Proxy: When connecting to websocket backend, reuse the connection isntead of starting a new one.

caddyhttp/proxy/reverseproxy.go

@@ -183,9 +183,80 @@ var hopHeaders = []string{
 
 type respUpdateFn func(resp *http.Response)
 
+type hijackedConn struct {
+	net.Conn
+	hj *connHijackerTransport
+}
+
+func (c *hijackedConn) Read(b []byte) (n int, err error) {
+	n, err = c.Conn.Read(b)
+	c.hj.Replay = append(c.hj.Replay, b[:n]...)
+	return
+}
+
+func (c *hijackedConn) Close() error {
+	return nil
+}
+
+type connHijackerTransport struct {
+	*http.Transport
+	Conn   net.Conn
+	Replay []byte
+}
+
+func newConnHijackerTransport(base http.RoundTripper) *connHijackerTransport {
+	transport := &http.Transport{
+		Proxy: http.ProxyFromEnvironment,
+		Dial: (&net.Dialer{
+			Timeout:   30 * time.Second,
+			KeepAlive: 30 * time.Second,
+		}).Dial,
+		TLSHandshakeTimeout: 10 * time.Second,
+		TLSClientConfig:     &tls.Config{InsecureSkipVerify: true},
+	}
+	if base != nil {
+		if baseTransport, ok := base.(*http.Transport); ok {
+			transport.Proxy = baseTransport.Proxy
+			transport.TLSClientConfig = baseTransport.TLSClientConfig
+			transport.TLSHandshakeTimeout = baseTransport.TLSHandshakeTimeout
+			transport.Dial = baseTransport.Dial
+			transport.DialTLS = baseTransport.DialTLS
+			transport.DisableKeepAlives = true
+		}
+	}
+	hjTransport := &connHijackerTransport{transport, nil, bufferPool.Get().([]byte)[:0]}
+	oldDial := transport.Dial
+	oldDialTLS := transport.DialTLS
+	if oldDial == nil {
+		oldDial = (&net.Dialer{
+			Timeout:   30 * time.Second,
+			KeepAlive: 30 * time.Second,
+		}).Dial
+	}
+	hjTransport.Dial = func(network, addr string) (net.Conn, error) {
+		c, err := oldDial(network, addr)
+		hjTransport.Conn = c
+		return &hijackedConn{c, hjTransport}, err
+	}
+	if oldDialTLS != nil {
+		hjTransport.DialTLS = func(network, addr string) (net.Conn, error) {
+			c, err := oldDialTLS(network, addr)
+			hjTransport.Conn = c
+			return &hijackedConn{c, hjTransport}, err
+		}
+	}
+	return hjTransport
+}
+
+func requestIsWebsocket(req *http.Request) bool {
+	return !(strings.ToLower(req.Header.Get("Upgrade")) != "websocket" || !strings.Contains(strings.ToLower(req.Header.Get("Connection")), "upgrade"))
+}
+
 func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, outreq *http.Request, respUpdateFn respUpdateFn) error {
 	transport := p.Transport
-	if transport == nil {
+	if requestIsWebsocket(outreq) {
+		transport = newConnHijackerTransport(transport)
+	} else if transport == nil {
 		transport = http.DefaultTransport
 	}
 
@@ -216,13 +287,22 @@ func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, outreq *http.Request, r
 		}
 		defer conn.Close()
 
-		backendConn, err := net.Dial("tcp", outreq.URL.Host)
+		var backendConn net.Conn
+		if hj, ok := transport.(*connHijackerTransport); ok {
+			backendConn = hj.Conn
+			if _, err := conn.Write(hj.Replay); err != nil {
+				return err
+			}
+			bufferPool.Put(hj.Replay)
+		} else {
+			backendConn, err = net.Dial("tcp", outreq.URL.Host)
 			if err != nil {
 				return err
 			}
 			defer backendConn.Close()
 
 			outreq.Write(backendConn)
+		}
 
 		go func() {
 			io.Copy(backendConn, conn) // write tcp stream to backend.