Introduce UDP Tracker Protocol sniffer

Signed-off-by: iosmanthus <myosmanthustree@gmail.com>

common/sniff/bittorrent.go

@@ -11,6 +11,18 @@ import (
 	"github.com/sagernet/sing-box/constant"
 )
 
+const (
+	trackerConnectFlag = iota
+	trackerAnnounceFlag
+	trackerScrapeFlag
+
+	trackerProtocolID = 0x41727101980
+
+	trackerConnectMinSize  = 16
+	trackerAnnounceMinSize = 20
+	trackerScrapeMinSize   = 8
+)
+
 // BitTorrent detects if the stream is a BitTorrent connection.
 // For the BitTorrent protocol specification, see https://www.bittorrent.org/beps/bep_0003.html
 func BitTorrent(_ context.Context, reader io.Reader) (*adapter.InboundContext, error) {
@@ -78,3 +90,24 @@ func UTP(_ context.Context, packet []byte) (*adapter.InboundContext, error) {
 		Protocol: constant.ProtocolUTP,
 	}, nil
 }
+
+// UDPTracker detects if the packet is a UDP Tracker Protocol packet.
+// For the UDP Tracker Protocol specification, see https://www.bittorrent.org/beps/bep_0015.html
+func UDPTracker(_ context.Context, packet []byte) (*adapter.InboundContext, error) {
+	switch {
+	case len(packet) >= trackerConnectMinSize &&
+		binary.BigEndian.Uint64(packet[:8]) == trackerProtocolID &&
+		binary.BigEndian.Uint32(packet[8:12]) == trackerConnectFlag:
+		fallthrough
+	case len(packet) >= trackerAnnounceMinSize &&
+		binary.BigEndian.Uint32(packet[8:12]) == trackerAnnounceFlag:
+		fallthrough
+	case len(packet) >= trackerScrapeMinSize &&
+		binary.BigEndian.Uint32(packet[8:12]) == trackerScrapeFlag:
+		return &adapter.InboundContext{
+			Protocol: constant.ProtocolUDPTracker,
+		}, nil
+	default:
+		return nil, os.ErrInvalid
+	}
+}

common/sniff/bittorrent_test.go

@@ -49,3 +49,33 @@ func TestSniffUTP(t *testing.T) {
 		require.Equal(t, constant.ProtocolUTP, metadata.Protocol)
 	}
 }
+
+func TestSniffUDPTracker(t *testing.T) {
+	t.Parallel()
+
+	connectPackets := []string{
+		// connect packets
+		"00000417271019800000000078e90560",
+		"00000417271019800000000022c5d64d",
+		"000004172710198000000000b3863541",
+
+		// announce packets
+		"3d7592ead4b8c9e300000001b871a3820000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000002092f616e6e6f756e6365",
+		"3d7592ead4b8c9e30000000188deed1c0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000002092f616e6e6f756e6365",
+		"3d7592ead4b8c9e300000001ceb948ad0beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a3362cdb7020ff920e5aa642c3d4066950dd1f01f4d00000000000000000000000000000000000000000000000000000000000000000000000000000000000002092f616e6e6f756e6365",
+
+		// scrape packets
+		"3d7592ead4b8c9e300000002d2f4bba5a94a8fe5ccb19ba61c4c0873d391e987982fbbd3",
+		"3d7592ead4b8c9e300000002441243292aae6c35c94fcfb415dbe95f408b9ce91ee846ed",
+		"3d7592ead4b8c9e300000002b2aa461b1ad1fa9661cf3fe45fb2504ad52ec6c67758e294",
+	}
+
+	for _, pkt := range connectPackets {
+		pkt, err := hex.DecodeString(pkt)
+		require.NoError(t, err)
+
+		metadata, err := sniff.UDPTracker(context.TODO(), pkt)
+		require.NoError(t, err)
+		require.Equal(t, constant.ProtocolUDPTracker, metadata.Protocol)
+	}
+}

constant/protocol.go

@@ -8,4 +8,5 @@ const (
 	ProtocolSTUN       = "stun"
 	ProtocolBitTorrent = "bittorrent"
 	ProtocolUTP        = "utp"
+	ProtocolUDPTracker = "udp-tracker"
 )

route/router.go

@@ -924,6 +924,7 @@ func (r *Router) RoutePacketConnection(ctx context.Context, conn N.PacketConn, m
 				sniff.QUICClientHello,
 				sniff.STUNMessage,
 				sniff.UTP,
+				sniff.UDPTracker,
 			)
 			if sniffMetadata != nil {
 				metadata.Protocol = sniffMetadata.Protocol