forwarder: support curl like interface parameter

README.md

@@ -222,6 +222,8 @@ Forwarder option scheme: FORWARD_URL#OPTIONS
   Examples:
     socks5://1.1.1.1:1080#priority=100
     vmess://[security:]uuid@host:port?alterID=num#priority=200
+    vmess://[security:]uuid@host:port?alterID=num#priority=200&interface=192.168.1.99
+    vmess://[security:]uuid@host:port?alterID=num#priority=200&interface=eth0
 
 Config file format(see `glider.conf.example` as an example):
   # COMMENT LINE

proxy/direct.go

@@ -8,51 +8,62 @@ import (
 
 // Direct proxy
 type Direct struct {
-	*net.Dialer
-	addr net.Addr
+	iface *net.Interface
+	ip    net.IP
 }
 
 // Default dialer
-var Default = &Direct{Dialer: &net.Dialer{}}
+var Default = &Direct{}
 
 // NewDirect returns a Direct dialer
-func NewDirect(intface string) *Direct {
-	d := &Direct{}
-	dialer := &net.Dialer{}
+func NewDirect(intface string) (*Direct, error) {
+	if intface == "" {
+		return &Direct{}, nil
+	}
 
 	ip := net.ParseIP(intface)
-	if ip == nil {
+	if ip != nil {
+		return &Direct{ip: ip}, nil
+	}
+
 	iface, err := net.InterfaceByName(intface)
 	if err != nil {
-			return nil
+		return nil, err
 	}
 
-		addrs, err := iface.Addrs()
-		if err != nil {
-			d.addr = addrs[0]
-		}
-	}
-
-	d.addr = &net.TCPAddr{
-		IP:   ip,
-		Port: 0,
-	}
-
-	dialer.LocalAddr = d.addr
-
-	return d
+	return &Direct{iface: iface}, nil
 }
 
 // Addr returns forwarder's address
 func (d *Direct) Addr() string { return "DIRECT" }
 
 // Dial connects to the address addr on the network net
-func (d *Direct) Dial(network, addr string) (net.Conn, error) {
+func (d *Direct) Dial(network, addr string) (c net.Conn, err error) {
+	for _, ip := range d.LocalIPs() {
+		c, err = d.dial(network, addr, ip)
+		// log.F("dial %s using ip: %s", addr, ip)
+		if err == nil {
+			break
+		}
+	}
+	return
+}
+
+func (d *Direct) dial(network, addr string, localIP net.IP) (net.Conn, error) {
 	if network == "uot" {
 		network = "udp"
 	}
 
-	c, err := d.Dialer.Dial(network, addr)
+	var localAddr net.Addr
+	switch network {
+	case "tcp":
+		localAddr = &net.TCPAddr{IP: localIP}
+	case "udp":
+		localAddr = &net.UDPAddr{IP: localIP}
+	}
+
+	dialer := &net.Dialer{LocalAddr: localAddr}
+	c, err := dialer.Dial(network, addr)
 	if err != nil {
 		return nil, err
 	}
@@ -66,7 +77,8 @@ func (d *Direct) Dial(network, addr string) (net.Conn, error) {
 
 // DialUDP connects to the given address
 func (d *Direct) DialUDP(network, addr string) (net.PacketConn, net.Addr, error) {
-	pc, err := net.ListenPacket(network, d.Dialer.LocalAddr.String())
+	// TODO: support specifying local interface
+	pc, err := net.ListenPacket(network, "")
 	if err != nil {
 		log.F("ListenPacket error: %s", err)
 		return nil, nil, err
@@ -78,3 +90,27 @@ func (d *Direct) DialUDP(network, addr string) (net.PacketConn, net.Addr, error)
 
 // NextDialer returns the next dialer
 func (d *Direct) NextDialer(dstAddr string) Dialer { return d }
+
+// LocalIPs returns ip addresses according to the specified interface
+func (d *Direct) LocalIPs() (ips []net.IP) {
+	if d.ip != nil {
+		ips = []net.IP{d.ip}
+		return
+	}
+
+	if d.iface == nil {
+		ips = []net.IP{nil}
+		return
+	}
+
+	ipnets, err := d.iface.Addrs()
+	if err != nil {
+		return
+	}
+
+	for _, ipnet := range ipnets {
+		ips = append(ips, ipnet.(*net.IPNet).IP)
+	}
+
+	return
+}

proxy/forwarder.go

@@ -31,7 +31,12 @@ func ForwarderFromURL(s string) (f *Forwarder, err error) {
 		err = f.parseOption(ss[1])
 	}
 
-	var d Dialer = NewDirect(f.intface)
+	var d Dialer
+	d, err = NewDirect(f.intface)
+	if err != nil {
+		return nil, err
+	}
+
 	for _, url := range strings.Split(ss[0], ",") {
 		d, err = DialerFromURL(url, d)
 		if err != nil {