Bug 2055001 - Github Pull Requests: Look for etag value before fetching pull request data to cut down on rate limiting

[dklawren]

Changes

lib/Constants.pm

• GITHUB_CACHE_SECONDS: 300 → 900 (15-min freshness window), with an updated comment explaining revalidation is now cheap.
• Added GITHUB_REVALIDATE_SECONDS => 86_400 (24h hard memcached TTL so ETags outlive the freshness window), and exported it.
• Left GITHUB_ERROR_CACHE_SECONDS at 60.

lib/API/V1/PullRequests.pm

• Versioned cache wrapper under a new github_pr.v2. key prefix. The stored value is now { pr_data, pr_etag, reviews_etag, fresh_until }, written with a hard TTL of GITHUB_REVALIDATE_SECONDS; freshness is tracked in-band via fresh_until. Old bare-$pr_data entries are simply ignored and expire on their own.
• Rewrote _fetch_pull_request into three paths: fresh hit (serve, zero calls), stale-hit-with-etags (revalidate), and miss/no-etags (full fetch).
• New _revalidate_pull_request does conditional GETs on both the PR and reviews endpoints — reusing cached fields on 304, recomputing on 200, treating a PR error as fatal (→ inaccessible) and a reviews error as non-fatal (→ empty), matching current behavior.
• _github_get gained conditional-request support ($etag arg → If-None-Match), returning { ok, not_modified, status, etag, data }. It explicitly treats HTTP 304 as success and carries the echoed ETag through.
• New _warn_fetch_failure classifies failures for logging: 401/403 → auth/permission message (token problem), 404 → not-found/private message, anything else → the original generic warning. Applied at both the PR and reviews failure sites.
• Extracted _pr_summary_fields and _store_wrapper helpers.

Behavior visible to users is unchanged; the API shape is identical.

[Copilot]

Pull request overview

Adds ETag-based GitHub PR cache revalidation to reduce API rate-limit consumption.

Changes:

• Introduces separate freshness and hard cache TTLs.
• Adds conditional PR/review requests and versioned cache wrappers.
• Improves GitHub failure logging.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
extensions/GitHubPullRequests/lib/Constants.pm	Defines cache freshness and revalidation TTLs.
extensions/GitHubPullRequests/lib/API/V1/PullRequests.pm	Implements ETag caching, revalidation, and failure classification.

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