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…request modes Serve expired entries within their stale-while-revalidate window in the generic middleware path not only when the request sends max-stale. This updates stale validation to honor response-side stale-while-revalidate in strict mode, and moves generic background revalidation onto a detached request context so async refresh can complete after the client request ends. Also adds regression coverage for stale-while-revalidate behavior in strict and bypass_request modes, plus an RFC-level test for SWR stale age validation.
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Summary
A soft purge marks cached entries stale instead of deleting them immediately, so the stale response can still be served while a background refresh or revalidation updates the object. This is similar to Nginx
fastcgi_cache_use_stale: updating.Created this while researching alternatives to Fastly's surrogate keys with soft purge, as it is super useful for large publishers that frequently publish content and want to ensure that end-user never experience slow response time (arriving on cold, invalidated responses).
Changes
Souin-Purge-Mode: softheaderCache-Status ... fwd=stale/flushbypass_requestbehavior unchanged for normal request handlingflushwhen clearing surrogate indexesCaddy / middleware fixes included
This also fixes the background revalidation path used by Caddy so the refresh does not reuse a canceled request context.
It also restores generic
stale-while-revalidatebehavior instrictandbypass_requestmodes.Tests
Added coverage for:
304 Not Modifiedbypass_requestbehavior with soft purgestale-while-revalidateinstrictmodestale-while-revalidateinbypass_requestmodeServerheaderRelated
stale-while-revalidatenot triggering background revalidation in eitherbypass_requestorstrictmode #684Disclaimer: GPT-5.4 was used to create the majority of this change.