#61 add transparent proxy support

README_en.md

@@ -265,7 +265,7 @@ gost -L=:8080 -F=ss://aes-128-cfb:123456@server_ip:8338
 #### TLS
 There is built-in TLS certificate in gost, if you need to use other TLS certificate, there are two ways:
 * Place two files cert.pem (public key) and key.pem (private key) in the current working directory, gost will automatically load them.
-* Use the parameter to specify the path to the certificate file：
+* Use the parameter to specify the path to the certificate file:
 ```bash
 gost -L="http2://:443?cert=/path/to/my/cert/file&key=/path/to/my/key/file"
 ```

node.go

@@ -71,7 +71,7 @@ func ParseProxyNode(s string) (node ProxyNode, err error) {
 	}
 
 	switch node.Transport {
-	case "ws", "wss", "tls", "http2", "ssu", "quic", "kcp":
+	case "ws", "wss", "tls", "http2", "ssu", "quic", "kcp", "redirect":
 	case "https":
 		node.Protocol = "http"
 		node.Transport = "tls"

redirect.go

+package gost
+
+import (
+	"errors"
+	"fmt"
+	"github.com/golang/glog"
+	"net"
+	"syscall"
+)
+
+const (
+	SO_ORIGINAL_DST = 80
+)
+
+type RedsocksTCPServer struct {
+	Base *ProxyServer
+}
+
+func NewRedsocksTCPServer(base *ProxyServer) *RedsocksTCPServer {
+	return &RedsocksTCPServer{
+		Base: base,
+	}
+}
+
+func (s *RedsocksTCPServer) ListenAndServe() error {
+	laddr, err := net.ResolveTCPAddr("tcp", s.Base.Node.Addr)
+	if err != nil {
+		return err
+	}
+	ln, err := net.ListenTCP("tcp", laddr)
+	if err != nil {
+		return err
+	}
+
+	defer ln.Close()
+	for {
+		conn, err := ln.AcceptTCP()
+		if err != nil {
+			glog.V(LWARNING).Infoln(err)
+			continue
+		}
+		go s.handleRedirectTCP(conn)
+	}
+}
+
+func (s *RedsocksTCPServer) handleRedirectTCP(conn *net.TCPConn) {
+	srcAddr := conn.RemoteAddr()
+	dstAddr, conn, err := getOriginalDstAddr(conn)
+	if err != nil {
+		glog.V(LWARNING).Infof("[red-tcp] %s -> %s : %s", srcAddr, dstAddr, err)
+		return
+	}
+	defer conn.Close()
+
+	glog.V(LINFO).Infof("[red-tcp] %s -> %s", srcAddr, dstAddr)
+
+	cc, err := s.Base.Chain.Dial(dstAddr.String())
+	if err != nil {
+		glog.V(LWARNING).Infof("[red-tcp] %s -> %s : %s", srcAddr, dstAddr, err)
+		return
+	}
+	defer cc.Close()
+
+	glog.V(LINFO).Infof("[red-tcp] %s <-> %s", srcAddr, dstAddr)
+	s.Base.transport(conn, cc)
+	glog.V(LINFO).Infof("[red-tcp] %s >-< %s", srcAddr, dstAddr)
+}
+
+func getOriginalDstAddr(conn *net.TCPConn) (addr net.Addr, c *net.TCPConn, err error) {
+	defer conn.Close()
+
+	fc, err := conn.File()
+	if err != nil {
+		return
+	}
+	defer fc.Close()
+
+	mreq, err := syscall.GetsockoptIPv6Mreq(int(fc.Fd()), syscall.IPPROTO_IP, SO_ORIGINAL_DST)
+	if err != nil {
+		return
+	}
+
+	// only ipv4 support
+	ip := net.IPv4(mreq.Multiaddr[4], mreq.Multiaddr[5], mreq.Multiaddr[6], mreq.Multiaddr[7])
+	port := uint16(mreq.Multiaddr[2])<<8 + uint16(mreq.Multiaddr[3])
+	addr, err = net.ResolveTCPAddr("tcp4", fmt.Sprintf("%s:%d", ip.String(), port))
+	if err != nil {
+		return
+	}
+
+	cc, err := net.FileConn(fc)
+	if err != nil {
+		return
+	}
+
+	c, ok := cc.(*net.TCPConn)
+	if !ok {
+		err = errors.New("not a TCP connection")
+	}
+	return
+}

server.go

@@ -95,6 +95,8 @@ func (s *ProxyServer) Serve() error {
 			config.Key, _ = s.Node.Users[0].Password()
 		}
 		return NewKCPServer(s, config).ListenAndServe()
+	case "redirect":
+		return NewRedsocksTCPServer(s).ListenAndServe()
 	default:
 		ln, err = net.Listen("tcp", node.Addr)
 	}