fix: discard buffered headers of the dropped 503 response - #60
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antoinemichea wants to merge 1 commit into
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fix: discard buffered headers of the dropped 503 response#60antoinemichea wants to merge 1 commit into
antoinemichea wants to merge 1 commit into
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When the load balancer aborts with http.Error(503) because the service
has no available server (e.g. a scaled-to-zero backend waking up), the
response writer drops the status code and the body, but kept the
headers http.Error wrote into the buffered map ("Content-Type:
text/plain; charset=utf-8", "X-Content-Type-Options: nosniff"). On the
final flush they leaked into the waiting page and overrode its
text/html Content-Type — browsers rendered the page as plain text.
Reset the buffered headers when discarding the 503 so the waiting page
keeps its own headers.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Fixes #59.
What
When the load balancer aborts with
http.Error(503)(service with no available server — typical for a scaled-to-zero backend whose session is ready but whose pods are still starting), the buffering writer drops the 503's status and body but keeps the headershttp.Errorwrote into the buffered map (Content-Type: text/plain; charset=utf-8,X-Content-Type-Options: nosniff). The finalWriteHeaderflush then merges them over the waiting page's own headers: the page is served astext/plainand browsers render the raw HTML as text (full mechanism in #59).How
Reset the buffered header map inside the not-ready-503 guard: if the 503 response is discarded, everything it wrote is discarded, headers included.
Tests
TestSablierMiddleware_ServeHTTP_WaitingPageContentTypeAfterLB503— end-to-end throughServeHTTP: Sablier answersready+Content-Type: text/html, the next handler doeshttp.Error(503)without firing the httptrace callbacks (exactly what Traefik's load balancer does with no backend). Asserts the waiting page keepsContent-Type: text/htmland noX-Content-Type-Optionsleaks. Fails onmain, passes with the fix.Independent from #58 (different lines, both branches based on
main); together they cover the two ways the buffered flush corrupts the final response.