loopback outbound, allow you to redirect connection to the dispatcher again (#770)

* Added Loop back proxy

* Added json processing for lo proxy

* Fix bug for lo proxy

* Fix bug for lo proxy

* rename the outbound name

* Loopback: update naming and fix lint issues

* Chore: change lo to loopback

Co-authored-by: kslr <kslrwang@gmail.com>
Co-authored-by: loyalsoldier <10487845+Loyalsoldier@users.noreply.github.com>

infra/conf/loopback.go

@@ -0,0 +1,14 @@
+package conf
+
+import (
+	"github.com/golang/protobuf/proto"
+	"github.com/v2fly/v2ray-core/v4/proxy/loopback"
+)
+
+type LoopbackConfig struct {
+	InboundTag string `json:"inboundTag"`
+}
+
+func (l LoopbackConfig) Build() (proto.Message, error) {
+	return &loopback.Config{InboundTag: l.InboundTag}, nil
+}

infra/conf/v2ray.go

@@ -36,6 +36,7 @@ var (
 		"trojan":      func() interface{} { return new(TrojanClientConfig) },
 		"mtproto":     func() interface{} { return new(MTProtoClientConfig) },
 		"dns":         func() interface{} { return new(DNSOutboundConfig) },
+		"loopback":    func() interface{} { return new(LoopbackConfig) },
 	}, "protocol", "settings")
 
 	ctllog = log.New(os.Stderr, "v2ctl> ", 0)

proxy/loopback/config.go

@@ -0,0 +1,3 @@
+package loopback
+
+//go:generate go run github.com/v2fly/v2ray-core/v4/common/errors/errorgen

proxy/loopback/config.pb.go

@@ -0,0 +1,155 @@
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// versions:
+// 	protoc-gen-go v1.25.0
+// 	protoc        v3.15.5
+// source: proxy/loopback/config.proto
+
+package loopback
+
+import (
+	proto "github.com/golang/protobuf/proto"
+	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
+	protoimpl "google.golang.org/protobuf/runtime/protoimpl"
+	reflect "reflect"
+	sync "sync"
+)
+
+const (
+	// Verify that this generated code is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(20 - protoimpl.MinVersion)
+	// Verify that runtime/protoimpl is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(protoimpl.MaxVersion - 20)
+)
+
+// This is a compile-time assertion that a sufficiently up-to-date version
+// of the legacy proto package is being used.
+const _ = proto.ProtoPackageIsVersion4
+
+type Config struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	InboundTag string `protobuf:"bytes,1,opt,name=inbound_tag,json=inboundTag,proto3" json:"inbound_tag,omitempty"`
+}
+
+func (x *Config) Reset() {
+	*x = Config{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_proxy_loopback_config_proto_msgTypes[0]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *Config) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*Config) ProtoMessage() {}
+
+func (x *Config) ProtoReflect() protoreflect.Message {
+	mi := &file_proxy_loopback_config_proto_msgTypes[0]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use Config.ProtoReflect.Descriptor instead.
+func (*Config) Descriptor() ([]byte, []int) {
+	return file_proxy_loopback_config_proto_rawDescGZIP(), []int{0}
+}
+
+func (x *Config) GetInboundTag() string {
+	if x != nil {
+		return x.InboundTag
+	}
+	return ""
+}
+
+var File_proxy_loopback_config_proto protoreflect.FileDescriptor
+
+var file_proxy_loopback_config_proto_rawDesc = []byte{
+	0x0a, 0x1b, 0x70, 0x72, 0x6f, 0x78, 0x79, 0x2f, 0x6c, 0x6f, 0x6f, 0x70, 0x62, 0x61, 0x63, 0x6b,
+	0x2f, 0x63, 0x6f, 0x6e, 0x66, 0x69, 0x67, 0x2e, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x12, 0x19, 0x76,
+	0x32, 0x72, 0x61, 0x79, 0x2e, 0x63, 0x6f, 0x72, 0x65, 0x2e, 0x70, 0x72, 0x6f, 0x78, 0x79, 0x2e,
+	0x6c, 0x6f, 0x6f, 0x70, 0x62, 0x61, 0x63, 0x6b, 0x22, 0x29, 0x0a, 0x06, 0x43, 0x6f, 0x6e, 0x66,
+	0x69, 0x67, 0x12, 0x1f, 0x0a, 0x0b, 0x69, 0x6e, 0x62, 0x6f, 0x75, 0x6e, 0x64, 0x5f, 0x74, 0x61,
+	0x67, 0x18, 0x01, 0x20, 0x01, 0x28, 0x09, 0x52, 0x0a, 0x69, 0x6e, 0x62, 0x6f, 0x75, 0x6e, 0x64,
+	0x54, 0x61, 0x67, 0x42, 0x6c, 0x0a, 0x1d, 0x63, 0x6f, 0x6d, 0x2e, 0x76, 0x32, 0x72, 0x61, 0x79,
+	0x2e, 0x63, 0x6f, 0x72, 0x65, 0x2e, 0x70, 0x72, 0x6f, 0x78, 0x79, 0x2e, 0x6c, 0x6f, 0x6f, 0x70,
+	0x62, 0x61, 0x63, 0x6b, 0x50, 0x01, 0x5a, 0x2d, 0x67, 0x69, 0x74, 0x68, 0x75, 0x62, 0x2e, 0x63,
+	0x6f, 0x6d, 0x2f, 0x76, 0x32, 0x66, 0x6c, 0x79, 0x2f, 0x76, 0x32, 0x72, 0x61, 0x79, 0x2d, 0x63,
+	0x6f, 0x72, 0x65, 0x2f, 0x76, 0x34, 0x2f, 0x70, 0x72, 0x6f, 0x78, 0x79, 0x2f, 0x6c, 0x6f, 0x6f,
+	0x70, 0x62, 0x61, 0x63, 0x6b, 0xaa, 0x02, 0x19, 0x56, 0x32, 0x52, 0x61, 0x79, 0x2e, 0x43, 0x6f,
+	0x72, 0x65, 0x2e, 0x50, 0x72, 0x6f, 0x78, 0x79, 0x2e, 0x4c, 0x6f, 0x6f, 0x70, 0x62, 0x61, 0x63,
+	0x6b, 0x62, 0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
+}
+
+var (
+	file_proxy_loopback_config_proto_rawDescOnce sync.Once
+	file_proxy_loopback_config_proto_rawDescData = file_proxy_loopback_config_proto_rawDesc
+)
+
+func file_proxy_loopback_config_proto_rawDescGZIP() []byte {
+	file_proxy_loopback_config_proto_rawDescOnce.Do(func() {
+		file_proxy_loopback_config_proto_rawDescData = protoimpl.X.CompressGZIP(file_proxy_loopback_config_proto_rawDescData)
+	})
+	return file_proxy_loopback_config_proto_rawDescData
+}
+
+var file_proxy_loopback_config_proto_msgTypes = make([]protoimpl.MessageInfo, 1)
+var file_proxy_loopback_config_proto_goTypes = []interface{}{
+	(*Config)(nil), // 0: v2ray.core.proxy.loopback.Config
+}
+var file_proxy_loopback_config_proto_depIdxs = []int32{
+	0, // [0:0] is the sub-list for method output_type
+	0, // [0:0] is the sub-list for method input_type
+	0, // [0:0] is the sub-list for extension type_name
+	0, // [0:0] is the sub-list for extension extendee
+	0, // [0:0] is the sub-list for field type_name
+}
+
+func init() { file_proxy_loopback_config_proto_init() }
+func file_proxy_loopback_config_proto_init() {
+	if File_proxy_loopback_config_proto != nil {
+		return
+	}
+	if !protoimpl.UnsafeEnabled {
+		file_proxy_loopback_config_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*Config); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+	}
+	type x struct{}
+	out := protoimpl.TypeBuilder{
+		File: protoimpl.DescBuilder{
+			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
+			RawDescriptor: file_proxy_loopback_config_proto_rawDesc,
+			NumEnums:      0,
+			NumMessages:   1,
+			NumExtensions: 0,
+			NumServices:   0,
+		},
+		GoTypes:           file_proxy_loopback_config_proto_goTypes,
+		DependencyIndexes: file_proxy_loopback_config_proto_depIdxs,
+		MessageInfos:      file_proxy_loopback_config_proto_msgTypes,
+	}.Build()
+	File_proxy_loopback_config_proto = out.File
+	file_proxy_loopback_config_proto_rawDesc = nil
+	file_proxy_loopback_config_proto_goTypes = nil
+	file_proxy_loopback_config_proto_depIdxs = nil
+}

proxy/loopback/config.proto

@@ -0,0 +1,11 @@
+syntax = "proto3";
+
+package v2ray.core.proxy.loopback;
+option csharp_namespace = "V2Ray.Core.Proxy.Loopback";
+option go_package = "github.com/v2fly/v2ray-core/v4/proxy/loopback";
+option java_package = "com.v2ray.core.proxy.loopback";
+option java_multiple_files = true;
+
+message Config {
+  string inbound_tag = 1;
+}

proxy/loopback/errors.generated.go

@@ -0,0 +1,9 @@
+package loopback
+
+import "github.com/v2fly/v2ray-core/v4/common/errors"
+
+type errPathObjHolder struct{}
+
+func newError(values ...interface{}) *errors.Error {
+	return errors.New(values...).WithPathObj(errPathObjHolder{})
+}

proxy/loopback/lookback.go

@@ -0,0 +1,122 @@
+// +build !confonly
+
+package loopback
+
+import (
+	"context"
+
+	core "github.com/v2fly/v2ray-core/v4"
+	"github.com/v2fly/v2ray-core/v4/common"
+	"github.com/v2fly/v2ray-core/v4/common/buf"
+	"github.com/v2fly/v2ray-core/v4/common/net"
+	"github.com/v2fly/v2ray-core/v4/common/retry"
+	"github.com/v2fly/v2ray-core/v4/common/session"
+	"github.com/v2fly/v2ray-core/v4/common/task"
+	"github.com/v2fly/v2ray-core/v4/features/routing"
+	"github.com/v2fly/v2ray-core/v4/transport"
+	"github.com/v2fly/v2ray-core/v4/transport/internet"
+)
+
+type Loopback struct {
+	config             *Config
+	dispatcherInstance routing.Dispatcher
+}
+
+func (l *Loopback) Process(ctx context.Context, link *transport.Link, _ internet.Dialer) error {
+	outbound := session.OutboundFromContext(ctx)
+	if outbound == nil || !outbound.Target.IsValid() {
+		return newError("target not specified.")
+	}
+	destination := outbound.Target
+
+	newError("opening connection to ", destination).WriteToLog(session.ExportIDToError(ctx))
+
+	input := link.Reader
+	output := link.Writer
+
+	var conn internet.Connection
+	err := retry.ExponentialBackoff(5, 100).On(func() error {
+		dialDest := destination
+
+		content := new(session.Content)
+		content.SkipDNSResolve = true
+
+		ctx = session.ContextWithContent(ctx, content)
+
+		inbound := session.InboundFromContext(ctx)
+
+		inbound.Tag = l.config.InboundTag
+
+		ctx = session.ContextWithInbound(ctx, inbound)
+
+		rawConn, err := l.dispatcherInstance.Dispatch(ctx, dialDest)
+		if err != nil {
+			return err
+		}
+
+		var readerOpt net.ConnectionOption
+		if dialDest.Network == net.Network_TCP {
+			readerOpt = net.ConnectionOutputMulti(rawConn.Reader)
+		} else {
+			readerOpt = net.ConnectionOutputMultiUDP(rawConn.Reader)
+		}
+
+		conn = net.NewConnection(net.ConnectionInputMulti(rawConn.Writer), readerOpt)
+		return nil
+	})
+	if err != nil {
+		return newError("failed to open connection to ", destination).Base(err)
+	}
+	defer conn.Close()
+
+	requestDone := func() error {
+		var writer buf.Writer
+		if destination.Network == net.Network_TCP {
+			writer = buf.NewWriter(conn)
+		} else {
+			writer = &buf.SequentialWriter{Writer: conn}
+		}
+
+		if err := buf.Copy(input, writer); err != nil {
+			return newError("failed to process request").Base(err)
+		}
+
+		return nil
+	}
+
+	responseDone := func() error {
+		var reader buf.Reader
+		if destination.Network == net.Network_TCP {
+			reader = buf.NewReader(conn)
+		} else {
+			reader = buf.NewPacketReader(conn)
+		}
+		if err := buf.Copy(reader, output); err != nil {
+			return newError("failed to process response").Base(err)
+		}
+
+		return nil
+	}
+
+	if err := task.Run(ctx, requestDone, task.OnSuccess(responseDone, task.Close(output))); err != nil {
+		return newError("connection ends").Base(err)
+	}
+
+	return nil
+}
+
+func (l *Loopback) init(config *Config, dispatcherInstance routing.Dispatcher) error {
+	l.dispatcherInstance = dispatcherInstance
+	l.config = config
+	return nil
+}
+
+func init() {
+	common.Must(common.RegisterConfig((*Config)(nil), func(ctx context.Context, config interface{}) (interface{}, error) {
+		l := new(Loopback)
+		err := core.RequireFeatures(ctx, func(dispatcherInstance routing.Dispatcher) error {
+			return l.init(config.(*Config), dispatcherInstance)
+		})
+		return l, err
+	}))
+}