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caddyhttp: demote Alt-Svc ErrNoAltSvcPort to debug level - #8000
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When HTTP/3 is enabled, ServeListener runs in a background goroutine. If early HTTP/1 or HTTP/2 requests arrive before that goroutine registers the listener with quic-go, SetQUICHeaders returns http3.ErrNoAltSvcPort. Because Alt-Svc is an opportunistic advertisement header and this startup window is transient, log ErrNoAltSvcPort at debug level instead of error level to avoid spurious error logs during startup and reloads.
francislavoie
approved these changes
Sep 7, 2026
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When HTTP/3 is enabled, ServeListener runs in a background goroutine. If early HTTP/1 or HTTP/2 requests arrive before that goroutine registers the listener with quic-go, SetQUICHeaders returns http3.ErrNoAltSvcPort.
Because Alt-Svc is an opportunistic advertisement header and this startup window is transient, log
ErrNoAltSvcPort at debug level instead of error level to avoid spurious error logs during startup and reloads.
Assistance Disclosure
I used Gemini to find the source of the problem and devise a fix. I verified the code and tested it in production.