Lo outbound, allow you to redirect connection to the dispatcher again

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.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
+	}))
+}