A cold `dnf makecache` against a github_rpm remote with many release
assets 500s on the first request: ServeRemote derives metadata for every
asset synchronously on the inbound request context, so once dnf hits its
makecache timeout and disconnects the canceled request context both
aborts the in-flight derive and poisons the subsequent repodata DB read,
which surfaces as HTTP 500. It only "works" on a lucky client retry that
finds the partially-populated cache fresh.
- detach the release scan to a background, timeout-bounded context so a
client cancel can neither abort the shared derive nor cancel the read
- single-flight the scan per remote so concurrent requests never launch
duplicate derives
- serve the current cache immediately when it is non-empty and derive in
the background; only a completely empty cache blocks on a bounded first
scan
- serve repodata on a context detached from the request, and treat a
canceled/deadline-exceeded metadata read as a retryable 503 instead of
a hard 500
unkinben
9ba96ace41