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)
 }

inbound/trojan.go

@@ -89,7 +89,7 @@ func NewTrojan(ctx context.Context, router adapter.Router, logger log.ContextLog
 		return nil, err
 	}
 	if options.Transport != nil {
-		inbound.transport, err = v2ray.NewServerTransport(ctx, common.PtrValueOrDefault(options.Transport), inbound.tlsConfig, adapter.NewUpstreamHandler(adapter.InboundContext{}, inbound.newTransportConnection, nil, nil), inbound)
+		inbound.transport, err = v2ray.NewServerTransport(ctx, common.PtrValueOrDefault(options.Transport), inbound.tlsConfig, (*trojanTransportHandler)(inbound))
 		if err != nil {
 			return nil, E.Cause(err, "create server transport: ", options.Transport.Type)
 		}
@@ -216,3 +216,21 @@ func (h *Trojan) newPacketConnection(ctx context.Context, conn N.PacketConn, met
 	h.logger.InfoContext(ctx, "[", user, "] inbound packet connection to ", metadata.Destination)
 	return h.router.RoutePacketConnection(ctx, conn, metadata)
 }
+
+var _ adapter.V2RayServerTransportHandler = (*trojanTransportHandler)(nil)
+
+type trojanTransportHandler Trojan
+
+func (t *trojanTransportHandler) NewConnection(ctx context.Context, conn net.Conn, metadata M.Metadata) error {
+	return (*Trojan)(t).newTransportConnection(ctx, conn, adapter.InboundContext{
+		Source:      metadata.Source,
+		Destination: metadata.Destination,
+	})
+}
+
+func (t *trojanTransportHandler) FallbackConnection(ctx context.Context, conn net.Conn, metadata M.Metadata) error {
+	return (*Trojan)(t).fallbackConnection(ctx, conn, adapter.InboundContext{
+		Source:      metadata.Source,
+		Destination: metadata.Destination,
+	})
+}

inbound/vmess.go

@@ -72,7 +72,7 @@ func NewVMess(ctx context.Context, router adapter.Router, logger log.ContextLogg
 		}
 	}
 	if options.Transport != nil {
-		inbound.transport, err = v2ray.NewServerTransport(ctx, common.PtrValueOrDefault(options.Transport), inbound.tlsConfig, adapter.NewUpstreamHandler(adapter.InboundContext{}, inbound.newTransportConnection, nil, nil), inbound)
+		inbound.transport, err = v2ray.NewServerTransport(ctx, common.PtrValueOrDefault(options.Transport), inbound.tlsConfig, (*vmessTransportHandler)(inbound))
 		if err != nil {
 			return nil, E.Cause(err, "create server transport: ", options.Transport.Type)
 		}
@@ -183,3 +183,18 @@ func (h *VMess) newPacketConnection(ctx context.Context, conn N.PacketConn, meta
 	}
 	return h.router.RoutePacketConnection(ctx, conn, metadata)
 }
+
+var _ adapter.V2RayServerTransportHandler = (*vmessTransportHandler)(nil)
+
+type vmessTransportHandler VMess
+
+func (t *vmessTransportHandler) NewConnection(ctx context.Context, conn net.Conn, metadata M.Metadata) error {
+	return (*VMess)(t).newTransportConnection(ctx, conn, adapter.InboundContext{
+		Source:      metadata.Source,
+		Destination: metadata.Destination,
+	})
+}
+
+func (t *vmessTransportHandler) FallbackConnection(ctx context.Context, conn net.Conn, metadata M.Metadata) error {
+	return os.ErrInvalid
+}

include/quic_stub.go

@@ -11,7 +11,6 @@ import (
 	"github.com/sagernet/sing-box/option"
 	"github.com/sagernet/sing-box/transport/v2ray"
 	"github.com/sagernet/sing-dns"
-	E "github.com/sagernet/sing/common/exceptions"
 	"github.com/sagernet/sing/common/logger"
 	M "github.com/sagernet/sing/common/metadata"
 	N "github.com/sagernet/sing/common/network"
@@ -24,7 +23,7 @@ func init() {
 		return nil, C.ErrQUICNotIncluded
 	})
 	v2ray.RegisterQUICConstructor(
-		func(ctx context.Context, options option.V2RayQUICOptions, tlsConfig tls.ServerConfig, handler N.TCPConnectionHandler, errorHandler E.Handler) (adapter.V2RayServerTransport, error) {
+		func(ctx context.Context, options option.V2RayQUICOptions, tlsConfig tls.ServerConfig, handler adapter.V2RayServerTransportHandler) (adapter.V2RayServerTransport, error) {
 			return nil, C.ErrQUICNotIncluded
 		},
 		func(ctx context.Context, dialer N.Dialer, serverAddr M.Socksaddr, options option.V2RayQUICOptions, tlsConfig tls.Config) (adapter.V2RayClientTransport, error) {

transport/v2ray/grpc.go

@@ -10,14 +10,13 @@ import (
 	"github.com/sagernet/sing-box/option"
 	"github.com/sagernet/sing-box/transport/v2raygrpc"
 	"github.com/sagernet/sing-box/transport/v2raygrpclite"
-	E "github.com/sagernet/sing/common/exceptions"
 	M "github.com/sagernet/sing/common/metadata"
 	N "github.com/sagernet/sing/common/network"
 )
 
-func NewGRPCServer(ctx context.Context, options option.V2RayGRPCOptions, tlsConfig tls.ServerConfig, handler N.TCPConnectionHandler, errorHandler E.Handler) (adapter.V2RayServerTransport, error) {
+func NewGRPCServer(ctx context.Context, options option.V2RayGRPCOptions, tlsConfig tls.ServerConfig, handler adapter.V2RayServerTransportHandler) (adapter.V2RayServerTransport, error) {
 	if options.ForceLite {
-		return v2raygrpclite.NewServer(ctx, options, tlsConfig, handler, errorHandler)
+		return v2raygrpclite.NewServer(ctx, options, tlsConfig, handler)
 	}
 	return v2raygrpc.NewServer(ctx, options, tlsConfig, handler)
 }

transport/v2ray/grpc_lite.go

@@ -9,13 +9,12 @@ import (
 	"github.com/sagernet/sing-box/common/tls"
 	"github.com/sagernet/sing-box/option"
 	"github.com/sagernet/sing-box/transport/v2raygrpclite"
-	E "github.com/sagernet/sing/common/exceptions"
 	M "github.com/sagernet/sing/common/metadata"
 	N "github.com/sagernet/sing/common/network"
 )
 
-func NewGRPCServer(ctx context.Context, options option.V2RayGRPCOptions, tlsConfig tls.ServerConfig, handler N.TCPConnectionHandler, errorHandler E.Handler) (adapter.V2RayServerTransport, error) {
-	return v2raygrpclite.NewServer(ctx, options, tlsConfig, handler, errorHandler)
+func NewGRPCServer(ctx context.Context, options option.V2RayGRPCOptions, tlsConfig tls.ServerConfig, handler adapter.V2RayServerTransportHandler) (adapter.V2RayServerTransport, error) {
+	return v2raygrpclite.NewServer(ctx, options, tlsConfig, handler)
 }
 
 func NewGRPCClient(ctx context.Context, dialer N.Dialer, serverAddr M.Socksaddr, options option.V2RayGRPCOptions, tlsConfig tls.Config) (adapter.V2RayClientTransport, error) {

transport/v2ray/quic.go

@@ -7,7 +7,6 @@ import (
 	"github.com/sagernet/sing-box/adapter"
 	"github.com/sagernet/sing-box/common/tls"
 	"github.com/sagernet/sing-box/option"
-	E "github.com/sagernet/sing/common/exceptions"
 	M "github.com/sagernet/sing/common/metadata"
 	N "github.com/sagernet/sing/common/network"
 )
@@ -22,11 +21,11 @@ func RegisterQUICConstructor(server ServerConstructor[option.V2RayQUICOptions],
 	quicClientConstructor = client
 }
 
-func NewQUICServer(ctx context.Context, options option.V2RayQUICOptions, tlsConfig tls.ServerConfig, handler N.TCPConnectionHandler, errorHandler E.Handler) (adapter.V2RayServerTransport, error) {
+func NewQUICServer(ctx context.Context, options option.V2RayQUICOptions, tlsConfig tls.ServerConfig, handler adapter.V2RayServerTransportHandler) (adapter.V2RayServerTransport, error) {
 	if quicServerConstructor == nil {
 		return nil, os.ErrInvalid
 	}
-	return quicServerConstructor(ctx, options, tlsConfig, handler, errorHandler)
+	return quicServerConstructor(ctx, options, tlsConfig, handler)
 }
 
 func NewQUICClient(ctx context.Context, dialer N.Dialer, serverAddr M.Socksaddr, options option.V2RayQUICOptions, tlsConfig tls.Config) (adapter.V2RayClientTransport, error) {

transport/v2ray/transport.go

@@ -15,26 +15,26 @@ import (
 )
 
 type (
-	ServerConstructor[O any] func(ctx context.Context, options O, tlsConfig tls.ServerConfig, handler N.TCPConnectionHandler, errorHandler E.Handler) (adapter.V2RayServerTransport, error)
+	ServerConstructor[O any] func(ctx context.Context, options O, tlsConfig tls.ServerConfig, handler adapter.V2RayServerTransportHandler) (adapter.V2RayServerTransport, error)
 	ClientConstructor[O any] func(ctx context.Context, dialer N.Dialer, serverAddr M.Socksaddr, options O, tlsConfig tls.Config) (adapter.V2RayClientTransport, error)
 )
 
-func NewServerTransport(ctx context.Context, options option.V2RayTransportOptions, tlsConfig tls.ServerConfig, handler N.TCPConnectionHandler, errorHandler E.Handler) (adapter.V2RayServerTransport, error) {
+func NewServerTransport(ctx context.Context, options option.V2RayTransportOptions, tlsConfig tls.ServerConfig, handler adapter.V2RayServerTransportHandler) (adapter.V2RayServerTransport, error) {
 	if options.Type == "" {
 		return nil, nil
 	}
 	switch options.Type {
 	case C.V2RayTransportTypeHTTP:
-		return v2rayhttp.NewServer(ctx, options.HTTPOptions, tlsConfig, handler, errorHandler)
+		return v2rayhttp.NewServer(ctx, options.HTTPOptions, tlsConfig, handler)
 	case C.V2RayTransportTypeWebsocket:
-		return v2raywebsocket.NewServer(ctx, options.WebsocketOptions, tlsConfig, handler, errorHandler)
+		return v2raywebsocket.NewServer(ctx, options.WebsocketOptions, tlsConfig, handler)
 	case C.V2RayTransportTypeQUIC:
 		if tlsConfig == nil {
 			return nil, C.ErrTLSRequired
 		}
-		return NewQUICServer(ctx, options.QUICOptions, tlsConfig, handler, errorHandler)
+		return NewQUICServer(ctx, options.QUICOptions, tlsConfig, handler)
 	case C.V2RayTransportTypeGRPC:
-		return NewGRPCServer(ctx, options.GRPCOptions, tlsConfig, handler, errorHandler)
+		return NewGRPCServer(ctx, options.GRPCOptions, tlsConfig, handler)
 	default:
 		return nil, E.New("unknown transport type: " + options.Type)
 	}

transport/v2raygrpclite/server.go

@@ -26,7 +26,7 @@ import (
 var _ adapter.V2RayServerTransport = (*Server)(nil)
 
 type Server struct {
-	handler      N.TCPConnectionHandler
+	handler      adapter.V2RayServerTransportHandler
 	errorHandler E.Handler
 	httpServer   *http.Server
 	h2Server     *http2.Server
@@ -38,12 +38,11 @@ func (s *Server) Network() []string {
 	return []string{N.NetworkTCP}
 }
 
-func NewServer(ctx context.Context, options option.V2RayGRPCOptions, tlsConfig tls.ServerConfig, handler N.TCPConnectionHandler, errorHandler E.Handler) (*Server, error) {
+func NewServer(ctx context.Context, options option.V2RayGRPCOptions, tlsConfig tls.ServerConfig, handler adapter.V2RayServerTransportHandler) (*Server, error) {
 	server := &Server{
-		handler:      handler,
-		errorHandler: errorHandler,
-		path:         fmt.Sprintf("/%s/Tun", url.QueryEscape(options.ServiceName)),
-		h2Server:     new(http2.Server),
+		handler:  handler,
+		path:     fmt.Sprintf("/%s/Tun", url.QueryEscape(options.ServiceName)),
+		h2Server: new(http2.Server),
 	}
 	server.httpServer = &http.Server{
 		Handler: server,
@@ -68,19 +67,15 @@ func (s *Server) ServeHTTP(writer http.ResponseWriter, request *http.Request) {
 		return
 	}
 	if request.URL.Path != s.path {
-		request.Write(os.Stdout)
-		writer.WriteHeader(http.StatusNotFound)
-		s.badRequest(request, E.New("bad path: ", request.URL.Path))
+		s.fallbackRequest(request.Context(), writer, request, http.StatusNotFound, E.New("bad path: ", request.URL.Path))
 		return
 	}
 	if request.Method != http.MethodPost {
-		writer.WriteHeader(http.StatusNotFound)
-		s.badRequest(request, E.New("bad method: ", request.Method))
+		s.fallbackRequest(request.Context(), writer, request, http.StatusNotFound, E.New("bad method: ", request.Method))
 		return
 	}
 	if ct := request.Header.Get("Content-Type"); !strings.HasPrefix(ct, "application/grpc") {
-		writer.WriteHeader(http.StatusNotFound)
-		s.badRequest(request, E.New("bad content type: ", ct))
+		s.fallbackRequest(request.Context(), writer, request, http.StatusNotFound, E.New("bad content type: ", ct))
 		return
 	}
 	writer.Header().Set("Content-Type", "application/grpc")
@@ -93,8 +88,16 @@ func (s *Server) ServeHTTP(writer http.ResponseWriter, request *http.Request) {
 	conn.CloseWrapper()
 }
 
-func (s *Server) badRequest(request *http.Request, err error) {
-	s.errorHandler.NewError(request.Context(), E.Cause(err, "process connection from ", request.RemoteAddr))
+func (s *Server) fallbackRequest(ctx context.Context, writer http.ResponseWriter, request *http.Request, statusCode int, err error) {
+	conn := v2rayhttp.NewHTTPConn(request.Body, writer)
+	fErr := s.handler.FallbackConnection(ctx, &conn, M.Metadata{})
+	if fErr == nil {
+		return
+	} else if fErr == os.ErrInvalid {
+		fErr = nil
+	}
+	writer.WriteHeader(statusCode)
+	s.handler.NewError(request.Context(), E.Cause(E.Errors(err, E.Cause(fErr, "fallback connection")), "process connection from ", request.RemoteAddr))
 }
 
 func (s *Server) Serve(listener net.Listener) error {

transport/v2rayhttp/conn.go

@@ -22,7 +22,7 @@ type HTTPConn struct {
 	err    error
 }
 
-func newHTTPConn(reader io.Reader, writer io.Writer) HTTPConn {
+func NewHTTPConn(reader io.Reader, writer io.Writer) HTTPConn {
 	return HTTPConn{
 		reader: reader,
 		writer: writer,

transport/v2rayhttp/server.go

@@ -24,32 +24,30 @@ import (
 var _ adapter.V2RayServerTransport = (*Server)(nil)
 
 type Server struct {
-	ctx          context.Context
-	handler      N.TCPConnectionHandler
-	errorHandler E.Handler
-	httpServer   *http.Server
-	h2Server     *http2.Server
-	h2cHandler   http.Handler
-	host         []string
-	path         string
-	method       string
-	headers      http.Header
+	ctx        context.Context
+	handler    adapter.V2RayServerTransportHandler
+	httpServer *http.Server
+	h2Server   *http2.Server
+	h2cHandler http.Handler
+	host       []string
+	path       string
+	method     string
+	headers    http.Header
 }
 
 func (s *Server) Network() []string {
 	return []string{N.NetworkTCP}
 }
 
-func NewServer(ctx context.Context, options option.V2RayHTTPOptions, tlsConfig tls.ServerConfig, handler N.TCPConnectionHandler, errorHandler E.Handler) (*Server, error) {
+func NewServer(ctx context.Context, options option.V2RayHTTPOptions, tlsConfig tls.ServerConfig, handler adapter.V2RayServerTransportHandler) (*Server, error) {
 	server := &Server{
-		ctx:          ctx,
-		handler:      handler,
-		errorHandler: errorHandler,
-		h2Server:     new(http2.Server),
-		host:         options.Host,
-		path:         options.Path,
-		method:       options.Method,
-		headers:      make(http.Header),
+		ctx:      ctx,
+		handler:  handler,
+		h2Server: new(http2.Server),
+		host:     options.Host,
+		path:     options.Path,
+		method:   options.Method,
+		headers:  make(http.Header),
 	}
 	if server.method == "" {
 		server.method = "PUT"
@@ -83,18 +81,15 @@ func (s *Server) ServeHTTP(writer http.ResponseWriter, request *http.Request) {
 	}
 	host := request.Host
 	if len(s.host) > 0 && !common.Contains(s.host, host) {
-		writer.WriteHeader(http.StatusBadRequest)
-		s.badRequest(request, E.New("bad host: ", host))
+		s.fallbackRequest(request.Context(), writer, request, http.StatusBadRequest, E.New("bad host: ", host))
 		return
 	}
 	if !strings.HasPrefix(request.URL.Path, s.path) {
-		writer.WriteHeader(http.StatusNotFound)
-		s.badRequest(request, E.New("bad path: ", request.URL.Path))
+		s.fallbackRequest(request.Context(), writer, request, http.StatusNotFound, E.New("bad path: ", request.URL.Path))
 		return
 	}
 	if request.Method != s.method {
-		writer.WriteHeader(http.StatusNotFound)
-		s.badRequest(request, E.New("bad method: ", request.Method))
+		s.fallbackRequest(request.Context(), writer, request, http.StatusNotFound, E.New("bad method: ", request.Method))
 		return
 	}
 
@@ -114,14 +109,13 @@ func (s *Server) ServeHTTP(writer http.ResponseWriter, request *http.Request) {
 	if h, ok := writer.(http.Hijacker); ok {
 		conn, _, err := h.Hijack()
 		if err != nil {
-			writer.WriteHeader(http.StatusInternalServerError)
-			s.badRequest(request, E.Cause(err, "hijack conn"))
+			s.fallbackRequest(request.Context(), writer, request, http.StatusInternalServerError, E.Cause(err, "hijack conn"))
 			return
 		}
 		s.handler.NewConnection(request.Context(), conn, metadata)
 	} else {
 		conn := NewHTTP2Wrapper(&ServerHTTPConn{
-			newHTTPConn(request.Body, writer),
+			NewHTTPConn(request.Body, writer),
 			writer.(http.Flusher),
 		})
 		s.handler.NewConnection(request.Context(), conn, metadata)
@@ -129,8 +123,16 @@ func (s *Server) ServeHTTP(writer http.ResponseWriter, request *http.Request) {
 	}
 }
 
-func (s *Server) badRequest(request *http.Request, err error) {
-	s.errorHandler.NewError(request.Context(), E.Cause(err, "process connection from ", request.RemoteAddr))
+func (s *Server) fallbackRequest(ctx context.Context, writer http.ResponseWriter, request *http.Request, statusCode int, err error) {
+	conn := NewHTTPConn(request.Body, writer)
+	fErr := s.handler.FallbackConnection(ctx, &conn, M.Metadata{})
+	if fErr == nil {
+		return
+	} else if fErr == os.ErrInvalid {
+		fErr = nil
+	}
+	writer.WriteHeader(statusCode)
+	s.handler.NewError(request.Context(), E.Cause(E.Errors(err, E.Cause(fErr, "fallback connection")), "process connection from ", request.RemoteAddr))
 }
 
 func (s *Server) Serve(listener net.Listener) error {

transport/v2rayquic/server.go

@@ -23,13 +23,13 @@ type Server struct {
 	ctx          context.Context
 	tlsConfig    *tls.STDConfig
 	quicConfig   *quic.Config
-	handler      N.TCPConnectionHandler
+	handler      adapter.V2RayServerTransportHandler
 	errorHandler E.Handler
 	udpListener  net.PacketConn
 	quicListener quic.Listener
 }
 
-func NewServer(ctx context.Context, options option.V2RayQUICOptions, tlsConfig tls.ServerConfig, handler N.TCPConnectionHandler, errorHandler E.Handler) (adapter.V2RayServerTransport, error) {
+func NewServer(ctx context.Context, options option.V2RayQUICOptions, tlsConfig tls.ServerConfig, handler adapter.V2RayServerTransportHandler) (adapter.V2RayServerTransport, error) {
 	quicConfig := &quic.Config{
 		DisablePathMTUDiscovery: !C.IsLinux && !C.IsWindows,
 	}
@@ -41,11 +41,10 @@ func NewServer(ctx context.Context, options option.V2RayQUICOptions, tlsConfig t
 		stdConfig.NextProtos = []string{"h2", "http/1.1"}
 	}
 	server := &Server{
-		ctx:          ctx,
-		tlsConfig:    stdConfig,
-		quicConfig:   quicConfig,
-		handler:      handler,
-		errorHandler: errorHandler,
+		ctx:        ctx,
+		tlsConfig:  stdConfig,
+		quicConfig: quicConfig,
+		handler:    handler,
 	}
 	return server, nil
 }

transport/v2raywebsocket/server.go

@@ -12,6 +12,7 @@ import (
 	"github.com/sagernet/sing-box/common/tls"
 	C "github.com/sagernet/sing-box/constant"
 	"github.com/sagernet/sing-box/option"
+	"github.com/sagernet/sing-box/transport/v2rayhttp"
 	"github.com/sagernet/sing/common"
 	"github.com/sagernet/sing/common/buf"
 	"github.com/sagernet/sing/common/bufio"
@@ -26,19 +27,17 @@ var _ adapter.V2RayServerTransport = (*Server)(nil)
 
 type Server struct {
 	ctx                 context.Context
-	handler             N.TCPConnectionHandler
-	errorHandler        E.Handler
+	handler             adapter.V2RayServerTransportHandler
 	httpServer          *http.Server
 	path                string
 	maxEarlyData        uint32
 	earlyDataHeaderName string
 }
 
-func NewServer(ctx context.Context, options option.V2RayWebsocketOptions, tlsConfig tls.ServerConfig, handler N.TCPConnectionHandler, errorHandler E.Handler) (*Server, error) {
+func NewServer(ctx context.Context, options option.V2RayWebsocketOptions, tlsConfig tls.ServerConfig, handler adapter.V2RayServerTransportHandler) (*Server, error) {
 	server := &Server{
 		ctx:                 ctx,
 		handler:             handler,
-		errorHandler:        errorHandler,
 		path:                options.Path,
 		maxEarlyData:        options.MaxEarlyData,
 		earlyDataHeaderName: options.EarlyDataHeaderName,
@@ -71,8 +70,7 @@ var upgrader = websocket.Upgrader{
 func (s *Server) ServeHTTP(writer http.ResponseWriter, request *http.Request) {
 	if s.maxEarlyData == 0 || s.earlyDataHeaderName != "" {
 		if request.URL.Path != s.path {
-			writer.WriteHeader(http.StatusNotFound)
-			s.badRequest(request, E.New("bad path: ", request.URL.Path))
+			s.fallbackRequest(request.Context(), writer, request, http.StatusNotFound, E.New("bad path: ", request.URL.Path))
 			return
 		}
 	}
@@ -86,8 +84,7 @@ func (s *Server) ServeHTTP(writer http.ResponseWriter, request *http.Request) {
 			earlyDataStr := request.URL.RequestURI()[len(s.path):]
 			earlyData, err = base64.RawURLEncoding.DecodeString(earlyDataStr)
 		} else {
-			writer.WriteHeader(http.StatusNotFound)
-			s.badRequest(request, E.New("bad path: ", request.URL.Path))
+			s.fallbackRequest(request.Context(), writer, request, http.StatusNotFound, E.New("bad path: ", request.URL.Path))
 			return
 		}
 	} else {
@@ -97,13 +94,12 @@ func (s *Server) ServeHTTP(writer http.ResponseWriter, request *http.Request) {
 		}
 	}
 	if err != nil {
-		writer.WriteHeader(http.StatusBadRequest)
-		s.badRequest(request, E.Cause(err, "decode early data"))
+		s.fallbackRequest(request.Context(), writer, request, http.StatusBadRequest, E.Cause(err, "decode early data"))
 		return
 	}
 	wsConn, err := upgrader.Upgrade(writer, request, nil)
 	if err != nil {
-		s.badRequest(request, E.Cause(err, "upgrade websocket connection"))
+		s.fallbackRequest(request.Context(), writer, request, http.StatusBadRequest, E.Cause(err, "upgrade websocket connection"))
 		return
 	}
 	var metadata M.Metadata
@@ -115,8 +111,16 @@ func (s *Server) ServeHTTP(writer http.ResponseWriter, request *http.Request) {
 	s.handler.NewConnection(request.Context(), conn, metadata)
 }
 
-func (s *Server) badRequest(request *http.Request, err error) {
-	s.errorHandler.NewError(request.Context(), E.Cause(err, "process connection from ", request.RemoteAddr))
+func (s *Server) fallbackRequest(ctx context.Context, writer http.ResponseWriter, request *http.Request, statusCode int, err error) {
+	conn := v2rayhttp.NewHTTPConn(request.Body, writer)
+	fErr := s.handler.FallbackConnection(ctx, &conn, M.Metadata{})
+	if fErr == nil {
+		return
+	} else if fErr == os.ErrInvalid {
+		fErr = nil
+	}
+	writer.WriteHeader(statusCode)
+	s.handler.NewError(request.Context(), E.Cause(E.Errors(err, E.Cause(fErr, "fallback connection")), "process connection from ", request.RemoteAddr))
 }
 
 func (s *Server) Network() []string {