Mirroring pkg:helm PURLs failed with an unsupported ecosystem error. The
namespace now names the upstream.helm repository, as the Helm handler
caches charts per repository: pkg:helm/{repository}/{chart}@{version}.
The chart is found in the repository's index through the handler's own
index lookup, fetched from the first URL the release lists, as helm does,
checked against the listed digest and cached under the repository,
digest and filename the handler serves it from. The index goes through
the metadata cache, so helm finds the chart there while the repository is
down. Unversioned PURLs list every version in the index.
Charts without a repository, from an unconfigured one, or listed in an
OCI registry are refused; the last are pulled through /v2, and the error
names the pkg:oci PURL that mirrors them.
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.
