ceremonyclient/go-libp2p/p2p/net/nat/nat.go

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2023-08-21 03:50:38 +00:00
package nat
import (
"context"
"errors"
"fmt"
"net/netip"
"sync"
"time"
logging "github.com/ipfs/go-log/v2"
"github.com/libp2p/go-nat"
)
// ErrNoMapping signals no mapping exists for an address
var ErrNoMapping = errors.New("mapping not established")
var log = logging.Logger("nat")
// MappingDuration is a default port mapping duration.
// Port mappings are renewed every (MappingDuration / 3)
const MappingDuration = time.Minute
// CacheTime is the time a mapping will cache an external address for
const CacheTime = 15 * time.Second
type entry struct {
protocol string
port int
}
// so we can mock it in tests
var discoverGateway = nat.DiscoverGateway
// DiscoverNAT looks for a NAT device in the network and returns an object that can manage port mappings.
func DiscoverNAT(ctx context.Context) (*NAT, error) {
natInstance, err := discoverGateway(ctx)
if err != nil {
return nil, err
}
var extAddr netip.Addr
extIP, err := natInstance.GetExternalAddress()
if err == nil {
extAddr, _ = netip.AddrFromSlice(extIP)
}
// Log the device addr.
addr, err := natInstance.GetDeviceAddress()
if err != nil {
log.Debug("DiscoverGateway address error:", err)
} else {
log.Debug("DiscoverGateway address:", addr)
}
ctx, cancel := context.WithCancel(context.Background())
nat := &NAT{
nat: natInstance,
extAddr: extAddr,
mappings: make(map[entry]int),
ctx: ctx,
ctxCancel: cancel,
}
nat.refCount.Add(1)
go func() {
defer nat.refCount.Done()
nat.background()
}()
return nat, nil
}
// NAT is an object that manages address port mappings in
// NATs (Network Address Translators). It is a long-running
// service that will periodically renew port mappings,
// and keep an up-to-date list of all the external addresses.
type NAT struct {
natmu sync.Mutex
nat nat.NAT
// External IP of the NAT. Will be renewed periodically (every CacheTime).
extAddr netip.Addr
refCount sync.WaitGroup
ctx context.Context
ctxCancel context.CancelFunc
mappingmu sync.RWMutex // guards mappings
closed bool
mappings map[entry]int
}
// Close shuts down all port mappings. NAT can no longer be used.
func (nat *NAT) Close() error {
nat.mappingmu.Lock()
nat.closed = true
nat.mappingmu.Unlock()
nat.ctxCancel()
nat.refCount.Wait()
return nil
}
func (nat *NAT) GetMapping(protocol string, port int) (addr netip.AddrPort, found bool) {
nat.mappingmu.Lock()
defer nat.mappingmu.Unlock()
if !nat.extAddr.IsValid() {
return netip.AddrPort{}, false
}
extPort, found := nat.mappings[entry{protocol: protocol, port: port}]
if !found {
return netip.AddrPort{}, false
}
return netip.AddrPortFrom(nat.extAddr, uint16(extPort)), true
}
// AddMapping attempts to construct a mapping on protocol and internal port.
// It blocks until a mapping was established. Once added, it periodically renews the mapping.
//
// May not succeed, and mappings may change over time;
// NAT devices may not respect our port requests, and even lie.
func (nat *NAT) AddMapping(ctx context.Context, protocol string, port int) error {
switch protocol {
case "tcp", "udp":
default:
return fmt.Errorf("invalid protocol: %s", protocol)
}
nat.mappingmu.Lock()
defer nat.mappingmu.Unlock()
if nat.closed {
return errors.New("closed")
}
// do it once synchronously, so first mapping is done right away, and before exiting,
// allowing users -- in the optimistic case -- to use results right after.
extPort := nat.establishMapping(ctx, protocol, port)
nat.mappings[entry{protocol: protocol, port: port}] = extPort
return nil
}
// RemoveMapping removes a port mapping.
// It blocks until the NAT has removed the mapping.
func (nat *NAT) RemoveMapping(ctx context.Context, protocol string, port int) error {
nat.mappingmu.Lock()
defer nat.mappingmu.Unlock()
switch protocol {
case "tcp", "udp":
e := entry{protocol: protocol, port: port}
if _, ok := nat.mappings[e]; ok {
delete(nat.mappings, e)
return nat.nat.DeletePortMapping(ctx, protocol, port)
}
return errors.New("unknown mapping")
default:
return fmt.Errorf("invalid protocol: %s", protocol)
}
}
func (nat *NAT) background() {
const mappingUpdate = MappingDuration / 3
now := time.Now()
nextMappingUpdate := now.Add(mappingUpdate)
nextAddrUpdate := now.Add(CacheTime)
t := time.NewTimer(minTime(nextMappingUpdate, nextAddrUpdate).Sub(now)) // don't use a ticker here. We don't know how long establishing the mappings takes.
defer t.Stop()
var in []entry
var out []int // port numbers
for {
select {
case now := <-t.C:
if now.After(nextMappingUpdate) {
in = in[:0]
out = out[:0]
nat.mappingmu.Lock()
for e := range nat.mappings {
in = append(in, e)
}
nat.mappingmu.Unlock()
// Establishing the mapping involves network requests.
// Don't hold the mutex, just save the ports.
for _, e := range in {
out = append(out, nat.establishMapping(nat.ctx, e.protocol, e.port))
}
nat.mappingmu.Lock()
for i, p := range in {
if _, ok := nat.mappings[p]; !ok {
continue // entry might have been deleted
}
nat.mappings[p] = out[i]
}
nat.mappingmu.Unlock()
nextMappingUpdate = time.Now().Add(mappingUpdate)
}
if now.After(nextAddrUpdate) {
var extAddr netip.Addr
extIP, err := nat.nat.GetExternalAddress()
if err == nil {
extAddr, _ = netip.AddrFromSlice(extIP)
}
nat.extAddr = extAddr
nextAddrUpdate = time.Now().Add(CacheTime)
}
t.Reset(time.Until(minTime(nextAddrUpdate, nextMappingUpdate)))
case <-nat.ctx.Done():
nat.mappingmu.Lock()
ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
defer cancel()
for e := range nat.mappings {
delete(nat.mappings, e)
nat.nat.DeletePortMapping(ctx, e.protocol, e.port)
}
nat.mappingmu.Unlock()
return
}
}
}
func (nat *NAT) establishMapping(ctx context.Context, protocol string, internalPort int) (externalPort int) {
log.Debugf("Attempting port map: %s/%d", protocol, internalPort)
const comment = "libp2p"
nat.natmu.Lock()
var err error
externalPort, err = nat.nat.AddPortMapping(ctx, protocol, internalPort, comment, MappingDuration)
if err != nil {
// Some hardware does not support mappings with timeout, so try that
externalPort, err = nat.nat.AddPortMapping(ctx, protocol, internalPort, comment, 0)
}
nat.natmu.Unlock()
if err != nil || externalPort == 0 {
// TODO: log.Event
if err != nil {
log.Warnf("failed to establish port mapping: %s", err)
} else {
log.Warnf("failed to establish port mapping: newport = 0")
}
// we do not close if the mapping failed,
// because it may work again next time.
return 0
}
log.Debugf("NAT Mapping: %d --> %d (%s)", externalPort, internalPort, protocol)
return externalPort
}
func minTime(a, b time.Time) time.Time {
if a.Before(b) {
return a
}
return b
}