1 files changed, 28 insertions, 33 deletions

diff --git a/src/net/http/httputil/reverseproxy.go b/src/net/http/httputil/reverseproxy.go
index eece455ac6..2a76b0b8dc 100644
--- a/src/net/http/httputil/reverseproxy.go
+++ b/src/net/http/httputil/reverseproxy.go
@@ -524,9 +524,7 @@ func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 		// Force chunking if we saw a response trailer.
 		// This prevents net/http from calculating the length for short
 		// bodies and adding a Content-Length.
-		if fl, ok := rw.(http.Flusher); ok {
-			fl.Flush()
-		}
+		http.NewResponseController(rw).Flush()
 	}
 
 	if len(res.Trailer) == announcedTrailers {
@@ -601,21 +599,22 @@ func (p *ReverseProxy) flushInterval(res *http.Response) time.Duration {
 	return p.FlushInterval
 }
 
-func (p *ReverseProxy) copyResponse(dst io.Writer, src io.Reader, flushInterval time.Duration) error {
+func (p *ReverseProxy) copyResponse(dst http.ResponseWriter, src io.Reader, flushInterval time.Duration) error {
+	var w io.Writer = dst
+
 	if flushInterval != 0 {
-		if wf, ok := dst.(writeFlusher); ok {
-			mlw := &maxLatencyWriter{
-				dst:     wf,
-				latency: flushInterval,
-			}
-			defer mlw.stop()
+		mlw := &maxLatencyWriter{
+			dst:     dst,
+			flush:   http.NewResponseController(dst).Flush,
+			latency: flushInterval,
+		}
+		defer mlw.stop()
 
-			// set up initial timer so headers get flushed even if body writes are delayed
-			mlw.flushPending = true
-			mlw.t = time.AfterFunc(flushInterval, mlw.delayedFlush)
+		// set up initial timer so headers get flushed even if body writes are delayed
+		mlw.flushPending = true
+		mlw.t = time.AfterFunc(flushInterval, mlw.delayedFlush)
 
-			dst = mlw
-		}
+		w = mlw
 	}
 
 	var buf []byte
@@ -623,7 +622,7 @@ func (p *ReverseProxy) copyResponse(dst io.Writer, src io.Reader, flushInterval
 		buf = p.BufferPool.Get()
 		defer p.BufferPool.Put(buf)
 	}
-	_, err := p.copyBuffer(dst, src, buf)
+	_, err := p.copyBuffer(w, src, buf)
 	return err
 }
 
@@ -668,13 +667,9 @@ func (p *ReverseProxy) logf(format string, args ...any) {
 	}
 }
 
-type writeFlusher interface {
-	io.Writer
-	http.Flusher
-}
-
 type maxLatencyWriter struct {
-	dst     writeFlusher
+	dst     io.Writer
+	flush   func() error
 	latency time.Duration // non-zero; negative means to flush immediately
 
 	mu           sync.Mutex // protects t, flushPending, and dst.Flush
@@ -687,7 +682,7 @@ func (m *maxLatencyWriter) Write(p []byte) (n int, err error) {
 	defer m.mu.Unlock()
 	n, err = m.dst.Write(p)
 	if m.latency < 0 {
-		m.dst.Flush()
+		m.flush()
 		return
 	}
 	if m.flushPending {
@@ -708,7 +703,7 @@ func (m *maxLatencyWriter) delayedFlush() {
 	if !m.flushPending { // if stop was called but AfterFunc already started this goroutine
 		return
 	}
-	m.dst.Flush()
+	m.flush()
 	m.flushPending = false
 }
 
@@ -739,17 +734,19 @@ func (p *ReverseProxy) handleUpgradeResponse(rw http.ResponseWriter, req *http.R
 		return
 	}
 
-	hj, ok := rw.(http.Hijacker)
-	if !ok {
-		p.getErrorHandler()(rw, req, fmt.Errorf("can't switch protocols using non-Hijacker ResponseWriter type %T", rw))
-		return
-	}
 	backConn, ok := res.Body.(io.ReadWriteCloser)
 	if !ok {
 		p.getErrorHandler()(rw, req, fmt.Errorf("internal error: 101 switching protocols response with non-writable body"))
 		return
 	}
 
+	rc := http.NewResponseController(rw)
+	conn, brw, hijackErr := rc.Hijack()
+	if errors.Is(hijackErr, http.ErrNotSupported) {
+		p.getErrorHandler()(rw, req, fmt.Errorf("can't switch protocols using non-Hijacker ResponseWriter type %T", rw))
+		return
+	}
+
 	backConnCloseCh := make(chan bool)
 	go func() {
 		// Ensure that the cancellation of a request closes the backend.
@@ -760,12 +757,10 @@ func (p *ReverseProxy) handleUpgradeResponse(rw http.ResponseWriter, req *http.R
 		}
 		backConn.Close()
 	}()
-
 	defer close(backConnCloseCh)
 
-	conn, brw, err := hj.Hijack()
-	if err != nil {
-		p.getErrorHandler()(rw, req, fmt.Errorf("Hijack failed on protocol switch: %v", err))
+	if hijackErr != nil {
+		p.getErrorHandler()(rw, req, fmt.Errorf("Hijack failed on protocol switch: %v", hijackErr))
 		return
 	}
 	defer conn.Close()