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Josh FreeandCopilot
2acfe7e829
Fixes #27627. ## What The chat diff-status gitsync worker polls open pull requests on a fixed 10s interval and re-downloads the full JSON body every tick, even when nothing changed, because the GitHub client never sends `If-None-Match` / ETag. This adds a small, concurrency-safe, bounded in-memory ETag+body cache (`coderd/externalauth/gitprovider/conditional.go`) and wires it into `githubProvider.decodeJSON`. When an ETag is cached for a request, we send `If-None-Match`; on `304 Not Modified` we decode the cached body; on `200` we cache `{etag, body}` when an ETag is present and the body is under a size cap. ## Why `304` responses do not count against GitHub's primary rate limit, but full `200`s do. Today every unchanged poll burns quota that the same token also needs for interactive Git and API operations, so busy instances can hit rate-limit errors and stalls elsewhere. Unchanged PRs now revalidate for free with no behavior change; only genuine changes transfer a body. ## Details - Cache key = request URL + a hash of the token, so one token's response is never served under another; raw tokens are not retained. - Bounded by entry count (LRU eviction, default 2048) and per-body size (1 MiB) to cap memory. - Scope limited to the JSON reads through `decodeJSON`; the raw-diff path (`fetchDiff`, up to `MaxDiffSize`) is intentionally left out to avoid caching large bodies. ## Tests `TestConditionalRequestReuse` in `github_test.go` covers: - `NotModifiedReusesCachedBody` — a warm poll sends `If-None-Match` with the prior ETag and reuses the cached body on `304`, yielding the same result with exactly two upstream requests. - `DifferentTokenDoesNotShareCache` — a different token never sends another token's cached ETag. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 4959e1f9-f8e6-4e97-a487-f395a0123c79