Introduce DTLS sniffer

common/sniff/dtls.go

@@ -0,0 +1,31 @@
+package sniff
+
+import (
+	"context"
+	"os"
+
+	"github.com/sagernet/sing-box/adapter"
+	C "github.com/sagernet/sing-box/constant"
+)
+
+func DTLSRecord(ctx context.Context, packet []byte) (*adapter.InboundContext, error) {
+	const fixedHeaderSize = 13
+	if len(packet) < fixedHeaderSize {
+		return nil, os.ErrInvalid
+	}
+	contentType := packet[0]
+	switch contentType {
+	case 20, 21, 22, 23, 25:
+	default:
+		return nil, os.ErrInvalid
+	}
+	versionMajor := packet[1]
+	if versionMajor != 0xfe {
+		return nil, os.ErrInvalid
+	}
+	versionMinor := packet[2]
+	if versionMinor != 0xff && versionMinor != 0xfd {
+		return nil, os.ErrInvalid
+	}
+	return &adapter.InboundContext{Protocol: C.ProtocolDTLS}, nil
+}

common/sniff/dtls_test.go

@@ -0,0 +1,30 @@
+package sniff_test
+
+import (
+	"context"
+	"encoding/hex"
+	"testing"
+
+	"github.com/sagernet/sing-box/common/sniff"
+	C "github.com/sagernet/sing-box/constant"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestSniffDTLSClientHello(t *testing.T) {
+	t.Parallel()
+	packet, err := hex.DecodeString("16fefd0000000000000000007e010000720000000000000072fefd668a43523798e064bd806d0c87660de9c611a59bbdfc3892c4e072d94f2cafc40000000cc02bc02fc00ac014c02cc0300100003c000d0010000e0403050306030401050106010807ff01000100000a00080006001d00170018000b00020100000e000900060008000700010000170000")
+	require.NoError(t, err)
+	metadata, err := sniff.DTLSRecord(context.Background(), packet)
+	require.NoError(t, err)
+	require.Equal(t, metadata.Protocol, C.ProtocolDTLS)
+}
+
+func TestSniffDTLSClientApplicationData(t *testing.T) {
+	t.Parallel()
+	packet, err := hex.DecodeString("17fefd000100000000000100440001000000000001a4f682b77ecadd10f3f3a2f78d90566212366ff8209fd77314f5a49352f9bb9bd12f4daba0b4736ae29e46b9714d3b424b3e6d0234736619b5aa0d3f")
+	require.NoError(t, err)
+	metadata, err := sniff.DTLSRecord(context.Background(), packet)
+	require.NoError(t, err)
+	require.Equal(t, metadata.Protocol, C.ProtocolDTLS)
+}