p2p/nat: new package for port mapping stuff

I have verified that UPnP and NAT-PMP work against an older version of
the MiniUPnP daemon running on pfSense. This code is kind of hard to
test automatically.

1 files changed, 235 insertions, 0 deletions

diff --git a/p2p/nat/nat.go b/p2p/nat/nat.go
new file mode 100644
index 000000000..12d355ba1
--- /dev/null
+++ b/p2p/nat/nat.go
@@ -0,0 +1,235 @@
+// 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/jackpal/go-nat-pmp"
+)
+
+var log = logger.NewLogger("P2P NAT")
+
+// 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()
+		log.Debugf("Deleting port mapping: %s %d -> %d (%s) using %s\n", protocol, extport, intport, name, m)
+		m.DeleteMapping(protocol, extport, intport)
+	}()
+	log.Debugf("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 {
+		log.Errorf("mapping error: %v\n", err)
+	}
+	for {
+		select {
+		case _, ok := <-c:
+			if !ok {
+				return
+			}
+		case <-refresh.C:
+			log.DebugDetailf("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 {
+				log.Errorf("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
+}