/
nat.go
204 lines (184 loc) · 5.58 KB
/
nat.go
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package nat
import (
"errors"
"fmt"
natpmp "github.com/jackpal/go-nat-pmp"
"net"
"strings"
"sync"
"time"
)
type Mapper interface {
AddMapping(protocol string, extport, intport int, name string, lifetime time.Duration) error
DeleteMapping(protocol string, extport, intport int) error
ExternalIP() (net.IP, error)
String() string
}
// Parse parses a NAT interface description.
// The following formats are currently accepted.
// Note that mechanism names are not case-sensitive.
//
// "" or "none" return nil
// "extip:77.12.33.4" will assume the local machine is reachable on the given IP
// "any" uses the first auto-detected mechanism
// "upnp" uses the Universal Plug and Play protocol
// "pmp" uses NAT-PMP with an auto-detected gateway address
// "pmp:192.168.0.1" uses NAT-PMP with the given gateway address
func Parse(spec string) (Mapper, error) {
var (
parts = strings.SplitN(spec, ":", 2)
mech = strings.ToLower(parts[0])
ip net.IP
)
if len(parts) > 1 {
ip = net.ParseIP(parts[1])
if ip == nil {
return nil, errors.New("invalid IP address")
}
}
switch mech {
case "", "none", "off":
return nil, nil
case "any", "auto", "on":
return Any(), nil
case "extip", "ip":
if ip == nil {
return nil, errors.New("missing IP address")
}
return ExtIP(ip), nil
case "upnp":
return UPnP(), nil
case "pmp", "natpmp", "nat-pmp":
return PMP(ip), nil
default:
return nil, fmt.Errorf("unknown mechanism %q", parts[0])
}
}
const (
mapTimeout = 20 * time.Minute
mapUpdateInterval = 15 * time.Minute
)
// Map adds a port mapping on m and keeps it alive until c is closed.
// This function is typically invoked in its own goroutine.
func Map(m Mapper, c chan struct{}, protocol string, extport, intport int, name string) {
refresh := time.NewTimer(mapUpdateInterval)
defer func() {
refresh.Stop()
if err := m.DeleteMapping(protocol, extport, intport); err != nil {
// empty
}
}()
if err := m.AddMapping(protocol, extport, intport, name, mapTimeout); err != nil {
// empty
}
for {
select {
case _, ok := <-c:
if !ok {
return
}
case <-refresh.C:
if err := m.AddMapping(protocol, extport, intport, name, mapTimeout); err != nil {
// empty
}
refresh.Reset(mapUpdateInterval)
}
}
}
// ExtIP assumes that the local machine is reachable on the given
// external IP address, and that any required ports were mapped manually.
// Mapping operations will not return an error but won't actually do anything.
type ExtIP net.IP
func (n ExtIP) ExternalIP() (net.IP, error) { return net.IP(n), nil }
func (n ExtIP) String() string { return fmt.Sprintf("ExtIP(%v)", net.IP(n)) }
// These do nothing.
func (ExtIP) AddMapping(string, int, int, string, time.Duration) error { return nil }
func (ExtIP) DeleteMapping(string, int, int) error { return nil }
// Any returns a port mapper that tries to discover any supported
// mechanism on the local network.
func Any() Mapper {
// TODO: attempt to discover whether the local machine has an
// Internet-class address. Return ExtIP in this case.
return startautodisc("UPnP or NAT-PMP", func() Mapper {
found := make(chan Mapper, 2)
go func() { found <- discoverUPnP() }()
go func() { found <- discoverPMP() }()
for i := 0; i < cap(found); i++ {
if c := <-found; c != nil {
return c
}
}
return nil
})
}
// UPnP returns a port mapper that uses UPnP. It will attempt to
// discover the address of your router using UDP broadcasts.
func UPnP() Mapper {
return startautodisc("UPnP", discoverUPnP)
}
// PMP returns a port mapper that uses NAT-PMP. The provided gateway
// address should be the IP of your router. If the given gateway
// address is nil, PMP will attempt to auto-discover the router.
func PMP(gateway net.IP) Mapper {
if gateway != nil {
return &pmp{gw: gateway, c: natpmp.NewClient(gateway)}
}
return startautodisc("NAT-PMP", discoverPMP)
}
// autodisc represents a port mapping mechanism that is still being
// auto-discovered. Calls to the Interface methods on this type will
// wait until the discovery is done and then call the method on the
// discovered mechanism.
//
// This type is useful because discovery can take a while but we
// want return an Interface value from UPnP, PMP and Auto immediately.
type autodisc struct {
what string // type of interface being autodiscovered
once sync.Once
doit func() Mapper
mu sync.Mutex
found Mapper
}
func startautodisc(what string, doit func() Mapper) Mapper {
// TODO: monitor network configuration and rerun doit when it changes.
return &autodisc{what: what, doit: doit}
}
func (n *autodisc) AddMapping(protocol string, extport, intport int, name string, lifetime time.Duration) error {
if err := n.wait(); err != nil {
return err
}
return n.found.AddMapping(protocol, extport, intport, name, lifetime)
}
func (n *autodisc) DeleteMapping(protocol string, extport, intport int) error {
if err := n.wait(); err != nil {
return err
}
return n.found.DeleteMapping(protocol, extport, intport)
}
func (n *autodisc) ExternalIP() (net.IP, error) {
if err := n.wait(); err != nil {
return nil, err
}
return n.found.ExternalIP()
}
func (n *autodisc) String() string {
n.mu.Lock()
defer n.mu.Unlock()
if n.found == nil {
return n.what
} else {
return n.found.String()
}
}
// wait blocks until auto-discovery has been performed.
func (n *autodisc) wait() error {
n.once.Do(func() {
n.mu.Lock()
n.found = n.doit()
n.mu.Unlock()
})
if n.found == nil {
return fmt.Errorf("no %s router discovered", n.what)
}
return nil
}