specifying features.knative.dev/http-full-duplex and h2c container port breaks the app

[dprotaso]

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: hoge
  namespace: hoge
spec:
  template:
    metadata:
      annotations:
        autoscaling.knative.dev/minScale: "0"
        features.knative.dev/http-full-duplex: Enabled
        instrumentation.opentelemetry.io/inject-nodejs: opentelemetry-collector/instrumentation
        refresh: "true"
      creationTimestamp: null
    spec:
      containerConcurrency: 0
      containers:
      - envFrom:
        - secretRef:
            name: hoge
        image: xxxxx
        name: hoge
        ports:
        - containerPort: 50052
          name: h2c
          protocol: TCP
        readinessProbe:
          successThreshold: 1
          tcpSocket:
            port: 0
        resources:
          limits:
            memory: 500Mi
          requests:
            cpu: 10m
            memory: 300Mi
      responseStartTimeoutSeconds: 1800
      serviceAccountName: hoge
      timeoutSeconds: 60
  traffic:
  - latestRevision: true
    percent: 100

You'll see in the queue-proxy logs Unable to enable full duplex and it doesn't work

{"severity":"error","timestamp":"2025-01-13T04:25:38.690Z","logger":"queueproxy","caller":"sharedmain/handlers.go:137","message":"Unable to enable full duplex","commit":"6a27004","knative.dev/key":"xxx/xxxx","knative.dev/pod":"xxxx","error":"feature not supported","stacktrace":"knative.dev/serving/pkg/queue/sharedmain.mainHandler.withFullDuplex.func5\n\tknative.dev/serving/pkg/queue/sharedmain/handlers.go:137\nnet/http.HandlerFunc.ServeHTTP\n\tnet/http/server.go:2171\nknative.dev/pkg/network/handlers.(*Drainer).ServeHTTP\n\tknative.dev/pkg@v0.0.0-20241021183759-9b9d535af5ad/network/handlers/drain.go:113\ngolang.org/x/net/http2.(*serverConn).runHandler\n\tgolang.org/x/net@v0.30.0/http2/server.go:2439"}

[skonto]

@dprotaso This comes from the fact that HTTP2 is used (h2c, http2 cleartext) along with the full-duplex feature. The latter was meant for HTTP1. Am I missing something? Copying from net/http:

// EnableFullDuplex indicates that the request handler will interleave reads from [Request.Body]
// with writes to the [ResponseWriter].
//
// For HTTP/1 requests, the Go HTTP server by default consumes any unread portion of
// the request body before beginning to write the response, preventing handlers from
// concurrently reading from the request and writing the response.
// Calling EnableFullDuplex disables this behavior and permits handlers to continue to read
// from the request while concurrently writing the response.
//
// For HTTP/2 requests, the Go HTTP server always permits concurrent reads and responses.
func (c *ResponseController) EnableFullDuplex() error {
	rw := c.rw
	for {
		switch t := rw.(type) {
		case interface{ EnableFullDuplex() error }:
			return t.EnableFullDuplex()
		case rwUnwrapper:
			rw = t.Unwrap()
		default:
			return errNotSupported()
		}
	}
}

Should we catch this earlier e.g. when we validate the revision?