From 8e846fe6f84d357371008bab30a6812d512edbbd Mon Sep 17 00:00:00 2001
From: Shelikhoo <xiaokangwang@outlook.com>
Date: Thu, 7 Sep 2017 06:55:15 +0800
Subject: [PATCH] Added UDP TPROXY Transmit Support

---
 proxy/dokodemo/dokodemo.go                    | 16 +++++-
 transport/internet/udp/sourceForgeSender.go   | 55 +++++++++++++++++++
 .../internet/udp/sourceForgeSender_bad.go     | 12 ++++
 3 files changed, 82 insertions(+), 1 deletion(-)
 create mode 100644 transport/internet/udp/sourceForgeSender.go
 create mode 100644 transport/internet/udp/sourceForgeSender_bad.go

diff --git a/proxy/dokodemo/dokodemo.go b/proxy/dokodemo/dokodemo.go
index 5b031aa25..faecbe12e 100644
--- a/proxy/dokodemo/dokodemo.go
+++ b/proxy/dokodemo/dokodemo.go
@@ -7,6 +7,8 @@ import (
 	"runtime"
 	"time"
 
+	gonet "net"
+
 	"v2ray.com/core/app"
 	"v2ray.com/core/app/dispatcher"
 	"v2ray.com/core/app/log"
@@ -16,6 +18,7 @@ import (
 	"v2ray.com/core/common/signal"
 	"v2ray.com/core/proxy"
 	"v2ray.com/core/transport/internet"
+	"v2ray.com/core/transport/internet/udp"
 )
 
 type DokodemoDoor struct {
@@ -88,7 +91,18 @@ func (d *DokodemoDoor) Process(ctx context.Context, network net.Network, conn in
 		if network == net.Network_TCP {
 			writer = buf.NewWriter(conn)
 		} else {
-			writer = buf.NewSequentialWriter(conn)
+			//if we are in TPROXY mode, use linux's udp forging functionality
+			if !d.config.FollowRedirect {
+				writer = buf.NewSequentialWriter(conn)
+			} else {
+				srca := gonet.UDPAddr{IP: dest.Address.IP(), Port: int(dest.Port.Value())}
+				origsend, err := udp.TransmitSocket(&srca, conn.RemoteAddr())
+				if err != nil {
+					return err
+				}
+				writer = buf.NewSequentialWriter(origsend)
+			}
+
 		}
 
 		if err := buf.Copy(inboundRay.InboundOutput(), writer, buf.UpdateActivity(timer)); err != nil {
diff --git a/transport/internet/udp/sourceForgeSender.go b/transport/internet/udp/sourceForgeSender.go
new file mode 100644
index 000000000..31d03a9e8
--- /dev/null
+++ b/transport/internet/udp/sourceForgeSender.go
@@ -0,0 +1,55 @@
+// +build linux
+
+package udp
+
+import (
+	"net"
+	"os"
+	"syscall"
+)
+
+//Currently, Only IPv4 Forge is supported
+func TransmitSocket(src net.Addr, dst net.Addr) (net.Conn, error) {
+	var fd int
+	var err error
+	fd, err = syscall.Socket(syscall.AF_INET, syscall.SOCK_DGRAM, 0)
+	if err != nil {
+		return nil, err
+	}
+	err = syscall.SetsockoptInt(fd, syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1)
+	if err != nil {
+		return nil, err
+	}
+
+	err = syscall.SetsockoptInt(fd, syscall.SOL_IP, syscall.IP_TRANSPARENT, 1)
+	if err != nil {
+		return nil, err
+	}
+
+	ip := src.(*net.UDPAddr).IP.To4()
+	var ip2 [4]byte
+	copy(ip2[:], ip)
+	srcaddr := syscall.SockaddrInet4{}
+	srcaddr.Addr = ip2
+	srcaddr.Port = src.(*net.UDPAddr).Port
+	err = syscall.Bind(fd, &srcaddr)
+	if err != nil {
+		return nil, err
+	}
+	ipd := dst.(*net.UDPAddr).IP.To4()
+	var ip2d [4]byte
+	copy(ip2d[:], ipd)
+	dstaddr := syscall.SockaddrInet4{}
+	dstaddr.Addr = ip2d
+	dstaddr.Port = dst.(*net.UDPAddr).Port
+	err = syscall.Connect(fd, &dstaddr)
+	if err != nil {
+		return nil, err
+	}
+	fdf := os.NewFile(uintptr(fd), "/dev/udp/")
+	c, err := net.FileConn(fdf)
+	if err != nil {
+		return nil, err
+	}
+	return c, nil
+}
diff --git a/transport/internet/udp/sourceForgeSender_bad.go b/transport/internet/udp/sourceForgeSender_bad.go
new file mode 100644
index 000000000..dadd40234
--- /dev/null
+++ b/transport/internet/udp/sourceForgeSender_bad.go
@@ -0,0 +1,12 @@
+// +build !linux
+
+package udp
+
+import (
+	"errors"
+	"net"
+)
+
+func TransmitionSocket(src net.Addr, dst net.Addr) (net.Conn, error) {
+	return nil, errors.New("Using an Linux only functionality on an non-Linux OS.")
+}