add optional Dial option

the dial function provider a way to connect to server

cmd/server/server.go

@@ -1,9 +1,10 @@
 package main
 
 import (
-	"github.com/fangdingjun/socks"
+	socks "github.com/fangdingjun/socks-go"
 	"log"
 	"net"
+	"time"
 )
 
 func main() {
@@ -18,7 +19,8 @@ func main() {
 			continue
 		}
 		log.Printf("connected from %s", c.RemoteAddr())
-		s := socks.SocksConn{ClientConn: c}
+		d := net.Dialer{Timeout: 10 * time.Second}
+		s := socks.SocksConn{ClientConn: c, Dial: d.Dial}
 		go s.Serve()
 	}
 }

socks.go

@@ -4,6 +4,7 @@ import (
 	"io"
 	"log"
 	"net"
+	"time"
 )
 
 const (
@@ -15,8 +16,11 @@ const (
 	addrTypeIPv6   = 0x04
 )
 
+type dialFunc func(network, addr string) (net.Conn, error)
+
 type SocksConn struct {
 	ClientConn net.Conn
+	Dial       dialFunc
 }
 
 func (s *SocksConn) Serve() {
@@ -25,12 +29,18 @@ func (s *SocksConn) Serve() {
 	// read version
 	io.ReadFull(s.ClientConn, buf)
 
+	dial := s.Dial
+	if s.Dial == nil {
+		d := net.Dialer{Timeout: 10 * time.Second}
+		dial = d.Dial
+	}
+
 	switch buf[0] {
 	case socks4Version:
-		s4 := socks4Conn{client_conn: s.ClientConn}
+		s4 := socks4Conn{client_conn: s.ClientConn, dial: dial}
 		s4.Serve()
 	case socks5Version:
-		s5 := socks5Conn{client_conn: s.ClientConn}
+		s5 := socks5Conn{client_conn: s.ClientConn, dial: dial}
 		s5.Serve()
 	default:
 		log.Printf("error version %s", buf[0])

socks4.go

@@ -11,6 +11,7 @@ import (
 type socks4Conn struct {
 	server_conn net.Conn
 	client_conn net.Conn
+	dial        dialFunc
 }
 
 func (s4 *socks4Conn) Serve() {
@@ -92,7 +93,7 @@ func (s4 *socks4Conn) processRequest() error {
 	log.Printf("connecting to %s", target)
 
 	// connect to the target
-	s4.server_conn, err = net.Dial("tcp", target)
+	s4.server_conn, err = s4.dial("tcp", target)
 	if err != nil {
 		return err
 	}

socks5.go

@@ -13,6 +13,7 @@ type socks5Conn struct {
 	//addr        string
 	client_conn net.Conn
 	server_conn net.Conn
+	dial        dialFunc
 }
 
 func (s5 *socks5Conn) Serve() {
@@ -107,7 +108,7 @@ func (s5 *socks5Conn) processRequest() error {
 	log.Printf("connecing to %s", target)
 
 	// connect to the target
-	s5.server_conn, err = net.Dial("tcp", target)
+	s5.server_conn, err = s5.dial("tcp", target)
 	if err != nil {
 		return err
 	}