lib/nat: Add a nat package and service to track mappings on multiple IGDs

lib/nat/structs.go

@@ -0,0 +1,129 @@
+// Copyright (C) 2015 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 nat
+
+import (
+	"fmt"
+	"net"
+	"time"
+
+	"github.com/syncthing/syncthing/lib/sync"
+)
+
+type MappingChangeSubscriber func(*Mapping, []Address, []Address)
+
+type Mapping struct {
+	protocol Protocol
+	address  Address
+
+	extAddresses map[string]Address // NAT ID -> Address
+	expires      time.Time
+	subscribers  []MappingChangeSubscriber
+	mut          sync.RWMutex
+}
+
+func (m *Mapping) setAddress(id string, address Address) {
+	m.mut.Lock()
+	if existing, ok := m.extAddresses[id]; !ok || !existing.Equal(address) {
+		l.Infof("New NAT port mapping: external %s address %s to local address %s.", m.protocol, address, m.address)
+		m.extAddresses[id] = address
+	}
+	m.mut.Unlock()
+}
+
+func (m *Mapping) removeAddress(id string) {
+	m.mut.Lock()
+	addr, ok := m.extAddresses[id]
+	if ok {
+		l.Infof("Removing NAT port mapping: external %s address %s, NAT %s is no longer available.", m.protocol, addr, id)
+		delete(m.extAddresses, id)
+	}
+	m.mut.Unlock()
+}
+
+func (m *Mapping) notify(added, removed []Address) {
+	m.mut.RLock()
+	for _, subscriber := range m.subscribers {
+		subscriber(m, added, removed)
+	}
+	m.mut.RUnlock()
+}
+
+func (m *Mapping) addressMap() map[string]Address {
+	m.mut.RLock()
+	addrMap := m.extAddresses
+	m.mut.RUnlock()
+	return addrMap
+}
+
+func (m *Mapping) Protocol() Protocol {
+	return m.protocol
+}
+
+func (m *Mapping) Address() Address {
+	return m.address
+}
+
+func (m *Mapping) ExternalAddresses() []Address {
+	m.mut.RLock()
+	addrs := make([]Address, 0, len(m.extAddresses))
+	for _, addr := range m.extAddresses {
+		addrs = append(addrs, addr)
+	}
+	m.mut.RUnlock()
+	return addrs
+}
+
+func (m *Mapping) OnChanged(subscribed MappingChangeSubscriber) {
+	m.mut.Lock()
+	m.subscribers = append(m.subscribers, subscribed)
+	m.mut.Unlock()
+}
+
+func (m *Mapping) String() string {
+	return fmt.Sprintf("%s %s", m.protocol, m.address)
+}
+
+func (m *Mapping) GoString() string {
+	return m.String()
+}
+
+// Checks if the mappings local IP address matches the IP address of the gateway
+// For example, if we are explicitly listening on 192.168.0.12, there is no
+// point trying to acquire a mapping on a gateway to which the local IP is
+// 10.0.0.1. Fallback to true if any of the IPs is not there.
+func (m *Mapping) validGateway(ip net.IP) bool {
+	if m.address.IP == nil || ip == nil || m.address.IP.IsUnspecified() || ip.IsUnspecified() {
+		return true
+	}
+	return m.address.IP.Equal(ip)
+}
+
+// Address is essentially net.TCPAddr yet is more general, and has a few helper
+// methods which reduce boilerplate code.
+type Address struct {
+	IP   net.IP
+	Port int
+}
+
+func (a Address) Equal(b Address) bool {
+	return a.Port == b.Port && a.IP.Equal(b.IP)
+}
+
+func (a Address) String() string {
+	var ipStr string
+	if a.IP == nil {
+		ipStr = net.IPv4zero.String()
+	} else {
+		ipStr = a.IP.String()
+	}
+	return net.JoinHostPort(ipStr, fmt.Sprintf("%d", a.Port))
+}
+
+func (a Address) GoString() string {
+	return a.String()
+}