Queue-Proxy adds header to response after ServeHTTP() is called

[bonavadeur]

Hi everyone,

In Knative Serving, specifically in the file pkg/queue/request_metric.go, within the function func (h *requestMetricsHandler) ServeHTTP(), how can I add a header to the response packet after h.next.ServeHTTP() is called? I attempted to add a header using the w parameter inside a deferred func(), but it didn't work.

func (h *requestMetricsHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
    rr := pkghttp.NewResponseRecorder(w, http.StatusOK)
    startTime := time.Now()
    defer func() {
        // Filter probe requests for revision metrics.
        if netheader.IsProbe(r) {
            return
        }
        // If ServeHTTP panics, recover, record the failure and panic again.
        err := recover()
        latency := time.Since(startTime)
        routeTag := GetRouteTagNameFromRequest(r)
        if err != nil {
            ctx := metrics.AugmentWithResponseAndRouteTag(h.statsCtx,
                http.StatusInternalServerError, routeTag)
            pkgmetrics.RecordBatch(ctx, requestCountM.M(1),
                responseTimeInMsecM.M(float64(latency.Milliseconds())))
            panic(err)
        }
        ctx := metrics.AugmentWithResponseAndRouteTag(h.statsCtx,
            rr.ResponseCode, routeTag)
        pkgmetrics.RecordBatch(ctx, requestCountM.M(1),
            responseTimeInMsecM.M(float64(latency.Milliseconds())))
    }()
    h.next.ServeHTTP(rr, r)
}

Thanks so much for help.

[skonto]

Hi @bonavadeur pls take a look here for a similar question.

You could however do:

diff --git a/pkg/queue/sharedmain/handlers.go b/pkg/queue/sharedmain/handlers.go
index 91aebfc77..8f6453ec9 100644
--- a/pkg/queue/sharedmain/handlers.go
+++ b/pkg/queue/sharedmain/handlers.go
@@ -51,6 +51,10 @@ func mainHandler(
        httpProxy.ErrorHandler = pkghandler.Error(logger)
        httpProxy.BufferPool = netproxy.NewBufferPool()
        httpProxy.FlushInterval = netproxy.FlushInterval
+       httpProxy.ModifyResponse = func(response *http.Response) error {
+               response.Header.Add("test", "test")
+               return nil
+       }
 
        breaker := buildBreaker(logger, env)
        tracingEnabled := env.TracingConfigBackend != tracingconfig.None


$ curl -v -H "Host: helloworld-go.default.example.com" http://192.168.39.148:30874
*   Trying 192.168.39.148:30874...
* Connected to 192.168.39.148 (192.168.39.148) port 30874
> GET / HTTP/1.1
> Host: helloworld-go.default.example.com
> User-Agent: curl/8.6.0
> Accept: */*
> 
< HTTP/1.1 200 OK
< content-length: 20
< content-type: text/plain; charset=utf-8
< date: Wed, 04 Dec 2024 16:44:52 GMT
< test: test
< x-envoy-upstream-service-time: 3
< server: envoy
< 
Hello Go Sample v1!
* Connection #0 to host 192.168.39.148 left intact

There is a similar answer to this here: #15606. Could you pls close the tickets if that works for you?