support udp in relay if last proxy could udp-over-tcp

adapter/outbound/base.go

@@ -42,6 +42,16 @@ func (b *Base) ListenPacketContext(ctx context.Context, metadata *C.Metadata, op
 	return nil, errors.New("no support")
 }
 
+// ListenPacketOnStreamConn implements C.ProxyAdapter
+func (b *Base) ListenPacketOnStreamConn(c net.Conn, metadata *C.Metadata) (_ C.PacketConn, err error) {
+	return nil, errors.New("no support")
+}
+
+// SupportUOT implements C.ProxyAdapter
+func (b *Base) SupportUOT() bool {
+	return false
+}
+
 // SupportUDP implements C.ProxyAdapter
 func (b *Base) SupportUDP() bool {
 	return b.udp

adapter/outbound/snell.go

@@ -95,6 +95,12 @@ func (s *Snell) ListenPacketContext(ctx context.Context, metadata *C.Metadata, o
 	tcpKeepAlive(c)
 	c = streamConn(c, streamOption{s.psk, s.version, s.addr, s.obfsOption})
 
+	return s.ListenPacketOnStreamConn(c, metadata)
+}
+
+// ListenPacketOnStreamConn implements C.ProxyAdapter
+func (s *Snell) ListenPacketOnStreamConn(c net.Conn, metadata *C.Metadata) (_ C.PacketConn, err error) {
+
 	err = snell.WriteUDPHeader(c, s.version)
 	if err != nil {
 		return nil, err
@@ -104,6 +110,11 @@ func (s *Snell) ListenPacketContext(ctx context.Context, metadata *C.Metadata, o
 	return newPacketConn(pc, s), nil
 }
 
+// SupportUOT implements C.ProxyAdapter
+func (s *Snell) SupportUOT() bool {
+	return true
+}
+
 func NewSnell(option SnellOption) (*Snell, error) {
 	addr := net.JoinHostPort(option.Server, strconv.Itoa(option.Port))
 	psk := []byte(option.Psk)

adapter/outbound/trojan.go

@@ -157,6 +157,11 @@ func (t *Trojan) ListenPacketContext(ctx context.Context, metadata *C.Metadata,
 		}
 	}
 
+	return t.ListenPacketOnStreamConn(c, metadata)
+}
+
+// ListenPacketOnStreamConn implements C.ProxyAdapter
+func (t *Trojan) ListenPacketOnStreamConn(c net.Conn, metadata *C.Metadata) (_ C.PacketConn, err error) {
 	err = t.instance.WriteHeader(c, trojan.CommandUDP, serializesSocksAddr(metadata))
 	if err != nil {
 		return nil, err
@@ -166,6 +171,11 @@ func (t *Trojan) ListenPacketContext(ctx context.Context, metadata *C.Metadata,
 	return newPacketConn(pc, t), err
 }
 
+// SupportUOT implements C.ProxyAdapter
+func (t *Trojan) SupportUOT() bool {
+	return true
+}
+
 func NewTrojan(option TrojanOption) (*Trojan, error) {
 	addr := net.JoinHostPort(option.Server, strconv.Itoa(option.Port))
 

adapter/outbound/vless.go

@@ -249,9 +249,19 @@ func (v *Vless) ListenPacketContext(ctx context.Context, metadata *C.Metadata, o
 		return nil, fmt.Errorf("new vless client error: %v", err)
 	}
 
+	return v.ListenPacketOnStreamConn(c, metadata)
+}
+
+// ListenPacketOnStreamConn implements C.ProxyAdapter
+func (v *Vless) ListenPacketOnStreamConn(c net.Conn, metadata *C.Metadata) (_ C.PacketConn, err error) {
 	return newPacketConn(&vlessPacketConn{Conn: c, rAddr: metadata.UDPAddr()}, v), nil
 }
 
+// SupportUOT implements C.ProxyAdapter
+func (v *Vless) SupportUOT() bool {
+	return true
+}
+
 func parseVlessAddr(metadata *C.Metadata) *vless.DstAddr {
 	var addrType byte
 	var addr []byte

adapter/outbound/vmess.go

@@ -260,9 +260,19 @@ func (v *Vmess) ListenPacketContext(ctx context.Context, metadata *C.Metadata, o
 		return nil, fmt.Errorf("new vmess client error: %v", err)
 	}
 
+	return v.ListenPacketOnStreamConn(c, metadata)
+}
+
+// ListenPacketOnStreamConn implements C.ProxyAdapter
+func (v *Vmess) ListenPacketOnStreamConn(c net.Conn, metadata *C.Metadata) (_ C.PacketConn, err error) {
 	return newPacketConn(&vmessPacketConn{Conn: c, rAddr: metadata.UDPAddr()}, v), nil
 }
 
+// SupportUOT implements C.ProxyAdapter
+func (v *Vmess) SupportUOT() bool {
+	return true
+}
+
 func NewVmess(option VmessOption) (*Vmess, error) {
 	security := strings.ToLower(option.Cipher)
 	client, err := vmess.NewClient(vmess.Config{