From 5e8875885206d90ffe2cbe42ed7dcc5b61ebe4b4 Mon Sep 17 00:00:00 2001
From: Andrew Nesbitt <andrewnez@gmail.com>
Date: Mon, 4 May 2026 11:33:35 +0100
Subject: [PATCH 01/21] Add .golangci.yml and clear gocognit/goconst findings

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 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 02/21] 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 03/21] 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 04/21] 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 05/21] 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 06/21] 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 07/21] 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 08/21] 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 09/21] 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 10/21] 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 11/21] 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 12/21] 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 13/21] 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 14/21] 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 15/21] 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 16/21] 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 17/21] 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 18/21] 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 19/21] 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 20/21] 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 21/21] 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