reverseproxy: make stream copy buffer size configurable (#7627)

modules/caddyhttp/reverseproxy/streaming.go

@@ -204,7 +204,12 @@ func (h *Handler) handleUpgradeResponse(logger *zap.Logger, wg *sync.WaitGroup,
 	defer deleteFrontConn()
 	defer deleteBackConn()
 
-	spc := switchProtocolCopier{user: conn, backend: backConn, wg: wg}
+	spc := switchProtocolCopier{
+		user:       conn,
+		backend:    backConn,
+		wg:         wg,
+		bufferSize: h.StreamBufferSize,
+	}
 
 	// setup the timeout if requested
 	var timeoutc <-chan time.Time
@@ -636,20 +641,29 @@ func (m *maxLatencyWriter) stop() {
 type switchProtocolCopier struct {
 	user, backend io.ReadWriteCloser
 	wg            *sync.WaitGroup
+	bufferSize    int
 }
 
 func (c switchProtocolCopier) copyFromBackend(errc chan<- error) {
-	_, err := io.Copy(c.user, c.backend)
+	_, err := io.CopyBuffer(c.user, c.backend, c.buffer())
 	errc <- err
 	c.wg.Done()
 }
 
 func (c switchProtocolCopier) copyToBackend(errc chan<- error) {
-	_, err := io.Copy(c.backend, c.user)
+	_, err := io.CopyBuffer(c.backend, c.user, c.buffer())
 	errc <- err
 	c.wg.Done()
 }
 
+func (c switchProtocolCopier) buffer() []byte {
+	size := c.bufferSize
+	if size <= 0 {
+		size = defaultBufferSize
+	}
+	return make([]byte, size)
+}
+
 var streamingBufPool = sync.Pool{
 	New: func() any {
 		// The Pool's New function should generally only return pointer