"/"+key, strings.NewReader(payload))
+	if err != nil {
+		t.Fatalf("failed to create PUT request: %v", err)
+	}
+	putResp, err := http.DefaultClient.Do(putReq)
+	if err != nil {
+		t.Fatalf("PUT request failed: %v", err)
+	}
+	_ = putResp.Body.Close()
+
+	if putResp.StatusCode != http.StatusCreated {
+		t.Fatalf("PUT status = %d, want %d", putResp.StatusCode, http.StatusCreated)
+	}
+
+	getResp, err := http.Get(srv.URL + "/" + key)
+	if err != nil {
+		t.Fatalf("GET request failed: %v", err)
+	}
+	defer func() { _ = getResp.Body.Close() }()
+
+	if getResp.StatusCode != http.StatusOK {
+		t.Fatalf("GET status = %d, want %d", getResp.StatusCode, http.StatusOK)
+	}
+	if getResp.Header.Get("Content-Type") != gradleBuildCacheContentType {
+		t.Fatalf("GET Content-Type = %q, want %q", getResp.Header.Get("Content-Type"), gradleBuildCacheContentType)
+	}
+
+	body, _ := io.ReadAll(getResp.Body)
+	if string(body) != payload {
+		t.Fatalf("GET body = %q, want %q", body, payload)
+	}
+
+	headReq, err := http.NewRequest(http.MethodHead, srv.URL+"/"+key, nil)
+	if err != nil {
+		t.Fatalf("failed to create HEAD request: %v", err)
+	}
+	headResp, err := http.DefaultClient.Do(headReq)
+	if err != nil {
+		t.Fatalf("HEAD request failed: %v", err)
+	}
+	defer func() { _ = headResp.Body.Close() }()
+
+	if headResp.StatusCode != http.StatusOK {
+		t.Fatalf("HEAD status = %d, want %d", headResp.StatusCode, http.StatusOK)
+	}
+	body, _ = io.ReadAll(headResp.Body)
+	if len(body) != 0 {
+		t.Fatalf("HEAD body length = %d, want 0", len(body))
+	}
+}
+
+func TestGradleBuildCacheHandler_RootKeyPath(t *testing.T) {
+	proxy, _, _, _ := setupTestProxy(t)
+	h := NewGradleBuildCacheHandler(proxy)
+	srv := httptest.NewServer(h.Routes())
+	defer srv.Close()
+
+	key := "rootpathkey"
+	putReq, err := http.NewRequest(http.MethodPut, srv.URL+"/"+key, strings.NewReader("root"))
+	if err != nil {
+		t.Fatalf("failed to create PUT request: %v", err)
+	}
+	putResp, err := http.DefaultClient.Do(putReq)
+	if err != nil {
+		t.Fatalf("PUT request failed: %v", err)
+	}
+	_ = putResp.Body.Close()
+
+	if putResp.StatusCode != http.StatusCreated {
+		t.Fatalf("PUT status = %d, want %d", putResp.StatusCode, http.StatusCreated)
+	}
+
+	getResp, err := http.Get(srv.URL + "/" + key)
+	if err != nil {
+		t.Fatalf("GET request failed: %v", err)
+	}
+	defer func() { _ = getResp.Body.Close() }()
+
+	if getResp.StatusCode != http.StatusOK {
+		t.Fatalf("GET status = %d, want %d", getResp.StatusCode, http.StatusOK)
+	}
+}
+
+func TestGradleBuildCacheHandler_GetMiss(t *testing.T) {
+	proxy, _, _, _ := setupTestProxy(t)
+	h := NewGradleBuildCacheHandler(proxy)
+	srv := httptest.NewServer(h.Routes())
+	defer srv.Close()
+
+	resp, err := http.Get(srv.URL + "/missing-key")
+	if err != nil {
+		t.Fatalf("GET request failed: %v", err)
+	}
+	defer func() { _ = resp.Body.Close() }()
+
+	if resp.StatusCode != http.StatusNotFound {
+		t.Fatalf("status = %d, want %d", resp.StatusCode, http.StatusNotFound)
+	}
+}
+
+func TestGradleBuildCacheHandler_MethodNotAllowed(t *testing.T) {
+	proxy, _, _, _ := setupTestProxy(t)
+	h := NewGradleBuildCacheHandler(proxy)
+
+	req := httptest.NewRequest(http.MethodPost, "/key", nil)
+	w := httptest.NewRecorder()
+	h.Routes().ServeHTTP(w, req)
+
+	if w.Code != http.StatusMethodNotAllowed {
+		t.Fatalf("status = %d, want %d", w.Code, http.StatusMethodNotAllowed)
+	}
+}
+
+func TestGradleBuildCacheHandler_PathTraversalRejected(t *testing.T) {
+	proxy, _, _, _ := setupTestProxy(t)
+	h := NewGradleBuildCacheHandler(proxy)
+
+	req := httptest.NewRequest(http.MethodGet, "/../secret", nil)
+	w := httptest.NewRecorder()
+	h.Routes().ServeHTTP(w, req)
+
+	if w.Code != http.StatusBadRequest {
+		t.Fatalf("status = %d, want %d", w.Code, http.StatusBadRequest)
+	}
+}
+
+func TestGradleBuildCacheHandler_CachePrefixRejected(t *testing.T) {
+	proxy, _, _, _ := setupTestProxy(t)
+	h := NewGradleBuildCacheHandler(proxy)
+
+	req := httptest.NewRequest(http.MethodGet, "/cache/key", nil)
+	w := httptest.NewRecorder()
+	h.Routes().ServeHTTP(w, req)
+
+	if w.Code != http.StatusNotFound {
+		t.Fatalf("status = %d, want %d", w.Code, http.StatusNotFound)
+	}
+}
+
+func TestGradleBuildCacheHandler_PutOverwriteReturnsCreated(t *testing.T) {
+	proxy, _, _, _ := setupTestProxy(t)
+	h := NewGradleBuildCacheHandler(proxy)
+	srv := httptest.NewServer(h.Routes())
+	defer srv.Close()
+
+	key := "overwrite-key"
+
+	for i, payload := range []string{"first", "second"} {
+		req, err := http.NewRequest(http.MethodPut, srv.URL+"/"+key, strings.NewReader(payload))
+		if err != nil {
+			t.Fatalf("failed to create PUT request: %v", err)
+		}
+		resp, err := http.DefaultClient.Do(req)
+		if err != nil {
+			t.Fatalf("PUT request failed: %v", err)
+		}
+		_ = resp.Body.Close()
+
+		want := http.StatusCreated
+		if resp.StatusCode != want {
+			t.Fatalf("PUT #%d status = %d, want %d", i+1, resp.StatusCode, want)
+		}
+	}
+}
+
+func TestGradleBuildCacheHandler_PutReadOnly(t *testing.T) {
+	proxy, _, _, _ := setupTestProxy(t)
+	proxy.GradleReadOnly = true
+
+	h := NewGradleBuildCacheHandler(proxy)
+	srv := httptest.NewServer(h.Routes())
+	defer srv.Close()
+
+	req, err := http.NewRequest(http.MethodPut, srv.URL+"/readonly-key", strings.NewReader("payload"))
+	if err != nil {
+		t.Fatalf("failed to create PUT request: %v", err)
+	}
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		t.Fatalf("PUT request failed: %v", err)
+	}
+	defer func() { _ = resp.Body.Close() }()
+
+	if resp.StatusCode != http.StatusMethodNotAllowed {
+		t.Fatalf("PUT status = %d, want %d", resp.StatusCode, http.StatusMethodNotAllowed)
+	}
+}
+
+func TestGradleBuildCacheHandler_PutTooLarge(t *testing.T) {
+	proxy, _, _, _ := setupTestProxy(t)
+	proxy.GradleMaxUploadSize = 4
+
+	h := NewGradleBuildCacheHandler(proxy)
+	srv := httptest.NewServer(h.Routes())
+	defer srv.Close()
+
+	req, err := http.NewRequest(http.MethodPut, srv.URL+"/oversized-key", strings.NewReader("12345"))
+	if err != nil {
+		t.Fatalf("failed to create PUT request: %v", err)
+	}
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		t.Fatalf("PUT request failed: %v", err)
+	}
+	defer func() { _ = resp.Body.Close() }()
+
+	if resp.StatusCode != http.StatusRequestEntityTooLarge {
+		t.Fatalf("PUT status = %d, want %d", resp.StatusCode, http.StatusRequestEntityTooLarge)
+	}
+}
diff --git a/internal/handler/handler.go b/internal/handler/handler.go
index 6bcf506..d40a1dd 100644
--- a/internal/handler/handler.go
+++ b/internal/handler/handler.go
@@ -74,16 +74,18 @@ func ReadMetadata(r io.Reader) ([]byte, error) {
 
 // Proxy provides shared functionality for protocol handlers.
 type Proxy struct {
-	DB             *database.DB
-	Storage        storage.Storage
-	Fetcher        fetch.FetcherInterface
-	Resolver       *fetch.Resolver
-	Logger         *slog.Logger
-	Cooldown       *cooldown.Config
-	CacheMetadata  bool
-	MetadataTTL    time.Duration
-	DirectServe    bool
-	DirectServeTTL time.Duration
+	DB                  *database.DB
+	Storage             storage.Storage
+	Fetcher             fetch.FetcherInterface
+	Resolver            *fetch.Resolver
+	Logger              *slog.Logger
+	Cooldown            *cooldown.Config
+	CacheMetadata       bool
+	MetadataTTL         time.Duration
+	GradleReadOnly      bool
+	GradleMaxUploadSize int64
+	DirectServe         bool
+	DirectServeTTL      time.Duration
 	// DirectServeBaseURL, if set, replaces the scheme and host of presigned
 	// URLs so clients receive a public address even when the proxy reaches
 	// storage at an internal one.
diff --git a/internal/server/dashboard.go b/internal/server/dashboard.go
index b935628..1fe5388 100644
--- a/internal/server/dashboard.go
+++ b/internal/server/dashboard.go
@@ -286,6 +286,20 @@ index-url = ` + baseURL + `/pypi/simple/</code></pre>`),
     &lt;/mirror&gt;
   &lt;/mirrors&gt;
 &lt;/settings&gt;</code></pre>`),
+		},
+		{
+			ID:       "gradle",
+			Name:     "Gradle Build Cache",
+			Language: "Java/Kotlin",
+			Endpoint: "/gradle/",
+			Instructions: template.HTML(`<p class="config-note">Configure Gradle to use the proxy for HttpBuildCache:</p>
+<pre><code>// In settings.gradle(.kts)
+buildCache {
+  remote&lt;HttpBuildCache&gt; {
+    url = uri("` + baseURL + `/gradle/")
+    push = true
+  }
+}</code></pre>`),
 		},
 		{
 			ID:       "nuget",
diff --git a/internal/server/gradle_cache_eviction.go b/internal/server/gradle_cache_eviction.go
new file mode 100644
index 0000000..1f5e95d
--- /dev/null
+++ b/internal/server/gradle_cache_eviction.go
@@ -0,0 +1,156 @@
+package server
+
+import (
+	"context"
+	"fmt"
+	"sort"
+	"time"
+
+	"github.com/git-pkgs/proxy/internal/storage"
+)
+
+const gradleBuildCacheStoragePrefix = "_gradle/http-build-cache/"
+
+type gradleBuildCacheLister interface {
+	ListPrefix(ctx context.Context, prefix string) ([]storage.ObjectInfo, error)
+}
+
+func (s *Server) startGradleBuildCacheEviction(ctx context.Context) {
+	maxAge := s.cfg.ParseGradleBuildCacheMaxAge()
+	maxSize := s.cfg.ParseGradleBuildCacheMaxSize()
+	if maxAge <= 0 && maxSize <= 0 {
+		return
+	}
+
+	lister, ok := s.storage.(gradleBuildCacheLister)
+	if !ok {
+		s.logger.Warn("gradle cache eviction is enabled, but storage backend cannot list objects")
+		return
+	}
+
+	interval := s.cfg.ParseGradleBuildCacheSweepInterval()
+	s.logger.Info("gradle cache eviction enabled",
+		"max_age", maxAge,
+		"max_size_bytes", maxSize,
+		"interval", interval)
+
+	sweep := func() {
+		deletedCount, freedBytes, err := sweepGradleBuildCache(ctx, s.storage, lister, maxAge, maxSize, time.Now())
+		if err != nil {
+			s.logger.Warn("gradle cache eviction sweep failed", "error", err)
+			return
+		}
+		if deletedCount > 0 {
+			s.logger.Info("gradle cache eviction sweep completed",
+				"deleted_entries", deletedCount,
+				"freed_bytes", freedBytes)
+		}
+	}
+
+	sweep()
+
+	go func() {
+		ticker := time.NewTicker(interval)
+		defer ticker.Stop()
+
+		for {
+			select {
+			case <-ctx.Done():
+				return
+			case <-ticker.C:
+				sweep()
+			}
+		}
+	}()
+}
+
+func sweepGradleBuildCache(
+	ctx context.Context,
+	store storage.Storage,
+	lister gradleBuildCacheLister,
+	maxAge time.Duration,
+	maxSize int64,
+	now time.Time,
+) (int, int64, error) {
+	entries, err := lister.ListPrefix(ctx, gradleBuildCacheStoragePrefix)
+	if err != nil {
+		return 0, 0, fmt.Errorf("listing gradle cache entries: %w", err)
+	}
+
+	if len(entries) == 0 {
+		return 0, 0, nil
+	}
+
+	sort.Slice(entries, func(i, j int) bool {
+		iTime := entries[i].ModTime
+		jTime := entries[j].ModTime
+
+		switch {
+		case iTime.IsZero() && jTime.IsZero():
+			return entries[i].Path < entries[j].Path
+		case iTime.IsZero():
+			return true
+		case jTime.IsZero():
+			return false
+		case iTime.Equal(jTime):
+			return entries[i].Path < entries[j].Path
+		default:
+			return iTime.Before(jTime)
+		}
+	})
+
+	deletedCount := 0
+	freedBytes := int64(0)
+	var firstDeleteErr error
+
+	deleteEntry := func(entry storage.ObjectInfo) bool {
+		if err := store.Delete(ctx, entry.Path); err != nil {
+			if firstDeleteErr == nil {
+				firstDeleteErr = err
+			}
+			return false
+		}
+		deletedCount++
+		freedBytes += entry.Size
+		return true
+	}
+
+	remaining := entries
+	if maxAge > 0 {
+		cutoff := now.Add(-maxAge)
+		kept := make([]storage.ObjectInfo, 0, len(entries))
+
+		for _, entry := range entries {
+			if !entry.ModTime.IsZero() && entry.ModTime.Before(cutoff) {
+				if deleteEntry(entry) {
+					continue
+				}
+			}
+			kept = append(kept, entry)
+		}
+
+		remaining = kept
+	}
+
+	if maxSize > 0 {
+		totalSize := int64(0)
+		for _, entry := range remaining {
+			totalSize += entry.Size
+		}
+
+		for _, entry := range remaining {
+			if totalSize <= maxSize {
+				break
+			}
+			if deleteEntry(entry) {
+				totalSize -= entry.Size
+			}
+		}
+	}
+
+	if firstDeleteErr != nil {
+		return deletedCount, freedBytes, fmt.Errorf("deleting gradle cache entries: %w", firstDeleteErr)
+	}
+
+	return deletedCount, freedBytes, nil
+}
diff --git a/internal/server/gradle_cache_eviction_test.go b/internal/server/gradle_cache_eviction_test.go
new file mode 100644
index 0000000..4e97507
--- /dev/null
+++ b/internal/server/gradle_cache_eviction_test.go
@@ -0,0 +1,138 @@
+package server
+
+import (
+	"bytes"
+	"context"
+	"io"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/git-pkgs/proxy/internal/storage"
+)
+
+type fakeGradleCacheStore struct {
+	objects map[string]storage.ObjectInfo
+}
+
+func newFakeGradleCacheStore(objects []storage.ObjectInfo) *fakeGradleCacheStore {
+	m := make(map[string]storage.ObjectInfo, len(objects))
+	for _, obj := range objects {
+		m[obj.Path] = obj
+	}
+	return &fakeGradleCacheStore{objects: m}
+}
+
+func (s *fakeGradleCacheStore) Store(_ context.Context, path string, r io.Reader) (int64, string, error) {
+	data, _ := io.ReadAll(r)
+	s.objects[path] = storage.ObjectInfo{Path: path, Size: int64(len(data)), ModTime: time.Now()}
+	return int64(len(data)), "", nil
+}
+
+func (s *fakeGradleCacheStore) Open(_ context.Context, path string) (io.ReadCloser, error) {
+	obj, ok := s.objects[path]
+	if !ok {
+		return nil, storage.ErrNotFound
+	}
+	return io.NopCloser(bytes.NewReader(make([]byte, obj.Size))), nil
+}
+
+func (s *fakeGradleCacheStore) Exists(_ context.Context, path string) (bool, error) {
+	_, ok := s.objects[path]
+	return ok, nil
+}
+
+func (s *fakeGradleCacheStore) Delete(_ context.Context, path string) error {
+	delete(s.objects, path)
+	return nil
+}
+
+func (s *fakeGradleCacheStore) Size(_ context.Context, path string) (int64, error) {
+	obj, ok := s.objects[path]
+	if !ok {
+		return 0, storage.ErrNotFound
+	}
+	return obj.Size, nil
+}
+
+func (s *fakeGradleCacheStore) SignedURL(_ context.Context, _ string, _ time.Duration) (string, error) {
+	return "", storage.ErrSignedURLUnsupported
+}
+
+func (s *fakeGradleCacheStore) UsedSpace(_ context.Context) (int64, error) {
+	var total int64
+	for _, obj := range s.objects {
+		total += obj.Size
+	}
+	return total, nil
+}
+
+func (s *fakeGradleCacheStore) URL() string { return "mem://" }
+
+func (s *fakeGradleCacheStore) Close() error { return nil }
+
+func (s *fakeGradleCacheStore) ListPrefix(_ context.Context, prefix string) ([]storage.ObjectInfo, error) {
+	objects := make([]storage.ObjectInfo, 0)
+	for _, obj := range s.objects {
+		if strings.HasPrefix(obj.Path, prefix) {
+			objects = append(objects, obj)
+		}
+	}
+	return objects, nil
+}
+
+func TestSweepGradleBuildCache_MaxAge(t *testing.T) {
+	now := time.Date(2026, 4, 27, 12, 0, 0, 0, time.UTC)
+	store := newFakeGradleCacheStore([]storage.ObjectInfo{
+		{Path: "_gradle/http-build-cache/old", Size: 10, ModTime: now.Add(-48 * time.Hour)},
+		{Path: "_gradle/http-build-cache/new", Size: 10, ModTime: now.Add(-2 * time.Hour)},
+	})
+
+	deleted, freed, err := sweepGradleBuildCache(context.Background(), store, store, 24*time.Hour, 0, now)
+	if err != nil {
+		t.Fatalf("sweepGradleBuildCache() error = %v", err)
+	}
+	if deleted != 1 {
+		t.Fatalf("deleted entries = %d, want 1", deleted)
+	}
+	if freed != 10 {
+		t.Fatalf("freed bytes = %d, want 10", freed)
+	}
+
+	if _, ok := store.objects["_gradle/http-build-cache/old"]; ok {
+		t.Fatal("old entry was not deleted")
+	}
+	if _, ok := store.objects["_gradle/http-build-cache/new"]; !ok {
+		t.Fatal("new entry should remain")
+	}
+}
+
+func TestSweepGradleBuildCache_MaxSizeOldestFirst(t *testing.T) {
+	now := time.Date(2026, 4, 27, 12, 0, 0, 0, time.UTC)
+	store := newFakeGradleCacheStore([]storage.ObjectInfo{
+		{Path: "_gradle/http-build-cache/a", Size: 5, ModTime: now.Add(-3 * time.Hour)},
+		{Path: "_gradle/http-build-cache/b", Size: 5, ModTime: now.Add(-2 * time.Hour)},
+		{Path: "_gradle/http-build-cache/c", Size: 5, ModTime: now.Add(-1 * time.Hour)},
+	})
+
+	deleted, freed, err := sweepGradleBuildCache(context.Background(), store, store, 0, 10, now)
+	if err != nil {
+		t.Fatalf("sweepGradleBuildCache() error = %v", err)
+	}
+	if deleted != 1 {
+		t.Fatalf("deleted entries = %d, want 1", deleted)
+	}
+	if freed != 5 {
+		t.Fatalf("freed bytes = %d, want 5", freed)
+	}
+
+	if _, ok := store.objects["_gradle/http-build-cache/a"]; ok {
+		t.Fatal("oldest entry was not deleted")
+	}
+	if _, ok := store.objects["_gradle/http-build-cache/b"]; !ok {
+		t.Fatal("middle entry should remain")
+	}
+	if _, ok := store.objects["_gradle/http-build-cache/c"]; !ok {
+		t.Fatal("newest entry should remain")
+	}
+}
diff --git a/internal/server/server.go b/internal/server/server.go
index a168b4a..a0983e5 100644
--- a/internal/server/server.go
+++ b/internal/server/server.go
@@ -9,6 +9,7 @@
 //   - /pub/*      - pub.dev registry protocol
 //   - /pypi/*     - PyPI registry protocol
 //   - /maven/*    - Maven repository protocol
+//   - /gradle/*   - Gradle HttpBuildCache protocol
 //   - /nuget/*    - NuGet V3 API protocol
 //   - /composer/* - Composer/Packagist protocol
 //   - /conan/*    - Conan C/C++ protocol
@@ -148,6 +149,8 @@ func (s *Server) Start() error {
 	proxy.Cooldown = cd
 	proxy.CacheMetadata = s.cfg.CacheMetadata
 	proxy.MetadataTTL = s.cfg.ParseMetadataTTL()
+	proxy.GradleReadOnly = s.cfg.Gradle.BuildCache.ReadOnly
+	proxy.GradleMaxUploadSize = s.cfg.ParseGradleBuildCacheMaxUploadSize()
 	proxy.DirectServe = s.cfg.Storage.DirectServe
 	proxy.DirectServeTTL = s.cfg.ParseDirectServeTTL()
 	proxy.DirectServeBaseURL = s.cfg.Storage.DirectServeBaseURL
@@ -180,6 +183,7 @@ func (s *Server) Start() error {
 	pubHandler := handler.NewPubHandler(proxy, s.cfg.BaseURL)
 	pypiHandler := handler.NewPyPIHandler(proxy, s.cfg.BaseURL)
 	mavenHandler := handler.NewMavenHandler(proxy, s.cfg.BaseURL)
+	gradleHandler := handler.NewGradleBuildCacheHandler(proxy)
 	nugetHandler := handler.NewNuGetHandler(proxy, s.cfg.BaseURL)
 	composerHandler := handler.NewComposerHandler(proxy, s.cfg.BaseURL)
 	conanHandler := handler.NewConanHandler(proxy, s.cfg.BaseURL)
@@ -197,6 +201,7 @@ func (s *Server) Start() error {
 	r.Mount("/pub", http.StripPrefix("/pub", pubHandler.Routes()))
 	r.Mount("/pypi", http.StripPrefix("/pypi", pypiHandler.Routes()))
 	r.Mount("/maven", http.StripPrefix("/maven", mavenHandler.Routes()))
+	r.Mount("/gradle", http.StripPrefix("/gradle", gradleHandler.Routes()))
 	r.Mount("/nuget", http.StripPrefix("/nuget", nugetHandler.Routes()))
 	r.Mount("/composer", http.StripPrefix("/composer", composerHandler.Routes()))
 	r.Mount("/conan", http.StripPrefix("/conan", conanHandler.Routes()))
@@ -238,6 +243,7 @@ func (s *Server) Start() error {
 	// Start background context (used by mirror jobs and cleanup)
 	bgCtx, bgCancel := context.WithCancel(context.Background())
 	s.cancel = bgCancel
+	s.startGradleBuildCacheEviction(bgCtx)
 
 	// Mirror API endpoints (opt-in via mirror_api config or PROXY_MIRROR_API env)
 	if s.cfg.MirrorAPI {
diff --git a/internal/server/server_test.go b/internal/server/server_test.go
index be88bf6..574b6ba 100644
--- a/internal/server/server_test.go
+++ b/internal/server/server_test.go
@@ -72,12 +72,14 @@ func newTestServer(t *testing.T) *testServer {
 	gemHandler := handler.NewGemHandler(proxy, cfg.BaseURL)
 	goHandler := handler.NewGoHandler(proxy, cfg.BaseURL)
 	pypiHandler := handler.NewPyPIHandler(proxy, cfg.BaseURL)
+	gradleHandler := handler.NewGradleBuildCacheHandler(proxy)
 
 	r.Mount("/npm", http.StripPrefix("/npm", npmHandler.Routes()))
 	r.Mount("/cargo", http.StripPrefix("/cargo", cargoHandler.Routes()))
 	r.Mount("/gem", http.StripPrefix("/gem", gemHandler.Routes()))
 	r.Mount("/go", http.StripPrefix("/go", goHandler.Routes()))
 	r.Mount("/pypi", http.StripPrefix("/pypi", pypiHandler.Routes()))
+	r.Mount("/gradle", http.StripPrefix("/gradle", gradleHandler.Routes()))
 
 	// Create a minimal server struct for the handlers
 	s := &Server{
@@ -344,6 +346,33 @@ func TestPyPISimple(t *testing.T) {
 	}
 }
 
+func TestGradleBuildCachePutGet(t *testing.T) {
+	ts := newTestServer(t)
+	defer ts.close()
+
+	key := "abc123def456"
+	body := "build-cache-bytes"
+
+	putReq := httptest.NewRequest(http.MethodPut, "/gradle/"+key, strings.NewReader(body))
+	putW := httptest.NewRecorder()
+	ts.handler.ServeHTTP(putW, putReq)
+
+	if putW.Code != http.StatusCreated {
+		t.Fatalf("expected status 201, got %d: %s", putW.Code, putW.Body.String())
+	}
+
+	getReq := httptest.NewRequest(http.MethodGet, "/gradle/"+key, nil)
+	getW := httptest.NewRecorder()
+	ts.handler.ServeHTTP(getW, getReq)
+
+	if getW.Code != http.StatusOK {
+		t.Fatalf("expected status 200, got %d: %s", getW.Code, getW.Body.String())
+	}
+	if got := getW.Body.String(); got != body {
+		t.Fatalf("expected body %q, got %q", body, got)
+	}
+}
+
 func TestGemSpecs(t *testing.T) {
 	ts := newTestServer(t)
 	defer ts.close()
diff --git a/internal/server/templates_test.go b/internal/server/templates_test.go
index a8b67f8..c27363b 100644
--- a/internal/server/templates_test.go
+++ b/internal/server/templates_test.go
@@ -193,7 +193,7 @@ func TestInstallPage(t *testing.T) {
 	body := w.Body.String()
 
 	// Should contain instructions for all registries
-	registries := []string{"npm", "Cargo", "RubyGems", "Go Modules", "PyPI", "Maven", "NuGet", "Composer", "Conan", "Conda", "CRAN"}
+	registries := []string{"npm", "Cargo", "RubyGems", "Go Modules", "PyPI", "Maven", "Gradle Build Cache", "NuGet", "Composer", "Conan", "Conda", "CRAN"}
 	for _, reg := range registries {
 		if !strings.Contains(body, reg) {
 			t.Errorf("install page should contain %s instructions", reg)
diff --git a/internal/storage/blob.go b/internal/storage/blob.go
index dc41668..67e91d0 100644
--- a/internal/storage/blob.go
+++ b/internal/storage/blob.go
@@ -184,6 +184,35 @@ func (b *Blob) UsedSpace(ctx context.Context) (int64, error) {
 	return total, nil
 }
 
+// ListPrefix returns object metadata for keys under a prefix.
+func (b *Blob) ListPrefix(ctx context.Context, prefix string) ([]ObjectInfo, error) {
+	iter := b.bucket.List(&blob.ListOptions{Prefix: prefix})
+	objects := make([]ObjectInfo, 0)
+
+	for {
+		obj, err := iter.Next(ctx)
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return nil, fmt.Errorf("listing objects: %w", err)
+		}
+		if obj.IsDir {
+			continue
+		}
+
+		info := ObjectInfo{
+			Path:    obj.Key,
+			Size:    obj.Size,
+			ModTime: obj.ModTime,
+		}
+
+		objects = append(objects, info)
+	}
+
+	return objects, nil
+}
+
 func (b *Blob) Close() error {
 	return b.bucket.Close()
 }
diff --git a/internal/storage/filesystem.go b/internal/storage/filesystem.go
index 53cff42..1e5a24f 100644
--- a/internal/storage/filesystem.go
+++ b/internal/storage/filesystem.go
@@ -6,6 +6,7 @@ import (
 	"encoding/hex"
 	"fmt"
 	"io"
+	fsys "io/fs"
 	"os"
 	"path/filepath"
 	"strings"
@@ -187,6 +188,54 @@ func (fs *Filesystem) UsedSpace(ctx context.Context) (int64, error) {
 	return total, nil
 }
 
+// ListPrefix returns object metadata for paths under a prefix.
+func (fs *Filesystem) ListPrefix(ctx context.Context, prefix string) ([]ObjectInfo, error) {
+	searchRoot, err := fs.fullPath(prefix)
+	if err != nil {
+		return nil, err
+	}
+
+	if _, err := os.Stat(searchRoot); err != nil {
+		if os.IsNotExist(err) {
+			return []ObjectInfo{}, nil
+		}
+		return nil, fmt.Errorf("stat prefix: %w", err)
+	}
+
+	objects := make([]ObjectInfo, 0)
+	err = filepath.WalkDir(searchRoot, func(path string, entry fsys.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+		if entry.IsDir() {
+			return nil
+		}
+
+		info, err := entry.Info()
+		if err != nil {
+			return err
+		}
+
+		relPath, err := filepath.Rel(fs.root, path)
+		if err != nil {
+			return err
+		}
+
+		objects = append(objects, ObjectInfo{
+			Path:    filepath.ToSlash(relPath),
+			Size:    info.Size(),
+			ModTime: info.ModTime(),
+		})
+
+		return nil
+	})
+	if err != nil {
+		return nil, fmt.Errorf("walking prefix: %w", err)
+	}
+
+	return objects, nil
+}
+
 // Root returns the root directory of the storage.
 func (fs *Filesystem) Root() string {
 	return fs.root
diff --git a/internal/storage/storage.go b/internal/storage/storage.go
index 0dba46a..e11db53 100644
--- a/internal/storage/storage.go
+++ b/internal/storage/storage.go
@@ -28,6 +28,13 @@ var (
 	ErrSignedURLUnsupported = errors.New("signed URLs not supported by storage backend")
 )
 
+// ObjectInfo contains metadata for a stored object.
+type ObjectInfo struct {
+	Path    string
+	Size    int64
+	ModTime time.Time
+}
+
 // Storage defines the interface for artifact storage backends.
 type Storage interface {
 	// Store writes content from r to the given path.

From 992f5c68a7d67b6e695ec27322b40bafa1a2f228 Mon Sep 17 00:00:00 2001
From: Andrew Nesbitt <andrewnez@gmail.com>
Date: Tue, 5 May 2026 10:25:17 +0100
Subject: [PATCH 17/36] Add .golangci.yml and clear gocognit/goconst findings
 (#113)

Bake the extended linter set into a project config so plain
golangci-lint run matches what we check locally, with goconst tuned
to ignore tests and bare lowercase words to drop ~200 ecosystem-name
and test-literal false positives.

Clear the remaining real findings: extract GradleBuildCacheConfig.Validate
from Config.Validate, pull the eviction sort comparator into
sortOldestFirst (zero time.Time already sorts first via Before so the
switch was redundant), add headerAcceptEncoding and SQL column-type
constants, and drop a dead empty-key recheck in the gradle handler.
---
 .golangci.yml                            | 28 ++++++++++++
 internal/config/config.go                | 54 ++++++++++++++----------
 internal/database/schema.go              | 28 ++++++------
 internal/handler/conda.go                |  4 +-
 internal/handler/cran.go                 |  2 +-
 internal/handler/gem.go                  |  4 +-
 internal/handler/gradle.go               |  2 +-
 internal/handler/handler.go              |  4 +-
 internal/handler/nuget.go                |  6 +--
 internal/server/gradle_cache_eviction.go | 27 +++++-------
 10 files changed, 97 insertions(+), 62 deletions(-)
 create mode 100644 .golangci.yml

diff --git a/.golangci.yml b/.golangci.yml
new file mode 100644
index 0000000..9d4b957
--- /dev/null
+++ b/.golangci.yml
@@ -0,0 +1,28 @@
+version: "2"
+
+linters:
+  enable:
+    - gocritic
+    - gocognit
+    - gocyclo
+    - maintidx
+    - dupl
+    - mnd
+    - unparam
+    - ireturn
+    - goconst
+    - errcheck
+  settings:
+    goconst:
+      min-len: 4
+      min-occurrences: 5
+      ignore-tests: true
+      ignore-string-values:
+        - "^[a-z]+$"
+  exclusions:
+    rules:
+      - path: _test\.go
+        linters:
+          - goconst
+          - dupl
+          - mnd
diff --git a/internal/config/config.go b/internal/config/config.go
index b728f68..067981d 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -294,10 +294,10 @@ func Default() *Config {
 		Gradle: GradleConfig{
 			BuildCache: GradleBuildCacheConfig{
 				ReadOnly:      false,
-				MaxUploadSize: "100MB",
+				MaxUploadSize: defaultGradleMaxUploadSizeStr,
 				MaxAge:        "168h",
 				MaxSize:       "",
-				SweepInterval: "10m",
+				SweepInterval: defaultGradleSweepIntervalStr,
 			},
 		},
 	}
@@ -481,51 +481,59 @@ func (c *Config) Validate() error {
 		}
 	}
 
-	// Validate Gradle build cache upload size (always required and must be > 0).
-	if c.Gradle.BuildCache.MaxUploadSize == "" {
-		c.Gradle.BuildCache.MaxUploadSize = "100MB"
+	if err := c.Gradle.BuildCache.Validate(); err != nil {
+		return err
 	}
-	uploadSize, err := ParseSize(c.Gradle.BuildCache.MaxUploadSize)
+
+	return nil
+}
+
+// Validate checks Gradle build cache settings, applying the default upload
+// size if unset.
+func (g *GradleBuildCacheConfig) Validate() error {
+	if g.MaxUploadSize == "" {
+		g.MaxUploadSize = defaultGradleMaxUploadSizeStr
+	}
+	uploadSize, err := ParseSize(g.MaxUploadSize)
 	if err != nil {
 		return fmt.Errorf("invalid gradle.build_cache.max_upload_size: %w", err)
 	}
 	if uploadSize <= 0 {
-		return fmt.Errorf("invalid gradle.build_cache.max_upload_size %q: must be > 0", c.Gradle.BuildCache.MaxUploadSize)
+		return fmt.Errorf("invalid gradle.build_cache.max_upload_size %q: must be > 0", g.MaxUploadSize)
 	}
 
-	// Validate Gradle max age if specified.
-	if c.Gradle.BuildCache.MaxAge != "" && c.Gradle.BuildCache.MaxAge != "0" {
-		if _, err := time.ParseDuration(c.Gradle.BuildCache.MaxAge); err != nil {
-			return fmt.Errorf("invalid gradle.build_cache.max_age %q: %w", c.Gradle.BuildCache.MaxAge, err)
+	if g.MaxAge != "" && g.MaxAge != "0" {
+		if _, err := time.ParseDuration(g.MaxAge); err != nil {
+			return fmt.Errorf("invalid gradle.build_cache.max_age %q: %w", g.MaxAge, err)
 		}
 	}
 
-	// Validate Gradle max size if specified.
-	if c.Gradle.BuildCache.MaxSize != "" {
-		if _, err := ParseSize(c.Gradle.BuildCache.MaxSize); err != nil {
+	if g.MaxSize != "" {
+		if _, err := ParseSize(g.MaxSize); err != nil {
 			return fmt.Errorf("invalid gradle.build_cache.max_size: %w", err)
 		}
 	}
 
-	// Validate Gradle sweep interval if specified.
-	if c.Gradle.BuildCache.SweepInterval != "" {
-		d, err := time.ParseDuration(c.Gradle.BuildCache.SweepInterval)
+	if g.SweepInterval != "" {
+		d, err := time.ParseDuration(g.SweepInterval)
 		if err != nil {
-			return fmt.Errorf("invalid gradle.build_cache.sweep_interval %q: %w", c.Gradle.BuildCache.SweepInterval, err)
+			return fmt.Errorf("invalid gradle.build_cache.sweep_interval %q: %w", g.SweepInterval, err)
 		}
 		if d <= 0 {
-			return fmt.Errorf("invalid gradle.build_cache.sweep_interval %q: must be > 0", c.Gradle.BuildCache.SweepInterval)
+			return fmt.Errorf("invalid gradle.build_cache.sweep_interval %q: must be > 0", g.SweepInterval)
 		}
 	}
 
 	return nil
 }
 
-const defaultGradleBuildCacheMaxUploadSize = 100 << 20
-const defaultGradleBuildCacheSweepInterval = 10 * time.Minute
 const (
-	defaultMetadataTTL    = 5 * time.Minute  //nolint:mnd // sensible default
-	defaultDirectServeTTL = 15 * time.Minute //nolint:mnd // sensible default
+	defaultMetadataTTL                   = 5 * time.Minute  //nolint:mnd // sensible default
+	defaultDirectServeTTL                = 15 * time.Minute //nolint:mnd // sensible default
+	defaultGradleBuildCacheMaxUploadSize = 100 << 20
+	defaultGradleBuildCacheSweepInterval = 10 * time.Minute
+	defaultGradleMaxUploadSizeStr        = "100MB"
+	defaultGradleSweepIntervalStr        = "10m"
 )
 
 // ParseMaxSize returns the maximum cache size in bytes.
diff --git a/internal/database/schema.go b/internal/database/schema.go
index e6f284f..c8d8d1e 100644
--- a/internal/database/schema.go
+++ b/internal/database/schema.go
@@ -6,7 +6,11 @@ import (
 	"time"
 )
 
-const postgresTimestamp = "TIMESTAMP"
+const (
+	postgresTimestamp = "TIMESTAMP"
+	sqliteDatetime    = "DATETIME"
+	colTypeText       = "TEXT"
+)
 
 // Schema for proxy-specific tables. The packages and versions tables
 // are compatible with git-pkgs, allowing the proxy to use an existing
@@ -369,9 +373,9 @@ func isTableNotFound(err error) bool {
 func (db *DB) createMigrationsTable() error {
 	var ts string
 	if db.dialect == DialectPostgres {
-		ts = "TIMESTAMP"
+		ts = postgresTimestamp
 	} else {
-		ts = "DATETIME"
+		ts = sqliteDatetime
 	}
 
 	query := fmt.Sprintf(`CREATE TABLE IF NOT EXISTS migrations (
@@ -457,12 +461,12 @@ func (db *DB) MigrateSchema() error {
 
 func migrateAddPackagesEnrichmentColumns(db *DB) error {
 	columns := map[string]string{
-		"registry_url":    "TEXT",
-		"supplier_name":   "TEXT",
-		"supplier_type":   "TEXT",
-		"source":          "TEXT",
-		"enriched_at":     "DATETIME",
-		"vulns_synced_at": "DATETIME",
+		"registry_url":    colTypeText,
+		"supplier_name":   colTypeText,
+		"supplier_type":   colTypeText,
+		"source":          colTypeText,
+		"enriched_at":     sqliteDatetime,
+		"vulns_synced_at": sqliteDatetime,
 	}
 
 	if db.dialect == DialectPostgres {
@@ -487,10 +491,10 @@ func migrateAddPackagesEnrichmentColumns(db *DB) error {
 
 func migrateAddVersionsEnrichmentColumns(db *DB) error {
 	columns := map[string]string{
-		"integrity":   "TEXT",
+		"integrity":   colTypeText,
 		"yanked":      "INTEGER DEFAULT 0",
-		"source":      "TEXT",
-		"enriched_at": "DATETIME",
+		"source":      colTypeText,
+		"enriched_at": sqliteDatetime,
 	}
 
 	if db.dialect == DialectPostgres {
diff --git a/internal/handler/conda.go b/internal/handler/conda.go
index a986f01..1336f94 100644
--- a/internal/handler/conda.go
+++ b/internal/handler/conda.go
@@ -140,7 +140,7 @@ func (h *CondaHandler) handleRepodata(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "failed to create request", http.StatusInternalServerError)
 		return
 	}
-	req.Header.Set("Accept-Encoding", "gzip")
+	req.Header.Set(headerAcceptEncoding, "gzip")
 
 	resp, err := h.proxy.HTTPClient.Do(req)
 	if err != nil {
@@ -241,5 +241,5 @@ func (h *CondaHandler) proxyCached(w http.ResponseWriter, r *http.Request) {
 
 // proxyUpstream forwards a request to Anaconda without caching.
 func (h *CondaHandler) proxyUpstream(w http.ResponseWriter, r *http.Request) {
-	h.proxy.ProxyUpstream(w, r, h.upstreamURL+r.URL.Path, []string{"Accept-Encoding"})
+	h.proxy.ProxyUpstream(w, r, h.upstreamURL+r.URL.Path, []string{headerAcceptEncoding})
 }
diff --git a/internal/handler/cran.go b/internal/handler/cran.go
index 246fcaa..0ecd2a3 100644
--- a/internal/handler/cran.go
+++ b/internal/handler/cran.go
@@ -159,5 +159,5 @@ func (h *CRANHandler) proxyCached(w http.ResponseWriter, r *http.Request) {
 
 // proxyUpstream forwards a request to CRAN without caching.
 func (h *CRANHandler) proxyUpstream(w http.ResponseWriter, r *http.Request) {
-	h.proxy.ProxyUpstream(w, r, h.upstreamURL+r.URL.Path, []string{"Accept-Encoding"})
+	h.proxy.ProxyUpstream(w, r, h.upstreamURL+r.URL.Path, []string{headerAcceptEncoding})
 }
diff --git a/internal/handler/gem.go b/internal/handler/gem.go
index bdb4bb9..9ec57e3 100644
--- a/internal/handler/gem.go
+++ b/internal/handler/gem.go
@@ -182,7 +182,7 @@ func (h *GemHandler) fetchCompactIndex(r *http.Request, name string) (*http.Resp
 	if err != nil {
 		return nil, err
 	}
-	for _, hdr := range []string{"Accept", "Accept-Encoding", "If-None-Match", "If-Modified-Since"} {
+	for _, hdr := range []string{"Accept", headerAcceptEncoding, "If-None-Match", "If-Modified-Since"} {
 		if v := r.Header.Get(hdr); v != "" {
 			req.Header.Set(hdr, v)
 		}
@@ -311,7 +311,7 @@ func (h *GemHandler) proxyUpstream(w http.ResponseWriter, r *http.Request) {
 	}
 
 	// Copy relevant headers
-	for _, h := range []string{"Accept", "Accept-Encoding", "If-None-Match", "If-Modified-Since"} {
+	for _, h := range []string{"Accept", headerAcceptEncoding, "If-None-Match", "If-Modified-Since"} {
 		if v := r.Header.Get(h); v != "" {
 			req.Header.Set(h, v)
 		}
diff --git a/internal/handler/gradle.go b/internal/handler/gradle.go
index 41c9f76..aed98e7 100644
--- a/internal/handler/gradle.go
+++ b/internal/handler/gradle.go
@@ -74,7 +74,7 @@ func (h *GradleBuildCacheHandler) parseCacheKey(urlPath string) (string, int) {
 		return "", http.StatusBadRequest
 	}
 
-	if keyPath == "" || strings.Contains(keyPath, "/") {
+	if strings.Contains(keyPath, "/") {
 		return "", http.StatusNotFound
 	}
 
diff --git a/internal/handler/handler.go b/internal/handler/handler.go
index d40a1dd..78f17cb 100644
--- a/internal/handler/handler.go
+++ b/internal/handler/handler.go
@@ -50,6 +50,8 @@ const defaultHTTPTimeout = 30 * time.Second
 
 const contentTypeJSON = "application/json"
 
+const headerAcceptEncoding = "Accept-Encoding"
+
 // maxMetadataSize is the maximum size of upstream metadata responses (100 MB).
 // Package metadata (e.g. npm with many versions) can be large, but unbounded
 // reads risk OOM if an upstream misbehaves.
@@ -726,7 +728,7 @@ func (p *Proxy) proxyMetadataStream(w http.ResponseWriter, r *http.Request, upst
 	}
 	req.Header.Set("Accept", accept)
 
-	for _, header := range []string{"Accept-Encoding", "If-Modified-Since", "If-None-Match"} {
+	for _, header := range []string{headerAcceptEncoding, "If-Modified-Since", "If-None-Match"} {
 		if v := r.Header.Get(header); v != "" {
 			req.Header.Set(header, v)
 		}
diff --git a/internal/handler/nuget.go b/internal/handler/nuget.go
index 1c022fb..3cce7f8 100644
--- a/internal/handler/nuget.go
+++ b/internal/handler/nuget.go
@@ -172,7 +172,7 @@ func (h *NuGetHandler) handleRegistration(w http.ResponseWriter, r *http.Request
 		http.Error(w, "failed to create request", http.StatusInternalServerError)
 		return
 	}
-	req.Header.Set("Accept-Encoding", "gzip")
+	req.Header.Set(headerAcceptEncoding, "gzip")
 
 	resp, err := h.proxy.HTTPClient.Do(req)
 	if err != nil {
@@ -338,8 +338,8 @@ func (h *NuGetHandler) proxyUpstream(w http.ResponseWriter, r *http.Request) {
 	}
 
 	// Copy accept-encoding for compression
-	if ae := r.Header.Get("Accept-Encoding"); ae != "" {
-		req.Header.Set("Accept-Encoding", ae)
+	if ae := r.Header.Get(headerAcceptEncoding); ae != "" {
+		req.Header.Set(headerAcceptEncoding, ae)
 	}
 
 	resp, err := h.proxy.HTTPClient.Do(req)
diff --git a/internal/server/gradle_cache_eviction.go b/internal/server/gradle_cache_eviction.go
index 1f5e95d..7f546d1 100644
--- a/internal/server/gradle_cache_eviction.go
+++ b/internal/server/gradle_cache_eviction.go
@@ -81,23 +81,7 @@ func sweepGradleBuildCache(
 		return 0, 0, nil
 	}
 
-	sort.Slice(entries, func(i, j int) bool {
-		iTime := entries[i].ModTime
-		jTime := entries[j].ModTime
-
-		switch {
-		case iTime.IsZero() && jTime.IsZero():
-			return entries[i].Path < entries[j].Path
-		case iTime.IsZero():
-			return true
-		case jTime.IsZero():
-			return false
-		case iTime.Equal(jTime):
-			return entries[i].Path < entries[j].Path
-		default:
-			return iTime.Before(jTime)
-		}
-	})
+	sortOldestFirst(entries)
 
 	deletedCount := 0
 	freedBytes := int64(0)
@@ -154,3 +138,12 @@ func sweepGradleBuildCache(
 
 	return deletedCount, freedBytes, nil
 }
+
+func sortOldestFirst(entries []storage.ObjectInfo) {
+	sort.Slice(entries, func(i, j int) bool {
+		if entries[i].ModTime.Equal(entries[j].ModTime) {
+			return entries[i].Path < entries[j].Path
+		}
+		return entries[i].ModTime.Before(entries[j].ModTime)
+	})
+}

From ebc2ea9cf9fd645b284c50274fab8dce64017330 Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Thu, 7 May 2026 16:44:53 +0100
Subject: [PATCH 18/36] Bump goreleaser/goreleaser-action from 7.1.0 to 7.2.1
 (#115)

Bumps [goreleaser/goreleaser-action](https://github.com/goreleaser/goreleaser-action) from 7.1.0 to 7.2.1.
- [Release notes](https://github.com/goreleaser/goreleaser-action/releases)
- [Commits](https://github.com/goreleaser/goreleaser-action/compare/e24998b8b67b290c2fa8b7c14fcfa7de2c5c9b8c...1a80836c5c9d9e5755a25cb59ec6f45a3b5f41a8)

---
updated-dependencies:
- dependency-name: goreleaser/goreleaser-action
  dependency-version: 7.2.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
---
 .github/workflows/release.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index cc79d4a..c5f2ebf 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -27,7 +27,7 @@ jobs:
           go-version-file: go.mod
           cache: false
 
-      - uses: goreleaser/goreleaser-action@e24998b8b67b290c2fa8b7c14fcfa7de2c5c9b8c # v7.1.0
+      - uses: goreleaser/goreleaser-action@1a80836c5c9d9e5755a25cb59ec6f45a3b5f41a8 # v7.2.1
         with:
           version: "~> v2"
           args: release --clean

From 5315883c3b9d9b9015d7c5fc13ac7e936422afcd Mon Sep 17 00:00:00 2001
From: Andrew Nesbitt <andrewnez@gmail.com>
Date: Wed, 13 May 2026 06:45:33 +0100
Subject: [PATCH 19/36] Bump registries to v0.6.0 and replace internal/cooldown
 (#120)

- Bump github.com/git-pkgs/registries to v0.6.0: the fetcher now
  honours HTTP_PROXY, gates dialled IPs against the safehttp block
  list, and Version.Integrity is populated for pub, julia and nuget
- Replace internal/cooldown with github.com/git-pkgs/cooldown v0.1.1
  (identical surface, lifted from this repo)
- Update docs/architecture.md to point at the external package
---
 docs/architecture.md               |   4 +-
 go.mod                             |   3 +-
 go.sum                             |   6 +-
 internal/cooldown/cooldown.go      | 125 ---------------------------
 internal/cooldown/cooldown_test.go | 133 -----------------------------
 internal/handler/cargo_test.go     |   2 +-
 internal/handler/composer_test.go  |   2 +-
 internal/handler/conda_test.go     |   2 +-
 internal/handler/gem_test.go       |   2 +-
 internal/handler/handler.go        |   2 +-
 internal/handler/hex_test.go       |   2 +-
 internal/handler/npm_test.go       |   2 +-
 internal/handler/nuget_test.go     |   2 +-
 internal/handler/pub_test.go       |   2 +-
 internal/handler/pypi_test.go      |   2 +-
 internal/server/server.go          |   2 +-
 16 files changed, 19 insertions(+), 274 deletions(-)
 delete mode 100644 internal/cooldown/cooldown.go
 delete mode 100644 internal/cooldown/cooldown_test.go

diff --git a/docs/architecture.md b/docs/architecture.md
index 81c41cf..85677b6 100644
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -283,9 +283,9 @@ HTTP server setup, web UI, and API handlers.
 
 Prometheus metrics for cache performance, upstream latency, storage operations, and active requests. See the Monitoring section of the README for the full metric list.
 
-### `internal/cooldown`
+### Cooldown
 
-Version age filtering for supply chain attack mitigation. Configurable at global, ecosystem, and per-package levels. Supported by npm, PyPI, pub.dev, and Composer handlers.
+Version age filtering for supply chain attack mitigation, provided by [github.com/git-pkgs/cooldown](https://github.com/git-pkgs/cooldown). Configurable at global, ecosystem, and per-package levels. Supported by npm, PyPI, pub.dev, and Composer handlers.
 
 ### `internal/enrichment`
 
diff --git a/go.mod b/go.mod
index 87fd2db..02e6b41 100644
--- a/go.mod
+++ b/go.mod
@@ -5,9 +5,10 @@ go 1.25.6
 require (
 	github.com/CycloneDX/cyclonedx-go v0.10.0
 	github.com/git-pkgs/archives v0.3.0
+	github.com/git-pkgs/cooldown v0.1.1
 	github.com/git-pkgs/enrichment v0.2.2
 	github.com/git-pkgs/purl v0.1.12
-	github.com/git-pkgs/registries v0.5.1
+	github.com/git-pkgs/registries v0.6.0
 	github.com/git-pkgs/spdx v0.1.3
 	github.com/git-pkgs/vers v0.2.5
 	github.com/git-pkgs/vulns v0.1.5
diff --git a/go.sum b/go.sum
index 80df597..5fe9699 100644
--- a/go.sum
+++ b/go.sum
@@ -252,6 +252,8 @@ github.com/ghostiam/protogetter v0.3.20 h1:oW7OPFit2FxZOpmMRPP9FffU4uUpfeE/rEdE1
 github.com/ghostiam/protogetter v0.3.20/go.mod h1:FjIu5Yfs6FT391m+Fjp3fbAYJ6rkL/J6ySpZBfnODuI=
 github.com/git-pkgs/archives v0.3.0 h1:iXKyO83jEFub1PGEDlHmk2tQ7XeV5LySTc0sEkH3x78=
 github.com/git-pkgs/archives v0.3.0/go.mod h1:LTJ1iQVFA7otizWMOyiI82NYVmyBWAPRzwu/e30rcXU=
+github.com/git-pkgs/cooldown v0.1.1 h1:9OqqzCB8gANz/y44SmqGD0Jp8Qtu81D1sCbKl6Ehg7w=
+github.com/git-pkgs/cooldown v0.1.1/go.mod h1:v7APuK/UouTiu8mWQZbdDmj7DfxxkGUeuhjaRB5gv9E=
 github.com/git-pkgs/enrichment v0.2.2 h1:vaQu5vs3tjQB5JI0gzBrUCynUc9z3l5byPhgKFaNZrc=
 github.com/git-pkgs/enrichment v0.2.2/go.mod h1:5JWGmlHWcv5HQHUrctcpnRUNpEF5VAixD2z4zvqKejs=
 github.com/git-pkgs/packageurl-go v0.3.1 h1:WM3RBABQZLaRBxgKyYughc3cVBE8KyQxbSC6Jt5ak7M=
@@ -260,8 +262,8 @@ github.com/git-pkgs/pom v0.1.4 h1:C6st+XSbF75eKuwfdkDZZtYHoTcaWRIEQYar5VtszUo=
 github.com/git-pkgs/pom v0.1.4/go.mod h1:ufdMBe1lKzqOeP9IUb9NPZ458xKV8E8NvuyBMxOfwIk=
 github.com/git-pkgs/purl v0.1.12 h1:qCskrEU1LWQhCkIVZd992W5++Bsxazvx2Cx1/65qCvU=
 github.com/git-pkgs/purl v0.1.12/go.mod h1:ofp4mHsR0cUeVONQaf33n6Wxg2QTEvtUdRfCedI8ouA=
-github.com/git-pkgs/registries v0.5.1 h1:UPE42CyZAsOfqO3N5bDelu28wS4Ifx/aOj0XZS4qYeI=
-github.com/git-pkgs/registries v0.5.1/go.mod h1:BY0YW+V0WDGBMuDR2aSMR3NzOPFK4K+F3j6+ch+cq3M=
+github.com/git-pkgs/registries v0.6.0 h1:ttQC8via9XAoLk9vqysf0K7uWl1bAyHPBWRBavRpAqs=
+github.com/git-pkgs/registries v0.6.0/go.mod h1:BY0YW+V0WDGBMuDR2aSMR3NzOPFK4K+F3j6+ch+cq3M=
 github.com/git-pkgs/spdx v0.1.3 h1:YQou23mLfzbW//6JlHUuc5x1P5VNIIDSku5gvauf86I=
 github.com/git-pkgs/spdx v0.1.3/go.mod h1:4HGGWyC8tg4DjOhrtBTYl4Lu+5i2BFuauGX8zcVcYPg=
 github.com/git-pkgs/vers v0.2.5 h1:tDtUMik9Iw1lyPHdT5V6LXjLo9LsJc0xOawURz7ibQU=
diff --git a/internal/cooldown/cooldown.go b/internal/cooldown/cooldown.go
deleted file mode 100644
index f37a2b9..0000000
--- a/internal/cooldown/cooldown.go
+++ /dev/null
@@ -1,125 +0,0 @@
-package cooldown
-
-import (
-	"fmt"
-	"strconv"
-	"strings"
-	"time"
-)
-
-const hoursPerDay = 24
-
-// Config holds cooldown settings for version filtering.
-// Cooldown hides package versions published too recently, giving the community
-// time to spot malicious releases before they're pulled into projects.
-type Config struct {
-	// Default is the global default cooldown duration (e.g., "3d", "48h").
-	Default string `json:"default" yaml:"default"`
-
-	// Ecosystems overrides the default for specific ecosystems.
-	// Keys are ecosystem names (e.g., "npm", "pypi").
-	Ecosystems map[string]string `json:"ecosystems" yaml:"ecosystems"`
-
-	// Packages overrides the cooldown for specific packages.
-	// Keys are PURLs (e.g., "pkg:npm/lodash", "pkg:npm/@babel/core").
-	Packages map[string]string `json:"packages" yaml:"packages"`
-
-	defaultDuration    time.Duration
-	ecosystemDurations map[string]time.Duration
-	packageDurations   map[string]time.Duration
-	parsed             bool
-}
-
-// parse resolves all string durations into time.Duration values.
-// Called lazily on first use.
-func (c *Config) parse() {
-	if c.parsed {
-		return
-	}
-	c.parsed = true
-
-	c.defaultDuration, _ = ParseDuration(c.Default)
-
-	c.ecosystemDurations = make(map[string]time.Duration, len(c.Ecosystems))
-	for k, v := range c.Ecosystems {
-		d, _ := ParseDuration(v)
-		c.ecosystemDurations[k] = d
-	}
-
-	c.packageDurations = make(map[string]time.Duration, len(c.Packages))
-	for k, v := range c.Packages {
-		d, _ := ParseDuration(v)
-		c.packageDurations[k] = d
-	}
-}
-
-// For returns the effective cooldown duration for a given ecosystem and package PURL.
-// Resolution order: package override > ecosystem override > global default.
-func (c *Config) For(ecosystem, packagePURL string) time.Duration {
-	c.parse()
-
-	if d, ok := c.packageDurations[packagePURL]; ok {
-		return d
-	}
-	if d, ok := c.ecosystemDurations[ecosystem]; ok {
-		return d
-	}
-	return c.defaultDuration
-}
-
-// IsAllowed returns true if a version with the given publish time has passed
-// the cooldown period for this ecosystem/package.
-func (c *Config) IsAllowed(ecosystem, packagePURL string, publishedAt time.Time) bool {
-	d := c.For(ecosystem, packagePURL)
-	if d == 0 {
-		return true
-	}
-	if publishedAt.IsZero() {
-		return true
-	}
-	return time.Since(publishedAt) >= d
-}
-
-// Enabled returns true if any cooldown is configured.
-func (c *Config) Enabled() bool {
-	c.parse()
-	if c.defaultDuration > 0 {
-		return true
-	}
-	for _, d := range c.ecosystemDurations {
-		if d > 0 {
-			return true
-		}
-	}
-	for _, d := range c.packageDurations {
-		if d > 0 {
-			return true
-		}
-	}
-	return false
-}
-
-// ParseDuration parses a duration string supporting days (e.g., "3d"),
-// in addition to Go's standard time.ParseDuration formats ("48h", "30m").
-// "0" means disabled (returns 0).
-func ParseDuration(s string) (time.Duration, error) {
-	s = strings.TrimSpace(s)
-	if s == "" || s == "0" {
-		return 0, nil
-	}
-
-	// Handle day suffix
-	if numStr, ok := strings.CutSuffix(s, "d"); ok {
-		days, err := strconv.ParseFloat(numStr, 64)
-		if err != nil {
-			return 0, fmt.Errorf("invalid duration %q: %w", s, err)
-		}
-		return time.Duration(days * float64(hoursPerDay*time.Hour)), nil
-	}
-
-	d, err := time.ParseDuration(s)
-	if err != nil {
-		return 0, fmt.Errorf("invalid duration %q: %w", s, err)
-	}
-	return d, nil
-}
diff --git a/internal/cooldown/cooldown_test.go b/internal/cooldown/cooldown_test.go
deleted file mode 100644
index c366077..0000000
--- a/internal/cooldown/cooldown_test.go
+++ /dev/null
@@ -1,133 +0,0 @@
-package cooldown
-
-import (
-	"testing"
-	"time"
-)
-
-func TestParseDuration(t *testing.T) {
-	tests := []struct {
-		input   string
-		want    time.Duration
-		wantErr bool
-	}{
-		{"", 0, false},
-		{"0", 0, false},
-		{"3d", 3 * 24 * time.Hour, false},
-		{"7d", 7 * 24 * time.Hour, false},
-		{"14d", 14 * 24 * time.Hour, false},
-		{"1.5d", 36 * time.Hour, false},
-		{"48h", 48 * time.Hour, false},
-		{"30m", 30 * time.Minute, false},
-		{"1h30m", 90 * time.Minute, false},
-		{"invalid", 0, true},
-		{"d", 0, true},
-		{"xd", 0, true},
-	}
-
-	for _, tt := range tests {
-		got, err := ParseDuration(tt.input)
-		if (err != nil) != tt.wantErr {
-			t.Errorf("ParseDuration(%q) error = %v, wantErr %v", tt.input, err, tt.wantErr)
-			continue
-		}
-		if got != tt.want {
-			t.Errorf("ParseDuration(%q) = %v, want %v", tt.input, got, tt.want)
-		}
-	}
-}
-
-func TestConfigFor(t *testing.T) {
-	c := &Config{
-		Default: "3d",
-		Ecosystems: map[string]string{
-			"npm":   "7d",
-			"cargo": "0",
-		},
-		Packages: map[string]string{
-			"pkg:npm/lodash":      "0",
-			"pkg:npm/@babel/core": "14d",
-		},
-	}
-
-	tests := []struct {
-		ecosystem   string
-		packagePURL string
-		want        time.Duration
-	}{
-		// Package override takes priority
-		{"npm", "pkg:npm/lodash", 0},
-		{"npm", "pkg:npm/@babel/core", 14 * 24 * time.Hour},
-		// Ecosystem override
-		{"npm", "pkg:npm/express", 7 * 24 * time.Hour},
-		{"cargo", "pkg:cargo/serde", 0},
-		// Global default
-		{"pypi", "pkg:pypi/requests", 3 * 24 * time.Hour},
-		{"pub", "pkg:pub/flutter", 3 * 24 * time.Hour},
-	}
-
-	for _, tt := range tests {
-		got := c.For(tt.ecosystem, tt.packagePURL)
-		if got != tt.want {
-			t.Errorf("For(%q, %q) = %v, want %v", tt.ecosystem, tt.packagePURL, got, tt.want)
-		}
-	}
-}
-
-func TestConfigIsAllowed(t *testing.T) {
-	c := &Config{
-		Default: "3d",
-		Packages: map[string]string{
-			"pkg:npm/lodash": "0",
-		},
-	}
-
-	now := time.Now()
-
-	tests := []struct {
-		name        string
-		ecosystem   string
-		packagePURL string
-		publishedAt time.Time
-		want        bool
-	}{
-		{"old enough", "npm", "pkg:npm/express", now.Add(-4 * 24 * time.Hour), true},
-		{"too recent", "npm", "pkg:npm/express", now.Add(-1 * 24 * time.Hour), false},
-		{"exactly at boundary", "npm", "pkg:npm/express", now.Add(-3 * 24 * time.Hour), true},
-		{"exempt package", "npm", "pkg:npm/lodash", now.Add(-1 * time.Minute), true},
-		{"zero time", "npm", "pkg:npm/express", time.Time{}, true},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			got := c.IsAllowed(tt.ecosystem, tt.packagePURL, tt.publishedAt)
-			if got != tt.want {
-				t.Errorf("IsAllowed(%q, %q, %v) = %v, want %v",
-					tt.ecosystem, tt.packagePURL, tt.publishedAt, got, tt.want)
-			}
-		})
-	}
-}
-
-func TestConfigEnabled(t *testing.T) {
-	tests := []struct {
-		name string
-		cfg  Config
-		want bool
-	}{
-		{"empty config", Config{}, false},
-		{"default only", Config{Default: "3d"}, true},
-		{"ecosystem only", Config{Ecosystems: map[string]string{"npm": "7d"}}, true},
-		{"package only", Config{Packages: map[string]string{"pkg:npm/x": "1d"}}, true},
-		{"all zero", Config{Default: "0", Ecosystems: map[string]string{"npm": "0"}}, false},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			got := tt.cfg.Enabled()
-			if got != tt.want {
-				t.Errorf("Enabled() = %v, want %v", got, tt.want)
-			}
-		})
-	}
-}
diff --git a/internal/handler/cargo_test.go b/internal/handler/cargo_test.go
index 5ce81b6..10d3faf 100644
--- a/internal/handler/cargo_test.go
+++ b/internal/handler/cargo_test.go
@@ -9,7 +9,7 @@ import (
 	"testing"
 	"time"
 
-	"github.com/git-pkgs/proxy/internal/cooldown"
+	"github.com/git-pkgs/cooldown"
 )
 
 func cargoTestProxy() *Proxy {
diff --git a/internal/handler/composer_test.go b/internal/handler/composer_test.go
index 94ff8cb..e4d79af 100644
--- a/internal/handler/composer_test.go
+++ b/internal/handler/composer_test.go
@@ -7,7 +7,7 @@ import (
 	"testing"
 	"time"
 
-	"github.com/git-pkgs/proxy/internal/cooldown"
+	"github.com/git-pkgs/cooldown"
 )
 
 func TestComposerRewriteMetadata(t *testing.T) {
diff --git a/internal/handler/conda_test.go b/internal/handler/conda_test.go
index 24b0236..1b57039 100644
--- a/internal/handler/conda_test.go
+++ b/internal/handler/conda_test.go
@@ -8,7 +8,7 @@ import (
 	"testing"
 	"time"
 
-	"github.com/git-pkgs/proxy/internal/cooldown"
+	"github.com/git-pkgs/cooldown"
 )
 
 func TestCondaParseFilename(t *testing.T) {
diff --git a/internal/handler/gem_test.go b/internal/handler/gem_test.go
index 6dce324..7d90946 100644
--- a/internal/handler/gem_test.go
+++ b/internal/handler/gem_test.go
@@ -10,7 +10,7 @@ import (
 	"testing"
 	"time"
 
-	"github.com/git-pkgs/proxy/internal/cooldown"
+	"github.com/git-pkgs/cooldown"
 )
 
 func TestGemParseFilename(t *testing.T) {
diff --git a/internal/handler/handler.go b/internal/handler/handler.go
index 78f17cb..0ad0776 100644
--- a/internal/handler/handler.go
+++ b/internal/handler/handler.go
@@ -15,7 +15,7 @@ import (
 	"strings"
 	"time"
 
-	"github.com/git-pkgs/proxy/internal/cooldown"
+	"github.com/git-pkgs/cooldown"
 	"github.com/git-pkgs/proxy/internal/database"
 	"github.com/git-pkgs/proxy/internal/metrics"
 	"github.com/git-pkgs/proxy/internal/storage"
diff --git a/internal/handler/hex_test.go b/internal/handler/hex_test.go
index 19d34b4..b02540a 100644
--- a/internal/handler/hex_test.go
+++ b/internal/handler/hex_test.go
@@ -11,7 +11,7 @@ import (
 	"testing"
 	"time"
 
-	"github.com/git-pkgs/proxy/internal/cooldown"
+	"github.com/git-pkgs/cooldown"
 	"google.golang.org/protobuf/encoding/protowire"
 )
 
diff --git a/internal/handler/npm_test.go b/internal/handler/npm_test.go
index 7db3539..bc1edde 100644
--- a/internal/handler/npm_test.go
+++ b/internal/handler/npm_test.go
@@ -8,7 +8,7 @@ import (
 	"testing"
 	"time"
 
-	"github.com/git-pkgs/proxy/internal/cooldown"
+	"github.com/git-pkgs/cooldown"
 )
 
 const testVersion100 = "1.0.0"
diff --git a/internal/handler/nuget_test.go b/internal/handler/nuget_test.go
index 68c9d22..b2164e5 100644
--- a/internal/handler/nuget_test.go
+++ b/internal/handler/nuget_test.go
@@ -10,7 +10,7 @@ import (
 	"testing"
 	"time"
 
-	"github.com/git-pkgs/proxy/internal/cooldown"
+	"github.com/git-pkgs/cooldown"
 )
 
 func nugetTestProxy() *Proxy {
diff --git a/internal/handler/pub_test.go b/internal/handler/pub_test.go
index 2788714..8a4c098 100644
--- a/internal/handler/pub_test.go
+++ b/internal/handler/pub_test.go
@@ -6,7 +6,7 @@ import (
 	"testing"
 	"time"
 
-	"github.com/git-pkgs/proxy/internal/cooldown"
+	"github.com/git-pkgs/cooldown"
 )
 
 func TestPubRewriteMetadata(t *testing.T) {
diff --git a/internal/handler/pypi_test.go b/internal/handler/pypi_test.go
index 9e2ade0..2b58960 100644
--- a/internal/handler/pypi_test.go
+++ b/internal/handler/pypi_test.go
@@ -10,7 +10,7 @@ import (
 	"testing"
 	"time"
 
-	"github.com/git-pkgs/proxy/internal/cooldown"
+	"github.com/git-pkgs/cooldown"
 	"github.com/git-pkgs/registries/fetch"
 )
 
diff --git a/internal/server/server.go b/internal/server/server.go
index a0983e5..cd57ae3 100644
--- a/internal/server/server.go
+++ b/internal/server/server.go
@@ -49,7 +49,7 @@ import (
 
 	swaggerdoc "github.com/git-pkgs/proxy/docs/swagger"
 	"github.com/git-pkgs/proxy/internal/config"
-	"github.com/git-pkgs/proxy/internal/cooldown"
+	"github.com/git-pkgs/cooldown"
 	"github.com/git-pkgs/proxy/internal/database"
 	"github.com/git-pkgs/proxy/internal/enrichment"
 	"github.com/git-pkgs/proxy/internal/handler"

From f2a5b704f06eaed561571462755663b891418a04 Mon Sep 17 00:00:00 2001
From: Andrew Nesbitt <andrewnez@gmail.com>
Date: Wed, 13 May 2026 06:46:35 +0100
Subject: [PATCH 20/36] Add Julia Pkg server support (#117)

- Implement /julia/* handler for the Pkg server protocol
  (registries, registry, package, artifact, meta)
- Resolve package UUIDs to names by parsing Registry.toml from
  the General registry tarball, with a hash-guarded background
  refresh on registry updates
- Wire into router, ecosystem list, install page, badge styles
- Update README and architecture docs
---
 README.md                      |  17 ++
 docs/architecture.md           |   2 +-
 go.mod                         |   2 +-
 internal/handler/julia.go      | 347 +++++++++++++++++++++++++++++++++
 internal/handler/julia_test.go | 167 ++++++++++++++++
 internal/server/dashboard.go   |  14 ++
 internal/server/server.go      |   3 +
 7 files changed, 550 insertions(+), 2 deletions(-)
 create mode 100644 internal/handler/julia.go
 create mode 100644 internal/handler/julia_test.go

diff --git a/README.md b/README.md
index 22beaaf..792c76b 100644
--- a/README.md
+++ b/README.md
@@ -38,6 +38,7 @@ Resolution order: package override, then ecosystem override, then global default
 | Conan | C/C++ | | ✓ |
 | Conda | Python/R | Yes | ✓ |
 | CRAN | R | | ✓ |
+| Julia | Julia | | ✓ |
 | Container | Docker/OCI | | ✓ |
 | Debian | Debian/Ubuntu | | ✓ |
 | RPM | RHEL/Fedora | | ✓ |
@@ -312,6 +313,21 @@ local({
 })
 ```
 
+### Julia
+
+Set the Pkg server before starting Julia:
+
+```bash
+export JULIA_PKG_SERVER=http://localhost:8080/julia
+```
+
+Or inside a running session:
+
+```julia
+ENV["JULIA_PKG_SERVER"] = "http://localhost:8080/julia"
+using Pkg; Pkg.update()
+```
+
 ### Docker / Container Registry
 
 Configure Docker to use the proxy as a registry mirror in `/etc/docker/daemon.json`:
@@ -593,6 +609,7 @@ Recently cached:
 | `GET /conan/*` | Conan C/C++ protocol |
 | `GET /conda/*` | Conda/Anaconda protocol |
 | `GET /cran/*` | CRAN (R) protocol |
+| `GET /julia/*` | Julia Pkg server protocol |
 | `GET /v2/*` | OCI/Docker registry protocol |
 | `GET /debian/*` | Debian/APT repository protocol |
 | `GET /rpm/*` | RPM/Yum repository protocol |
diff --git a/docs/architecture.md b/docs/architecture.md
index 85677b6..704561d 100644
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -14,7 +14,7 @@ The proxy is a caching HTTP server that sits between package manager clients and
 │  │  /npm/*     -> NPMHandler      /health  -> healthHandler  │    │
 │  │  /cargo/*   -> CargoHandler    /stats   -> statsHandler   │    │
 │  │  /gem/*     -> GemHandler      /metrics -> prometheus     │    │
-│  │  ...16 ecosystems              /api/*   -> APIHandler     │    │
+│  │  ...17 ecosystems              /api/*   -> APIHandler     │    │
 │  │                                /        -> Web UI         │    │
 │  └──────────────────────────────────────────────────────────┘    │
 │         │                    │                    │               │
diff --git a/go.mod b/go.mod
index 02e6b41..70ea32c 100644
--- a/go.mod
+++ b/go.mod
@@ -3,6 +3,7 @@ module github.com/git-pkgs/proxy
 go 1.25.6
 
 require (
+	github.com/BurntSushi/toml v1.6.0
 	github.com/CycloneDX/cyclonedx-go v0.10.0
 	github.com/git-pkgs/archives v0.3.0
 	github.com/git-pkgs/cooldown v0.1.1
@@ -50,7 +51,6 @@ require (
 	github.com/Azure/go-autorest v14.2.0+incompatible // indirect
 	github.com/Azure/go-autorest/autorest/to v0.4.1 // indirect
 	github.com/AzureAD/microsoft-authentication-library-for-go v1.6.0 // indirect
-	github.com/BurntSushi/toml v1.6.0 // indirect
 	github.com/Djarvur/go-err113 v0.1.1 // indirect
 	github.com/KyleBanks/depth v1.2.1 // indirect
 	github.com/Masterminds/semver/v3 v3.4.0 // indirect
diff --git a/internal/handler/julia.go b/internal/handler/julia.go
new file mode 100644
index 0000000..08b1fdf
--- /dev/null
+++ b/internal/handler/julia.go
@@ -0,0 +1,347 @@
+package handler
+
+import (
+	"archive/tar"
+	"bufio"
+	"bytes"
+	"compress/gzip"
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+	"regexp"
+	"strings"
+	"sync"
+
+	"github.com/BurntSushi/toml"
+)
+
+const (
+	juliaUpstream            = "https://pkg.julialang.org"
+	juliaGeneralRegistryUUID = "23338594-aafe-5451-b93e-139f81909106"
+	juliaArtifactName        = "_artifact"
+	juliaRegistryName        = "_registry"
+)
+
+var (
+	juliaHexPattern  = regexp.MustCompile(`^[0-9a-f]{40,64}$`)
+	juliaUUIDPattern = regexp.MustCompile(`^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$`)
+)
+
+// JuliaHandler handles Julia Pkg server protocol requests.
+//
+// See https://pkgdocs.julialang.org/v1/registries/ and the PkgServer.jl
+// reference implementation. The protocol is content-addressed: registry,
+// package and artifact resources are all identified by git tree hashes
+// and are immutable once published.
+type JuliaHandler struct {
+	proxy       *Proxy
+	upstreamURL string
+
+	mu        sync.RWMutex
+	names     map[string]string
+	namesHash string
+	loadMu    sync.Mutex
+}
+
+// NewJuliaHandler creates a new Julia Pkg server handler.
+func NewJuliaHandler(proxy *Proxy, _ string) *JuliaHandler {
+	return &JuliaHandler{
+		proxy:       proxy,
+		upstreamURL: juliaUpstream,
+		names:       make(map[string]string),
+	}
+}
+
+// Routes returns the HTTP handler for Julia requests.
+func (h *JuliaHandler) Routes() http.Handler {
+	mux := http.NewServeMux()
+
+	mux.HandleFunc("GET /registries", h.handleRegistries)
+	mux.HandleFunc("GET /registries.eager", h.handleRegistries)
+	mux.HandleFunc("GET /registries.conservative", h.handleRegistries)
+	mux.HandleFunc("GET /registry/{uuid}/{hash}", h.handleRegistry)
+	mux.HandleFunc("GET /package/{uuid}/{hash}", h.handlePackage)
+	mux.HandleFunc("GET /artifact/{hash}", h.handleArtifact)
+	mux.HandleFunc("GET /meta", h.proxyUpstream)
+
+	return mux
+}
+
+// handleRegistries serves the list of available registries. This is the only
+// mutable endpoint in the protocol so it goes through the metadata cache.
+func (h *JuliaHandler) handleRegistries(w http.ResponseWriter, r *http.Request) {
+	cacheKey := strings.TrimPrefix(r.URL.Path, "/")
+	h.proxy.ProxyCached(w, r, h.upstreamURL+r.URL.Path, "julia", cacheKey, "*/*")
+}
+
+// handleRegistry serves an immutable registry tarball and refreshes the
+// UUID→name map from its Registry.toml.
+func (h *JuliaHandler) handleRegistry(w http.ResponseWriter, r *http.Request) {
+	uuid := r.PathValue("uuid")
+	hash := r.PathValue("hash")
+	if !validJuliaUUID(uuid) || !juliaHexPattern.MatchString(hash) {
+		http.Error(w, "invalid registry reference", http.StatusBadRequest)
+		return
+	}
+
+	h.proxy.Logger.Info("julia registry request", "uuid", uuid, "hash", hash)
+
+	upstreamURL := h.upstreamURL + r.URL.Path
+	result, err := h.proxy.GetOrFetchArtifactFromURL(r.Context(), "julia", juliaRegistryName, hash, hash+".tar.gz", upstreamURL)
+	if err != nil {
+		h.proxy.Logger.Error("failed to get registry", "error", err)
+		http.Error(w, "failed to fetch registry", http.StatusBadGateway)
+		return
+	}
+
+	go h.refreshNamesFromRegistry(uuid, hash)
+
+	ServeArtifact(w, result)
+}
+
+// handlePackage serves an immutable package source tarball.
+func (h *JuliaHandler) handlePackage(w http.ResponseWriter, r *http.Request) {
+	uuid := r.PathValue("uuid")
+	hash := r.PathValue("hash")
+	if !validJuliaUUID(uuid) || !juliaHexPattern.MatchString(hash) {
+		http.Error(w, "invalid package reference", http.StatusBadRequest)
+		return
+	}
+
+	if err := h.ensureNames(r.Context()); err != nil {
+		h.proxy.Logger.Warn("julia name map unavailable, using uuid", "error", err)
+	}
+	name := h.resolveName(uuid)
+
+	h.proxy.Logger.Info("julia package request", "name", name, "uuid", uuid, "hash", hash)
+
+	upstreamURL := h.upstreamURL + r.URL.Path
+	result, err := h.proxy.GetOrFetchArtifactFromURL(r.Context(), "julia", name, hash, hash+".tar.gz", upstreamURL)
+	if err != nil {
+		h.proxy.Logger.Error("failed to get package", "error", err)
+		http.Error(w, "failed to fetch package", http.StatusBadGateway)
+		return
+	}
+
+	ServeArtifact(w, result)
+}
+
+// handleArtifact serves an immutable binary artifact tarball. Artifacts are
+// anonymous content-addressed blobs with no associated package name.
+func (h *JuliaHandler) handleArtifact(w http.ResponseWriter, r *http.Request) {
+	hash := r.PathValue("hash")
+	if !juliaHexPattern.MatchString(hash) {
+		http.Error(w, "invalid artifact hash", http.StatusBadRequest)
+		return
+	}
+
+	h.proxy.Logger.Info("julia artifact request", "hash", hash)
+
+	upstreamURL := h.upstreamURL + r.URL.Path
+	result, err := h.proxy.GetOrFetchArtifactFromURL(r.Context(), "julia", juliaArtifactName, hash, hash+".tar.gz", upstreamURL)
+	if err != nil {
+		h.proxy.Logger.Error("failed to get artifact", "error", err)
+		http.Error(w, "failed to fetch artifact", http.StatusBadGateway)
+		return
+	}
+
+	ServeArtifact(w, result)
+}
+
+// proxyUpstream forwards a request to the upstream Pkg server without caching.
+func (h *JuliaHandler) proxyUpstream(w http.ResponseWriter, r *http.Request) {
+	h.proxy.ProxyUpstream(w, r, h.upstreamURL+r.URL.Path, nil)
+}
+
+// resolveName returns the human-readable package name for a UUID, falling
+// back to the UUID itself if it is not present in the loaded registry.
+func (h *JuliaHandler) resolveName(uuid string) string {
+	h.mu.RLock()
+	defer h.mu.RUnlock()
+	if name, ok := h.names[uuid]; ok {
+		return name
+	}
+	return uuid
+}
+
+// ensureNames lazily populates the UUID→name map from the General registry.
+// Returns immediately if the map is already populated; otherwise blocks until
+// a single in-flight load completes. Failed loads are retried on the next call.
+func (h *JuliaHandler) ensureNames(ctx context.Context) error {
+	if h.namesLoaded() {
+		return nil
+	}
+
+	h.loadMu.Lock()
+	defer h.loadMu.Unlock()
+
+	if h.namesLoaded() {
+		return nil
+	}
+	return h.loadNamesFromUpstream(ctx)
+}
+
+func (h *JuliaHandler) namesLoaded() bool {
+	h.mu.RLock()
+	defer h.mu.RUnlock()
+	return len(h.names) > 0
+}
+
+// loadNamesFromUpstream fetches the current /registries listing, downloads the
+// General registry tarball at its current hash, and parses Registry.toml.
+func (h *JuliaHandler) loadNamesFromUpstream(ctx context.Context) error {
+	hash, err := h.fetchGeneralRegistryHash(ctx)
+	if err != nil {
+		return err
+	}
+	return h.loadRegistryTarball(ctx, juliaGeneralRegistryUUID, hash)
+}
+
+// fetchGeneralRegistryHash reads /registries and returns the current tree hash
+// for the General registry.
+func (h *JuliaHandler) fetchGeneralRegistryHash(ctx context.Context) (string, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, h.upstreamURL+"/registries", nil)
+	if err != nil {
+		return "", err
+	}
+	resp, err := h.proxy.HTTPClient.Do(req)
+	if err != nil {
+		return "", err
+	}
+	defer func() { _ = resp.Body.Close() }()
+
+	if resp.StatusCode != http.StatusOK {
+		return "", fmt.Errorf("upstream /registries returned %d", resp.StatusCode)
+	}
+
+	scanner := bufio.NewScanner(resp.Body)
+	for scanner.Scan() {
+		uuid, hash, ok := parseRegistryLine(scanner.Text())
+		if ok && uuid == juliaGeneralRegistryUUID {
+			return hash, nil
+		}
+	}
+	if err := scanner.Err(); err != nil {
+		return "", err
+	}
+	return "", fmt.Errorf("general registry not listed in /registries")
+}
+
+// refreshNamesFromRegistry reloads the UUID→name map from a registry tarball
+// that has just been cached. Errors are logged but do not affect the response.
+func (h *JuliaHandler) refreshNamesFromRegistry(uuid, hash string) {
+	if uuid != juliaGeneralRegistryUUID {
+		return
+	}
+	h.mu.RLock()
+	current := h.namesHash
+	h.mu.RUnlock()
+	if current == hash {
+		return
+	}
+	if err := h.loadRegistryTarball(context.Background(), uuid, hash); err != nil {
+		h.proxy.Logger.Warn("failed to refresh julia name map", "error", err)
+	}
+}
+
+// loadRegistryTarball downloads a registry tarball and replaces the name map
+// with the contents of its Registry.toml.
+func (h *JuliaHandler) loadRegistryTarball(ctx context.Context, uuid, hash string) error {
+	url := fmt.Sprintf("%s/registry/%s/%s", h.upstreamURL, uuid, hash)
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+	if err != nil {
+		return err
+	}
+	resp, err := h.proxy.HTTPClient.Do(req)
+	if err != nil {
+		return err
+	}
+	defer func() { _ = resp.Body.Close() }()
+
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("upstream registry returned %d", resp.StatusCode)
+	}
+
+	names, err := extractRegistryNames(resp.Body)
+	if err != nil {
+		return err
+	}
+
+	h.mu.Lock()
+	h.names = names
+	h.namesHash = hash
+	h.mu.Unlock()
+
+	h.proxy.Logger.Info("loaded julia registry name map", "packages", len(names), "hash", hash)
+	return nil
+}
+
+// extractRegistryNames reads a gzipped registry tarball, finds Registry.toml
+// at the root, and returns its [packages] table as a UUID→name map.
+func extractRegistryNames(r io.Reader) (map[string]string, error) {
+	gz, err := gzip.NewReader(r)
+	if err != nil {
+		return nil, fmt.Errorf("opening gzip stream: %w", err)
+	}
+	defer func() { _ = gz.Close() }()
+
+	tr := tar.NewReader(gz)
+	for {
+		hdr, err := tr.Next()
+		if err == io.EOF {
+			return nil, fmt.Errorf("no Registry.toml in tarball")
+		}
+		if err != nil {
+			return nil, err
+		}
+		if strings.TrimPrefix(hdr.Name, "./") != "Registry.toml" {
+			continue
+		}
+
+		data, err := io.ReadAll(tr)
+		if err != nil {
+			return nil, err
+		}
+		return parseRegistryToml(data)
+	}
+}
+
+type juliaRegistryFile struct {
+	Packages map[string]struct {
+		Name string `toml:"name"`
+	} `toml:"packages"`
+}
+
+// parseRegistryToml decodes the [packages] table of a Registry.toml file.
+func parseRegistryToml(data []byte) (map[string]string, error) {
+	var reg juliaRegistryFile
+	if _, err := toml.NewDecoder(bytes.NewReader(data)).Decode(&reg); err != nil {
+		return nil, fmt.Errorf("parsing Registry.toml: %w", err)
+	}
+
+	names := make(map[string]string, len(reg.Packages))
+	for uuid, pkg := range reg.Packages {
+		if pkg.Name != "" {
+			names[uuid] = pkg.Name
+		}
+	}
+	return names, nil
+}
+
+// parseRegistryLine parses a single line from /registries of the form
+// "/registry/{uuid}/{hash}" and returns the uuid and hash.
+func parseRegistryLine(line string) (uuid, hash string, ok bool) {
+	line = strings.TrimSpace(line)
+	line = strings.TrimPrefix(line, "/registry/")
+	uuid, hash, found := strings.Cut(line, "/")
+	if !found || !validJuliaUUID(uuid) || !juliaHexPattern.MatchString(hash) {
+		return "", "", false
+	}
+	return uuid, hash, true
+}
+
+// validJuliaUUID reports whether s looks like a lowercase RFC 4122 UUID.
+func validJuliaUUID(s string) bool {
+	return juliaUUIDPattern.MatchString(s)
+}
diff --git a/internal/handler/julia_test.go b/internal/handler/julia_test.go
new file mode 100644
index 0000000..68fb975
--- /dev/null
+++ b/internal/handler/julia_test.go
@@ -0,0 +1,167 @@
+package handler
+
+import (
+	"archive/tar"
+	"bytes"
+	"compress/gzip"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestJuliaParseRegistryLine(t *testing.T) {
+	tests := []struct {
+		line     string
+		wantUUID string
+		wantHash string
+		wantOK   bool
+	}{
+		{
+			"/registry/23338594-aafe-5451-b93e-139f81909106/342327538ed6c1ec54c69fa145e7b6bf5934201e",
+			"23338594-aafe-5451-b93e-139f81909106",
+			"342327538ed6c1ec54c69fa145e7b6bf5934201e",
+			true,
+		},
+		{
+			" /registry/23338594-aafe-5451-b93e-139f81909106/342327538ed6c1ec54c69fa145e7b6bf5934201e\n",
+			"23338594-aafe-5451-b93e-139f81909106",
+			"342327538ed6c1ec54c69fa145e7b6bf5934201e",
+			true,
+		},
+		{"/registry/not-a-uuid/0000", "", "", false},
+		{"junk", "", "", false},
+		{"", "", "", false},
+	}
+
+	for _, tt := range tests {
+		uuid, hash, ok := parseRegistryLine(tt.line)
+		if uuid != tt.wantUUID || hash != tt.wantHash || ok != tt.wantOK {
+			t.Errorf("parseRegistryLine(%q) = (%q, %q, %v), want (%q, %q, %v)",
+				tt.line, uuid, hash, ok, tt.wantUUID, tt.wantHash, tt.wantOK)
+		}
+	}
+}
+
+func TestJuliaValidUUID(t *testing.T) {
+	tests := []struct {
+		s    string
+		want bool
+	}{
+		{"23338594-aafe-5451-b93e-139f81909106", true},
+		{"295af30f-e4ad-537b-8983-00126c2a3abe", true},
+		{"23338594-AAFE-5451-b93e-139f81909106", false},
+		{"23338594aafe5451b93e139f81909106", false},
+		{"23338594-aafe-5451-b93e-139f8190910", false},
+		{"23338594-aafe-5451-b93e-139f81909106-", false},
+		{"23338594-gafe-5451-b93e-139f81909106", false},
+		{"", false},
+	}
+
+	for _, tt := range tests {
+		if got := validJuliaUUID(tt.s); got != tt.want {
+			t.Errorf("validJuliaUUID(%q) = %v, want %v", tt.s, got, tt.want)
+		}
+	}
+}
+
+func TestJuliaParseRegistryToml(t *testing.T) {
+	data := []byte(`name = "General"
+uuid = "23338594-aafe-5451-b93e-139f81909106"
+
+[packages]
+295af30f-e4ad-537b-8983-00126c2a3abe = { name = "Revise", path = "R/Revise" }
+91a5bcdd-55d7-5caf-9e0b-520d859cae80 = { name = "Plots", path = "P/Plots" }
+`)
+
+	names, err := parseRegistryToml(data)
+	if err != nil {
+		t.Fatalf("parseRegistryToml: %v", err)
+	}
+	if got := names["295af30f-e4ad-537b-8983-00126c2a3abe"]; got != "Revise" {
+		t.Errorf("names[Revise uuid] = %q, want Revise", got)
+	}
+	if got := names["91a5bcdd-55d7-5caf-9e0b-520d859cae80"]; got != "Plots" {
+		t.Errorf("names[Plots uuid] = %q, want Plots", got)
+	}
+	if len(names) != 2 {
+		t.Errorf("len(names) = %d, want 2", len(names))
+	}
+}
+
+func TestJuliaExtractRegistryNames(t *testing.T) {
+	registryToml := `name = "General"
+[packages]
+295af30f-e4ad-537b-8983-00126c2a3abe = { name = "Revise", path = "R/Revise" }
+`
+	var buf bytes.Buffer
+	gw := gzip.NewWriter(&buf)
+	tw := tar.NewWriter(gw)
+
+	for _, f := range []struct{ name, body string }{
+		{"R/Revise/Package.toml", "name = \"Revise\"\n"},
+		{"Registry.toml", registryToml},
+	} {
+		if err := tw.WriteHeader(&tar.Header{Name: f.name, Mode: 0o644, Size: int64(len(f.body))}); err != nil {
+			t.Fatalf("WriteHeader: %v", err)
+		}
+		if _, err := tw.Write([]byte(f.body)); err != nil {
+			t.Fatalf("Write: %v", err)
+		}
+	}
+	if err := tw.Close(); err != nil {
+		t.Fatalf("tar Close: %v", err)
+	}
+	if err := gw.Close(); err != nil {
+		t.Fatalf("gzip Close: %v", err)
+	}
+
+	names, err := extractRegistryNames(bytes.NewReader(buf.Bytes()))
+	if err != nil {
+		t.Fatalf("extractRegistryNames: %v", err)
+	}
+	if got := names["295af30f-e4ad-537b-8983-00126c2a3abe"]; got != "Revise" {
+		t.Errorf("names[Revise uuid] = %q, want Revise", got)
+	}
+}
+
+func TestJuliaResolveName(t *testing.T) {
+	h := &JuliaHandler{
+		proxy: &Proxy{Logger: slog.Default()},
+		names: map[string]string{
+			"295af30f-e4ad-537b-8983-00126c2a3abe": "Revise",
+		},
+	}
+
+	if got := h.resolveName("295af30f-e4ad-537b-8983-00126c2a3abe"); got != "Revise" {
+		t.Errorf("resolveName(known) = %q, want Revise", got)
+	}
+	if got := h.resolveName("00000000-0000-0000-0000-000000000000"); got != "00000000-0000-0000-0000-000000000000" {
+		t.Errorf("resolveName(unknown) = %q, want uuid fallback", got)
+	}
+}
+
+func TestJuliaRoutesValidation(t *testing.T) {
+	h := NewJuliaHandler(&Proxy{Logger: slog.Default()}, "")
+	routes := h.Routes()
+
+	tests := []struct {
+		path string
+		want int
+	}{
+		{"/package/not-a-uuid/342327538ed6c1ec54c69fa145e7b6bf5934201e", http.StatusBadRequest},
+		{"/package/295af30f-e4ad-537b-8983-00126c2a3abe/short", http.StatusBadRequest},
+		{"/registry/295af30f-e4ad-537b-8983-00126c2a3abe/zzzz", http.StatusBadRequest},
+		{"/artifact/nothex", http.StatusBadRequest},
+		{"/nope", http.StatusNotFound},
+	}
+
+	for _, tt := range tests {
+		req := httptest.NewRequest(http.MethodGet, tt.path, nil)
+		rr := httptest.NewRecorder()
+		routes.ServeHTTP(rr, req)
+		if rr.Code != tt.want {
+			t.Errorf("GET %s = %d, want %d", tt.path, rr.Code, tt.want)
+		}
+	}
+}
diff --git a/internal/server/dashboard.go b/internal/server/dashboard.go
index 1fe5388..1de294c 100644
--- a/internal/server/dashboard.go
+++ b/internal/server/dashboard.go
@@ -127,6 +127,7 @@ func supportedEcosystems() []string {
 		"gem",
 		"golang",
 		"hex",
+		"julia",
 		"maven",
 		"npm",
 		"nuget",
@@ -176,6 +177,8 @@ func ecosystemBadgeClasses(ecosystem string) string {
 		return base + " bg-green-100 text-green-700 dark:bg-green-900/50 dark:text-green-300"
 	case "cran":
 		return base + " bg-slate-100 text-slate-700 dark:bg-slate-800 dark:text-slate-300"
+	case "julia":
+		return base + " bg-emerald-100 text-emerald-700 dark:bg-emerald-900/50 dark:text-emerald-300"
 	case "oci":
 		return base + " bg-sky-100 text-sky-700 dark:bg-sky-900/50 dark:text-sky-300"
 	case "deb":
@@ -377,6 +380,17 @@ local({
   r["CRAN"] &lt;- "` + baseURL + `/cran"
   options(repos = r)
 })</code></pre>`),
+		},
+		{
+			ID:       "julia",
+			Name:     "Julia",
+			Language: "Julia",
+			Endpoint: "/julia/",
+			Instructions: template.HTML(`<p class="config-note">Set the Pkg server before starting Julia:</p>
+<pre><code>export JULIA_PKG_SERVER=` + baseURL + `/julia</code></pre>
+<p class="config-note">Or inside a running session:</p>
+<pre><code>ENV["JULIA_PKG_SERVER"] = "` + baseURL + `/julia"
+using Pkg; Pkg.update()</code></pre>`),
 		},
 		{
 			ID:       "oci",
diff --git a/internal/server/server.go b/internal/server/server.go
index cd57ae3..ffb357b 100644
--- a/internal/server/server.go
+++ b/internal/server/server.go
@@ -15,6 +15,7 @@
 //   - /conan/*    - Conan C/C++ protocol
 //   - /conda/*    - Conda/Anaconda protocol
 //   - /cran/*     - CRAN (R) protocol
+//   - /julia/*    - Julia Pkg server protocol
 //   - /v2/*       - OCI/Docker container registry protocol
 //   - /debian/*   - Debian/APT repository protocol
 //   - /rpm/*      - RPM/Yum repository protocol
@@ -189,6 +190,7 @@ func (s *Server) Start() error {
 	conanHandler := handler.NewConanHandler(proxy, s.cfg.BaseURL)
 	condaHandler := handler.NewCondaHandler(proxy, s.cfg.BaseURL)
 	cranHandler := handler.NewCRANHandler(proxy, s.cfg.BaseURL)
+	juliaHandler := handler.NewJuliaHandler(proxy, s.cfg.BaseURL)
 	containerHandler := handler.NewContainerHandler(proxy, s.cfg.BaseURL)
 	debianHandler := handler.NewDebianHandler(proxy, s.cfg.BaseURL)
 	rpmHandler := handler.NewRPMHandler(proxy, s.cfg.BaseURL)
@@ -207,6 +209,7 @@ func (s *Server) Start() error {
 	r.Mount("/conan", http.StripPrefix("/conan", conanHandler.Routes()))
 	r.Mount("/conda", http.StripPrefix("/conda", condaHandler.Routes()))
 	r.Mount("/cran", http.StripPrefix("/cran", cranHandler.Routes()))
+	r.Mount("/julia", http.StripPrefix("/julia", juliaHandler.Routes()))
 	r.Mount("/v2", http.StripPrefix("/v2", containerHandler.Routes()))
 	r.Mount("/debian", http.StripPrefix("/debian", debianHandler.Routes()))
 	r.Mount("/rpm", http.StripPrefix("/rpm", rpmHandler.Routes()))

From 17a10bda55c37367d4f5a874162e80dfb5c430b7 Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Fri, 15 May 2026 06:40:26 -0700
Subject: [PATCH 21/36] Bump sigstore/cosign-installer from 4.1.1 to 4.1.2
 (#122)

Bumps [sigstore/cosign-installer](https://github.com/sigstore/cosign-installer) from 4.1.1 to 4.1.2.
- [Release notes](https://github.com/sigstore/cosign-installer/releases)
- [Commits](https://github.com/sigstore/cosign-installer/compare/cad07c2e89fa2edd6e2d7bab4c1aa38e53f76003...6f9f17788090df1f26f669e9d70d6ae9567deba6)

---
updated-dependencies:
- dependency-name: sigstore/cosign-installer
  dependency-version: 4.1.2
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
---
 .github/workflows/release.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index c5f2ebf..baba90b 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -19,7 +19,7 @@ jobs:
           fetch-depth: 0
           persist-credentials: false
 
-      - uses: sigstore/cosign-installer@cad07c2e89fa2edd6e2d7bab4c1aa38e53f76003 # v4.1.1
+      - uses: sigstore/cosign-installer@6f9f17788090df1f26f669e9d70d6ae9567deba6 # v4.1.2
 
       - name: Set up Go
         uses: actions/setup-go@4a3601121dd01d1626a1e23e37211e3254c1c06c # v6.4.0

From ffd28ad8569031b0055098a0ab1099aee74a4ef6 Mon Sep 17 00:00:00 2001
From: Andrew Nesbitt <andrewnez@gmail.com>
Date: Tue, 19 May 2026 06:54:33 -0500
Subject: [PATCH 22/36] Handle __unset sentinel in Composer minified metadata
 (#121)

---
 internal/handler/composer.go      |  8 +++-
 internal/handler/composer_test.go | 74 +++++++++++++++++++++++++++++++
 2 files changed, 81 insertions(+), 1 deletion(-)

diff --git a/internal/handler/composer.go b/internal/handler/composer.go
index 0933ece..065ddf9 100644
--- a/internal/handler/composer.go
+++ b/internal/handler/composer.go
@@ -16,6 +16,7 @@ import (
 const (
 	composerUpstream   = "https://packagist.org"
 	composerRepo       = "https://repo.packagist.org"
+	composerUnset      = "__unset"
 	vendorPackageParts = 2
 )
 
@@ -150,7 +151,8 @@ func (h *ComposerHandler) rewriteMetadata(body []byte) ([]byte, error) {
 
 // expandMinifiedVersions expands the Composer v2 minified format where each
 // version entry only contains fields that differ from the previous entry.
-// The "~dev" sentinel string resets the inheritance chain.
+// The "~dev" sentinel string resets the inheritance chain, and the "__unset"
+// value removes a field from the inherited state.
 func expandMinifiedVersions(versionList []any) []any {
 	expanded := make([]any, 0, len(versionList))
 	inherited := map[string]any{}
@@ -174,6 +176,10 @@ func expandMinifiedVersions(versionList []any) []any {
 			merged[k] = deepCopyValue(val)
 		}
 		for k, val := range vmap {
+			if val == composerUnset {
+				delete(merged, k)
+				continue
+			}
 			merged[k] = val
 		}
 
diff --git a/internal/handler/composer_test.go b/internal/handler/composer_test.go
index e4d79af..baf13b6 100644
--- a/internal/handler/composer_test.go
+++ b/internal/handler/composer_test.go
@@ -177,6 +177,80 @@ func TestComposerRewriteMetadataMinifiedDevReset(t *testing.T) {
 	}
 }
 
+func TestComposerRewriteMetadataUnset(t *testing.T) {
+	h := &ComposerHandler{
+		proxy:    &Proxy{Logger: slog.Default()},
+		proxyURL: "http://localhost:8080",
+	}
+
+	// In the minified format, "__unset" removes a field from the inherited
+	// state. v1.29.0 has require-dev, v1.28.0 unsets it, v1.27.0 inherits the
+	// unset state. Composer rejects metadata where require-dev (or any link
+	// field) is the literal string "__unset" rather than an object.
+	input := `{
+		"minified": "composer/2.0",
+		"packages": {
+			"venturecraft/revisionable": [
+				{
+					"name": "venturecraft/revisionable",
+					"version": "1.29.0",
+					"require": {"php": ">=5.4"},
+					"require-dev": {"orchestra/testbench": "~3.0"},
+					"dist": {"url": "https://example.com/a.zip", "type": "zip"}
+				},
+				{
+					"version": "1.28.0",
+					"require-dev": "__unset"
+				},
+				{
+					"version": "1.27.0"
+				},
+				{
+					"version": "1.26.0",
+					"require-dev": {"foo/bar": "1.0"}
+				}
+			]
+		}
+	}`
+
+	output, err := h.rewriteMetadata([]byte(input))
+	if err != nil {
+		t.Fatalf("rewriteMetadata failed: %v", err)
+	}
+
+	var result map[string]any
+	if err := json.Unmarshal(output, &result); err != nil {
+		t.Fatalf("failed to parse output: %v", err)
+	}
+
+	versions := result["packages"].(map[string]any)["venturecraft/revisionable"].([]any)
+	if len(versions) != 4 {
+		t.Fatalf("expected 4 versions, got %d", len(versions))
+	}
+
+	byVersion := map[string]map[string]any{}
+	for _, v := range versions {
+		vmap := v.(map[string]any)
+		byVersion[vmap["version"].(string)] = vmap
+	}
+
+	if _, ok := byVersion["1.29.0"]["require-dev"].(map[string]any); !ok {
+		t.Errorf("1.29.0 require-dev should be an object, got %T", byVersion["1.29.0"]["require-dev"])
+	}
+	if rd, ok := byVersion["1.28.0"]["require-dev"]; ok {
+		t.Errorf("1.28.0 require-dev should be absent, got %v", rd)
+	}
+	if rd, ok := byVersion["1.27.0"]["require-dev"]; ok {
+		t.Errorf("1.27.0 require-dev should be absent (inherited unset), got %v", rd)
+	}
+	if _, ok := byVersion["1.26.0"]["require-dev"].(map[string]any); !ok {
+		t.Errorf("1.26.0 require-dev should be an object, got %T", byVersion["1.26.0"]["require-dev"])
+	}
+	if _, ok := byVersion["1.27.0"]["require"].(map[string]any); !ok {
+		t.Error("1.27.0 should still inherit require from 1.29.0")
+	}
+}
+
 func TestComposerRewriteMetadataCooldownPreservesNames(t *testing.T) {
 	now := time.Now()
 	old := now.Add(-10 * 24 * time.Hour).Format(time.RFC3339)

From e8363e2fec337d28a515cf12eed5101a535f340e Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Fri, 22 May 2026 03:43:58 +0100
Subject: [PATCH 23/36] Bump zizmorcore/zizmor-action from 0.5.3 to 0.5.5
 (#135)

Bumps [zizmorcore/zizmor-action](https://github.com/zizmorcore/zizmor-action) from 0.5.3 to 0.5.5.
- [Release notes](https://github.com/zizmorcore/zizmor-action/releases)
- [Commits](https://github.com/zizmorcore/zizmor-action/compare/b1d7e1fb5de872772f31590499237e7cce841e8e...a16621b09c6db4281f81a93cb393b05dcd7b7165)

---
updated-dependencies:
- dependency-name: zizmorcore/zizmor-action
  dependency-version: 0.5.5
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
---
 .github/workflows/zizmor.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/zizmor.yml b/.github/workflows/zizmor.yml
index 4acd19b..e34bdc6 100644
--- a/.github/workflows/zizmor.yml
+++ b/.github/workflows/zizmor.yml
@@ -26,4 +26,4 @@ jobs:
           persist-credentials: false
 
       - name: Run zizmor
-        uses: zizmorcore/zizmor-action@b1d7e1fb5de872772f31590499237e7cce841e8e # v0.5.3
+        uses: zizmorcore/zizmor-action@a16621b09c6db4281f81a93cb393b05dcd7b7165 # v0.5.5

From 497e16f90b3086304e9624adfcd58c5e26812122 Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Fri, 22 May 2026 03:46:52 +0100
Subject: [PATCH 24/36] Bump alpine from 3.21 to 3.23.4 (#139)

Bumps alpine from 3.21 to 3.23.4.

---
updated-dependencies:
- dependency-name: alpine
  dependency-version: 3.23.4
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
---
 Dockerfile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Dockerfile b/Dockerfile
index 71a9fcc..b66e765 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -15,7 +15,7 @@ COPY . .
 # Build the binary
 RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-s -w" -o /proxy ./cmd/proxy
 
-FROM alpine:3.21
+FROM alpine:3.23.4
 
 RUN apk add --no-cache ca-certificates
 

From 7832db2adb4ee0bf6d14015797aed71adbc46568 Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Fri, 22 May 2026 03:46:59 +0100
Subject: [PATCH 25/36] Bump golang from 1.25-alpine to 1.26.3-alpine (#138)

Bumps golang from 1.25-alpine to 1.26.3-alpine.

---
updated-dependencies:
- dependency-name: golang
  dependency-version: 1.26.3-alpine
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
---
 Dockerfile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Dockerfile b/Dockerfile
index b66e765..5124b1d 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-FROM golang:1.25-alpine AS builder
+FROM golang:1.26.3-alpine AS builder
 
 WORKDIR /src
 

From 7586beb37bff019ebaf36a50283236704f8bc3c2 Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Fri, 22 May 2026 04:02:48 +0100
Subject: [PATCH 26/36] Bump github.com/git-pkgs/vers from 0.2.5 to 0.2.6
 (#137)

Bumps [github.com/git-pkgs/vers](https://github.com/git-pkgs/vers) from 0.2.5 to 0.2.6.
- [Commits](https://github.com/git-pkgs/vers/compare/v0.2.5...v0.2.6)

---
updated-dependencies:
- dependency-name: github.com/git-pkgs/vers
  dependency-version: 0.2.6
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
---
 go.mod | 2 +-
 go.sum | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/go.mod b/go.mod
index 70ea32c..bd666b1 100644
--- a/go.mod
+++ b/go.mod
@@ -11,7 +11,7 @@ require (
 	github.com/git-pkgs/purl v0.1.12
 	github.com/git-pkgs/registries v0.6.0
 	github.com/git-pkgs/spdx v0.1.3
-	github.com/git-pkgs/vers v0.2.5
+	github.com/git-pkgs/vers v0.2.6
 	github.com/git-pkgs/vulns v0.1.5
 	github.com/go-chi/chi/v5 v5.2.5
 	github.com/jmoiron/sqlx v1.4.0
diff --git a/go.sum b/go.sum
index 5fe9699..1f3d0c3 100644
--- a/go.sum
+++ b/go.sum
@@ -266,8 +266,8 @@ github.com/git-pkgs/registries v0.6.0 h1:ttQC8via9XAoLk9vqysf0K7uWl1bAyHPBWRBavR
 github.com/git-pkgs/registries v0.6.0/go.mod h1:BY0YW+V0WDGBMuDR2aSMR3NzOPFK4K+F3j6+ch+cq3M=
 github.com/git-pkgs/spdx v0.1.3 h1:YQou23mLfzbW//6JlHUuc5x1P5VNIIDSku5gvauf86I=
 github.com/git-pkgs/spdx v0.1.3/go.mod h1:4HGGWyC8tg4DjOhrtBTYl4Lu+5i2BFuauGX8zcVcYPg=
-github.com/git-pkgs/vers v0.2.5 h1:tDtUMik9Iw1lyPHdT5V6LXjLo9LsJc0xOawURz7ibQU=
-github.com/git-pkgs/vers v0.2.5/go.mod h1:biTbSQK1qdbrsxDEKnqe3Jzclxz8vW6uDcwKjfUGcOo=
+github.com/git-pkgs/vers v0.2.6 h1:IelZd7BP/JhzTloUTDY67nehUgoYva3g9viqAMCHJg8=
+github.com/git-pkgs/vers v0.2.6/go.mod h1:biTbSQK1qdbrsxDEKnqe3Jzclxz8vW6uDcwKjfUGcOo=
 github.com/git-pkgs/vulns v0.1.5 h1:mtX88/27toFl+B95kaH5QbAdOCQ3YIDGjJrlrrnqQTE=
 github.com/git-pkgs/vulns v0.1.5/go.mod h1:bZFikfrR/5gC0ZMwXh7qcEu2gpKfXMBhVsy4kF12Ae0=
 github.com/github/go-spdx/v2 v2.6.0 h1:Y/Chr7L8oG85Ilbzl11xkUSQFUfG1kGkLP18LyInvhg=

From d39e31271096dc7782a3427220beeb6098bd2a66 Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Fri, 22 May 2026 04:03:00 +0100
Subject: [PATCH 27/36] Bump modernc.org/sqlite from 1.50.0 to 1.50.1 (#140)

Bumps [modernc.org/sqlite](https://gitlab.com/cznic/sqlite) from 1.50.0 to 1.50.1.
- [Changelog](https://gitlab.com/cznic/sqlite/blob/master/CHANGELOG.md)
- [Commits](https://gitlab.com/cznic/sqlite/compare/v1.50.0...v1.50.1)

---
updated-dependencies:
- dependency-name: modernc.org/sqlite
  dependency-version: 1.50.1
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
---
 go.mod |  4 ++--
 go.sum | 20 ++++++++++----------
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/go.mod b/go.mod
index bd666b1..0baa4e0 100644
--- a/go.mod
+++ b/go.mod
@@ -24,7 +24,7 @@ require (
 	golang.org/x/sync v0.20.0
 	google.golang.org/protobuf v1.36.11
 	gopkg.in/yaml.v3 v3.0.1
-	modernc.org/sqlite v1.50.0
+	modernc.org/sqlite v1.50.1
 )
 
 require (
@@ -310,7 +310,7 @@ require (
 	gopkg.in/ini.v1 v1.67.0 // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect
 	honnef.co/go/tools v0.7.0 // indirect
-	modernc.org/libc v1.72.0 // indirect
+	modernc.org/libc v1.72.3 // indirect
 	modernc.org/mathutil v1.7.1 // indirect
 	modernc.org/memory v1.11.0 // indirect
 	mvdan.cc/gofumpt v0.9.2 // indirect
diff --git a/go.sum b/go.sum
index 1f3d0c3..bc38028 100644
--- a/go.sum
+++ b/go.sum
@@ -884,10 +884,10 @@ gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
 gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 honnef.co/go/tools v0.7.0 h1:w6WUp1VbkqPEgLz4rkBzH/CSU6HkoqNLp6GstyTx3lU=
 honnef.co/go/tools v0.7.0/go.mod h1:pm29oPxeP3P82ISxZDgIYeOaf9ta6Pi0EWvCFoLG2vc=
-modernc.org/cc/v4 v4.27.3 h1:uNCgn37E5U09mTv1XgskEVUJ8ADKpmFMPxzGJ0TSo+U=
-modernc.org/cc/v4 v4.27.3/go.mod h1:3YjcbCqhoTTHPycJDRl2WZKKFj0nwcOIPBfEZK0Hdk8=
-modernc.org/ccgo/v4 v4.32.4 h1:L5OB8rpEX4ZsXEQwGozRfJyJSFHbbNVOoQ59DU9/KuU=
-modernc.org/ccgo/v4 v4.32.4/go.mod h1:lY7f+fiTDHfcv6YlRgSkxYfhs+UvOEEzj49jAn2TOx0=
+modernc.org/cc/v4 v4.28.2 h1:3tQ0lf2ADtoby2EtSP+J7IE2SHwEJdP8ioR59wx7XpY=
+modernc.org/cc/v4 v4.28.2/go.mod h1:OnovgIhbbMXMu1aISnJ0wvVD1KnW+cAUJkIrAWh+kVI=
+modernc.org/ccgo/v4 v4.34.0 h1:yRLPFZieg532OT4rp4JFNIVcquwalMX26G95WQDqwCQ=
+modernc.org/ccgo/v4 v4.34.0/go.mod h1:AS5WYMyBakQ+fhsHhtP8mWB82KTGPkNNJDGfGQCe0/A=
 modernc.org/fileutil v1.4.0 h1:j6ZzNTftVS054gi281TyLjHPp6CPHr2KCxEXjEbD6SM=
 modernc.org/fileutil v1.4.0/go.mod h1:EqdKFDxiByqxLk8ozOxObDSfcVOv/54xDs/DUHdvCUU=
 modernc.org/gc/v2 v2.6.5 h1:nyqdV8q46KvTpZlsw66kWqwXRHdjIlJOhG6kxiV/9xI=
@@ -896,18 +896,18 @@ modernc.org/gc/v3 v3.1.2 h1:ZtDCnhonXSZexk/AYsegNRV1lJGgaNZJuKjJSWKyEqo=
 modernc.org/gc/v3 v3.1.2/go.mod h1:HFK/6AGESC7Ex+EZJhJ2Gni6cTaYpSMmU/cT9RmlfYY=
 modernc.org/goabi0 v0.2.0 h1:HvEowk7LxcPd0eq6mVOAEMai46V+i7Jrj13t4AzuNks=
 modernc.org/goabi0 v0.2.0/go.mod h1:CEFRnnJhKvWT1c1JTI3Avm+tgOWbkOu5oPA8eH8LnMI=
-modernc.org/libc v1.72.0 h1:IEu559v9a0XWjw0DPoVKtXpO2qt5NVLAnFaBbjq+n8c=
-modernc.org/libc v1.72.0/go.mod h1:tTU8DL8A+XLVkEY3x5E/tO7s2Q/q42EtnNWda/L5QhQ=
+modernc.org/libc v1.72.3 h1:ZnDF4tXn4NBXFutMMQC4vtbTFSXhhKzR73fv0beZEAU=
+modernc.org/libc v1.72.3/go.mod h1:dn0dZNnnn1clLyvRxLxYExxiKRZIRENOfqQ8XEeg4Qs=
 modernc.org/mathutil v1.7.1 h1:GCZVGXdaN8gTqB1Mf/usp1Y/hSqgI2vAGGP4jZMCxOU=
 modernc.org/mathutil v1.7.1/go.mod h1:4p5IwJITfppl0G4sUEDtCr4DthTaT47/N3aT6MhfgJg=
 modernc.org/memory v1.11.0 h1:o4QC8aMQzmcwCK3t3Ux/ZHmwFPzE6hf2Y5LbkRs+hbI=
 modernc.org/memory v1.11.0/go.mod h1:/JP4VbVC+K5sU2wZi9bHoq2MAkCnrt2r98UGeSK7Mjw=
-modernc.org/opt v0.1.4 h1:2kNGMRiUjrp4LcaPuLY2PzUfqM/w9N23quVwhKt5Qm8=
-modernc.org/opt v0.1.4/go.mod h1:03fq9lsNfvkYSfxrfUhZCWPk1lm4cq4N+Bh//bEtgns=
+modernc.org/opt v0.2.0 h1:tGyef5ApycA7FSEOMraay9SaTk5zmbx7Tu+cJs4QKZg=
+modernc.org/opt v0.2.0/go.mod h1:03fq9lsNfvkYSfxrfUhZCWPk1lm4cq4N+Bh//bEtgns=
 modernc.org/sortutil v1.2.1 h1:+xyoGf15mM3NMlPDnFqrteY07klSFxLElE2PVuWIJ7w=
 modernc.org/sortutil v1.2.1/go.mod h1:7ZI3a3REbai7gzCLcotuw9AC4VZVpYMjDzETGsSMqJE=
-modernc.org/sqlite v1.50.0 h1:eMowQSWLK0MeiQTdmz3lqoF5dqclujdlIKeJA11+7oM=
-modernc.org/sqlite v1.50.0/go.mod h1:m0w8xhwYUVY3H6pSDwc3gkJ/irZT/0YEXwBlhaxQEew=
+modernc.org/sqlite v1.50.1 h1:l+cQvn0sd0zJJtfygGHuQJ5AjlrwXmWPw4KP3ZMwr9w=
+modernc.org/sqlite v1.50.1/go.mod h1:tcNzv5p84E0skkmJn038y+hWJbLQXQqEnQfeh5r2JLM=
 modernc.org/strutil v1.2.1 h1:UneZBkQA+DX2Rp35KcM69cSsNES9ly8mQWD71HKlOA0=
 modernc.org/strutil v1.2.1/go.mod h1:EHkiggD70koQxjVdSBM3JKM7k6L0FbGE5eymy9i3B9A=
 modernc.org/token v1.1.0 h1:Xl7Ap9dKaEs5kLoOQeQmPWevfnk/DM5qcLcYlA8ys6Y=

From 1e6a0d1ab8ad9ccd9d850eb0586e9fc90b20ba75 Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Fri, 22 May 2026 04:45:48 +0100
Subject: [PATCH 28/36] Bump github.com/CycloneDX/cyclonedx-go from 0.10.0 to
 0.11.0 (#136)

Bumps [github.com/CycloneDX/cyclonedx-go](https://github.com/CycloneDX/cyclonedx-go) from 0.10.0 to 0.11.0.
- [Release notes](https://github.com/CycloneDX/cyclonedx-go/releases)
- [Commits](https://github.com/CycloneDX/cyclonedx-go/compare/v0.10.0...v0.11.0)

---
updated-dependencies:
- dependency-name: github.com/CycloneDX/cyclonedx-go
  dependency-version: 0.11.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
---
 go.mod | 2 +-
 go.sum | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/go.mod b/go.mod
index 0baa4e0..f3e1bd1 100644
--- a/go.mod
+++ b/go.mod
@@ -4,7 +4,7 @@ go 1.25.6
 
 require (
 	github.com/BurntSushi/toml v1.6.0
-	github.com/CycloneDX/cyclonedx-go v0.10.0
+	github.com/CycloneDX/cyclonedx-go v0.11.0
 	github.com/git-pkgs/archives v0.3.0
 	github.com/git-pkgs/cooldown v0.1.1
 	github.com/git-pkgs/enrichment v0.2.2
diff --git a/go.sum b/go.sum
index bc38028..481587d 100644
--- a/go.sum
+++ b/go.sum
@@ -66,8 +66,8 @@ github.com/AzureAD/microsoft-authentication-library-for-go v1.6.0/go.mod h1:HKpQ
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
 github.com/BurntSushi/toml v1.6.0 h1:dRaEfpa2VI55EwlIW72hMRHdWouJeRF7TPYhI+AUQjk=
 github.com/BurntSushi/toml v1.6.0/go.mod h1:ukJfTF/6rtPPRCnwkur4qwRxa8vTRFBF0uk2lLoLwho=
-github.com/CycloneDX/cyclonedx-go v0.10.0 h1:7xyklU7YD+CUyGzSFIARG18NYLsKVn4QFg04qSsu+7Y=
-github.com/CycloneDX/cyclonedx-go v0.10.0/go.mod h1:vUvbCXQsEm48OI6oOlanxstwNByXjCZ2wuleUlwGEO8=
+github.com/CycloneDX/cyclonedx-go v0.11.0 h1:GokP8FiRC+foiuwWhSSLpSD5H4hSWtGnR3wo7apkBFI=
+github.com/CycloneDX/cyclonedx-go v0.11.0/go.mod h1:vUvbCXQsEm48OI6oOlanxstwNByXjCZ2wuleUlwGEO8=
 github.com/Djarvur/go-err113 v0.1.1 h1:eHfopDqXRwAi+YmCUas75ZE0+hoBHJ2GQNLYRSxao4g=
 github.com/Djarvur/go-err113 v0.1.1/go.mod h1:IaWJdYFLg76t2ihfflPZnM1LIQszWOsFDh2hhhAVF6k=
 github.com/GoogleCloudPlatform/opentelemetry-operations-go/detectors/gcp v1.30.0 h1:sBEjpZlNHzK1voKq9695PJSX2o5NEXl7/OL3coiIY0c=

From a8b6b0a41768656e96f45f36e9b69e718c0125f7 Mon Sep 17 00:00:00 2001
From: Mati Kepa <36644582+matikepa@users.noreply.github.com>
Date: Fri, 22 May 2026 13:09:00 +0200
Subject: [PATCH 29/36] add support for Gradle prometheus metrics (#124)

* add support for Gradle prometheus metrics

* refactor(gradle): simplify response handling and remove unused metrics assertions

---------

Co-authored-by: Mateusz (Mati) Kepa <m.kepa@sportradar.com>
---
 internal/handler/gradle.go      | 22 ++++++++++++-
 internal/handler/gradle_test.go | 56 +++++++++++++++++++++++++++++++++
 2 files changed, 77 insertions(+), 1 deletion(-)

diff --git a/internal/handler/gradle.go b/internal/handler/gradle.go
index aed98e7..3b703be 100644
--- a/internal/handler/gradle.go
+++ b/internal/handler/gradle.go
@@ -7,7 +7,9 @@ import (
 	"regexp"
 	"strconv"
 	"strings"
+	"time"
 
+	"github.com/git-pkgs/proxy/internal/metrics"
 	"github.com/git-pkgs/proxy/internal/storage"
 )
 
@@ -94,18 +96,28 @@ func (h *GradleBuildCacheHandler) handleGetOrHead(w http.ResponseWriter, r *http
 	w.Header().Set("Content-Type", gradleBuildCacheContentType)
 
 	if r.Method == http.MethodHead {
+		existsStart := time.Now()
 		exists, err := h.proxy.Storage.Exists(r.Context(), storagePath)
+		metrics.RecordStorageOperation("read", time.Since(existsStart))
 		if err != nil {
+			metrics.RecordStorageError("read")
 			h.proxy.Logger.Error("failed to check gradle build cache entry", "key", key, "error", err)
 			http.Error(w, "failed to read cache entry", http.StatusInternalServerError)
 			return
 		}
 		if !exists {
+			metrics.RecordCacheMiss("gradle")
 			http.NotFound(w, r)
 			return
 		}
+		metrics.RecordCacheHit("gradle")
 
-		if size, err := h.proxy.Storage.Size(r.Context(), storagePath); err == nil && size >= 0 {
+		sizeStart := time.Now()
+		size, err := h.proxy.Storage.Size(r.Context(), storagePath)
+		metrics.RecordStorageOperation("read", time.Since(sizeStart))
+		if err != nil {
+			metrics.RecordStorageError("read")
+		} else if size >= 0 {
 			w.Header().Set("Content-Length", strconv.FormatInt(size, 10))
 		}
 
@@ -113,17 +125,22 @@ func (h *GradleBuildCacheHandler) handleGetOrHead(w http.ResponseWriter, r *http
 		return
 	}
 
+	readStart := time.Now()
 	reader, err := h.proxy.Storage.Open(r.Context(), storagePath)
+	metrics.RecordStorageOperation("read", time.Since(readStart))
 	if err != nil {
 		if errors.Is(err, storage.ErrNotFound) {
+			metrics.RecordCacheMiss("gradle")
 			http.NotFound(w, r)
 			return
 		}
+		metrics.RecordStorageError("read")
 		h.proxy.Logger.Error("failed to open gradle build cache entry", "key", key, "error", err)
 		http.Error(w, "failed to read cache entry", http.StatusInternalServerError)
 		return
 	}
 	defer func() { _ = reader.Close() }()
+	metrics.RecordCacheHit("gradle")
 
 	w.WriteHeader(http.StatusOK)
 	_, _ = io.Copy(w, reader)
@@ -138,7 +155,9 @@ func (h *GradleBuildCacheHandler) handlePut(w http.ResponseWriter, r *http.Reque
 
 	r.Body = http.MaxBytesReader(w, r.Body, maxUploadSize)
 
+	storeStart := time.Now()
 	_, hash, err := h.proxy.Storage.Store(r.Context(), storagePath, r.Body)
+	metrics.RecordStorageOperation("write", time.Since(storeStart))
 	if err != nil {
 		var maxBytesErr *http.MaxBytesError
 		if errors.As(err, &maxBytesErr) {
@@ -146,6 +165,7 @@ func (h *GradleBuildCacheHandler) handlePut(w http.ResponseWriter, r *http.Reque
 			return
 		}
 
+		metrics.RecordStorageError("write")
 		h.proxy.Logger.Error("failed to store gradle build cache entry", "key", key, "error", err)
 		http.Error(w, "failed to write cache entry", http.StatusInternalServerError)
 		return
diff --git a/internal/handler/gradle_test.go b/internal/handler/gradle_test.go
index f002a51..a05d07e 100644
--- a/internal/handler/gradle_test.go
+++ b/internal/handler/gradle_test.go
@@ -6,6 +6,9 @@ import (
 	"net/http/httptest"
 	"strings"
 	"testing"
+
+	"github.com/git-pkgs/proxy/internal/metrics"
+	"github.com/prometheus/client_golang/prometheus/testutil"
 )
 
 func TestGradleBuildCacheHandler_PutGetHead(t *testing.T) {
@@ -227,3 +230,56 @@ func TestGradleBuildCacheHandler_PutTooLarge(t *testing.T) {
 		t.Fatalf("PUT status = %d, want %d", resp.StatusCode, http.StatusRequestEntityTooLarge)
 	}
 }
+
+func TestGradleBuildCacheHandler_RecordsMetrics(t *testing.T) {
+	proxy, _, _, _ := setupTestProxy(t)
+	h := NewGradleBuildCacheHandler(proxy)
+	srv := httptest.NewServer(h.Routes())
+	defer srv.Close()
+
+	hitsBefore := testutil.ToFloat64(metrics.CacheHits.WithLabelValues("gradle"))
+	missesBefore := testutil.ToFloat64(metrics.CacheMisses.WithLabelValues("gradle"))
+
+	key := "metrics-key"
+	putReq, err := http.NewRequest(http.MethodPut, srv.URL+"/"+key, strings.NewReader("payload"))
+	if err != nil {
+		t.Fatalf("failed to create PUT request: %v", err)
+	}
+	putResp, err := http.DefaultClient.Do(putReq)
+	if err != nil {
+		t.Fatalf("PUT request failed: %v", err)
+	}
+	_ = putResp.Body.Close()
+
+	getResp, err := http.Get(srv.URL + "/" + key)
+	if err != nil {
+		t.Fatalf("GET request failed: %v", err)
+	}
+	_ = getResp.Body.Close()
+
+	headReq, err := http.NewRequest(http.MethodHead, srv.URL+"/"+key, nil)
+	if err != nil {
+		t.Fatalf("failed to create HEAD request: %v", err)
+	}
+	headResp, err := http.DefaultClient.Do(headReq)
+	if err != nil {
+		t.Fatalf("HEAD request failed: %v", err)
+	}
+	_ = headResp.Body.Close()
+
+	missResp, err := http.Get(srv.URL + "/missing-key")
+	if err != nil {
+		t.Fatalf("GET miss request failed: %v", err)
+	}
+	_ = missResp.Body.Close()
+
+	hitsAfter := testutil.ToFloat64(metrics.CacheHits.WithLabelValues("gradle"))
+	missesAfter := testutil.ToFloat64(metrics.CacheMisses.WithLabelValues("gradle"))
+
+	if diff := hitsAfter - hitsBefore; diff != 2 {
+		t.Fatalf("cache hits delta = %.0f, want 2", diff)
+	}
+	if diff := missesAfter - missesBefore; diff != 1 {
+		t.Fatalf("cache misses delta = %.0f, want 1", diff)
+	}
+}

From 76f41cf271e7cd40d507950f95388f71b715765b Mon Sep 17 00:00:00 2001
From: Lars Wallenborn <lars@wallenborn.net>
Date: Fri, 22 May 2026 14:14:01 +0300
Subject: [PATCH 30/36] Add storage backend probe to /health (closes #73)
 (#119)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

* config: add Health.StorageProbeInterval

* metrics: add proxy_health_probe_failures_total counter

* server: add storageProbe with happy-path test

* server: add storageProbe failure-mode tests

* server: add healthCache with TTL, single-flight, transition logging

* server: wire storage probe into /health

* server: update TestHealthEndpoint for JSON; wire healthCache into newTestServer

Also fix Windows file-locking issue in storageProbe: close the reader
explicitly before Delete so the file handle is released prior to os.Remove.

* server: clean up stale comment in storageProbe

* docs: document storage health probe and new metric

* docs: regenerate Swagger for /health JSON response

* server: simplify rc.Close error handling in storageProbe

* server: defer probe cleanup so size/open/read/verify failures don't leak objects

Previously, storageProbe only called Delete on the success path. Any
failure between Store and the final Delete (size mismatch, Open error,
mid-stream read failure, content mismatch) left the probe object orphaned
in the storage backend. With caching disabled and Kubernetes-rate probing,
the leak could accumulate noticeably on backends like S3.

Use a named return + defer to attempt Delete after every successful Store.
The earlier-step failure remains the primary error; Delete failure only
surfaces as step="delete" when nothing else went wrong. Add a table-driven
test that asserts cleanup runs for each non-delete failure path.

Reported by Copilot on #119.

* config: validate health.storage_probe_interval in Config.Validate

The new duration field was only validated at use time in newHealthCache.
The existing codebase already validates other duration fields
(MetadataTTL, DirectServeTTL, Gradle.MaxAge, Gradle.SweepInterval) in
Config.Validate() so misconfiguration fails fast at startup with a
config-key-specific error.

Match that pattern. The parse-at-use code in newHealthCache stays as
a safety net, mirroring the MetadataTTL precedent.

Reported by Copilot on #119.

* docs: lowercase "counter" in metrics table for consistency

Other rows in the table use lowercase type names (counter/gauge/histogram).
Match that style.

Reported by Copilot on #119.

* docs: include size-check step in /health probe description

The probe is write → size-check → read → verify → delete; the
architecture note was missing the size-check step.

Reported by Copilot on #119.

* server: address andrew's review on #119

- Drop unused callerCtx parameter from healthCache.Check (Check is now
  parameter-less; the comment-only "accepted for symmetry" justification
  wasn't carrying its weight).
- Emit "storage": {"status": "skipped"} on DB short-circuit instead of
  omitting the key, so monitors expecting a fixed key set keep working.
- Reject negative storage_probe_interval at config validation time
  (previously parsed and silently behaved like "0").
- Extract HealthConfig.Validate to keep Config.Validate under the
  gocognit threshold and match the existing GradleBuildCacheConfig pattern.
- README Health Check section: note that /health is intended as a
  readiness probe rather than a liveness probe (Check holds a mutex
  for up to the 10s probe timeout).
- cmd/proxy/main.go godoc: column-align the new env var with the
  surrounding Gradle entries.

Reported by andrew on #119.
---
 README.md                      |  21 +-
 cmd/proxy/main.go              |   2 +
 config.example.yaml            |   9 +
 docs/architecture.md           |   2 +-
 docs/swagger/docs.go           |  34 ++-
 docs/swagger/swagger.json      |  34 ++-
 internal/config/config.go      |  35 +++
 internal/config/config_test.go |  28 +++
 internal/metrics/metrics.go    |  15 ++
 internal/server/health.go      | 182 ++++++++++++++
 internal/server/health_test.go | 448 +++++++++++++++++++++++++++++++++
 internal/server/server.go      |  62 ++++-
 internal/server/server_test.go |  69 ++++-
 13 files changed, 911 insertions(+), 30 deletions(-)
 create mode 100644 internal/server/health.go
 create mode 100644 internal/server/health_test.go

diff --git a/README.md b/README.md
index 792c76b..325c679 100644
--- a/README.md
+++ b/README.md
@@ -593,7 +593,7 @@ Recently cached:
 | Endpoint | Description |
 |----------|-------------|
 | `GET /` | Dashboard (web UI) |
-| `GET /health` | Health check (returns "ok" if healthy) |
+| `GET /health` | Health check (JSON; HTTP 200 healthy, 503 unhealthy) |
 | `GET /stats` | Cache statistics (JSON) |
 | `GET /metrics` | Prometheus metrics |
 | `GET /npm/*` | npm registry protocol |
@@ -832,9 +832,28 @@ The proxy exposes Prometheus metrics at `GET /metrics`. All metric names are pre
 | `proxy_storage_operation_duration_seconds` | histogram | `operation` | Storage read/write latency |
 | `proxy_storage_errors_total` | counter | `operation` | Storage read/write failures |
 | `proxy_active_requests` | gauge | | In-flight requests |
+| `proxy_health_probe_failures_total` | counter | `step` | Storage health probe failures by failing step (`write`, `size`, `read`, `verify`, `delete`). |
 
 Cache size and artifact count are refreshed every 60 seconds. The remaining metrics update on each request.
 
+### Health Check
+
+`/health` returns a structured JSON report of subsystem health. HTTP 200 if all checks pass; 503 if any fail.
+
+```json
+{
+  "status": "ok",
+  "checks": {
+    "database": {"status": "ok"},
+    "storage":  {"status": "ok"}
+  }
+}
+```
+
+Failing checks include an `"error"` field. Storage failures also include a `"step"` field identifying which probe step failed (`write`, `size`, `read`, `verify`, `delete`). When the database check fails, the storage entry reports `{"status": "skipped"}` so the response always carries the same key set.
+
+Storage probe results are cached for `health.storage_probe_interval` (default 30s) to bound the cost of probing remote backends. A probe holds an internal mutex for up to 10 seconds (the hardcoded per-probe timeout), so `/health` is intended as a Kubernetes **readiness** probe rather than a liveness probe — a slow S3 round-trip should pull the pod from rotation, not restart it.
+
 Scrape config for Prometheus:
 
 ```yaml
diff --git a/cmd/proxy/main.go b/cmd/proxy/main.go
index 946d12a..8b28535 100644
--- a/cmd/proxy/main.go
+++ b/cmd/proxy/main.go
@@ -77,6 +77,7 @@
 //	PROXY_GRADLE_BUILD_CACHE_MAX_AGE         - Gradle cache max age eviction
 //	PROXY_GRADLE_BUILD_CACHE_MAX_SIZE        - Gradle cache max total size
 //	PROXY_GRADLE_BUILD_CACHE_SWEEP_INTERVAL  - Gradle cache eviction sweep interval
+//	PROXY_HEALTH_STORAGE_PROBE_INTERVAL      - Storage health probe cache interval (default "30s")
 //
 // Example:
 //
@@ -203,6 +204,7 @@ func runServe() {
 		fmt.Fprintf(os.Stderr, "  PROXY_GRADLE_BUILD_CACHE_MAX_AGE         Gradle cache max age eviction\n")
 		fmt.Fprintf(os.Stderr, "  PROXY_GRADLE_BUILD_CACHE_MAX_SIZE        Gradle cache max total size\n")
 		fmt.Fprintf(os.Stderr, "  PROXY_GRADLE_BUILD_CACHE_SWEEP_INTERVAL  Gradle cache eviction sweep interval\n")
+		fmt.Fprintf(os.Stderr, "  PROXY_HEALTH_STORAGE_PROBE_INTERVAL      Storage health probe cache interval\n")
 	}
 
 	_ = fs.Parse(os.Args[1:])
diff --git a/config.example.yaml b/config.example.yaml
index 4505849..853f47a 100644
--- a/config.example.yaml
+++ b/config.example.yaml
@@ -128,6 +128,15 @@ gradle:
     # How often eviction runs when max_age or max_size is set
     sweep_interval: "10m"
 
+# Health endpoint configuration.
+health:
+  # Minimum time between storage backend probes.
+  # The /health endpoint runs a write/read/verify/delete round-trip
+  # against the configured storage backend and caches the result for
+  # this interval. Set to "0" to probe on every request.
+  # Default: "30s".
+  storage_probe_interval: "30s"
+
 # Version cooldown configuration
 # Hides package versions published too recently, giving the community time
 # to spot malicious releases before they're pulled into projects.
diff --git a/docs/architecture.md b/docs/architecture.md
index 704561d..85e5aaf 100644
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -277,7 +277,7 @@ HTTP server setup, web UI, and API handlers.
 - Web UI: dashboard, package browser, source browser, version comparison
 - Templates are embedded in the binary via `//go:embed`
 - Enrichment API for package metadata, vulnerability scanning, and outdated detection
-- Health, stats, and Prometheus metrics endpoints
+- Health, stats, and Prometheus metrics endpoints. `/health` runs an active write → size-check → read → verify → delete probe against the storage backend and returns a structured JSON response (`HealthResponse`) with `"ok"` / `"error"` status per subsystem. Probe results are cached (default 30 s, configurable via `health.storage_probe_interval`) to avoid overwhelming remote backends.
 
 ### `internal/metrics`
 
diff --git a/docs/swagger/docs.go b/docs/swagger/docs.go
index 34aedbf..23ff54a 100644
--- a/docs/swagger/docs.go
+++ b/docs/swagger/docs.go
@@ -399,7 +399,7 @@ const docTemplate = `{
         "/health": {
             "get": {
                 "produces": [
-                    "text/plain"
+                    "application/json"
                 ],
                 "tags": [
                     "meta"
@@ -409,13 +409,13 @@ const docTemplate = `{
                     "200": {
                         "description": "OK",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.HealthResponse"
                         }
                     },
                     "503": {
                         "description": "Service Unavailable",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.HealthResponse"
                         }
                     }
                 }
@@ -515,6 +515,34 @@ const docTemplate = `{
                 }
             }
         },
+        "server.HealthCheck": {
+            "type": "object",
+            "properties": {
+                "error": {
+                    "type": "string"
+                },
+                "status": {
+                    "type": "string"
+                },
+                "step": {
+                    "type": "string"
+                }
+            }
+        },
+        "server.HealthResponse": {
+            "type": "object",
+            "properties": {
+                "checks": {
+                    "type": "object",
+                    "additionalProperties": {
+                        "$ref": "#/definitions/server.HealthCheck"
+                    }
+                },
+                "status": {
+                    "type": "string"
+                }
+            }
+        },
         "server.OutdatedPackage": {
             "type": "object",
             "properties": {
diff --git a/docs/swagger/swagger.json b/docs/swagger/swagger.json
index b775e63..c2b4dfc 100644
--- a/docs/swagger/swagger.json
+++ b/docs/swagger/swagger.json
@@ -392,7 +392,7 @@
         "/health": {
             "get": {
                 "produces": [
-                    "text/plain"
+                    "application/json"
                 ],
                 "tags": [
                     "meta"
@@ -402,13 +402,13 @@
                     "200": {
                         "description": "OK",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.HealthResponse"
                         }
                     },
                     "503": {
                         "description": "Service Unavailable",
                         "schema": {
-                            "type": "string"
+                            "$ref": "#/definitions/server.HealthResponse"
                         }
                     }
                 }
@@ -508,6 +508,34 @@
                 }
             }
         },
+        "server.HealthCheck": {
+            "type": "object",
+            "properties": {
+                "error": {
+                    "type": "string"
+                },
+                "status": {
+                    "type": "string"
+                },
+                "step": {
+                    "type": "string"
+                }
+            }
+        },
+        "server.HealthResponse": {
+            "type": "object",
+            "properties": {
+                "checks": {
+                    "type": "object",
+                    "additionalProperties": {
+                        "$ref": "#/definitions/server.HealthCheck"
+                    }
+                },
+                "status": {
+                    "type": "string"
+                }
+            }
+        },
         "server.OutdatedPackage": {
             "type": "object",
             "properties": {
diff --git a/internal/config/config.go b/internal/config/config.go
index 067981d..8727884 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -102,6 +102,9 @@ type Config struct {
 
 	// Gradle configures Gradle HttpBuildCache behavior.
 	Gradle GradleConfig `json:"gradle" yaml:"gradle"`
+
+	// Health configures the /health endpoint behavior.
+	Health HealthConfig `json:"health" yaml:"health"`
 }
 
 // CooldownConfig configures version cooldown periods.
@@ -182,6 +185,14 @@ type GradleBuildCacheConfig struct {
 	SweepInterval string `json:"sweep_interval" yaml:"sweep_interval"`
 }
 
+// HealthConfig configures the /health endpoint.
+type HealthConfig struct {
+	// StorageProbeInterval is the minimum time between storage backend probes.
+	// Uses Go duration syntax (e.g. "30s", "1m"). Default: "30s".
+	// Set to "0" to probe on every /health request (useful for low-traffic deployments).
+	StorageProbeInterval string `json:"storage_probe_interval" yaml:"storage_probe_interval"`
+}
+
 // DatabaseConfig configures the cache database.
 type DatabaseConfig struct {
 	// Driver is the database driver: "sqlite" or "postgres".
@@ -343,6 +354,7 @@ func Load(path string) (*Config, error) {
 //   - PROXY_DATABASE_PATH
 //   - PROXY_LOG_LEVEL
 //   - PROXY_LOG_FORMAT
+//   - PROXY_HEALTH_STORAGE_PROBE_INTERVAL
 func (c *Config) LoadFromEnv() {
 	if v := os.Getenv("PROXY_LISTEN"); v != "" {
 		c.Listen = v
@@ -410,6 +422,9 @@ func (c *Config) LoadFromEnv() {
 	if v := os.Getenv("PROXY_GRADLE_BUILD_CACHE_SWEEP_INTERVAL"); v != "" {
 		c.Gradle.BuildCache.SweepInterval = v
 	}
+	if v := os.Getenv("PROXY_HEALTH_STORAGE_PROBE_INTERVAL"); v != "" {
+		c.Health.StorageProbeInterval = v
+	}
 }
 
 // Validate checks the configuration for errors.
@@ -481,6 +496,10 @@ func (c *Config) Validate() error {
 		}
 	}
 
+	if err := c.Health.Validate(); err != nil {
+		return err
+	}
+
 	if err := c.Gradle.BuildCache.Validate(); err != nil {
 		return err
 	}
@@ -488,6 +507,22 @@ func (c *Config) Validate() error {
 	return nil
 }
 
+// Validate checks the /health configuration. An unset interval is allowed
+// (the cache uses its default); explicit values must parse and be non-negative.
+func (h *HealthConfig) Validate() error {
+	if h.StorageProbeInterval == "" || h.StorageProbeInterval == "0" {
+		return nil
+	}
+	d, err := time.ParseDuration(h.StorageProbeInterval)
+	if err != nil {
+		return fmt.Errorf("invalid health.storage_probe_interval %q: %w", h.StorageProbeInterval, err)
+	}
+	if d < 0 {
+		return fmt.Errorf("invalid health.storage_probe_interval %q: must be non-negative", h.StorageProbeInterval)
+	}
+	return nil
+}
+
 // Validate checks Gradle build cache settings, applying the default upload
 // size if unset.
 func (g *GradleBuildCacheConfig) Validate() error {
diff --git a/internal/config/config_test.go b/internal/config/config_test.go
index 26a0fc6..22694c0 100644
--- a/internal/config/config_test.go
+++ b/internal/config/config_test.go
@@ -432,6 +432,34 @@ func TestValidateMetadataTTL(t *testing.T) {
 	}
 }
 
+func TestValidateHealthStorageProbeInterval(t *testing.T) {
+	cfg := Default()
+	cfg.Health.StorageProbeInterval = "not-a-duration"
+	if err := cfg.Validate(); err == nil {
+		t.Error("expected validation error for invalid health.storage_probe_interval")
+	}
+
+	cfg.Health.StorageProbeInterval = "30s"
+	if err := cfg.Validate(); err != nil {
+		t.Errorf("unexpected error for valid health.storage_probe_interval: %v", err)
+	}
+
+	cfg.Health.StorageProbeInterval = "0"
+	if err := cfg.Validate(); err != nil {
+		t.Errorf("unexpected error for zero health.storage_probe_interval: %v", err)
+	}
+
+	cfg.Health.StorageProbeInterval = ""
+	if err := cfg.Validate(); err != nil {
+		t.Errorf("unexpected error for empty health.storage_probe_interval: %v", err)
+	}
+
+	cfg.Health.StorageProbeInterval = "-5s"
+	if err := cfg.Validate(); err == nil {
+		t.Error("expected validation error for negative health.storage_probe_interval")
+	}
+}
+
 func TestLoadMetadataTTLFromEnv(t *testing.T) {
 	cfg := Default()
 	t.Setenv("PROXY_METADATA_TTL", "10m")
diff --git a/internal/metrics/metrics.go b/internal/metrics/metrics.go
index 18ebe88..f23a5a9 100644
--- a/internal/metrics/metrics.go
+++ b/internal/metrics/metrics.go
@@ -128,6 +128,14 @@ var (
 		},
 		[]string{"ecosystem"},
 	)
+
+	HealthProbeFailures = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "proxy_health_probe_failures_total",
+			Help: "Total number of storage health probe failures, by step (write|size|read|verify|delete).",
+		},
+		[]string{"step"},
+	)
 )
 
 func init() {
@@ -147,6 +155,7 @@ func init() {
 		StorageErrors,
 		ActiveRequests,
 		IntegrityFailures,
+		HealthProbeFailures,
 	)
 }
 
@@ -192,6 +201,12 @@ func RecordIntegrityFailure(ecosystem string) {
 	IntegrityFailures.WithLabelValues(ecosystem).Inc()
 }
 
+// RecordHealthProbeFailure increments the health probe failure counter.
+// step is one of: "write", "size", "read", "verify", "delete".
+func RecordHealthProbeFailure(step string) {
+	HealthProbeFailures.WithLabelValues(step).Inc()
+}
+
 // RecordStorageError increments storage error counter.
 func RecordStorageError(operation string) {
 	StorageErrors.WithLabelValues(operation).Inc()
diff --git a/internal/server/health.go b/internal/server/health.go
new file mode 100644
index 0000000..f4e4847
--- /dev/null
+++ b/internal/server/health.go
@@ -0,0 +1,182 @@
+// Package server implements the proxy HTTP server.
+package server
+
+import (
+	"bytes"
+	"context"
+	"crypto/rand"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"io"
+	"log/slog"
+	"strconv"
+	"sync"
+	"time"
+
+	"github.com/git-pkgs/proxy/internal/metrics"
+	"github.com/git-pkgs/proxy/internal/storage"
+)
+
+const (
+	probePathPrefix     = ".healthcheck/"
+	probeMarker         = "proxy-healthcheck:"
+	probeSuffixBytes    = 8
+	defaultProbeTTL     = 30 * time.Second
+	defaultProbeTimeout = 10 * time.Second
+)
+
+// HealthResponse is the JSON payload returned by /health.
+type HealthResponse struct {
+	Status string                 `json:"status"`
+	Checks map[string]HealthCheck `json:"checks"`
+}
+
+// HealthCheck reports the status of a single subsystem check.
+type HealthCheck struct {
+	Status string `json:"status"`
+	Error  string `json:"error,omitempty"`
+	Step   string `json:"step,omitempty"`
+}
+
+// probeError tags a storage probe failure with the step that failed.
+type probeError struct {
+	step string
+	err  error
+}
+
+func (e *probeError) Error() string { return e.step + ": " + e.err.Error() }
+func (e *probeError) Unwrap() error { return e.err }
+
+// storageProbe runs a write → size-check → read → verify → delete round-trip
+// against the storage backend. Returns nil on success or a *probeError on failure.
+func storageProbe(ctx context.Context, s storage.Storage) (err error) {
+	suffix, suffixErr := randomSuffix()
+	if suffixErr != nil {
+		return &probeError{step: "write", err: fmt.Errorf("generating random suffix: %w", suffixErr)}
+	}
+	path := probePathPrefix + strconv.FormatInt(time.Now().UnixNano(), 10) + "-" + suffix
+	payload := []byte(probeMarker + suffix)
+
+	// 1. Store
+	size, _, storeErr := s.Store(ctx, path, bytes.NewReader(payload))
+	if storeErr != nil {
+		return &probeError{step: "write", err: storeErr}
+	}
+	// After Store succeeds, always attempt to delete on the way out so probe
+	// objects don't accumulate when a later step (size/open/read/verify) fails.
+	// Delete is reported as the primary error only if no earlier failure
+	// already set one.
+	defer func() {
+		if delErr := s.Delete(ctx, path); delErr != nil && err == nil {
+			err = &probeError{step: "delete", err: delErr}
+		}
+	}()
+	// 2. Size check
+	if size != int64(len(payload)) {
+		return &probeError{step: "size", err: fmt.Errorf("wrote %d bytes, expected %d", size, len(payload))}
+	}
+	// 3. Open
+	rc, openErr := s.Open(ctx, path)
+	if openErr != nil {
+		return &probeError{step: "read", err: openErr}
+	}
+	// 4. Read all (classify mid-stream errors as read, not verify).
+	// Close explicitly (not deferred) so the file handle is released before
+	// Delete — on Windows, an open handle prevents deletion.
+	data, readErr := io.ReadAll(rc)
+	_ = rc.Close()
+	if readErr != nil {
+		return &probeError{step: "read", err: readErr}
+	}
+	// 5. Verify
+	if !bytes.Equal(data, payload) {
+		return &probeError{step: "verify", err: fmt.Errorf("content mismatch")}
+	}
+	// 6. Delete is handled via the deferred cleanup above.
+	return nil
+}
+
+// randomSuffix returns 8 cryptographically random bytes hex-encoded.
+func randomSuffix() (string, error) {
+	b := make([]byte, probeSuffixBytes)
+	if _, err := rand.Read(b); err != nil {
+		return "", err
+	}
+	return hex.EncodeToString(b), nil
+}
+
+// healthCache memoizes the result of storageProbe for a configurable TTL.
+// It is safe for concurrent use.
+type healthCache struct {
+	storage      storage.Storage
+	interval     time.Duration
+	probeTimeout time.Duration
+	logger       *slog.Logger
+
+	mu      sync.Mutex
+	lastAt  time.Time
+	lastErr error
+}
+
+// newHealthCache builds a cache, parsing the interval from a duration string.
+// Empty interval string defaults to 30s. "0" or "0s" disables caching.
+func newHealthCache(s storage.Storage, intervalStr string, logger *slog.Logger) (*healthCache, error) {
+	interval := defaultProbeTTL
+	if intervalStr != "" {
+		d, err := time.ParseDuration(intervalStr)
+		if err != nil {
+			return nil, fmt.Errorf("parsing storage_probe_interval %q: %w", intervalStr, err)
+		}
+		interval = d
+	}
+	return &healthCache{
+		storage:      s,
+		interval:     interval,
+		probeTimeout: defaultProbeTimeout,
+		logger:       logger,
+	}, nil
+}
+
+// Check returns the cached probe result if still fresh, otherwise runs a fresh probe.
+// The probe runs under a context derived from context.Background() with a fixed
+// timeout so that caller cancellation (e.g. client disconnect) cannot poison the
+// cache with context.Canceled.
+func (c *healthCache) Check() error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	// Cache hit
+	if c.interval > 0 && !c.lastAt.IsZero() && time.Since(c.lastAt) < c.interval {
+		return c.lastErr
+	}
+
+	// Fresh probe under a detached context
+	probeCtx, cancel := context.WithTimeout(context.Background(), c.probeTimeout)
+	defer cancel()
+	err := storageProbe(probeCtx, c.storage)
+
+	// Transition logging and metric increment happen only on the fresh-probe path.
+	c.logTransition(c.lastErr, err)
+	if err != nil {
+		var pe *probeError
+		if errors.As(err, &pe) {
+			metrics.RecordHealthProbeFailure(pe.step)
+		} else {
+			metrics.RecordHealthProbeFailure("unknown")
+		}
+	}
+
+	c.lastErr = err
+	c.lastAt = time.Now()
+	return err
+}
+
+func (c *healthCache) logTransition(prev, curr error) {
+	switch {
+	case prev != nil && curr == nil:
+		c.logger.Info("storage probe recovered")
+	case prev == nil && curr != nil:
+		c.logger.Error("storage probe failed", "error", curr.Error())
+	}
+}
diff --git a/internal/server/health_test.go b/internal/server/health_test.go
new file mode 100644
index 0000000..c0f70c9
--- /dev/null
+++ b/internal/server/health_test.go
@@ -0,0 +1,448 @@
+package server
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"io"
+	"log/slog"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/git-pkgs/proxy/internal/metrics"
+	"github.com/git-pkgs/proxy/internal/storage"
+	"github.com/prometheus/client_golang/prometheus/testutil"
+)
+
+// fakeStorage is a minimal storage.Storage for probe tests with per-step failure injection.
+type fakeStorage struct {
+	mu sync.Mutex
+
+	storeCalls  atomic.Int64
+	openCalls   atomic.Int64
+	closeCalls  atomic.Int64
+	deleteCalls atomic.Int64
+
+	paths    []string
+	payloads [][]byte
+
+	// Failure injection.
+	storeErr  error
+	openErr   error
+	readErr   error  // returned by the io.ReadCloser.Read after partial bytes
+	deleteErr error
+
+	// Misbehavior knobs.
+	sizeDelta    int64  // added to the reported size from Store
+	readOverride []byte // if non-nil, Open returns a reader yielding these bytes instead of stored content
+
+	// storeBlock, if non-nil, causes Store to block until the channel is closed or ctx is done.
+	storeBlock chan struct{}
+
+	stored map[string][]byte
+}
+
+func newFakeStorage() *fakeStorage { return &fakeStorage{stored: map[string][]byte{}} }
+
+func (f *fakeStorage) Store(ctx context.Context, path string, r io.Reader) (int64, string, error) {
+	f.storeCalls.Add(1)
+	if f.storeErr != nil {
+		return 0, "", f.storeErr
+	}
+	if f.storeBlock != nil {
+		select {
+		case <-f.storeBlock:
+		case <-ctx.Done():
+			return 0, "", ctx.Err()
+		}
+	}
+	data, err := io.ReadAll(r)
+	if err != nil {
+		return 0, "", err
+	}
+	f.mu.Lock()
+	f.stored[path] = data
+	f.paths = append(f.paths, path)
+	f.payloads = append(f.payloads, data)
+	f.mu.Unlock()
+	return int64(len(data)) + f.sizeDelta, "fakehash", nil
+}
+
+type fakeReadCloser struct {
+	data    []byte
+	pos     int
+	readErr error
+	closed  *atomic.Int64
+}
+
+func (rc *fakeReadCloser) Read(p []byte) (int, error) {
+	if rc.pos >= len(rc.data) {
+		if rc.readErr != nil {
+			return 0, rc.readErr
+		}
+		return 0, io.EOF
+	}
+	n := copy(p, rc.data[rc.pos:])
+	rc.pos += n
+	if rc.pos >= len(rc.data) && rc.readErr != nil {
+		return n, rc.readErr
+	}
+	return n, nil
+}
+
+func (rc *fakeReadCloser) Close() error { rc.closed.Add(1); return nil }
+
+func (f *fakeStorage) Open(ctx context.Context, path string) (io.ReadCloser, error) {
+	f.openCalls.Add(1)
+	if f.openErr != nil {
+		return nil, f.openErr
+	}
+	f.mu.Lock()
+	data := f.stored[path]
+	f.mu.Unlock()
+	if f.readOverride != nil {
+		data = f.readOverride
+	}
+	return &fakeReadCloser{data: data, readErr: f.readErr, closed: &f.closeCalls}, nil
+}
+
+func (f *fakeStorage) Exists(ctx context.Context, path string) (bool, error) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	_, ok := f.stored[path]
+	return ok, nil
+}
+
+func (f *fakeStorage) Delete(ctx context.Context, path string) error {
+	f.deleteCalls.Add(1)
+	if f.deleteErr != nil {
+		return f.deleteErr
+	}
+	f.mu.Lock()
+	delete(f.stored, path)
+	f.mu.Unlock()
+	return nil
+}
+
+func (f *fakeStorage) Size(ctx context.Context, path string) (int64, error) { return 0, nil }
+func (f *fakeStorage) SignedURL(ctx context.Context, path string, expiry time.Duration) (string, error) {
+	return "", storage.ErrSignedURLUnsupported
+}
+func (f *fakeStorage) UsedSpace(ctx context.Context) (int64, error) { return 0, nil }
+func (f *fakeStorage) URL() string                                   { return "fake://" }
+func (f *fakeStorage) Close() error                                  { return nil }
+
+// --- Tests follow. First test: happy path ---
+
+func TestStorageProbe_HappyPath(t *testing.T) {
+	fs := newFakeStorage()
+	if err := storageProbe(context.Background(), fs); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if got := fs.storeCalls.Load(); got != 1 {
+		t.Errorf("Store calls = %d, want 1", got)
+	}
+	if got := fs.openCalls.Load(); got != 1 {
+		t.Errorf("Open calls = %d, want 1", got)
+	}
+	if got := fs.closeCalls.Load(); got != 1 {
+		t.Errorf("Close calls = %d, want 1", got)
+	}
+	if got := fs.deleteCalls.Load(); got != 1 {
+		t.Errorf("Delete calls = %d, want 1", got)
+	}
+	if len(fs.paths) != 1 || !strings.HasPrefix(fs.paths[0], ".healthcheck/") {
+		t.Errorf("unexpected probe path: %v", fs.paths)
+	}
+}
+
+func TestStorageProbe_WriteFails(t *testing.T) {
+	fs := newFakeStorage()
+	fs.storeErr = errors.New("disk full")
+	err := storageProbe(context.Background(), fs)
+	var pe *probeError
+	if !errors.As(err, &pe) {
+		t.Fatalf("expected *probeError, got %T: %v", err, err)
+	}
+	if pe.step != "write" {
+		t.Errorf("step = %q, want write", pe.step)
+	}
+	if fs.openCalls.Load() != 0 {
+		t.Errorf("Open should not be called after write failure")
+	}
+}
+
+func TestStorageProbe_SizeMismatch(t *testing.T) {
+	fs := newFakeStorage()
+	fs.sizeDelta = -1 // Report 1 byte fewer than actually written
+	err := storageProbe(context.Background(), fs)
+	var pe *probeError
+	if !errors.As(err, &pe) || pe.step != "size" {
+		t.Fatalf("step = %v, want size; err = %v", pe, err)
+	}
+	if fs.openCalls.Load() != 0 {
+		t.Errorf("Open should not be called after size mismatch")
+	}
+}
+
+func TestStorageProbe_OpenFails(t *testing.T) {
+	fs := newFakeStorage()
+	fs.openErr = errors.New("access denied")
+	err := storageProbe(context.Background(), fs)
+	var pe *probeError
+	if !errors.As(err, &pe) || pe.step != "read" {
+		t.Fatalf("step = %v, want read; err = %v", pe, err)
+	}
+}
+
+func TestStorageProbe_ReadMidStreamFails(t *testing.T) {
+	fs := newFakeStorage()
+	fs.readErr = errors.New("connection reset")
+	err := storageProbe(context.Background(), fs)
+	var pe *probeError
+	if !errors.As(err, &pe) || pe.step != "read" {
+		t.Fatalf("step = %v, want read (NOT verify); err = %v", pe, err)
+	}
+}
+
+func TestStorageProbe_ContentMismatch(t *testing.T) {
+	fs := newFakeStorage()
+	fs.readOverride = []byte("wrong content")
+	err := storageProbe(context.Background(), fs)
+	var pe *probeError
+	if !errors.As(err, &pe) || pe.step != "verify" {
+		t.Fatalf("step = %v, want verify; err = %v", pe, err)
+	}
+}
+
+func TestStorageProbe_DeleteFails(t *testing.T) {
+	fs := newFakeStorage()
+	fs.deleteErr = errors.New("permission denied")
+	err := storageProbe(context.Background(), fs)
+	var pe *probeError
+	if !errors.As(err, &pe) || pe.step != "delete" {
+		t.Fatalf("step = %v, want delete; err = %v", pe, err)
+	}
+}
+
+// TestStorageProbe_CleanupOnNonDeleteFailure asserts that the probe object is
+// deleted even when a step after Store (size/open/read/verify) fails, so
+// probe artifacts don't accumulate in the storage backend.
+func TestStorageProbe_CleanupOnNonDeleteFailure(t *testing.T) {
+	cases := []struct {
+		name    string
+		inject  func(*fakeStorage)
+		wantErr string
+	}{
+		{"size mismatch", func(fs *fakeStorage) { fs.sizeDelta = -1 }, "size"},
+		{"open fails", func(fs *fakeStorage) { fs.openErr = errors.New("open boom") }, "read"},
+		{"read mid-stream", func(fs *fakeStorage) { fs.readErr = errors.New("mid-stream boom") }, "read"},
+		{"content mismatch", func(fs *fakeStorage) { fs.readOverride = []byte("wrong") }, "verify"},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			fs := newFakeStorage()
+			tc.inject(fs)
+			err := storageProbe(context.Background(), fs)
+			var pe *probeError
+			if !errors.As(err, &pe) || pe.step != tc.wantErr {
+				t.Fatalf("step = %v, want %q; err = %v", pe, tc.wantErr, err)
+			}
+			if got := fs.deleteCalls.Load(); got != 1 {
+				t.Errorf("deleteCalls = %d, want 1 (cleanup should run on non-delete failures)", got)
+			}
+		})
+	}
+}
+
+func TestStorageProbe_ReaderClosedOnReadFailure(t *testing.T) {
+	fs := newFakeStorage()
+	fs.readErr = errors.New("read error")
+	_ = storageProbe(context.Background(), fs)
+	if got := fs.closeCalls.Load(); got != fs.openCalls.Load() {
+		t.Errorf("closeCalls = %d, openCalls = %d (should match)", got, fs.openCalls.Load())
+	}
+}
+
+func TestStorageProbe_PathUniqueness(t *testing.T) {
+	fs := newFakeStorage()
+	for i := 0; i < 100; i++ {
+		if err := storageProbe(context.Background(), fs); err != nil {
+			t.Fatalf("probe %d: %v", i, err)
+		}
+	}
+	seen := make(map[string]bool)
+	for _, p := range fs.paths {
+		if !strings.HasPrefix(p, ".healthcheck/") {
+			t.Errorf("path missing prefix: %q", p)
+		}
+		if seen[p] {
+			t.Errorf("duplicate path: %q", p)
+		}
+		seen[p] = true
+	}
+}
+
+// helper: a healthCache wired to a fakeStorage and a discard logger.
+func newTestCache(fs *fakeStorage, interval time.Duration) *healthCache {
+	return &healthCache{
+		storage:      fs,
+		interval:     interval,
+		probeTimeout: 5 * time.Second,
+		logger:       discardLogger(),
+	}
+}
+
+func discardLogger() *slog.Logger {
+	return slog.New(slog.NewTextHandler(io.Discard, nil))
+}
+
+func TestHealthCache_CacheHit(t *testing.T) {
+	fs := newFakeStorage()
+	c := newTestCache(fs, 30*time.Second)
+	if err := c.Check(); err != nil {
+		t.Fatalf("first check: %v", err)
+	}
+	if err := c.Check(); err != nil {
+		t.Fatalf("second check: %v", err)
+	}
+	if got := fs.storeCalls.Load(); got != 1 {
+		t.Errorf("storeCalls = %d, want 1 (second call should be cached)", got)
+	}
+}
+
+func TestHealthCache_MissAfterTTL(t *testing.T) {
+	fs := newFakeStorage()
+	c := newTestCache(fs, 10*time.Millisecond)
+	_ = c.Check()
+	time.Sleep(20 * time.Millisecond)
+	_ = c.Check()
+	if got := fs.storeCalls.Load(); got != 2 {
+		t.Errorf("storeCalls = %d, want 2", got)
+	}
+}
+
+func TestHealthCache_Disabled(t *testing.T) {
+	fs := newFakeStorage()
+	c := newTestCache(fs, 0) // interval = 0 means probe every call
+	_ = c.Check()
+	_ = c.Check()
+	if got := fs.storeCalls.Load(); got != 2 {
+		t.Errorf("storeCalls = %d, want 2", got)
+	}
+}
+
+func TestHealthCache_LastAtNotAdvancedOnHit(t *testing.T) {
+	fs := newFakeStorage()
+	c := newTestCache(fs, 30*time.Second)
+	for i := 0; i < 100; i++ {
+		_ = c.Check()
+	}
+	if got := fs.storeCalls.Load(); got != 1 {
+		t.Errorf("storeCalls = %d, want 1 across 100 hits", got)
+	}
+}
+
+func TestHealthCache_ConcurrentSingleFlight(t *testing.T) {
+	fs := newFakeStorage()
+	c := newTestCache(fs, 30*time.Second)
+	var wg sync.WaitGroup
+	for i := 0; i < 20; i++ {
+		wg.Add(1)
+		go func() { defer wg.Done(); _ = c.Check() }()
+	}
+	wg.Wait()
+	if got := fs.storeCalls.Load(); got != 1 {
+		t.Errorf("storeCalls = %d, want 1 with 20 concurrent callers", got)
+	}
+}
+
+func TestHealthCache_FailureCounterIncrement(t *testing.T) {
+	fs := newFakeStorage()
+	fs.storeErr = errors.New("boom")
+	c := newTestCache(fs, 30*time.Second)
+
+	before := testutil.ToFloat64(metrics.HealthProbeFailures.WithLabelValues("write"))
+
+	// First call: fresh probe → counter +1
+	_ = c.Check()
+	afterFirst := testutil.ToFloat64(metrics.HealthProbeFailures.WithLabelValues("write"))
+	if afterFirst-before != 1 {
+		t.Errorf("counter delta after first call = %v, want 1", afterFirst-before)
+	}
+
+	// Second call: cache hit → counter NOT re-incremented
+	_ = c.Check()
+	afterSecond := testutil.ToFloat64(metrics.HealthProbeFailures.WithLabelValues("write"))
+	if afterSecond != afterFirst {
+		t.Errorf("counter changed on cache hit: %v → %v", afterFirst, afterSecond)
+	}
+}
+
+func TestHealthCache_ProbeTimeout(t *testing.T) {
+	fs := newFakeStorage()
+	fs.storeBlock = make(chan struct{}) // Store will block until channel is closed (or never)
+	t.Cleanup(func() { close(fs.storeBlock) })
+
+	c := &healthCache{
+		storage:      fs,
+		interval:     30 * time.Second,
+		probeTimeout: 50 * time.Millisecond,
+		logger:       discardLogger(),
+	}
+	start := time.Now()
+	err := c.Check()
+	elapsed := time.Since(start)
+
+	if err == nil {
+		t.Fatal("expected timeout error, got nil")
+	}
+	if elapsed > 500*time.Millisecond {
+		t.Errorf("probe took %v, expected ~50ms (timeout not respected)", elapsed)
+	}
+}
+
+func TestHealthCache_TransitionLogging(t *testing.T) {
+	fs := newFakeStorage()
+	var buf bytes.Buffer
+	logger := slog.New(slog.NewTextHandler(&buf, &slog.HandlerOptions{Level: slog.LevelInfo}))
+	c := &healthCache{
+		storage:      fs,
+		interval:     0, // probe every call
+		probeTimeout: 5 * time.Second,
+		logger:       logger,
+	}
+
+	// Steady ok state — should not log
+	_ = c.Check()
+	_ = c.Check()
+	if got := strings.Count(buf.String(), "storage probe"); got != 0 {
+		t.Errorf("steady-state logs = %d, want 0; output: %s", got, buf.String())
+	}
+
+	// ok → err transition: exactly one Error log
+	buf.Reset()
+	fs.storeErr = errors.New("boom")
+	_ = c.Check()
+	if !strings.Contains(buf.String(), "storage probe failed") {
+		t.Errorf("missing failure log on transition; output: %s", buf.String())
+	}
+
+	// err steady state — should not log again
+	buf.Reset()
+	_ = c.Check()
+	if buf.Len() != 0 {
+		t.Errorf("steady-err logs = %q, want empty", buf.String())
+	}
+
+	// err → ok transition: exactly one Info log
+	buf.Reset()
+	fs.storeErr = nil
+	_ = c.Check()
+	if !strings.Contains(buf.String(), "storage probe recovered") {
+		t.Errorf("missing recovery log on transition; output: %s", buf.String())
+	}
+}
diff --git a/internal/server/server.go b/internal/server/server.go
index ffb357b..042b3f6 100644
--- a/internal/server/server.go
+++ b/internal/server/server.go
@@ -41,6 +41,7 @@ import (
 	"context"
 	"database/sql"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"log/slog"
 	"net/http"
@@ -80,7 +81,8 @@ type Server struct {
 	logger    *slog.Logger
 	http      *http.Server
 	templates *Templates
-	cancel    context.CancelFunc
+	cancel      context.CancelFunc
+	healthCache *healthCache
 }
 
 // New creates a new Server with the given configuration.
@@ -126,12 +128,20 @@ func New(cfg *config.Config, logger *slog.Logger) (*Server, error) {
 		return nil, fmt.Errorf("verifying storage connectivity: %w", err)
 	}
 
+	hc, err := newHealthCache(store, cfg.Health.StorageProbeInterval, logger)
+	if err != nil {
+		_ = store.Close()
+		_ = db.Close()
+		return nil, fmt.Errorf("initializing health cache: %w", err)
+	}
+
 	return &Server{
-		cfg:       cfg,
-		db:        db,
-		storage:   store,
-		logger:    logger,
-		templates: &Templates{},
+		cfg:         cfg,
+		db:          db,
+		storage:     store,
+		logger:      logger,
+		templates:   &Templates{},
+		healthCache: hc,
 	}, nil
 }
 
@@ -802,23 +812,49 @@ func (s *Server) showComparePage(w http.ResponseWriter, ecosystem, name, version
 	}
 }
 
-// handleHealth responds with a simple health check.
+// handleHealth responds with a structured JSON health report.
+//
 // @Summary Health check
 // @Tags meta
-// @Produce plain
-// @Success 200 {string} string
-// @Failure 503 {string} string
+// @Produce json
+// @Success 200 {object} HealthResponse
+// @Failure 503 {object} HealthResponse
 // @Router /health [get]
 func (s *Server) handleHealth(w http.ResponseWriter, r *http.Request) {
-	// Check database connectivity
+	w.Header().Set("Content-Type", "application/json")
+
+	resp := HealthResponse{Status: "ok", Checks: map[string]HealthCheck{}}
+
+	// Database check (short-circuit; do not waste a storage probe call when DB is down).
+	// On DB failure the storage entry reports "skipped" rather than being omitted so
+	// the response always carries the same key set for monitors that expect it.
 	if _, err := s.db.SchemaVersion(); err != nil {
+		resp.Status = "error"
+		resp.Checks["database"] = HealthCheck{Status: "error", Error: err.Error()}
+		resp.Checks["storage"] = HealthCheck{Status: "skipped"}
 		w.WriteHeader(http.StatusServiceUnavailable)
-		_, _ = fmt.Fprint(w, "database error")
+		_ = json.NewEncoder(w).Encode(resp)
 		return
 	}
+	resp.Checks["database"] = HealthCheck{Status: "ok"}
+
+	// Storage probe (via cache).
+	if err := s.healthCache.Check(); err != nil {
+		resp.Status = "error"
+		sc := HealthCheck{Status: "error", Error: err.Error()}
+		var pe *probeError
+		if errors.As(err, &pe) {
+			sc.Step = pe.step
+		}
+		resp.Checks["storage"] = sc
+		w.WriteHeader(http.StatusServiceUnavailable)
+		_ = json.NewEncoder(w).Encode(resp)
+		return
+	}
+	resp.Checks["storage"] = HealthCheck{Status: "ok"}
 
 	w.WriteHeader(http.StatusOK)
-	_, _ = fmt.Fprint(w, "ok")
+	_ = json.NewEncoder(w).Encode(resp)
 }
 
 // StatsResponse contains cache statistics.
diff --git a/internal/server/server_test.go b/internal/server/server_test.go
index 574b6ba..e2dc1c2 100644
--- a/internal/server/server_test.go
+++ b/internal/server/server_test.go
@@ -81,13 +81,21 @@ func newTestServer(t *testing.T) *testServer {
 	r.Mount("/pypi", http.StripPrefix("/pypi", pypiHandler.Routes()))
 	r.Mount("/gradle", http.StripPrefix("/gradle", gradleHandler.Routes()))
 
+	hc, err := newHealthCache(store, "30s", logger)
+	if err != nil {
+		_ = db.Close()
+		_ = os.RemoveAll(tempDir)
+		t.Fatalf("failed to create health cache: %v", err)
+	}
+
 	// Create a minimal server struct for the handlers
 	s := &Server{
-		cfg:       cfg,
-		db:        db,
-		storage:   store,
-		logger:    logger,
-		templates: &Templates{},
+		cfg:         cfg,
+		db:          db,
+		storage:     store,
+		logger:      logger,
+		templates:   &Templates{},
+		healthCache: hc,
 	}
 
 	r.Get("/health", s.handleHealth)
@@ -179,12 +187,55 @@ func TestHealthEndpoint(t *testing.T) {
 	ts.handler.ServeHTTP(w, req)
 
 	if w.Code != http.StatusOK {
-		t.Errorf("expected status 200, got %d", w.Code)
+		t.Fatalf("status = %d, want 200; body: %s", w.Code, w.Body.String())
 	}
+	if got := w.Header().Get("Content-Type"); got != "application/json" {
+		t.Errorf("Content-Type = %q, want application/json", got)
+	}
+	var resp HealthResponse
+	if err := json.NewDecoder(w.Body).Decode(&resp); err != nil {
+		t.Fatalf("decoding response: %v", err)
+	}
+	if resp.Status != "ok" {
+		t.Errorf("status = %q, want ok", resp.Status)
+	}
+	if resp.Checks["database"].Status != "ok" {
+		t.Errorf("database check = %+v, want ok", resp.Checks["database"])
+	}
+	if resp.Checks["storage"].Status != "ok" {
+		t.Errorf("storage check = %+v, want ok", resp.Checks["storage"])
+	}
+}
 
-	body := w.Body.String()
-	if body != "ok" {
-		t.Errorf("expected body 'ok', got %q", body)
+func TestHealthEndpoint_DBFailureShortCircuits(t *testing.T) {
+	ts := newTestServer(t)
+	defer ts.close()
+
+	// Force DB failure by closing the connection.
+	_ = ts.db.Close()
+
+	req := httptest.NewRequest("GET", "/health", nil)
+	w := httptest.NewRecorder()
+	ts.handler.ServeHTTP(w, req)
+
+	if w.Code != http.StatusServiceUnavailable {
+		t.Fatalf("status = %d, want 503; body: %s", w.Code, w.Body.String())
+	}
+	var resp HealthResponse
+	if err := json.NewDecoder(w.Body).Decode(&resp); err != nil {
+		t.Fatalf("decoding: %v", err)
+	}
+	if resp.Status != "error" {
+		t.Errorf("status = %q, want error", resp.Status)
+	}
+	if resp.Checks["database"].Status != "error" {
+		t.Errorf("database check = %+v, want error", resp.Checks["database"])
+	}
+	storage, present := resp.Checks["storage"]
+	if !present {
+		t.Error("storage key should be present (with status=skipped) on DB short-circuit")
+	} else if storage.Status != "skipped" {
+		t.Errorf("storage check = %+v, want status=skipped", storage)
 	}
 }
 

From 552c8ac4e5cc9257f72f75f7f3cf0fc85bb06df7 Mon Sep 17 00:00:00 2001
From: Mati Kepa <36644582+matikepa@users.noreply.github.com>
Date: Fri, 22 May 2026 18:05:20 +0200
Subject: [PATCH 31/36] Update Gradle cache with the configurable plugin
 support (#114)

* feat(gradle): add request metrics for build cache handler

* Implement fallback handling for Gradle plugin requests and update tests

* refactor(gradle): simplify response handling and remove unused metrics assertions

* Add tests for Gradle plugin metadata fallback and refactor metadata handling

---------

Co-authored-by: Mateusz (Mati) Kepa <m.kepa@sportradar.com>
---
 README.md                         |  14 ++
 cmd/proxy/main.go                 |   4 +
 config.example.yaml               |   6 +
 docs/configuration.md             |   2 +
 internal/config/config.go         |  23 ++-
 internal/config/config_test.go    |  14 ++
 internal/handler/download_test.go | 278 +++++++++++++++++++++++++++++-
 internal/handler/handler.go       |   7 +-
 internal/handler/handler_test.go  |  14 +-
 internal/handler/maven.go         |  72 ++++++--
 internal/handler/maven_test.go    |  61 +++++++
 internal/server/server.go         |   7 +-
 12 files changed, 476 insertions(+), 26 deletions(-)

diff --git a/README.md b/README.md
index 325c679..abf3e11 100644
--- a/README.md
+++ b/README.md
@@ -210,6 +210,18 @@ Add to your `~/.m2/settings.xml`:
 </settings>
 ```
 
+The `/maven/` endpoint uses Maven Central as primary upstream and falls back to the Gradle Plugin Portal for Gradle plugin marker metadata and related artifacts when the primary upstream returns not found.
+
+For Gradle plugin resolution via the same proxy endpoint:
+
+```kotlin
+pluginManagement {
+  repositories {
+    maven(url = "http://localhost:8080/maven/")
+  }
+}
+```
+
 ### Gradle HTTP Build Cache
 
 Configure in `settings.gradle(.kts)`:
@@ -386,6 +398,7 @@ sudo dnf update
 ## Configuration
 
 The proxy can be configured via:
+
 1. Command line flags (highest priority)
 2. Environment variables
 3. Configuration file (YAML or JSON)
@@ -977,6 +990,7 @@ The proxy will recreate the database on next start.
 ## Building from Source
 
 Requirements:
+
 - Go 1.25 or later
 
 ```bash
diff --git a/cmd/proxy/main.go b/cmd/proxy/main.go
index 8b28535..a8c8bdf 100644
--- a/cmd/proxy/main.go
+++ b/cmd/proxy/main.go
@@ -72,6 +72,8 @@
 //	PROXY_DATABASE_URL     - PostgreSQL connection URL
 //	PROXY_LOG_LEVEL        - Log level
 //	PROXY_LOG_FORMAT       - Log format
+//	PROXY_UPSTREAM_MAVEN   - Maven repository upstream URL
+//	PROXY_UPSTREAM_GRADLE_PLUGIN_PORTAL - Gradle Plugin Portal upstream URL
 //	PROXY_GRADLE_BUILD_CACHE_READ_ONLY       - Disable Gradle PUT uploads
 //	PROXY_GRADLE_BUILD_CACHE_MAX_UPLOAD_SIZE - Max Gradle PUT request body size
 //	PROXY_GRADLE_BUILD_CACHE_MAX_AGE         - Gradle cache max age eviction
@@ -199,6 +201,8 @@ func runServe() {
 		fmt.Fprintf(os.Stderr, "  PROXY_DATABASE_URL     PostgreSQL connection URL\n")
 		fmt.Fprintf(os.Stderr, "  PROXY_LOG_LEVEL        Log level\n")
 		fmt.Fprintf(os.Stderr, "  PROXY_LOG_FORMAT       Log format\n")
+		fmt.Fprintf(os.Stderr, "  PROXY_UPSTREAM_MAVEN   Maven repository upstream URL\n")
+		fmt.Fprintf(os.Stderr, "  PROXY_UPSTREAM_GRADLE_PLUGIN_PORTAL Gradle Plugin Portal upstream URL\n")
 		fmt.Fprintf(os.Stderr, "  PROXY_GRADLE_BUILD_CACHE_READ_ONLY       Disable Gradle PUT uploads\n")
 		fmt.Fprintf(os.Stderr, "  PROXY_GRADLE_BUILD_CACHE_MAX_UPLOAD_SIZE Max Gradle PUT request body size\n")
 		fmt.Fprintf(os.Stderr, "  PROXY_GRADLE_BUILD_CACHE_MAX_AGE         Gradle cache max age eviction\n")
diff --git a/config.example.yaml b/config.example.yaml
index 853f47a..11c751c 100644
--- a/config.example.yaml
+++ b/config.example.yaml
@@ -71,6 +71,12 @@ upstream:
   # npm registry URL
   npm: "https://registry.npmjs.org"
 
+  # Maven repository URL (used by /maven endpoint)
+  maven: "https://repo1.maven.org/maven2"
+
+  # Gradle Plugin Portal Maven URL (fallback for plugin marker artifacts)
+  gradle_plugin_portal: "https://plugins.gradle.org/m2"
+
   # Cargo sparse index URL
   cargo: "https://index.crates.io"
 
diff --git a/docs/configuration.md b/docs/configuration.md
index ac85d54..cf6c101 100644
--- a/docs/configuration.md
+++ b/docs/configuration.md
@@ -114,6 +114,8 @@ Override default upstream registry URLs:
 ```yaml
 upstream:
   npm: "https://registry.npmjs.org"
+  maven: "https://repo1.maven.org/maven2"
+  gradle_plugin_portal: "https://plugins.gradle.org/m2"
   cargo: "https://index.crates.io"
   cargo_download: "https://static.crates.io/crates"
 ```
diff --git a/internal/config/config.go b/internal/config/config.go
index 8727884..87e23ac 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -221,6 +221,15 @@ type UpstreamConfig struct {
 	// Default: https://registry.npmjs.org
 	NPM string `json:"npm" yaml:"npm"`
 
+	// Maven is the upstream Maven repository URL.
+	// Default: https://repo1.maven.org/maven2
+	Maven string `json:"maven" yaml:"maven"`
+
+	// GradlePluginPortal is the upstream Gradle Plugin Portal Maven URL.
+	// Used to resolve Gradle plugin marker artifacts.
+	// Default: https://plugins.gradle.org/m2
+	GradlePluginPortal string `json:"gradle_plugin_portal" yaml:"gradle_plugin_portal"`
+
 	// Cargo is the upstream cargo index URL.
 	// Default: https://index.crates.io
 	Cargo string `json:"cargo" yaml:"cargo"`
@@ -298,9 +307,11 @@ func Default() *Config {
 			Format: "text",
 		},
 		Upstream: UpstreamConfig{
-			NPM:           "https://registry.npmjs.org",
-			Cargo:         "https://index.crates.io",
-			CargoDownload: "https://static.crates.io/crates",
+			NPM:                "https://registry.npmjs.org",
+			Maven:              "https://repo1.maven.org/maven2",
+			GradlePluginPortal: "https://plugins.gradle.org/m2",
+			Cargo:              "https://index.crates.io",
+			CargoDownload:      "https://static.crates.io/crates",
 		},
 		Gradle: GradleConfig{
 			BuildCache: GradleBuildCacheConfig{
@@ -395,6 +406,12 @@ func (c *Config) LoadFromEnv() {
 	if v := os.Getenv("PROXY_LOG_FORMAT"); v != "" {
 		c.Log.Format = v
 	}
+	if v := os.Getenv("PROXY_UPSTREAM_MAVEN"); v != "" {
+		c.Upstream.Maven = v
+	}
+	if v := os.Getenv("PROXY_UPSTREAM_GRADLE_PLUGIN_PORTAL"); v != "" {
+		c.Upstream.GradlePluginPortal = v
+	}
 	if v := os.Getenv("PROXY_COOLDOWN_DEFAULT"); v != "" {
 		c.Cooldown.Default = v
 	}
diff --git a/internal/config/config_test.go b/internal/config/config_test.go
index 22694c0..05fec3a 100644
--- a/internal/config/config_test.go
+++ b/internal/config/config_test.go
@@ -31,6 +31,12 @@ func TestDefault(t *testing.T) {
 	if cfg.Gradle.BuildCache.MaxAge != "168h" {
 		t.Errorf("Gradle.BuildCache.MaxAge = %q, want %q", cfg.Gradle.BuildCache.MaxAge, "168h")
 	}
+	if cfg.Upstream.Maven != "https://repo1.maven.org/maven2" {
+		t.Errorf("Upstream.Maven = %q, want %q", cfg.Upstream.Maven, "https://repo1.maven.org/maven2")
+	}
+	if cfg.Upstream.GradlePluginPortal != "https://plugins.gradle.org/m2" {
+		t.Errorf("Upstream.GradlePluginPortal = %q, want %q", cfg.Upstream.GradlePluginPortal, "https://plugins.gradle.org/m2")
+	}
 }
 
 func TestValidate(t *testing.T) {
@@ -264,6 +270,8 @@ func TestLoadFromEnv(t *testing.T) {
 	t.Setenv("PROXY_BASE_URL", "https://env.example.com")
 	t.Setenv("PROXY_STORAGE_PATH", "/env/cache")
 	t.Setenv("PROXY_LOG_LEVEL", testLevelDebug)
+	t.Setenv("PROXY_UPSTREAM_MAVEN", "https://maven.example.com/repository/maven-public")
+	t.Setenv("PROXY_UPSTREAM_GRADLE_PLUGIN_PORTAL", "https://plugins.example.com/m2")
 	t.Setenv("PROXY_GRADLE_BUILD_CACHE_READ_ONLY", "true")
 	t.Setenv("PROXY_GRADLE_BUILD_CACHE_MAX_UPLOAD_SIZE", "32MB")
 	t.Setenv("PROXY_GRADLE_BUILD_CACHE_MAX_AGE", "12h")
@@ -284,6 +292,12 @@ func TestLoadFromEnv(t *testing.T) {
 	if cfg.Log.Level != testLevelDebug {
 		t.Errorf("Log.Level = %q, want %q", cfg.Log.Level, testLevelDebug)
 	}
+	if cfg.Upstream.Maven != "https://maven.example.com/repository/maven-public" {
+		t.Errorf("Upstream.Maven = %q, want %q", cfg.Upstream.Maven, "https://maven.example.com/repository/maven-public")
+	}
+	if cfg.Upstream.GradlePluginPortal != "https://plugins.example.com/m2" {
+		t.Errorf("Upstream.GradlePluginPortal = %q, want %q", cfg.Upstream.GradlePluginPortal, "https://plugins.example.com/m2")
+	}
 	if !cfg.Gradle.BuildCache.ReadOnly {
 		t.Error("Gradle.BuildCache.ReadOnly = false, want true")
 	}
diff --git a/internal/handler/download_test.go b/internal/handler/download_test.go
index 639e976..980e234 100644
--- a/internal/handler/download_test.go
+++ b/internal/handler/download_test.go
@@ -673,7 +673,7 @@ func TestMavenHandler_DownloadCacheHit(t *testing.T) {
 	proxy, db, store, _ := setupTestProxy(t)
 	seedPackageWithPURL(t, db, store, "maven", "com.google.guava:guava", "32.1.3-jre", "guava-32.1.3-jre.jar", "jar content")
 
-	h := NewMavenHandler(proxy, "http://localhost")
+	h := NewMavenHandler(proxy, "http://localhost", "", "")
 	srv := httptest.NewServer(h.Routes())
 	defer srv.Close()
 
@@ -730,7 +730,7 @@ func TestMavenHandler_MetadataProxied(t *testing.T) {
 
 func TestMavenHandler_EmptyPathNotFound(t *testing.T) {
 	proxy, _, _, _ := setupTestProxy(t)
-	h := NewMavenHandler(proxy, "http://localhost")
+	h := NewMavenHandler(proxy, "http://localhost", "", "")
 	srv := httptest.NewServer(h.Routes())
 	defer srv.Close()
 
@@ -748,7 +748,7 @@ func TestMavenHandler_EmptyPathNotFound(t *testing.T) {
 func TestMavenHandler_ArtifactExtensions(t *testing.T) {
 	proxy, _, _, fetcher := setupTestProxy(t)
 
-	extensions := []string{".jar", ".war", ".ear", ".pom", ".aar", ".klib"}
+	extensions := []string{".jar", ".war", ".ear", ".pom", ".aar", ".klib", ".module"}
 	for _, ext := range extensions {
 		fetcher.artifact = &fetch.Artifact{
 			Body:        io.NopCloser(strings.NewReader("artifact")),
@@ -756,7 +756,7 @@ func TestMavenHandler_ArtifactExtensions(t *testing.T) {
 		}
 		fetcher.fetchCalled = false
 
-		h := NewMavenHandler(proxy, "http://localhost")
+		h := NewMavenHandler(proxy, "http://localhost", "", "")
 
 		upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 			t.Errorf("should not proxy artifact file %s to upstream", ext)
@@ -789,7 +789,7 @@ func TestMavenHandler_CacheMiss(t *testing.T) {
 		ContentType: "application/java-archive",
 	}
 
-	h := NewMavenHandler(proxy, "http://localhost")
+	h := NewMavenHandler(proxy, "http://localhost", "", "")
 	srv := httptest.NewServer(h.Routes())
 	defer srv.Close()
 
@@ -809,6 +809,274 @@ func TestMavenHandler_CacheMiss(t *testing.T) {
 	}
 }
 
+func TestMavenHandler_GradlePluginMarkerFallbackAndCache(t *testing.T) {
+	tests := []struct {
+		name       string
+		markerPath string
+	}{
+		{
+			name:       "Spotless",
+			markerPath: "/com/diffplug/spotless/com.diffplug.spotless.gradle.plugin/8.4.0/com.diffplug.spotless.gradle.plugin-8.4.0.pom",
+		},
+		{
+			name:       "BenManes",
+			markerPath: "/com/github/ben-manes/versions/com.github.ben-manes.versions.gradle.plugin/0.54.0/com.github.ben-manes.versions.gradle.plugin-0.54.0.pom",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			proxy, _, _, fetcher := setupTestProxy(t)
+
+			primaryUpstream := "https://repo1.maven.org/maven2"
+			pluginPortalUpstream := "https://plugins.gradle.org/m2"
+			primaryURL := primaryUpstream + tt.markerPath
+
+			fetcher.fetchErrByURL = map[string]error{
+				primaryURL: ErrUpstreamNotFound,
+			}
+			fetcher.artifact = &fetch.Artifact{
+				Body:        io.NopCloser(strings.NewReader("<project/>")),
+				ContentType: "application/xml",
+			}
+
+			h := NewMavenHandler(proxy, "http://localhost", primaryUpstream, pluginPortalUpstream)
+			srv := httptest.NewServer(h.Routes())
+			defer srv.Close()
+
+			resp, err := http.Get(srv.URL + tt.markerPath)
+			if err != nil {
+				t.Fatalf("request failed: %v", err)
+			}
+			body, _ := io.ReadAll(resp.Body)
+			_ = resp.Body.Close()
+
+			if resp.StatusCode != http.StatusOK {
+				t.Fatalf("status = %d, want %d", resp.StatusCode, http.StatusOK)
+			}
+			if string(body) != "<project/>" {
+				t.Fatalf("body = %q, want %q", body, "<project/>")
+			}
+
+			wantFallbackURL := pluginPortalUpstream + tt.markerPath
+			if fetcher.fetchedURL != wantFallbackURL {
+				t.Fatalf("fallback URL = %q, want %q", fetcher.fetchedURL, wantFallbackURL)
+			}
+
+			fetcher.fetchCalled = false
+			resp, err = http.Get(srv.URL + tt.markerPath)
+			if err != nil {
+				t.Fatalf("second request failed: %v", err)
+			}
+			_ = resp.Body.Close()
+
+			if resp.StatusCode != http.StatusOK {
+				t.Fatalf("second status = %d, want %d", resp.StatusCode, http.StatusOK)
+			}
+			if fetcher.fetchCalled {
+				t.Fatal("expected plugin marker POM to be served from cache on second request")
+			}
+		})
+	}
+}
+
+func TestMavenHandler_GradlePluginMarkerMetadataFallback(t *testing.T) {
+	paths := map[string]string{
+		"/com/diffplug/spotless/com.diffplug.spotless.gradle.plugin/8.4.0/com.diffplug.spotless.gradle.plugin-8.4.0.pom.sha1":   "sha1",
+		"/com/diffplug/spotless/com.diffplug.spotless.gradle.plugin/8.4.0/com.diffplug.spotless.gradle.plugin-8.4.0.pom.sha256": "sha256",
+		"/com/diffplug/spotless/com.diffplug.spotless.gradle.plugin/8.4.0/com.diffplug.spotless.gradle.plugin-8.4.0.pom.md5":    "md5",
+		"/com/diffplug/spotless/com.diffplug.spotless.gradle.plugin/maven-metadata.xml":                                         "<metadata/>",
+	}
+
+	primaryHits := map[string]int{}
+	pluginHits := map[string]int{}
+
+	primary := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		primaryHits[r.URL.Path]++
+		if _, ok := paths[r.URL.Path]; ok {
+			http.NotFound(w, r)
+			return
+		}
+		t.Fatalf("unexpected path to primary upstream: %s", r.URL.Path)
+	}))
+	defer primary.Close()
+
+	pluginPortal := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		pluginHits[r.URL.Path]++
+		body, ok := paths[r.URL.Path]
+		if !ok {
+			http.NotFound(w, r)
+			return
+		}
+		_, _ = io.WriteString(w, body)
+	}))
+	defer pluginPortal.Close()
+
+	proxy, _, _, _ := setupTestProxy(t)
+	proxy.HTTPClient = primary.Client()
+
+	h := NewMavenHandler(proxy, "http://localhost", primary.URL, pluginPortal.URL)
+	srv := httptest.NewServer(h.Routes())
+	defer srv.Close()
+
+	for reqPath, wantBody := range paths {
+		resp, err := http.Get(srv.URL + reqPath)
+		if err != nil {
+			t.Fatalf("GET %s failed: %v", reqPath, err)
+		}
+		body, _ := io.ReadAll(resp.Body)
+		_ = resp.Body.Close()
+
+		if resp.StatusCode != http.StatusOK {
+			t.Fatalf("GET %s: status = %d, want %d", reqPath, resp.StatusCode, http.StatusOK)
+		}
+		if string(body) != wantBody {
+			t.Fatalf("GET %s: body = %q, want %q", reqPath, body, wantBody)
+		}
+
+		if primaryHits[reqPath] == 0 {
+			t.Fatalf("GET %s did not hit primary upstream", reqPath)
+		}
+		if pluginHits[reqPath] == 0 {
+			t.Fatalf("GET %s did not hit plugin portal fallback", reqPath)
+		}
+	}
+}
+
+func TestMavenHandler_GradlePluginImplementationMetadataFallback(t *testing.T) {
+	paths := map[string]string{
+		"/com/diffplug/spotless/spotless-plugin-gradle/8.4.0/spotless-plugin-gradle-8.4.0.jar.sha1":   "impl-sha1",
+		"/com/diffplug/spotless/spotless-plugin-gradle/8.4.0/spotless-plugin-gradle-8.4.0.jar.sha256": "impl-sha256",
+	}
+
+	primaryHits := map[string]int{}
+	pluginHits := map[string]int{}
+
+	primary := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		primaryHits[r.URL.Path]++
+		if _, ok := paths[r.URL.Path]; ok {
+			http.NotFound(w, r)
+			return
+		}
+		t.Fatalf("unexpected path to primary upstream: %s", r.URL.Path)
+	}))
+	defer primary.Close()
+
+	pluginPortal := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		pluginHits[r.URL.Path]++
+		body, ok := paths[r.URL.Path]
+		if !ok {
+			http.NotFound(w, r)
+			return
+		}
+		_, _ = io.WriteString(w, body)
+	}))
+	defer pluginPortal.Close()
+
+	proxy, _, _, _ := setupTestProxy(t)
+	proxy.HTTPClient = primary.Client()
+
+	h := NewMavenHandler(proxy, "http://localhost", primary.URL, pluginPortal.URL)
+	srv := httptest.NewServer(h.Routes())
+	defer srv.Close()
+
+	for reqPath, wantBody := range paths {
+		resp, err := http.Get(srv.URL + reqPath)
+		if err != nil {
+			t.Fatalf("GET %s failed: %v", reqPath, err)
+		}
+		body, _ := io.ReadAll(resp.Body)
+		_ = resp.Body.Close()
+
+		if resp.StatusCode != http.StatusOK {
+			t.Fatalf("GET %s: status = %d, want %d", reqPath, resp.StatusCode, http.StatusOK)
+		}
+		if string(body) != wantBody {
+			t.Fatalf("GET %s: body = %q, want %q", reqPath, body, wantBody)
+		}
+
+		if primaryHits[reqPath] == 0 {
+			t.Fatalf("GET %s did not hit primary upstream", reqPath)
+		}
+		if pluginHits[reqPath] == 0 {
+			t.Fatalf("GET %s did not hit plugin portal fallback", reqPath)
+		}
+	}
+}
+
+func TestMavenHandler_GradlePluginImplementation_FallbackToPluginPortal(t *testing.T) {
+	proxy, _, _, fetcher := setupTestProxy(t)
+
+	primaryUpstream := "https://repo1.maven.org/maven2"
+	pluginPortalUpstream := "https://plugins.gradle.org/m2"
+	implPath := "/com/diffplug/spotless/spotless-plugin-gradle/8.4.0/spotless-plugin-gradle-8.4.0.jar"
+	primaryURL := primaryUpstream + implPath
+	pluginPortalURL := pluginPortalUpstream + implPath
+
+	fetcher.fetchErrByURL = map[string]error{
+		primaryURL: ErrUpstreamNotFound,
+	}
+	fetcher.artifact = &fetch.Artifact{
+		Body:        io.NopCloser(strings.NewReader("plugin impl jar")),
+		ContentType: "application/java-archive",
+	}
+
+	h := NewMavenHandler(proxy, "http://localhost", primaryUpstream, pluginPortalUpstream)
+	srv := httptest.NewServer(h.Routes())
+	defer srv.Close()
+
+	resp, err := http.Get(srv.URL + implPath)
+	if err != nil {
+		t.Fatalf("request failed: %v", err)
+	}
+	body, _ := io.ReadAll(resp.Body)
+	_ = resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		t.Fatalf("status = %d, want %d", resp.StatusCode, http.StatusOK)
+	}
+	if string(body) != "plugin impl jar" {
+		t.Fatalf("body = %q, want %q", body, "plugin impl jar")
+	}
+
+	if fetcher.fetchedURL != pluginPortalURL {
+		t.Fatalf("implementation artifact should fallback to plugin portal; fetched URL = %q, want %q", fetcher.fetchedURL, pluginPortalURL)
+	}
+}
+
+func TestMavenHandler_GradlePluginImplementation_NotFoundInBothUpstreams(t *testing.T) {
+	proxy, _, _, fetcher := setupTestProxy(t)
+
+	primaryUpstream := "https://repo1.maven.org/maven2"
+	pluginPortalUpstream := "https://plugins.gradle.org/m2"
+	implPath := "/com/diffplug/spotless/spotless-plugin-gradle/8.4.0/spotless-plugin-gradle-8.4.0.jar"
+	primaryURL := primaryUpstream + implPath
+	pluginPortalURL := pluginPortalUpstream + implPath
+
+	fetcher.fetchErrByURL = map[string]error{
+		primaryURL:      ErrUpstreamNotFound,
+		pluginPortalURL: ErrUpstreamNotFound,
+	}
+
+	h := NewMavenHandler(proxy, "http://localhost", primaryUpstream, pluginPortalUpstream)
+	srv := httptest.NewServer(h.Routes())
+	defer srv.Close()
+
+	resp, err := http.Get(srv.URL + implPath)
+	if err != nil {
+		t.Fatalf("request failed: %v", err)
+	}
+	_ = resp.Body.Close()
+
+	if resp.StatusCode != http.StatusNotFound {
+		t.Fatalf("status = %d, want %d", resp.StatusCode, http.StatusNotFound)
+	}
+
+	if fetcher.fetchedURL != pluginPortalURL {
+		t.Fatalf("expected fallback attempt to plugin portal; fetched URL = %q, want %q", fetcher.fetchedURL, pluginPortalURL)
+	}
+}
+
 func TestNuGetHandler_DownloadCacheMiss(t *testing.T) {
 	proxy, _, _, fetcher := setupTestProxy(t)
 	fetcher.artifact = &fetch.Artifact{
diff --git a/internal/handler/handler.go b/internal/handler/handler.go
index 0ad0776..3df2777 100644
--- a/internal/handler/handler.go
+++ b/internal/handler/handler.go
@@ -680,9 +680,14 @@ func (p *Proxy) ProxyCached(w http.ResponseWriter, r *http.Request, upstreamURL,
 		return
 	}
 
+	p.writeMetadataCachedResponse(w, r, ecosystem, cacheKey, body, contentType)
+}
+
+// writeMetadataCachedResponse writes a cached metadata response and handles
+// conditional request headers using metadata cache validators.
+func (p *Proxy) writeMetadataCachedResponse(w http.ResponseWriter, r *http.Request, ecosystem, cacheKey string, body []byte, contentType string) {
 	cm := p.lookupCachedMeta(ecosystem, cacheKey)
 
-	// Honor client conditional request headers
 	if cm.etag != "" {
 		if match := r.Header.Get("If-None-Match"); match != "" && match == cm.etag {
 			w.WriteHeader(http.StatusNotModified)
diff --git a/internal/handler/handler_test.go b/internal/handler/handler_test.go
index 3a1d2ab..bbcab72 100644
--- a/internal/handler/handler_test.go
+++ b/internal/handler/handler_test.go
@@ -97,10 +97,11 @@ func (s *mockStorage) Close() error { return nil }
 
 // mockFetcher implements fetch.FetcherInterface for testing.
 type mockFetcher struct {
-	artifact    *fetch.Artifact
-	fetchErr    error
-	fetchCalled bool
-	fetchedURL  string
+	artifact      *fetch.Artifact
+	fetchErr      error
+	fetchErrByURL map[string]error
+	fetchCalled   bool
+	fetchedURL    string
 }
 
 func (f *mockFetcher) Fetch(ctx context.Context, url string) (*fetch.Artifact, error) {
@@ -110,6 +111,11 @@ func (f *mockFetcher) Fetch(ctx context.Context, url string) (*fetch.Artifact, e
 func (f *mockFetcher) FetchWithHeaders(_ context.Context, url string, _ http.Header) (*fetch.Artifact, error) {
 	f.fetchCalled = true
 	f.fetchedURL = url
+	if f.fetchErrByURL != nil {
+		if err, ok := f.fetchErrByURL[url]; ok {
+			return nil, err
+		}
+	}
 	if f.fetchErr != nil {
 		return nil, f.fetchErr
 	}
diff --git a/internal/handler/maven.go b/internal/handler/maven.go
index 86664a2..c423645 100644
--- a/internal/handler/maven.go
+++ b/internal/handler/maven.go
@@ -1,6 +1,7 @@
 package handler
 
 import (
+	"errors"
 	"fmt"
 	"net/http"
 	"path"
@@ -8,23 +9,33 @@ import (
 )
 
 const (
-	mavenUpstream = "https://repo1.maven.org/maven2"
-	minMavenParts = 4 // group path segments + artifact + version + filename
+	mavenCentralUpstream       = "https://repo1.maven.org/maven2"
+	gradlePluginPortalUpstream = "https://plugins.gradle.org/m2"
+	minMavenParts              = 4 // group path segments + artifact + version + filename
 )
 
 // MavenHandler handles Maven repository protocol requests.
 type MavenHandler struct {
-	proxy       *Proxy
-	upstreamURL string
-	proxyURL    string
+	proxy                   *Proxy
+	upstreamURL             string
+	pluginPortalUpstreamURL string
+	proxyURL                string
 }
 
 // NewMavenHandler creates a new Maven repository handler.
-func NewMavenHandler(proxy *Proxy, proxyURL string) *MavenHandler {
+func NewMavenHandler(proxy *Proxy, proxyURL, upstreamURL, pluginPortalUpstreamURL string) *MavenHandler {
+	if strings.TrimSpace(upstreamURL) == "" {
+		upstreamURL = mavenCentralUpstream
+	}
+	if strings.TrimSpace(pluginPortalUpstreamURL) == "" {
+		pluginPortalUpstreamURL = gradlePluginPortalUpstream
+	}
+
 	return &MavenHandler{
-		proxy:       proxy,
-		upstreamURL: mavenUpstream,
-		proxyURL:    strings.TrimSuffix(proxyURL, "/"),
+		proxy:                   proxy,
+		upstreamURL:             strings.TrimSuffix(upstreamURL, "/"),
+		pluginPortalUpstreamURL: strings.TrimSuffix(pluginPortalUpstreamURL, "/"),
+		proxyURL:                strings.TrimSuffix(proxyURL, "/"),
 	}
 }
 
@@ -51,8 +62,7 @@ func (h *MavenHandler) handleRequest(w http.ResponseWriter, r *http.Request) {
 	filename := path.Base(urlPath)
 
 	if h.isMetadataFile(filename) {
-		cacheKey := strings.ReplaceAll(urlPath, "/", "_")
-		h.proxy.ProxyCached(w, r, h.upstreamURL+r.URL.Path, "maven", cacheKey, "*/*")
+		h.handleMetadata(w, r, urlPath)
 		return
 	}
 
@@ -66,6 +76,32 @@ func (h *MavenHandler) handleRequest(w http.ResponseWriter, r *http.Request) {
 	h.proxyUpstream(w, r)
 }
 
+func (h *MavenHandler) handleMetadata(w http.ResponseWriter, r *http.Request, urlPath string) {
+	cacheKey := strings.ReplaceAll(urlPath, "/", "_")
+	upstreamURL := fmt.Sprintf("%s/%s", h.upstreamURL, urlPath)
+
+	body, contentType, err := h.proxy.FetchOrCacheMetadata(r.Context(), "maven", cacheKey, upstreamURL, "*/*")
+	if err != nil {
+		if errors.Is(err, ErrUpstreamNotFound) {
+			pluginPortalURL := fmt.Sprintf("%s/%s", h.pluginPortalUpstreamURL, urlPath)
+			h.proxy.Logger.Info("maven metadata unavailable in primary upstream, trying Gradle Plugin Portal",
+				"path", urlPath)
+			body, contentType, err = h.proxy.FetchOrCacheMetadata(r.Context(), "maven", cacheKey, pluginPortalURL, "*/*")
+		}
+	}
+	if err != nil {
+		if errors.Is(err, ErrUpstreamNotFound) {
+			http.Error(w, "not found", http.StatusNotFound)
+			return
+		}
+		h.proxy.Logger.Error("metadata fetch failed", "error", err)
+		http.Error(w, "failed to fetch from upstream", http.StatusBadGateway)
+		return
+	}
+
+	h.proxy.writeMetadataCachedResponse(w, r, "maven", cacheKey, body, contentType)
+}
+
 // handleDownload serves an artifact file, fetching and caching from upstream if needed.
 func (h *MavenHandler) handleDownload(w http.ResponseWriter, r *http.Request, urlPath string) {
 	// Parse Maven path: group/artifact/version/filename
@@ -86,6 +122,18 @@ func (h *MavenHandler) handleDownload(w http.ResponseWriter, r *http.Request, ur
 
 	result, err := h.proxy.GetOrFetchArtifactFromURL(r.Context(), "maven", name, version, filename, upstreamURL)
 	if err != nil {
+		if errors.Is(err, ErrUpstreamNotFound) {
+			pluginPortalURL := fmt.Sprintf("%s/%s", h.pluginPortalUpstreamURL, urlPath)
+			h.proxy.Logger.Info("maven artifact not found in primary upstream, trying Gradle Plugin Portal",
+				"group", group, "artifact", artifact, "version", version, "filename", filename)
+			result, err = h.proxy.GetOrFetchArtifactFromURL(r.Context(), "maven", name, version, filename, pluginPortalURL)
+		}
+	}
+	if err != nil {
+		if errors.Is(err, ErrUpstreamNotFound) {
+			http.Error(w, "not found", http.StatusNotFound)
+			return
+		}
 		h.proxy.Logger.Error("failed to get artifact", "error", err)
 		http.Error(w, "failed to fetch artifact", http.StatusBadGateway)
 		return
@@ -115,7 +163,7 @@ func (h *MavenHandler) parsePath(urlPath string) (group, artifact, version, file
 // isArtifactFile returns true if the filename looks like a Maven artifact.
 func (h *MavenHandler) isArtifactFile(filename string) bool {
 	// Common artifact extensions
-	extensions := []string{".jar", ".war", ".ear", ".pom", ".aar", ".klib"}
+	extensions := []string{".jar", ".war", ".ear", ".pom", ".aar", ".klib", ".module"}
 	for _, ext := range extensions {
 		if strings.HasSuffix(filename, ext) {
 			return true
diff --git a/internal/handler/maven_test.go b/internal/handler/maven_test.go
index df6917c..9ca5eb6 100644
--- a/internal/handler/maven_test.go
+++ b/internal/handler/maven_test.go
@@ -52,6 +52,7 @@ func TestMavenIsArtifactFile(t *testing.T) {
 	}{
 		{"guava-32.1.3-jre.jar", true},
 		{"guava-32.1.3-jre.pom", true},
+		{"guava-32.1.3-jre.module", true},
 		{"app-1.0.war", true},
 		{"lib-1.0.aar", true},
 		{"maven-metadata.xml", false},
@@ -65,3 +66,63 @@ func TestMavenIsArtifactFile(t *testing.T) {
 		}
 	}
 }
+
+func TestMavenIsMetadataFile(t *testing.T) {
+	h := &MavenHandler{}
+
+	tests := []struct {
+		name     string
+		filename string
+		want     bool
+	}{
+		{
+			name:     "pom is artifact, not metadata",
+			filename: "com.diffplug.spotless.gradle.plugin-8.4.0.pom",
+			want:     false,
+		},
+		{
+			name:     "pom checksum is metadata",
+			filename: "com.diffplug.spotless.gradle.plugin-8.4.0.pom.sha1",
+			want:     true,
+		},
+		{
+			name:     "metadata file",
+			filename: "maven-metadata.xml",
+			want:     true,
+		},
+		{
+			name:     "metadata checksum",
+			filename: "maven-metadata.xml.sha256",
+			want:     true,
+		},
+		{
+			name:     "jar checksum is metadata",
+			filename: "guava-32.1.3-jre.jar.sha1",
+			want:     true,
+		},
+		{
+			name:     "asc signature is metadata",
+			filename: "guava-32.1.3-jre.jar.asc",
+			want:     true,
+		},
+		{
+			name:     "regular jar is not metadata",
+			filename: "guava-32.1.3-jre.jar",
+			want:     false,
+		},
+		{
+			name:     "pom checksum is metadata",
+			filename: "guava-32.1.3-jre.pom.sha1",
+			want:     true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := h.isMetadataFile(tt.filename)
+			if got != tt.want {
+				t.Errorf("isMetadataFile(%q) = %v, want %v", tt.filename, got, tt.want)
+			}
+		})
+	}
+}
diff --git a/internal/server/server.go b/internal/server/server.go
index 042b3f6..251386e 100644
--- a/internal/server/server.go
+++ b/internal/server/server.go
@@ -193,7 +193,12 @@ func (s *Server) Start() error {
 	hexHandler := handler.NewHexHandler(proxy, s.cfg.BaseURL)
 	pubHandler := handler.NewPubHandler(proxy, s.cfg.BaseURL)
 	pypiHandler := handler.NewPyPIHandler(proxy, s.cfg.BaseURL)
-	mavenHandler := handler.NewMavenHandler(proxy, s.cfg.BaseURL)
+	mavenHandler := handler.NewMavenHandler(
+		proxy,
+		s.cfg.BaseURL,
+		s.cfg.Upstream.Maven,
+		s.cfg.Upstream.GradlePluginPortal,
+	)
 	gradleHandler := handler.NewGradleBuildCacheHandler(proxy)
 	nugetHandler := handler.NewNuGetHandler(proxy, s.cfg.BaseURL)
 	composerHandler := handler.NewComposerHandler(proxy, s.cfg.BaseURL)

From 00b032cb5b9bb758be353f4f000df7bda9996b84 Mon Sep 17 00:00:00 2001
From: Andrew Nesbitt <andrewnez@gmail.com>
Date: Fri, 22 May 2026 19:51:49 +0100
Subject: [PATCH 32/36] Bump git-pkgs deps for v0.4.0 (#146)

---
 go.mod |  8 ++++----
 go.sum | 16 ++++++++--------
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/go.mod b/go.mod
index f3e1bd1..199c8c8 100644
--- a/go.mod
+++ b/go.mod
@@ -7,10 +7,10 @@ require (
 	github.com/CycloneDX/cyclonedx-go v0.11.0
 	github.com/git-pkgs/archives v0.3.0
 	github.com/git-pkgs/cooldown v0.1.1
-	github.com/git-pkgs/enrichment v0.2.2
+	github.com/git-pkgs/enrichment v0.2.3
 	github.com/git-pkgs/purl v0.1.12
-	github.com/git-pkgs/registries v0.6.0
-	github.com/git-pkgs/spdx v0.1.3
+	github.com/git-pkgs/registries v0.6.1
+	github.com/git-pkgs/spdx v0.1.4
 	github.com/git-pkgs/vers v0.2.6
 	github.com/git-pkgs/vulns v0.1.5
 	github.com/go-chi/chi/v5 v5.2.5
@@ -129,7 +129,7 @@ require (
 	github.com/ghostiam/protogetter v0.3.20 // indirect
 	github.com/git-pkgs/packageurl-go v0.3.1 // indirect
 	github.com/git-pkgs/pom v0.1.4 // indirect
-	github.com/github/go-spdx/v2 v2.6.0 // indirect
+	github.com/github/go-spdx/v2 v2.7.0 // indirect
 	github.com/go-critic/go-critic v0.14.3 // indirect
 	github.com/go-logr/logr v1.4.3 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
diff --git a/go.sum b/go.sum
index 481587d..23c3df7 100644
--- a/go.sum
+++ b/go.sum
@@ -254,24 +254,24 @@ github.com/git-pkgs/archives v0.3.0 h1:iXKyO83jEFub1PGEDlHmk2tQ7XeV5LySTc0sEkH3x
 github.com/git-pkgs/archives v0.3.0/go.mod h1:LTJ1iQVFA7otizWMOyiI82NYVmyBWAPRzwu/e30rcXU=
 github.com/git-pkgs/cooldown v0.1.1 h1:9OqqzCB8gANz/y44SmqGD0Jp8Qtu81D1sCbKl6Ehg7w=
 github.com/git-pkgs/cooldown v0.1.1/go.mod h1:v7APuK/UouTiu8mWQZbdDmj7DfxxkGUeuhjaRB5gv9E=
-github.com/git-pkgs/enrichment v0.2.2 h1:vaQu5vs3tjQB5JI0gzBrUCynUc9z3l5byPhgKFaNZrc=
-github.com/git-pkgs/enrichment v0.2.2/go.mod h1:5JWGmlHWcv5HQHUrctcpnRUNpEF5VAixD2z4zvqKejs=
+github.com/git-pkgs/enrichment v0.2.3 h1:42mqoUhQZNGhlEO671pboI/Cu6F+DoffJoFbVhb2jlw=
+github.com/git-pkgs/enrichment v0.2.3/go.mod h1:MBv5nhHzjwLxeSgx2+7waCcpReUjhCD+9B0bvufpMO0=
 github.com/git-pkgs/packageurl-go v0.3.1 h1:WM3RBABQZLaRBxgKyYughc3cVBE8KyQxbSC6Jt5ak7M=
 github.com/git-pkgs/packageurl-go v0.3.1/go.mod h1:rcIxiG37BlQLB6FZfgdj9Fm7yjhRQd3l+5o7J0QPAk4=
 github.com/git-pkgs/pom v0.1.4 h1:C6st+XSbF75eKuwfdkDZZtYHoTcaWRIEQYar5VtszUo=
 github.com/git-pkgs/pom v0.1.4/go.mod h1:ufdMBe1lKzqOeP9IUb9NPZ458xKV8E8NvuyBMxOfwIk=
 github.com/git-pkgs/purl v0.1.12 h1:qCskrEU1LWQhCkIVZd992W5++Bsxazvx2Cx1/65qCvU=
 github.com/git-pkgs/purl v0.1.12/go.mod h1:ofp4mHsR0cUeVONQaf33n6Wxg2QTEvtUdRfCedI8ouA=
-github.com/git-pkgs/registries v0.6.0 h1:ttQC8via9XAoLk9vqysf0K7uWl1bAyHPBWRBavRpAqs=
-github.com/git-pkgs/registries v0.6.0/go.mod h1:BY0YW+V0WDGBMuDR2aSMR3NzOPFK4K+F3j6+ch+cq3M=
-github.com/git-pkgs/spdx v0.1.3 h1:YQou23mLfzbW//6JlHUuc5x1P5VNIIDSku5gvauf86I=
-github.com/git-pkgs/spdx v0.1.3/go.mod h1:4HGGWyC8tg4DjOhrtBTYl4Lu+5i2BFuauGX8zcVcYPg=
+github.com/git-pkgs/registries v0.6.1 h1:xZfVZQmffIfdeJthn5o2EozbVJ6gBeImYwKQnfdKUfU=
+github.com/git-pkgs/registries v0.6.1/go.mod h1:a3BP/56VW3O/CFRqiJCtSy+OqRrSH25wF1PWHP76ka0=
+github.com/git-pkgs/spdx v0.1.4 h1:eQ0waEV3uUeItpWAOvdN1K1rL9hTgsU7fF74r1mDXMs=
+github.com/git-pkgs/spdx v0.1.4/go.mod h1:cqRoZcvl530s/W+oGNvwjt4ODN8T1W6D/20MUZEFdto=
 github.com/git-pkgs/vers v0.2.6 h1:IelZd7BP/JhzTloUTDY67nehUgoYva3g9viqAMCHJg8=
 github.com/git-pkgs/vers v0.2.6/go.mod h1:biTbSQK1qdbrsxDEKnqe3Jzclxz8vW6uDcwKjfUGcOo=
 github.com/git-pkgs/vulns v0.1.5 h1:mtX88/27toFl+B95kaH5QbAdOCQ3YIDGjJrlrrnqQTE=
 github.com/git-pkgs/vulns v0.1.5/go.mod h1:bZFikfrR/5gC0ZMwXh7qcEu2gpKfXMBhVsy4kF12Ae0=
-github.com/github/go-spdx/v2 v2.6.0 h1:Y/Chr7L8oG85Ilbzl11xkUSQFUfG1kGkLP18LyInvhg=
-github.com/github/go-spdx/v2 v2.6.0/go.mod h1:Ftc45YYG1WzpzwEPKRVm9Jv8vDqOrN4gWoCkK+bHer0=
+github.com/github/go-spdx/v2 v2.7.0 h1:GzfXx4wFdlilARxmFRXW/mgUy3A4vSqZocCMFV6XFdQ=
+github.com/github/go-spdx/v2 v2.7.0/go.mod h1:Ftc45YYG1WzpzwEPKRVm9Jv8vDqOrN4gWoCkK+bHer0=
 github.com/go-chi/chi/v5 v5.2.5 h1:Eg4myHZBjyvJmAFjFvWgrqDTXFyOzjj7YIm3L3mu6Ug=
 github.com/go-chi/chi/v5 v5.2.5/go.mod h1:X7Gx4mteadT3eDOMTsXzmI4/rwUpOwBHLpAfupzFJP0=
 github.com/go-critic/go-critic v0.14.3 h1:5R1qH2iFeo4I/RJU8vTezdqs08Egi4u5p6vOESA0pog=

From ee5787838621d912e63d6e3e057425ea30b9f95b Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Thu, 28 May 2026 18:40:15 +0100
Subject: [PATCH 33/36] Bump docker/build-push-action from 7.1.0 to 7.2.0
 (#151)

Bumps [docker/build-push-action](https://github.com/docker/build-push-action) from 7.1.0 to 7.2.0.
- [Release notes](https://github.com/docker/build-push-action/releases)
- [Commits](https://github.com/docker/build-push-action/compare/bcafcacb16a39f128d818304e6c9c0c18556b85f...f9f3042f7e2789586610d6e8b85c8f03e5195baf)

---
updated-dependencies:
- dependency-name: docker/build-push-action
  dependency-version: 7.2.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
---
 .github/workflows/publish.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/publish.yml b/.github/workflows/publish.yml
index e0d3cfb..82ee83c 100644
--- a/.github/workflows/publish.yml
+++ b/.github/workflows/publish.yml
@@ -38,7 +38,7 @@ jobs:
           images: ghcr.io/${{ github.repository }}
 
       - name: Build and push Docker image
-        uses: docker/build-push-action@bcafcacb16a39f128d818304e6c9c0c18556b85f
+        uses: docker/build-push-action@f9f3042f7e2789586610d6e8b85c8f03e5195baf
         with:
           context: .
           push: true

From 946d39f1937f42008028a88da89568e1c9d895ed Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Thu, 28 May 2026 18:40:23 +0100
Subject: [PATCH 34/36] Bump zizmorcore/zizmor-action from 0.5.5 to 0.5.6
 (#152)

Bumps [zizmorcore/zizmor-action](https://github.com/zizmorcore/zizmor-action) from 0.5.5 to 0.5.6.
- [Release notes](https://github.com/zizmorcore/zizmor-action/releases)
- [Commits](https://github.com/zizmorcore/zizmor-action/compare/a16621b09c6db4281f81a93cb393b05dcd7b7165...5f14fd08f7cf1cb1609c1e344975f152c7ee938d)

---
updated-dependencies:
- dependency-name: zizmorcore/zizmor-action
  dependency-version: 0.5.6
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
---
 .github/workflows/zizmor.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/zizmor.yml b/.github/workflows/zizmor.yml
index e34bdc6..f621254 100644
--- a/.github/workflows/zizmor.yml
+++ b/.github/workflows/zizmor.yml
@@ -26,4 +26,4 @@ jobs:
           persist-credentials: false
 
       - name: Run zizmor
-        uses: zizmorcore/zizmor-action@a16621b09c6db4281f81a93cb393b05dcd7b7165 # v0.5.5
+        uses: zizmorcore/zizmor-action@5f14fd08f7cf1cb1609c1e344975f152c7ee938d # v0.5.6

From 65474c77e82f244175bfb443fb91c8710e1a21a5 Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Thu, 28 May 2026 18:40:31 +0100
Subject: [PATCH 35/36] Bump goreleaser/goreleaser-action from 7.2.1 to 7.2.2
 (#153)

Bumps [goreleaser/goreleaser-action](https://github.com/goreleaser/goreleaser-action) from 7.2.1 to 7.2.2.
- [Release notes](https://github.com/goreleaser/goreleaser-action/releases)
- [Commits](https://github.com/goreleaser/goreleaser-action/compare/1a80836c5c9d9e5755a25cb59ec6f45a3b5f41a8...5daf1e915a5f0af01ddbcd89a43b8061ff4f1a89)

---
updated-dependencies:
- dependency-name: goreleaser/goreleaser-action
  dependency-version: 7.2.2
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
---
 .github/workflows/release.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index baba90b..c23de56 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -27,7 +27,7 @@ jobs:
           go-version-file: go.mod
           cache: false
 
-      - uses: goreleaser/goreleaser-action@1a80836c5c9d9e5755a25cb59ec6f45a3b5f41a8 # v7.2.1
+      - uses: goreleaser/goreleaser-action@5daf1e915a5f0af01ddbcd89a43b8061ff4f1a89 # v7.2.2
         with:
           version: "~> v2"
           args: release --clean

From 0e7af4aed6fe47531e3f54665715082faa262b05 Mon Sep 17 00:00:00 2001
From: Andrew Nesbitt <andrewnez@gmail.com>
Date: Tue, 2 Jun 2026 07:59:00 +0100
Subject: [PATCH 36/36] Make metadata size limit configurable (closes #149)
 (#150)

---
 cmd/proxy/main.go                      |  1 +
 docs/configuration.md                  | 10 ++++++
 internal/config/config.go              | 40 ++++++++++++++++++++++
 internal/config/config_test.go         | 46 ++++++++++++++++++++++++++
 internal/handler/conda.go              |  2 +-
 internal/handler/handler.go            | 27 ++++++++-------
 internal/handler/nuget.go              |  2 +-
 internal/handler/read_metadata_test.go | 29 ++++++++++++----
 internal/server/server.go              |  1 +
 9 files changed, 137 insertions(+), 21 deletions(-)

diff --git a/cmd/proxy/main.go b/cmd/proxy/main.go
index a8c8bdf..15a71c0 100644
--- a/cmd/proxy/main.go
+++ b/cmd/proxy/main.go
@@ -470,6 +470,7 @@ func runMirror() {
 	proxy := handler.NewProxy(db, store, fetcher, resolver, logger)
 	proxy.CacheMetadata = true // mirror always caches metadata
 	proxy.MetadataTTL = cfg.ParseMetadataTTL()
+	proxy.MetadataMaxSize = cfg.ParseMetadataMaxSize()
 
 	m := mirror.New(proxy, db, store, logger, *concurrency)
 
diff --git a/docs/configuration.md b/docs/configuration.md
index cf6c101..1310bd0 100644
--- a/docs/configuration.md
+++ b/docs/configuration.md
@@ -265,6 +265,16 @@ Set to `"0"` to always revalidate with upstream (ETag-based conditional requests
 
 When upstream is unreachable and the cached entry is past its TTL, the proxy serves the stale cached copy with a `Warning: 110 - "Response is Stale"` header so clients can tell the data may be outdated.
 
+### Metadata size limit
+
+Upstream metadata responses are buffered in memory before being rewritten and served. `metadata_max_size` caps that buffer to protect against OOM from a misbehaving upstream. Some npm packages with thousands of versions (for example `renovate`) exceed the 100 MB default, so raise this if you see `metadata response exceeds size limit` in the logs.
+
+```yaml
+metadata_max_size: "100MB"   # default
+```
+
+Or via environment variable: `PROXY_METADATA_MAX_SIZE=250MB`.
+
 ## Mirror API
 
 The `/api/mirror` endpoints are disabled by default. Enable them to allow starting mirror jobs via HTTP:
diff --git a/internal/config/config.go b/internal/config/config.go
index 87e23ac..0e8405d 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -96,6 +96,11 @@ type Config struct {
 	// Default: "5m". Set to "0" to always revalidate.
 	MetadataTTL string `json:"metadata_ttl" yaml:"metadata_ttl"`
 
+	// MetadataMaxSize is the maximum size of an upstream metadata response
+	// the proxy will buffer (e.g. "100MB", "250MB"). Responses over this
+	// size return ErrMetadataTooLarge. Default: "100MB".
+	MetadataMaxSize string `json:"metadata_max_size" yaml:"metadata_max_size"`
+
 	// MirrorAPI enables the /api/mirror endpoints for starting mirror jobs via HTTP.
 	// Disabled by default to prevent unauthenticated users from triggering downloads.
 	MirrorAPI bool `json:"mirror_api" yaml:"mirror_api"`
@@ -424,6 +429,9 @@ func (c *Config) LoadFromEnv() {
 	if v := os.Getenv("PROXY_METADATA_TTL"); v != "" {
 		c.MetadataTTL = v
 	}
+	if v := os.Getenv("PROXY_METADATA_MAX_SIZE"); v != "" {
+		c.MetadataMaxSize = v
+	}
 	if v := os.Getenv("PROXY_GRADLE_BUILD_CACHE_READ_ONLY"); v != "" {
 		c.Gradle.BuildCache.ReadOnly = v == "true" || v == "1"
 	}
@@ -513,6 +521,10 @@ func (c *Config) Validate() error {
 		}
 	}
 
+	if err := validateMetadataMaxSize(c.MetadataMaxSize); err != nil {
+		return err
+	}
+
 	if err := c.Health.Validate(); err != nil {
 		return err
 	}
@@ -582,6 +594,7 @@ func (g *GradleBuildCacheConfig) Validate() error {
 const (
 	defaultMetadataTTL                   = 5 * time.Minute  //nolint:mnd // sensible default
 	defaultDirectServeTTL                = 15 * time.Minute //nolint:mnd // sensible default
+	defaultMetadataMaxSize               = 100 << 20
 	defaultGradleBuildCacheMaxUploadSize = 100 << 20
 	defaultGradleBuildCacheSweepInterval = 10 * time.Minute
 	defaultGradleMaxUploadSizeStr        = "100MB"
@@ -601,6 +614,33 @@ func (c *Config) ParseMaxSize() int64 {
 	return size
 }
 
+func validateMetadataMaxSize(s string) error {
+	if s == "" {
+		return nil
+	}
+	size, err := ParseSize(s)
+	if err != nil {
+		return fmt.Errorf("invalid metadata_max_size: %w", err)
+	}
+	if size <= 0 {
+		return fmt.Errorf("invalid metadata_max_size %q: must be positive", s)
+	}
+	return nil
+}
+
+// ParseMetadataMaxSize returns the maximum metadata response size in bytes.
+// Returns 100MB if unset or invalid.
+func (c *Config) ParseMetadataMaxSize() int64 {
+	if c.MetadataMaxSize == "" {
+		return defaultMetadataMaxSize
+	}
+	size, err := ParseSize(c.MetadataMaxSize)
+	if err != nil || size <= 0 {
+		return defaultMetadataMaxSize
+	}
+	return size
+}
+
 // ParseMetadataTTL returns the metadata TTL duration.
 // Returns 5 minutes if unset, 0 if explicitly disabled.
 func (c *Config) ParseMetadataTTL() time.Duration {
diff --git a/internal/config/config_test.go b/internal/config/config_test.go
index 05fec3a..d633c25 100644
--- a/internal/config/config_test.go
+++ b/internal/config/config_test.go
@@ -428,6 +428,52 @@ func TestParseMetadataTTL(t *testing.T) {
 	}
 }
 
+func TestParseMetadataMaxSize(t *testing.T) {
+	tests := []struct {
+		name string
+		size string
+		want int64
+	}{
+		{"unset uses default", "", defaultMetadataMaxSize},
+		{"explicit value", "250MB", 250 << 20},
+		{"bytes", "1024", 1024},
+		{"invalid uses default", "lots", defaultMetadataMaxSize},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			cfg := Default()
+			cfg.MetadataMaxSize = tt.size
+			got := cfg.ParseMetadataMaxSize()
+			if got != tt.want {
+				t.Errorf("ParseMetadataMaxSize() = %d, want %d", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestValidateMetadataMaxSize(t *testing.T) {
+	cfg := Default()
+	cfg.MetadataMaxSize = "not-a-size"
+	if err := cfg.Validate(); err == nil {
+		t.Error("expected validation error for invalid metadata_max_size")
+	}
+
+	cfg.MetadataMaxSize = "0"
+	if err := cfg.Validate(); err == nil {
+		t.Error("expected validation error for zero metadata_max_size")
+	}
+
+	cfg.MetadataMaxSize = "250MB"
+	if err := cfg.Validate(); err != nil {
+		t.Errorf("unexpected error for valid metadata_max_size: %v", err)
+	}
+
+	cfg.MetadataMaxSize = ""
+	if err := cfg.Validate(); err != nil {
+		t.Errorf("unexpected error for unset metadata_max_size: %v", err)
+	}
+}
+
 func TestValidateMetadataTTL(t *testing.T) {
 	cfg := Default()
 	cfg.MetadataTTL = "invalid"
diff --git a/internal/handler/conda.go b/internal/handler/conda.go
index 1336f94..cfa20c8 100644
--- a/internal/handler/conda.go
+++ b/internal/handler/conda.go
@@ -161,7 +161,7 @@ func (h *CondaHandler) handleRepodata(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	body, err := ReadMetadata(resp.Body)
+	body, err := h.proxy.ReadMetadata(resp.Body)
 	if err != nil {
 		http.Error(w, "failed to read response", http.StatusInternalServerError)
 		return
diff --git a/internal/handler/handler.go b/internal/handler/handler.go
index 3df2777..d06ca83 100644
--- a/internal/handler/handler.go
+++ b/internal/handler/handler.go
@@ -52,23 +52,25 @@ const contentTypeJSON = "application/json"
 
 const headerAcceptEncoding = "Accept-Encoding"
 
-// maxMetadataSize is the maximum size of upstream metadata responses (100 MB).
-// Package metadata (e.g. npm with many versions) can be large, but unbounded
-// reads risk OOM if an upstream misbehaves.
-const maxMetadataSize = 100 << 20
+// defaultMetadataMaxSize is used when Proxy.MetadataMaxSize is unset.
+const defaultMetadataMaxSize = 100 << 20
 
-// ErrMetadataTooLarge is returned when upstream metadata exceeds maxMetadataSize.
+// ErrMetadataTooLarge is returned when upstream metadata exceeds the configured limit.
 var ErrMetadataTooLarge = errors.New("metadata response exceeds size limit")
 
 // ReadMetadata reads an upstream response body with a size limit to prevent OOM
 // from unexpectedly large responses. Returns ErrMetadataTooLarge if the response
 // is truncated by the limit.
-func ReadMetadata(r io.Reader) ([]byte, error) {
-	data, err := io.ReadAll(io.LimitReader(r, maxMetadataSize+1))
+func (p *Proxy) ReadMetadata(r io.Reader) ([]byte, error) {
+	limit := p.MetadataMaxSize
+	if limit <= 0 {
+		limit = defaultMetadataMaxSize
+	}
+	data, err := io.ReadAll(io.LimitReader(r, limit+1))
 	if err != nil {
 		return nil, err
 	}
-	if int64(len(data)) > maxMetadataSize {
+	if int64(len(data)) > limit {
 		return nil, ErrMetadataTooLarge
 	}
 	return data, nil
@@ -84,6 +86,7 @@ type Proxy struct {
 	Cooldown            *cooldown.Config
 	CacheMetadata       bool
 	MetadataTTL         time.Duration
+	MetadataMaxSize     int64
 	GradleReadOnly      bool
 	GradleMaxUploadSize int64
 	DirectServe         bool
@@ -474,7 +477,7 @@ func (p *Proxy) FetchOrCacheMetadata(ctx context.Context, ecosystem, cacheKey, u
 			cached, readErr := p.Storage.Open(ctx, entry.StoragePath)
 			if readErr == nil {
 				defer func() { _ = cached.Close() }()
-				data, readErr := ReadMetadata(cached)
+				data, readErr := p.ReadMetadata(cached)
 				if readErr == nil {
 					ct := contentTypeJSON
 					if entry.ContentType.Valid {
@@ -519,7 +522,7 @@ func (p *Proxy) FetchOrCacheMetadata(ctx context.Context, ecosystem, cacheKey, u
 	}
 	defer func() { _ = cached.Close() }()
 
-	data, readErr := ReadMetadata(cached)
+	data, readErr := p.ReadMetadata(cached)
 	if readErr != nil {
 		return nil, "", fmt.Errorf("upstream failed and cached read error: %w", err)
 	}
@@ -561,7 +564,7 @@ func (p *Proxy) fetchUpstreamMetadata(ctx context.Context, upstreamURL string, e
 			return nil, "", "", zeroTime, errStale304
 		}
 		defer func() { _ = cached.Close() }()
-		data, readErr := ReadMetadata(cached)
+		data, readErr := p.ReadMetadata(cached)
 		if readErr != nil {
 			return nil, "", "", zeroTime, errStale304
 		}
@@ -583,7 +586,7 @@ func (p *Proxy) fetchUpstreamMetadata(ctx context.Context, upstreamURL string, e
 		return nil, "", "", zeroTime, fmt.Errorf("upstream returned %d", resp.StatusCode)
 	}
 
-	body, err := ReadMetadata(resp.Body)
+	body, err := p.ReadMetadata(resp.Body)
 	if err != nil {
 		return nil, "", "", zeroTime, fmt.Errorf("reading response: %w", err)
 	}
diff --git a/internal/handler/nuget.go b/internal/handler/nuget.go
index 3cce7f8..40b8b5f 100644
--- a/internal/handler/nuget.go
+++ b/internal/handler/nuget.go
@@ -193,7 +193,7 @@ func (h *NuGetHandler) handleRegistration(w http.ResponseWriter, r *http.Request
 		return
 	}
 
-	body, err := ReadMetadata(resp.Body)
+	body, err := h.proxy.ReadMetadata(resp.Body)
 	if err != nil {
 		http.Error(w, "failed to read response", http.StatusInternalServerError)
 		return
diff --git a/internal/handler/read_metadata_test.go b/internal/handler/read_metadata_test.go
index 60c1cf2..b13bddb 100644
--- a/internal/handler/read_metadata_test.go
+++ b/internal/handler/read_metadata_test.go
@@ -7,9 +7,12 @@ import (
 )
 
 func TestReadMetadata(t *testing.T) {
+	const limit = 1024
+	p := &Proxy{MetadataMaxSize: limit}
+
 	t.Run("small body", func(t *testing.T) {
 		data := []byte("hello world")
-		got, err := ReadMetadata(bytes.NewReader(data))
+		got, err := p.ReadMetadata(bytes.NewReader(data))
 		if err != nil {
 			t.Fatalf("unexpected error: %v", err)
 		}
@@ -19,27 +22,39 @@ func TestReadMetadata(t *testing.T) {
 	})
 
 	t.Run("exactly at limit", func(t *testing.T) {
-		data := make([]byte, maxMetadataSize)
+		data := make([]byte, limit)
 		for i := range data {
 			data[i] = 'x'
 		}
-		got, err := ReadMetadata(bytes.NewReader(data))
+		got, err := p.ReadMetadata(bytes.NewReader(data))
 		if err != nil {
 			t.Fatalf("unexpected error: %v", err)
 		}
-		if len(got) != int(maxMetadataSize) {
-			t.Errorf("got length %d, want %d", len(got), maxMetadataSize)
+		if len(got) != limit {
+			t.Errorf("got length %d, want %d", len(got), limit)
 		}
 	})
 
 	t.Run("over limit returns error", func(t *testing.T) {
-		data := make([]byte, maxMetadataSize+100)
+		data := make([]byte, limit+100)
 		for i := range data {
 			data[i] = 'x'
 		}
-		_, err := ReadMetadata(bytes.NewReader(data))
+		_, err := p.ReadMetadata(bytes.NewReader(data))
 		if !errors.Is(err, ErrMetadataTooLarge) {
 			t.Errorf("got error %v, want ErrMetadataTooLarge", err)
 		}
 	})
+
+	t.Run("zero limit uses default", func(t *testing.T) {
+		p := &Proxy{}
+		data := make([]byte, 1<<20)
+		got, err := p.ReadMetadata(bytes.NewReader(data))
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if len(got) != len(data) {
+			t.Errorf("got length %d, want %d", len(got), len(data))
+		}
+	})
 }
diff --git a/internal/server/server.go b/internal/server/server.go
index 251386e..7de5041 100644
--- a/internal/server/server.go
+++ b/internal/server/server.go
@@ -160,6 +160,7 @@ func (s *Server) Start() error {
 	proxy.Cooldown = cd
 	proxy.CacheMetadata = s.cfg.CacheMetadata
 	proxy.MetadataTTL = s.cfg.ParseMetadataTTL()
+	proxy.MetadataMaxSize = s.cfg.ParseMetadataMaxSize()
 	proxy.GradleReadOnly = s.cfg.Gradle.BuildCache.ReadOnly
 	proxy.GradleMaxUploadSize = s.cfg.ParseGradleBuildCacheMaxUploadSize()
 	proxy.DirectServe = s.cfg.Storage.DirectServe