lib/pmp: Add NAT-PMP support (ref #698)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/2968

lib/pmp/pmp.go

@@ -0,0 +1,105 @@
+// Copyright (C) 2016 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package pmp
+
+import (
+	"fmt"
+	"net"
+	"strings"
+	"time"
+
+	"github.com/AudriusButkevicius/go-nat-pmp"
+	"github.com/jackpal/gateway"
+	"github.com/syncthing/syncthing/lib/nat"
+)
+
+func init() {
+	nat.Register(Discover)
+}
+
+func Discover(renewal, timeout time.Duration) []nat.Device {
+	ip, err := gateway.DiscoverGateway()
+	if err != nil {
+		l.Debugln("Failed to discover gateway", err)
+		return nil
+	}
+
+	l.Debugln("Discovered gateway at", ip)
+
+	c := natpmp.NewClient(ip, timeout)
+	// Try contacting the gateway, if it does not respond, assume it does not
+	// speak NAT-PMP.
+	_, err = c.GetExternalAddress()
+	if err != nil && strings.Contains(err.Error(), "Timed out") {
+		l.Debugln("Timeout trying to get external address, assume no NAT-PMP available")
+		return nil
+	}
+
+	var localIP net.IP
+	// Port comes from the natpmp package
+	conn, err := net.DialTimeout("udp", net.JoinHostPort(ip.String(), "5351"), timeout)
+	if err == nil {
+		conn.Close()
+		localIPAddress, _, err := net.SplitHostPort(conn.LocalAddr().String())
+		if err == nil {
+			localIP = net.ParseIP(localIPAddress)
+		} else {
+			l.Debugln("Failed to lookup local IP", err)
+		}
+	}
+
+	return []nat.Device{&wrapper{
+		renewal:   renewal,
+		localIP:   localIP,
+		gatewayIP: ip,
+		client:    c,
+	}}
+}
+
+type wrapper struct {
+	renewal   time.Duration
+	localIP   net.IP
+	gatewayIP net.IP
+	client    *natpmp.Client
+}
+
+func (w *wrapper) ID() string {
+	return fmt.Sprintf("NAT-PMP@%s", w.gatewayIP.String())
+}
+
+func (w *wrapper) GetLocalIPAddress() net.IP {
+	return w.localIP
+}
+
+func (w *wrapper) AddPortMapping(protocol nat.Protocol, internalPort, externalPort int, description string, duration time.Duration) (int, error) {
+	// NAT-PMP says that if duration is 0, the mapping is actually removed
+	// Swap the zero with the renewal value, which should make the lease for the
+	// exact amount of time between the calls.
+	if duration == 0 {
+		duration = w.renewal
+	}
+	result, err := w.client.AddPortMapping(strings.ToLower(string(protocol)), internalPort, externalPort, int(duration/time.Second))
+	port := 0
+	if result != nil {
+		port = int(result.MappedExternalPort)
+	}
+	return port, err
+}
+
+func (w *wrapper) GetExternalIPAddress() (net.IP, error) {
+	result, err := w.client.GetExternalAddress()
+	ip := net.IPv4zero
+	if result != nil {
+		ip = net.IPv4(
+			result.ExternalIPAddress[0],
+			result.ExternalIPAddress[1],
+			result.ExternalIPAddress[2],
+			result.ExternalIPAddress[3],
+		)
+	}
+	return ip, err
+}