The Helm index.yaml and PyPI simple pages and JSON API documents were
parsed and rewritten on every request, cache hits and conditional
requests included. They now go through the rewrite cache like npm and
Composer, so a repeat request is served from memory with an ETag of
its own, a dated Last-Modified, a gzip copy and 304 when it matches.
PyPI simple pages are keyed by their content type and the versions
filtered out as well as the upstream page. Download hrefs are now
rewritten with a literal prefix search that makes the same changes as
the old regular expression, and the link filter's expressions are
compiled once.
A chart cache miss no longer parses the whole Helm index again while
the stored index is unchanged: the chart downloads it lists are kept
per repository, keyed by the index digest.
