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{

adapter/outboundgroup/relay.go

@@ -17,12 +17,7 @@ type Relay struct {
 
 // DialContext implements C.ProxyAdapter
 func (r *Relay) DialContext(ctx context.Context, metadata *C.Metadata, opts ...dialer.Option) (C.Conn, error) {
-	var proxies []C.Proxy
+	proxies, chainProxies := r.proxies(metadata, true)
-	for _, proxy := range r.proxies(metadata, true) {
-		if proxy.Type() != C.Direct && proxy.Type() != C.Compatible {
-			proxies = append(proxies, proxy)
-		}
-	}
 
 	switch len(proxies) {
 	case 0:
@@ -60,7 +55,80 @@ func (r *Relay) DialContext(ctx context.Context, metadata *C.Metadata, opts ...d
 		return nil, fmt.Errorf("%s connect error: %w", last.Addr(), err)
 	}
 
-	return outbound.NewConn(c, r), nil
+	conn := outbound.NewConn(c, last)
+
+	for i := len(chainProxies) - 2; i >= 0; i-- {
+		conn.AppendToChains(chainProxies[i])
+	}
+
+	conn.AppendToChains(r)
+
+	return conn, nil
+}
+
+// ListenPacketContext implements C.ProxyAdapter
+func (r *Relay) ListenPacketContext(ctx context.Context, metadata *C.Metadata, opts ...dialer.Option) (_ C.PacketConn, err error) {
+	proxies, chainProxies := r.proxies(metadata, true)
+
+	switch len(proxies) {
+	case 0:
+		return outbound.NewDirect().ListenPacketContext(ctx, metadata, r.Base.DialOptions(opts...)...)
+	case 1:
+		return proxies[0].ListenPacketContext(ctx, metadata, r.Base.DialOptions(opts...)...)
+	}
+
+	first := proxies[0]
+	last := proxies[len(proxies)-1]
+
+	c, err := dialer.DialContext(ctx, "tcp", first.Addr(), r.Base.DialOptions(opts...)...)
+	if err != nil {
+		return nil, fmt.Errorf("%s connect error: %w", first.Addr(), err)
+	}
+	tcpKeepAlive(c)
+
+	var currentMeta *C.Metadata
+	for _, proxy := range proxies[1:] {
+		currentMeta, err = addrToMetadata(proxy.Addr())
+		if err != nil {
+			return nil, err
+		}
+
+		c, err = first.StreamConn(c, currentMeta)
+		if err != nil {
+			return nil, fmt.Errorf("%s connect error: %w", first.Addr(), err)
+		}
+
+		first = proxy
+	}
+
+	c, err = last.StreamConn(c, metadata)
+	if err != nil {
+		return nil, fmt.Errorf("%s connect error: %w", last.Addr(), err)
+	}
+
+	var pc C.PacketConn
+	pc, err = last.ListenPacketOnStreamConn(c, metadata)
+	if err != nil {
+		return nil, fmt.Errorf("%s connect error: %w", first.Addr(), err)
+	}
+
+	for i := len(chainProxies) - 2; i >= 0; i-- {
+		pc.AppendToChains(chainProxies[i])
+	}
+
+	pc.AppendToChains(r)
+
+	return pc, nil
+}
+
+// SupportUDP implements C.ProxyAdapter
+func (r *Relay) SupportUDP() bool {
+	proxies, _ := r.proxies(nil, false)
+	if len(proxies) == 0 { // C.Direct
+		return true
+	}
+	last := proxies[len(proxies)-1]
+	return last.SupportUDP() && last.SupportUOT()
 }
 
 // MarshalJSON implements C.ProxyAdapter
@@ -75,18 +143,31 @@ func (r *Relay) MarshalJSON() ([]byte, error) {
 	})
 }
 
-func (r *Relay) proxies(metadata *C.Metadata, touch bool) []C.Proxy {
+func (r *Relay) proxies(metadata *C.Metadata, touch bool) ([]C.Proxy, []C.Proxy) {
-	proxies := r.GetProxies(touch)
+	rawProxies := r.GetProxies(touch)
 
-	for n, proxy := range proxies {
+	var proxies []C.Proxy
+	var chainProxies []C.Proxy
+	var targetProxies []C.Proxy
+
+	for n, proxy := range rawProxies {
+		proxies = append(proxies, proxy)
+		chainProxies = append(chainProxies, proxy)
 		subproxy := proxy.Unwrap(metadata)
 		for subproxy != nil {
+			chainProxies = append(chainProxies, subproxy)
 			proxies[n] = subproxy
 			subproxy = subproxy.Unwrap(metadata)
 		}
 	}
 
-	return proxies
+	for _, proxy := range proxies {
+		if proxy.Type() != C.Direct && proxy.Type() != C.Compatible {
+			targetProxies = append(targetProxies, proxy)
+		}
+	}
+
+	return targetProxies, chainProxies
 }
 
 func NewRelay(option *GroupCommonOption, providers []provider.ProxyProvider) *Relay {

constant/adapters.go

@@ -99,6 +99,10 @@ type ProxyAdapter interface {
 	DialContext(ctx context.Context, metadata *Metadata, opts ...dialer.Option) (Conn, error)
 	ListenPacketContext(ctx context.Context, metadata *Metadata, opts ...dialer.Option) (PacketConn, error)
 
+	// SupportUOT return UDP over TCP support
+	SupportUOT() bool
+	ListenPacketOnStreamConn(c net.Conn, metadata *Metadata) (PacketConn, error)
+
 	// Unwrap extracts the proxy from a proxy-group. It returns nil when nothing to extract.
 	Unwrap(metadata *Metadata) Proxy
 }