[WIP] Introduce TCP/UDP local/remote port forwarding

Signed-off-by: Vasyl Gello <vasek.gello@gmail.com>

cmd/yggstack/main.go

@@ -40,15 +40,22 @@ type node struct {
 	socks5Listener net.Listener
 }
 
-type UDPSession struct {
+type UDPConnSession struct {
 	conn       *net.UDPConn
 	remoteAddr net.Addr
 }
 
+type UDPPacketConnSession struct {
+	conn       *net.PacketConn
+	remoteAddr net.Addr
+}
+
 // The main function is responsible for configuring and starting Yggdrasil.
 func main() {
-	var exposetcp types.TCPMappings
+	var localtcp types.TCPLocalMappings
-	var exposeudp types.UDPMappings
+	var localudp types.UDPLocalMappings
+	var remotetcp types.TCPRemoteMappings
+	var remoteudp types.UDPRemoteMappings
 	genconf := flag.Bool("genconf", false, "print a new config to stdout")
 	useconf := flag.Bool("useconf", false, "read HJSON/JSON config from stdin")
 	useconffile := flag.String("useconffile", "", "read HJSON/JSON config from specified file path")
@@ -64,8 +71,10 @@ func main() {
 	loglevel := flag.String("loglevel", "info", "loglevel to enable")
 	socks := flag.String("socks", "", "address to listen on for SOCKS, i.e. :1080; or UNIX socket file path, i.e. /tmp/yggstack.sock")
 	nameserver := flag.String("nameserver", "", "the Yggdrasil IPv6 address to use as a DNS server for SOCKS")
-	flag.Var(&exposetcp, "exposetcp", "TCP ports to expose to the network, e.g. 22, 2022:22, 22:192.168.1.1:2022")
+	flag.Var(&localtcp, "local-tcp", "TCP ports to forward to the remote Yggdradil node, e.g. 22:[a:b:c:d]:22, 127.0.0.1:22:[a:b:c:d]:22")
-	flag.Var(&exposeudp, "exposeudp", "UDP ports to expose to the network, e.g. 22, 2022:22, 22:192.168.1.1:2022")
+	flag.Var(&localudp, "local-udp", "UDP ports to forward to the remote Yggdrasil node, e.g. 22:[a:b:c:d]:2022, 127.0.0.1:[a:b:c:d]:22")
+	flag.Var(&remotetcp, "remote-tcp", "TCP ports to expose to the network, e.g. 22, 2022:22, 22:192.168.1.1:2022")
+	flag.Var(&remoteudp, "remote-udp", "UDP ports to expose to the network, e.g. 22, 2022:22, 22:192.168.1.1:2022")
 	flag.Parse()
 
 	// Catch interrupts from the operating system to exit gracefully.
@@ -328,9 +337,96 @@ func main() {
 		}
 	}
 
-	// Create TCP mappings
+	// Create local TCP mappings (forwarding connections from local port
+	// to remote Yggdrasil node)
 	{
-		for _, mapping := range exposetcp {
+		for _, mapping := range localtcp {
+			go func(mapping types.TCPMapping) {
+				listener, err := net.ListenTCP("tcp", mapping.Listen)
+				if err != nil {
+					panic(err)
+				}
+				logger.Infof("Mapping local TCP port %d to Yggdrasil %s", mapping.Listen.Port, mapping.Mapped)
+				for {
+					c, err := listener.Accept()
+					if err != nil {
+						panic(err)
+					}
+					r, err := s.DialTCP(mapping.Mapped)
+					if err != nil {
+						logger.Errorf("Failed to connect to %s: %s", mapping.Mapped, err)
+						_ = c.Close()
+						continue
+					}
+					go types.ProxyTCP(n.core.MTU(), c, r)
+				}
+			}(mapping)
+		}
+	}
+
+	// Create local UDP mappings (forwarding connections from local port
+	// to remote Yggdrasil node)
+	{
+		for _, mapping := range localudp {
+			go func(mapping types.UDPMapping) {
+				mtu := n.core.MTU()
+				udpListenConn, err := net.ListenUDP("udp", mapping.Listen)
+				if err != nil {
+					panic(err)
+				}
+				logger.Infof("Mapping local UDP port %d to Yggdrasil %s", mapping.Listen.Port, mapping.Mapped)
+				localUdpConnections := new(sync.Map)
+				udpBuffer := make([]byte, mtu)
+				for {
+					bytesRead, remoteUdpAddr, err := udpListenConn.ReadFrom(udpBuffer)
+					if err != nil {
+						if bytesRead == 0 {
+							continue
+						}
+					}
+
+					remoteUdpAddrStr := remoteUdpAddr.String()
+
+					connVal, ok := localUdpConnections.Load(remoteUdpAddrStr)
+
+					if !ok {
+						logger.Infof("Creating new session for %s", remoteUdpAddr.String())
+						udpFwdConn, err := s.DialUDP(mapping.Mapped)
+						if err != nil {
+							logger.Errorf("Failed to connect to %s: %s", mapping.Mapped, err)
+							continue
+						}
+						udpSession := &UDPPacketConnSession{
+							conn:       &udpFwdConn,
+							remoteAddr: remoteUdpAddr,
+						}
+						localUdpConnections.Store(remoteUdpAddrStr, udpSession)
+						go types.ReverseProxyUDPPacketConn(mtu, udpListenConn, remoteUdpAddr, udpFwdConn)
+					}
+
+					udpSession, ok := connVal.(*UDPPacketConnSession)
+					if !ok {
+						continue
+					}
+
+					udpFwdConn := *udpSession.conn
+
+					_, err = udpFwdConn.WriteTo(udpBuffer[:bytesRead], mapping.Mapped)
+					if err != nil {
+						logger.Debugf("Cannot write from yggdrasil to udp listener: %q", err)
+						udpFwdConn.Close()
+						localUdpConnections.Delete(remoteUdpAddrStr)
+						continue
+					}
+				}
+			}(mapping)
+		}
+	}
+
+	// Create remote TCP mappings (forwarding connections from Yggdrasil
+	// node to local port)
+	{
+		for _, mapping := range remotetcp {
 			go func(mapping types.TCPMapping) {
 				listener, err := s.ListenTCP(mapping.Listen)
 				if err != nil {
@@ -354,9 +450,10 @@ func main() {
 		}
 	}
 
-	// Create UDP mappings
+	// Create remote UDP mappings (forwarding connections from Yggdrasil
+	// node to local port)
 	{
-		for _, mapping := range exposeudp {
+		for _, mapping := range remoteudp {
 			go func(mapping types.UDPMapping) {
 				mtu := n.core.MTU()
 				udpListenConn, err := s.ListenUDP(mapping.Listen)
@@ -385,16 +482,15 @@ func main() {
 							logger.Errorf("Failed to connect to %s: %s", mapping.Mapped, err)
 							continue
 						}
-						udpSession := &UDPSession{
+						udpSession := &UDPConnSession{
 							conn:       udpFwdConn,
 							remoteAddr: remoteUdpAddr,
 						}
 						remoteUdpConnections.Store(remoteUdpAddrStr, udpSession)
-						go types.ReverseProxyUDP(mtu, udpListenConn, remoteUdpAddr, *udpFwdConn)
+						go types.ReverseProxyUDPConn(mtu, udpListenConn, remoteUdpAddr, *udpFwdConn)
 					}
 
-
+					udpSession, ok := connVal.(*UDPConnSession)
-					udpSession, ok := connVal.(*UDPSession)
 					if !ok {
 						continue
 					}

src/types/mapping.go

@@ -7,62 +7,269 @@ import (
 	"strings"
 )
 
+func parseMappingString(value string) (first_address string, first_port int, second_address string, second_port int, err error) {
+	var first_port_string string = ""
+	var second_port_string string = ""
+
+	tokens := strings.Split(value, ":")
+	tokens_len := len(tokens)
+
+	// If token count is 1, then it is first and second port the same
+
+	if tokens_len == 1 {
+		first_port, err = strconv.Atoi(tokens[0])
+		if err != nil {
+			return "", 0, "", 0, fmt.Errorf("Malformed mapping spec '%s'", value)
+		}
+		second_port = first_port
+	}
+
+	// If token count is 2, then it is <first-port>:<second-port>
+
+	if tokens_len == 2 {
+		first_port, err = strconv.Atoi(tokens[0])
+		if err != nil {
+			return "", 0, "", 0, fmt.Errorf("Malformed mapping spec '%s'", value)
+		}
+		second_port, err = strconv.Atoi(tokens[1])
+		if err != nil {
+			return "", 0, "", 0, fmt.Errorf("Malformed mapping spec '%s'", value)
+		}
+	}
+
+	// If token count is 3, parse it as
+	// <first-port>:<second-address>:<second-port>
+
+	if tokens_len == 3 {
+		first_port, err = strconv.Atoi(tokens[0])
+		if err != nil {
+			return "", 0, "", 0, fmt.Errorf("Malformed mapping spec '%s'", value)
+		}
+		second_address, second_port_string, err = net.SplitHostPort(
+			tokens[1] + ":" + tokens[2])
+		if err != nil {
+			return "", 0, "", 0, fmt.Errorf("Malformed mapping spec '%s'", value)
+		}
+		second_port, err = strconv.Atoi(second_port_string)
+		if err != nil {
+			return "", 0, "", 0, fmt.Errorf("Malformed mapping spec '%s'", value)
+		}
+	}
+
+	// If token count is 4, parse it as
+	// <first-address>:<first-port>:<second-address>:<second-port>
+
+	if tokens_len == 4 {
+		first_address, first_port_string, err = net.SplitHostPort(
+			tokens[0] + ":" + tokens[1])
+		if err != nil {
+			return "", 0, "", 0, fmt.Errorf("Malformed mapping spec '%s'", value)
+		}
+		second_address, second_port_string, err = net.SplitHostPort(
+			tokens[0] + ":" + tokens[1])
+		if err != nil {
+			return "", 0, "", 0, fmt.Errorf("Malformed mapping spec '%s'", value)
+		}
+		first_port, err = strconv.Atoi(first_port_string)
+		if err != nil {
+			return "", 0, "", 0, fmt.Errorf("Malformed mapping spec '%s'", value)
+		}
+		second_port, err = strconv.Atoi(second_port_string)
+		if err != nil {
+			return "", 0, "", 0, fmt.Errorf("Malformed mapping spec '%s'", value)
+		}
+	}
+
+	if tokens_len > 4 {
+		// Last token needs to be the second_port
+
+		second_port, err = strconv.Atoi(tokens[tokens_len-1])
+		if err != nil {
+			return "", 0, "", 0, fmt.Errorf("Malformed mapping spec '%s'", value)
+		}
+
+		// Cut seen tokens
+
+		tokens = tokens[:tokens_len-1]
+		tokens_len = len(tokens)
+
+		if strings.HasSuffix(tokens[tokens_len-1], "]") {
+			// Reverse-walk over tokens to find the end of
+			// numeric ipv6 address
+
+			for i := tokens_len - 1; i >= 0; i-- {
+				if strings.HasPrefix(tokens[i], "[") {
+					// Store second address
+					second_address = strings.Join(tokens[i:], ":")
+					second_address, _ = strings.CutPrefix(second_address, "[")
+					second_address, _ = strings.CutSuffix(second_address, "]")
+					// Cut seen tokens
+					tokens = tokens[:i]
+					// break from loop
+					break
+				}
+			}
+		} else {
+			// next is second address in non-numerical-ipv6 form
+			second_address = tokens[tokens_len-1]
+			tokens = tokens[:tokens_len-1]
+		}
+
+		tokens_len = len(tokens)
+
+		if tokens_len < 1 {
+			return "", 0, "", 0, fmt.Errorf("Malformed mapping spec '%s'", value)
+		}
+
+		// Last token needs to be the first_port
+
+		first_port, err = strconv.Atoi(tokens[tokens_len-1])
+		if err != nil {
+			return "", 0, "", 0, fmt.Errorf("Malformed mapping spec '%s'", value)
+		}
+
+		// Cut seen tokens
+
+		tokens = tokens[:tokens_len-1]
+		tokens_len = len(tokens)
+
+		if tokens_len > 0 {
+			if strings.HasSuffix(tokens[tokens_len-1], "]") {
+				// Reverse-walk over tokens to find the end of
+				// numeric ipv6 address
+
+				for i := tokens_len - 1; i >= 0; i-- {
+					if strings.HasPrefix(tokens[i], "[") {
+						// Store first address
+						first_address = strings.Join(tokens[i:], ":")
+						first_address, _ = strings.CutPrefix(first_address, "[")
+						first_address, _ = strings.CutSuffix(first_address, "]")
+						// break from loop
+						break
+					}
+				}
+			} else {
+				// next is first address in non-numerical-ipv6 form
+				first_address = tokens[tokens_len-1]
+			}
+		}
+	}
+
+	if first_port == 0 || second_port == 0 {
+		return "", 0, "", 0, fmt.Errorf("Ports must not be zero")
+	}
+
+	return first_address, first_port, second_address, second_port, nil
+}
+
 type TCPMapping struct {
 	Listen *net.TCPAddr
 	Mapped *net.TCPAddr
 }
 
-type TCPMappings []TCPMapping
+type TCPLocalMappings []TCPMapping
 
-func (m *TCPMappings) String() string {
+func (m *TCPLocalMappings) String() string {
 	return ""
 }
 
-func (m *TCPMappings) Set(value string) error {
+func (m *TCPLocalMappings) Set(value string) error {
-	tokens := strings.Split(value, ":")
+	first_address, first_port, second_address, second_port, err :=
-	if len(tokens) > 2 {
+		parseMappingString(value)
-		tokens = strings.SplitN(value, ":", 2)
+
-		host, port, err := net.SplitHostPort(tokens[1])
 	if err != nil {
-			return fmt.Errorf("failed to split host and port: %w", err)
+		return err
 	}
-		tokens = append(tokens[:1], host, port)
+
-	}
+	// First address can be ipv4/ipv6
-	listenport, err := strconv.Atoi(tokens[0])
+	// Second address can be only Yggdrasil ipv6
-	if err != nil {
+
-		return fmt.Errorf("listen port is invalid: %w", err)
+	if !strings.Contains(second_address, ":") {
-	}
+		return fmt.Errorf("Yggdrasil listening address can be only IPv6")
-	if listenport == 0 {
-		return fmt.Errorf("listen port must not be zero")
 	}
+
+	// Create mapping
+
 	mapping := TCPMapping{
 		Listen: &net.TCPAddr{
-			Port: listenport,
+			Port: first_port,
 		},
 		Mapped: &net.TCPAddr{
 			IP:   net.IPv6loopback,
-			Port: listenport,
+			Port: second_port,
 		},
 	}
-	tokens = tokens[1:]
+
-	if len(tokens) > 0 {
+	if first_address != "" {
-		mappedaddr := net.ParseIP(tokens[0])
+		listenaddr := net.ParseIP(first_address)
+		if listenaddr == nil {
+			return fmt.Errorf("invalid listen address %q", first_address)
+		}
+		mapping.Listen.IP = listenaddr
+	}
+
+	if second_address != "" {
+		mappedaddr := net.ParseIP(second_address)
 		if mappedaddr == nil {
-			return fmt.Errorf("invalid mapped address %q", tokens[0])
+			return fmt.Errorf("invalid mapped address %q", second_address)
+		}
+		// TODO: Filter Yggdrasil IPs here
+		mapping.Mapped.IP = mappedaddr
+	}
+
+	*m = append(*m, mapping)
+	return nil
+}
+
+type TCPRemoteMappings []TCPMapping
+
+func (m *TCPRemoteMappings) String() string {
+	return ""
+}
+
+func (m *TCPRemoteMappings) Set(value string) error {
+	first_address, first_port, second_address, second_port, err :=
+		parseMappingString(value)
+
+	if err != nil {
+		return err
+	}
+
+	// First address must be empty
+	// Second address can be ipv4/ipv6
+
+	if first_address != "" {
+		return fmt.Errorf("Yggdrasil listening must be empty")
+	}
+
+	// Create mapping
+
+	mapping := TCPMapping{
+		Listen: &net.TCPAddr{
+			Port: first_port,
+		},
+		Mapped: &net.TCPAddr{
+			IP:   net.IPv6loopback,
+			Port: second_port,
+		},
+	}
+
+	if first_address != "" {
+		listenaddr := net.ParseIP(first_address)
+		if listenaddr == nil {
+			return fmt.Errorf("invalid listen address %q", first_address)
+		}
+		mapping.Listen.IP = listenaddr
+	}
+
+	if second_address != "" {
+		mappedaddr := net.ParseIP(second_address)
+		if mappedaddr == nil {
+			return fmt.Errorf("invalid mapped address %q", second_address)
 		}
 		mapping.Mapped.IP = mappedaddr
-		tokens = tokens[1:]
-	}
-	if len(tokens) > 0 {
-		mappedport, err := strconv.Atoi(tokens[0])
-		if err != nil {
-			return fmt.Errorf("mapped port is invalid: %w", err)
-		}
-		if mappedport == 0 {
-			return fmt.Errorf("mapped port must not be zero")
-		}
-		mapping.Mapped.Port = mappedport
 	}
+
 	*m = append(*m, mapping)
 	return nil
 }
@@ -72,57 +279,109 @@ type UDPMapping struct {
 	Mapped *net.UDPAddr
 }
 
-type UDPMappings []UDPMapping
+type UDPLocalMappings []UDPMapping
 
-func (m *UDPMappings) String() string {
+func (m *UDPLocalMappings) String() string {
 	return ""
 }
 
-func (m *UDPMappings) Set(value string) error {
+func (m *UDPLocalMappings) Set(value string) error {
-	tokens := strings.Split(value, ":")
+	first_address, first_port, second_address, second_port, err :=
-	if len(tokens) > 2 {
+		parseMappingString(value)
-		tokens = strings.SplitN(value, ":", 2)
+
-		host, port, err := net.SplitHostPort(tokens[1])
 	if err != nil {
-			return fmt.Errorf("failed to split host and port: %w", err)
+		return err
 	}
-		tokens = append(tokens[:1], host, port)
+
-	}
+	// First address can be ipv4/ipv6
-	listenport, err := strconv.Atoi(tokens[0])
+	// Second address can be only Yggdrasil ipv6
-	if err != nil {
+
-		return fmt.Errorf("listen port is invalid: %w", err)
+	if !strings.Contains(second_address, ":") {
-	}
+		return fmt.Errorf("Yggdrasil listening address can be only IPv6")
-	if listenport == 0 {
-		return fmt.Errorf("listen port must not be zero")
 	}
+
+	// Create mapping
+
 	mapping := UDPMapping{
 		Listen: &net.UDPAddr{
-			Port: listenport,
+			Port: first_port,
 		},
 		Mapped: &net.UDPAddr{
 			IP:   net.IPv6loopback,
-			Port: listenport,
+			Port: second_port,
 		},
 	}
-	tokens = tokens[1:]
+
-	if len(tokens) > 0 {
+	if first_address != "" {
-		mappedaddr := net.ParseIP(tokens[0])
+		listenaddr := net.ParseIP(first_address)
+		if listenaddr == nil {
+			return fmt.Errorf("invalid listen address %q", first_address)
+		}
+		mapping.Listen.IP = listenaddr
+	}
+
+	if second_address != "" {
+		mappedaddr := net.ParseIP(second_address)
 		if mappedaddr == nil {
-			return fmt.Errorf("invalid mapped address %q", tokens[0])
+			return fmt.Errorf("invalid mapped address %q", second_address)
 		}
+		// TODO: Filter Yggdrasil IPs here
 		mapping.Mapped.IP = mappedaddr
-		tokens = tokens[1:]
-	}
-	if len(tokens) > 0 {
-		mappedport, err := strconv.Atoi(tokens[0])
-		if err != nil {
-			return fmt.Errorf("mapped port is invalid: %w", err)
-		}
-		if mappedport == 0 {
-			return fmt.Errorf("mapped port must not be zero")
-		}
-		mapping.Mapped.Port = mappedport
 	}
+
+	*m = append(*m, mapping)
+	return nil
+}
+
+type UDPRemoteMappings []UDPMapping
+
+func (m *UDPRemoteMappings) String() string {
+	return ""
+}
+
+func (m *UDPRemoteMappings) Set(value string) error {
+	first_address, first_port, second_address, second_port, err :=
+		parseMappingString(value)
+
+	if err != nil {
+		return err
+	}
+
+	// First address must be empty
+	// Second address can be ipv4/ipv6
+
+	if first_address != "" {
+		return fmt.Errorf("Yggdrasil listening must be empty")
+	}
+
+	// Create mapping
+
+	mapping := UDPMapping{
+		Listen: &net.UDPAddr{
+			Port: first_port,
+		},
+		Mapped: &net.UDPAddr{
+			IP:   net.IPv6loopback,
+			Port: second_port,
+		},
+	}
+
+	if first_address != "" {
+		listenaddr := net.ParseIP(first_address)
+		if listenaddr == nil {
+			return fmt.Errorf("invalid listen address %q", first_address)
+		}
+		mapping.Listen.IP = listenaddr
+	}
+
+	if second_address != "" {
+		mappedaddr := net.ParseIP(second_address)
+		if mappedaddr == nil {
+			return fmt.Errorf("invalid mapped address %q", second_address)
+		}
+		mapping.Mapped.IP = mappedaddr
+	}
+
 	*m = append(*m, mapping)
 	return nil
 }

src/types/mapping_test.go

@@ -13,18 +13,48 @@ func TestEndpointMappings(t *testing.T) {
 	if err := tcpMappings.Set("1234:192.168.1.1:4321"); err != nil {
 		t.Fatal(err)
 	}
+	if err := tcpMappings.Set("192.168.1.2:1234:192.168.1.1:4321"); err != nil {
+		t.Fatal(err)
+	}
 	if err := tcpMappings.Set("1234:[2000::1]:4321"); err != nil {
 		t.Fatal(err)
 	}
+	if err := tcpMappings.Set("[2001:1]:1234:[2000::1]:4321"); err != nil {
+		t.Fatal(err)
+	}
 	if err := tcpMappings.Set("a"); err == nil {
 		t.Fatal("'a' should be an invalid exposed port")
 	}
 	if err := tcpMappings.Set("1234:localhost"); err == nil {
 		t.Fatal("mapped address must be an IP literal")
 	}
+	if err := tcpMappings.Set("127.0.0.1:1234:localhost"); err == nil {
+		t.Fatal("mapped address must be an IP literal")
+	}
+	if err := tcpMappings.Set("[2000:1]:1234:localhost"); err == nil {
+		t.Fatal("mapped address must be an IP literal")
+	}
+	if err := tcpMappings.Set("localhost:1234:127.0.0.1"); err == nil {
+		t.Fatal("listen address must be an IP literal")
+	}
+	if err := tcpMappings.Set("localhost:1234:127.0.0.1"); err == nil {
+		t.Fatal("listen address must be an IP literal")
+	}
+	if err := tcpMappings.Set("localhost:1234:[2000:1]"); err == nil {
+		t.Fatal("listen address must be an IP literal")
+	}
+	if err := tcpMappings.Set("localhost:1234:[2000:1]"); err == nil {
+		t.Fatal("listen address must be an IP literal")
+	}
 	if err := tcpMappings.Set("1234:localhost:a"); err == nil {
 		t.Fatal("'a' should be an invalid mapped port")
 	}
+	if err := tcpMappings.Set("127.0.0.1:1234:127.0.0.1:a"); err == nil {
+		t.Fatal("'a' should be an invalid mapped port")
+	}
+	if err := tcpMappings.Set("[2000::1]:1234:[2000::1]:a"); err == nil {
+		t.Fatal("'a' should be an invalid mapped port")
+	}
 	var udpMappings UDPMappings
 	if err := udpMappings.Set("1234"); err != nil {
 		t.Fatal(err)
@@ -35,16 +65,46 @@ func TestEndpointMappings(t *testing.T) {
 	if err := udpMappings.Set("1234:192.168.1.1:4321"); err != nil {
 		t.Fatal(err)
 	}
+	if err := udpMappings.Set("192.168.1.2:1234:192.168.1.1:4321"); err != nil {
+		t.Fatal(err)
+	}
 	if err := udpMappings.Set("1234:[2000::1]:4321"); err != nil {
 		t.Fatal(err)
 	}
+	if err := udpMappings.Set("[2001:1]:1234:[2000::1]:4321"); err != nil {
+		t.Fatal(err)
+	}
 	if err := udpMappings.Set("a"); err == nil {
 		t.Fatal("'a' should be an invalid exposed port")
 	}
 	if err := udpMappings.Set("1234:localhost"); err == nil {
 		t.Fatal("mapped address must be an IP literal")
 	}
+	if err := udpMappings.Set("127.0.0.1:1234:localhost"); err == nil {
+		t.Fatal("mapped address must be an IP literal")
+	}
+	if err := udpMappings.Set("[2000:1]:1234:localhost"); err == nil {
+		t.Fatal("mapped address must be an IP literal")
+	}
+	if err := udpMappings.Set("localhost:1234:127.0.0.1"); err == nil {
+		t.Fatal("listen address must be an IP literal")
+	}
+	if err := udpMappings.Set("localhost:1234:127.0.0.1"); err == nil {
+		t.Fatal("listen address must be an IP literal")
+	}
+	if err := udpMappings.Set("localhost:1234:[2000:1]"); err == nil {
+		t.Fatal("listen address must be an IP literal")
+	}
+	if err := udpMappings.Set("localhost:1234:[2000:1]"); err == nil {
+		t.Fatal("listen address must be an IP literal")
+	}
 	if err := udpMappings.Set("1234:localhost:a"); err == nil {
 		t.Fatal("'a' should be an invalid mapped port")
 	}
+	if err := udpMappings.Set("127.0.0.1:1234:127.0.0.1:a"); err == nil {
+		t.Fatal("'a' should be an invalid mapped port")
+	}
+	if err := udpMappings.Set("[2000::1]:1234:[2000::1]:a"); err == nil {
+		t.Fatal("'a' should be an invalid mapped port")
+	}
 }

src/types/udpproxy.go

@@ -4,7 +4,7 @@ import (
 	"net"
 )
 
-func ReverseProxyUDP(mtu uint64, dst net.PacketConn, dstAddr net.Addr, src net.UDPConn) error {
+func ReverseProxyUDPConn(mtu uint64, dst net.PacketConn, dstAddr net.Addr, src net.UDPConn) error {
 	buf := make([]byte, mtu)
 	for {
 		n, err := src.Read(buf[:])
@@ -20,3 +20,20 @@ func ReverseProxyUDP(mtu uint64, dst net.PacketConn, dstAddr net.Addr, src net.U
 	}
 	return nil
 }
+
+func ReverseProxyUDPPacketConn(mtu uint64, dst net.PacketConn, dstAddr net.Addr, src net.PacketConn) error {
+	buf := make([]byte, mtu)
+	for {
+		n, _, err := src.ReadFrom(buf[:])
+		if err != nil {
+			return err
+		}
+		if n > 0 {
+			n, err = dst.WriteTo(buf[:n], dstAddr)
+			if err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}