path: root/p2p/nat/nat.go

// Package nat provides access to common port mapping protocols.
package nat

import (
    "errors"
    "fmt"
    "net"
    "strings"
    "sync"
    "time"

    "github.com/ethereum/go-ethereum/logger"
    "github.com/ethereum/go-ethereum/logger/glog"
    "github.com/jackpal/go-nat-pmp"
)

// An implementation of nat.Interface can map local ports to ports
// accessible from the Internet.
type Interface interface {
    // These methods manage a mapping between a port on the local
    // machine to a port that can be connected to from the internet.
    //
    // protocol is "UDP" or "TCP". Some implementations allow setting
    // a display name for the mapping. The mapping may be removed by
    // the gateway when its lifetime ends.
    AddMapping(protocol string, extport, intport int, name string, lifetime time.Duration) error
    DeleteMapping(protocol string, extport, intport int) error

    // This method should return the external (Internet-facing)
    // address of the gateway device.
    ExternalIP() (net.IP, error)

    // Should return name of the method. This is used for logging.
    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) (Interface, 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 Interface, c chan struct{}, protocol string, extport, intport int, name string) {
    refresh := time.NewTimer(mapUpdateInterval)
    defer func() {
        refresh.Stop()
        glog.V(logger.Debug).Infof("Deleting port mapping: %s %d -> %d (%s) using %s\n", protocol, extport, intport, name, m)
        m.DeleteMapping(protocol, extport, intport)
    }()
    glog.V(logger.Debug).Infof("add mapping: %s %d -> %d (%s) using %s\n", protocol, extport, intport, name, m)
    if err := m.AddMapping(protocol, intport, extport, name, mapTimeout); err != nil {
        glog.V(logger.Error).Infof("mapping error: %v\n", err)
    }
    for {
        select {
        case _, ok := <-c:
            if !ok {
                return
            }
        case <-refresh.C:
            glog.V(logger.Detail).Infof("refresh mapping: %s %d -> %d (%s) using %s\n", protocol, extport, intport, name, m)
            if err := m.AddMapping(protocol, intport, extport, name, mapTimeout); err != nil {
                glog.V(logger.Error).Infof("mapping error: %v\n", err)
            }
            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.
func ExtIP(ip net.IP) Interface {
    if ip == nil {
        panic("IP must not be nil")
    }
    return extIP(ip)
}

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() Interface {
    // 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() Interface {
        found := make(chan Interface, 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() Interface {
    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) Interface {
    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
    done <-chan Interface

    mu    sync.Mutex
    found Interface
}

func startautodisc(what string, doit func() Interface) Interface {
    // TODO: monitor network configuration and rerun doit when it changes.
    done := make(chan Interface)
    ad := &autodisc{what: what, done: done}
    go func() { done <- doit(); close(done) }()
    return ad
}

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()
    }
}

func (n *autodisc) wait() error {
    n.mu.Lock()
    found := n.found
    n.mu.Unlock()
    if found != nil {
        // already discovered
        return nil
    }
    if found = <-n.done; found == nil {
        return errors.New("no devices discovered")
    }
    n.mu.Lock()
    n.found = found
    n.mu.Unlock()
    return nil
}