Changes from v2ray-core (#93)

proxy/socks/client.go

@@ -51,14 +51,19 @@ func (c *Client) Process(ctx context.Context, link *transport.Link, dialer inter
 	if outbound == nil || !outbound.Target.IsValid() {
 		return newError("target not specified.")
 	}
+	// Destination of the inner request.
 	destination := outbound.Target
 
+	// Outbound server.
 	var server *protocol.ServerSpec
+	// Outbound server's destination.
+	var dest net.Destination
+	// Connection to the outbound server.
 	var conn internet.Connection
 
 	if err := retry.ExponentialBackoff(5, 100).On(func() error {
 		server = c.serverPicker.PickServer()
-		dest := server.Destination()
+		dest = server.Destination()
 		rawConn, err := dialer.Dial(ctx, dest)
 		if err != nil {
 			return err
@@ -101,6 +106,11 @@ func (c *Client) Process(ctx context.Context, link *transport.Link, dialer inter
 	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
+		}
+	}
 
 	if err := conn.SetDeadline(time.Time{}); err != nil {
 		newError("failed to clear deadline after handshake").Base(err).WriteToLog(session.ExportIDToError(ctx))

proxy/socks/protocol.go

@@ -16,7 +16,7 @@ const (
 
 	cmdTCPConnect    = 0x01
 	cmdTCPBind       = 0x02
-	cmdUDPPort       = 0x03
+	cmdUDPAssociate  = 0x03
 	cmdTorResolve    = 0xF0
 	cmdTorResolvePTR = 0xF1
 
@@ -39,8 +39,10 @@ var addrParser = protocol.NewAddressParser(
 )
 
 type ServerSession struct {
-	config *ServerConfig
-	port   net.Port
+	config        *ServerConfig
+	address       net.Address
+	port          net.Port
+	clientAddress net.Address
 }
 
 func (s *ServerSession) handshake4(cmd byte, reader io.Reader, writer io.Writer) (*protocol.RequestHeader, error) {
@@ -162,7 +164,7 @@ func (s *ServerSession) handshake5(nMethod byte, reader io.Reader, writer io.Wri
 	case cmdTCPConnect, cmdTorResolve, cmdTorResolvePTR:
 		// We don't have a solution for Tor case now. Simply treat it as connect command.
 		request.Command = protocol.RequestCommandTCP
-	case cmdUDPPort:
+	case cmdUDPAssociate:
 		if !s.config.UdpEnabled {
 			writeSocks5Response(writer, statusCmdNotSupport, net.AnyIP, net.Port(0))
 			return nil, newError("UDP is not enabled.")
@@ -185,15 +187,20 @@ func (s *ServerSession) handshake5(nMethod byte, reader io.Reader, writer io.Wri
 	request.Address = addr
 	request.Port = port
 
-	responseAddress := net.AnyIP
-	responsePort := net.Port(1717)
+	responseAddress := s.address
+	responsePort := s.port
+	//nolint:gocritic // Use if else chain for clarity
 	if request.Command == protocol.RequestCommandUDP {
-		addr := s.config.Address.AsAddress()
-		if addr == nil {
-			addr = net.LocalHostIP
+		if s.config.Address != nil {
+			// Use configured IP as remote address in the response to UdpAssociate
+			responseAddress = s.config.Address.AsAddress()
+		} else if s.clientAddress == net.LocalHostIP || s.clientAddress == net.LocalHostIPv6 {
+			// For localhost clients use loopback IP
+			responseAddress = s.clientAddress
+		} else {
+			// For non-localhost clients use inbound listening address
+			responseAddress = s.address
 		}
-		responseAddress = addr
-		responsePort = s.port
 	}
 	if err := writeSocks5Response(writer, statusSuccess, responseAddress, responsePort); err != nil {
 		return nil, err
@@ -446,7 +453,7 @@ func ClientHandshake(request *protocol.RequestHeader, reader io.Reader, writer i
 
 	command := byte(cmdTCPConnect)
 	if request.Command == protocol.RequestCommandUDP {
-		command = byte(cmdUDPPort)
+		command = byte(cmdUDPAssociate)
 	}
 	common.Must2(b.Write([]byte{socks5Version, command, 0x00 /* reserved */}))
 	if err := addrParser.WriteAddressPort(b, request.Address, request.Port); err != nil {

proxy/socks/server.go

@@ -89,8 +89,10 @@ func (s *Server) processTCP(ctx context.Context, conn internet.Connection, dispa
 	}
 
 	svrSession := &ServerSession{
-		config: s.config,
-		port:   inbound.Gateway.Port,
+		config:        s.config,
+		address:       inbound.Gateway.Address,
+		port:          inbound.Gateway.Port,
+		clientAddress: inbound.Source.Address,
 	}
 
 	reader := &buf.BufferedReader{Reader: buf.NewReader(conn)}