fix: socks4/4a client handshake (#1971)

proxy/socks/client.go

@@ -146,10 +146,21 @@ func (c *Client) Process(ctx context.Context, link *transport.Link, dialer inter
 	if err := conn.SetDeadline(time.Now().Add(p.Timeouts.Handshake)); err != nil {
 		newError("failed to set deadline for handshake").Base(err).WriteToLog(session.ExportIDToError(ctx))
 	}
-	udpRequest, err := ClientHandshake(request, conn, conn)
-	if err != nil {
-		return newError("failed to establish connection to server").AtWarning().Base(err)
+
+	var udpRequest *protocol.RequestHeader
+	var err error
+	if request.Version == socks4Version {
+		err = ClientHandshake4(request, conn, conn)
+		if err != nil {
+			return newError("failed to establish connection to server").AtWarning().Base(err)
+		}
+	} else {
+		udpRequest, err = ClientHandshake(request, conn, conn)
+		if err != nil {
+			return newError("failed to establish connection to server").AtWarning().Base(err)
+		}
 	}
+
 	if udpRequest != nil {
 		if udpRequest.Address == net.AnyIP || udpRequest.Address == net.AnyIPv6 {
 			udpRequest.Address = dest.Address

proxy/socks/protocol.go

@@ -537,3 +537,46 @@ func ClientHandshake(request *protocol.RequestHeader, reader io.Reader, writer i
 
 	return nil, nil
 }
+
+func ClientHandshake4(request *protocol.RequestHeader, reader io.Reader, writer io.Writer) error {
+	b := buf.New()
+	defer b.Release()
+
+	common.Must2(b.Write([]byte{socks4Version, cmdTCPConnect}))
+	portBytes := b.Extend(2)
+	binary.BigEndian.PutUint16(portBytes, request.Port.Value())
+	switch request.Address.Family() {
+	case net.AddressFamilyIPv4:
+		common.Must2(b.Write(request.Address.IP()))
+	case net.AddressFamilyDomain:
+		common.Must2(b.Write([]byte{0x00, 0x00, 0x00, 0x01}))
+	case net.AddressFamilyIPv6:
+		return newError("ipv6 is not supported in socks4")
+	default:
+		panic("Unknown family type.")
+	}
+	if request.User != nil {
+		account := request.User.Account.(*Account)
+		common.Must2(b.WriteString(account.Username))
+	}
+	common.Must(b.WriteByte(0x00))
+	if request.Address.Family() == net.AddressFamilyDomain {
+		common.Must2(b.WriteString(request.Address.Domain()))
+		common.Must(b.WriteByte(0x00))
+	}
+	if err := buf.WriteAllBytes(writer, b.Bytes()); err != nil {
+		return err
+	}
+
+	b.Clear()
+	if _, err := b.ReadFullFrom(reader, 8); err != nil {
+		return err
+	}
+	if b.Byte(0) != 0x00 {
+		return newError("unexpected version of the reply code: ", b.Byte(0))
+	}
+	if b.Byte(1) != socks4RequestGranted {
+		return newError("server rejects request: ", b.Byte(1))
+	}
+	return nil
+}