Add fallback support for v2ray transport

adapter/v2ray.go

@@ -3,6 +3,10 @@ package adapter
 import (
 	"context"
 	"net"
+
+	E "github.com/sagernet/sing/common/exceptions"
+	M "github.com/sagernet/sing/common/metadata"
+	N "github.com/sagernet/sing/common/network"
 )
 
 type V2RayServerTransport interface {
@@ -12,6 +16,12 @@ type V2RayServerTransport interface {
 	Close() error
 }
 
+type V2RayServerTransportHandler interface {
+	N.TCPConnectionHandler
+	E.Handler
+	FallbackConnection(ctx context.Context, conn net.Conn, metadata M.Metadata) error
+}
+
 type V2RayClientTransport interface {
 	DialContext(ctx context.Context) (net.Conn, error)
 }