chore: use early conn to support real ws 0-rtt

tunnel/tunnel.go

@@ -366,8 +366,20 @@ func handleTCPConn(connCtx C.ConnContext) {
 		return
 	}
 
+	conn := connCtx.Conn()
 	if sniffer.Dispatcher.Enable() && sniffingEnable {
-		sniffer.Dispatcher.TCPSniff(connCtx.Conn(), metadata)
+		sniffer.Dispatcher.TCPSniff(conn, metadata)
+	}
+
+	peekMutex := sync.Mutex{}
+	if !conn.Peeked() {
+		peekMutex.Lock()
+		go func() {
+			defer peekMutex.Unlock()
+			_ = conn.SetReadDeadline(time.Now().Add(200 * time.Millisecond))
+			_, _ = conn.Peek(1)
+			_ = conn.SetReadDeadline(time.Time{})
+		}()
 	}
 
 	proxy, rule, err := resolveMetadata(connCtx, metadata)
@@ -387,10 +399,26 @@ func handleTCPConn(connCtx C.ConnContext) {
 		}
 	}
 
+	var peekBytes []byte
+
 	ctx, cancel := context.WithTimeout(context.Background(), C.DefaultTCPTimeout)
 	defer cancel()
 	remoteConn, err := retry(ctx, func(ctx context.Context) (C.Conn, error) {
-		return proxy.DialContext(ctx, dialMetadata)
+		remoteConn, err := proxy.DialContext(ctx, dialMetadata)
+		if err != nil {
+			return nil, err
+		}
+		peekMutex.Lock()
+		defer peekMutex.Unlock()
+		peekBytes, _ = conn.Peek(conn.Buffered())
+		_, err = remoteConn.Write(peekBytes)
+		if err != nil {
+			return nil, err
+		}
+		if peekLen := len(peekBytes); peekLen > 0 {
+			_, _ = conn.Discard(peekLen)
+		}
+		return remoteConn, err
 	}, func(err error) {
 		if rule == nil {
 			log.Warnln(