Drop the session cookie if it's useless#2865
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Drop the session cookie if it's useless, to improve our CDN caching. A browser that received a session cookie (e.g. just logged out, or shown a stored flash) keeps sending it until the browser closes. Then the Fastly rule passes every such request to origin and the user never gets the CDN-cached anonymous pages. The method omit_session_cookie only skips *writing* a cookie; it can't remove one the browser already holds. This commit adds an after_action, drop_unneeded_session_cookie, that actively expires the cookie when: the browser sent it, the user is not logged in, there is no flash to carry, and the session holds no real per-user content. The "real content" check (session_has_user_content?) ignores framework bookkeeping keys (Rack's always-present session_id and a spent flash) and is read-only, since mutating the session itself generates a session_id. It fails safe: unknown keys count as content, and anonymous requests that did not send the cookie get no Set-Cookie at all (so cached responses are never polluted). SESSION_COOKIE_NAME is read from config so a cookie rename stays correct. Tests (test/integration/drop_session_cookie_test.rb) check various cases. They assert the observable cookie outcome (not middleware internals) across: spent cookie deleted, no-cookie emits nothing, logged-in kept, CSRF-token kept, flash-display kept, and spent-flash gone on the next request. Co-Authored-By: David A. Wheeler <dwheeler@dwheeler.com> Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> Signed-off-by: David A. Wheeler <dwheeler@dwheeler.com>
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #2865 +/- ##
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Files 79 79
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Drop the session cookie if it's useless, to improve our CDN caching.
A browser that received a session cookie (e.g. just logged out, or shown a stored flash) keeps sending it until the browser closes. Then the Fastly rule passes every such request to origin and the user never gets the CDN-cached anonymous pages. The method omit_session_cookie only skips writing a cookie; it can't remove one the browser already holds.
This commit adds an after_action, drop_unneeded_session_cookie, that actively expires the cookie when: the browser sent it, the user is not logged in, there is no
flash to carry, and the session holds no real per-user content. The "real content" check (session_has_user_content?) ignores framework bookkeeping keys (Rack's always-present session_id and a spent flash) and is read-only, since mutating the session itself generates a session_id. It fails safe: unknown keys count as content, and anonymous requests that did not send the cookie get no Set-Cookie at all (so cached responses are never polluted).
SESSION_COOKIE_NAME is read from config so a cookie rename stays correct.
Tests (test/integration/drop_session_cookie_test.rb) check various cases. They assert the observable
cookie outcome (not middleware internals) across: spent cookie deleted, no-cookie emits nothing, logged-in kept, CSRF-token kept, flash-display kept, and spent-flash gone on the next request.