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.

p2p/nat/natupnp.go

@@ -0,0 +1,149 @@
+package nat
+
+import (
+	"errors"
+	"fmt"
+	"net"
+	"strings"
+	"time"
+
+	"github.com/fjl/goupnp"
+	"github.com/fjl/goupnp/dcps/internetgateway1"
+	"github.com/fjl/goupnp/dcps/internetgateway2"
+)
+
+type upnp struct {
+	dev     *goupnp.RootDevice
+	service string
+	client  upnpClient
+}
+
+type upnpClient interface {
+	GetExternalIPAddress() (string, error)
+	AddPortMapping(string, uint16, string, uint16, string, bool, string, uint32) error
+	DeletePortMapping(string, uint16, string) error
+	GetNATRSIPStatus() (sip bool, nat bool, err error)
+}
+
+func (n *upnp) ExternalIP() (addr net.IP, err error) {
+	ipString, err := n.client.GetExternalIPAddress()
+	if err != nil {
+		return nil, err
+	}
+	ip := net.ParseIP(ipString)
+	if ip == nil {
+		return nil, errors.New("bad IP in response")
+	}
+	return ip, nil
+}
+
+func (n *upnp) AddMapping(protocol string, extport, intport int, desc string, lifetime time.Duration) error {
+	ip, err := n.internalAddress()
+	if err != nil {
+		return nil
+	}
+	protocol = strings.ToUpper(protocol)
+	lifetimeS := uint32(lifetime / time.Second)
+	return n.client.AddPortMapping("", uint16(extport), protocol, uint16(intport), ip.String(), true, desc, lifetimeS)
+}
+
+func (n *upnp) internalAddress() (net.IP, error) {
+	devaddr, err := net.ResolveUDPAddr("udp4", n.dev.URLBase.Host)
+	if err != nil {
+		return nil, err
+	}
+	ifaces, err := net.Interfaces()
+	if err != nil {
+		return nil, err
+	}
+	for _, iface := range ifaces {
+		addrs, err := iface.Addrs()
+		if err != nil {
+			return nil, err
+		}
+		for _, addr := range addrs {
+			switch x := addr.(type) {
+			case *net.IPNet:
+				if x.Contains(devaddr.IP) {
+					return x.IP, nil
+				}
+			}
+		}
+	}
+	return nil, fmt.Errorf("could not find local address in same net as %v", devaddr)
+}
+
+func (n *upnp) DeleteMapping(protocol string, extport, intport int) error {
+	return n.client.DeletePortMapping("", uint16(extport), strings.ToUpper(protocol))
+}
+
+func (n *upnp) String() string {
+	return "UPNP " + n.service
+}
+
+// discoverUPnP searches for Internet Gateway Devices
+// and returns the first one it can find on the local network.
+func discoverUPnP() Interface {
+	found := make(chan *upnp, 2)
+	// IGDv1
+	go discover(found, internetgateway1.URN_WANConnectionDevice_1, func(dev *goupnp.RootDevice, sc goupnp.ServiceClient) *upnp {
+		switch sc.Service.ServiceType {
+		case internetgateway1.URN_WANIPConnection_1:
+			return &upnp{dev, "IGDv1-IP1", &internetgateway1.WANIPConnection1{sc}}
+		case internetgateway1.URN_WANPPPConnection_1:
+			return &upnp{dev, "IGDv1-PPP1", &internetgateway1.WANPPPConnection1{sc}}
+		}
+		return nil
+	})
+	// IGDv2
+	go discover(found, internetgateway2.URN_WANConnectionDevice_2, func(dev *goupnp.RootDevice, sc goupnp.ServiceClient) *upnp {
+		switch sc.Service.ServiceType {
+		case internetgateway2.URN_WANIPConnection_1:
+			return &upnp{dev, "IGDv2-IP1", &internetgateway2.WANIPConnection1{sc}}
+		case internetgateway2.URN_WANIPConnection_2:
+			return &upnp{dev, "IGDv2-IP2", &internetgateway2.WANIPConnection2{sc}}
+		case internetgateway2.URN_WANPPPConnection_1:
+			return &upnp{dev, "IGDv2-PPP1", &internetgateway2.WANPPPConnection1{sc}}
+		}
+		return nil
+	})
+	for i := 0; i < cap(found); i++ {
+		if c := <-found; c != nil {
+			return c
+		}
+	}
+	return nil
+}
+
+func discover(out chan<- *upnp, target string, matcher func(*goupnp.RootDevice, goupnp.ServiceClient) *upnp) {
+	devs, err := goupnp.DiscoverDevices(target)
+	if err != nil {
+		return
+	}
+	found := false
+	for i := 0; i < len(devs) && !found; i++ {
+		if devs[i].Root == nil {
+			continue
+		}
+		devs[i].Root.Device.VisitServices(func(service *goupnp.Service) {
+			if found {
+				return
+			}
+			// check for a matching IGD service
+			sc := goupnp.ServiceClient{service.NewSOAPClient(), devs[i].Root, service}
+			upnp := matcher(devs[i].Root, sc)
+			if upnp == nil {
+				return
+			}
+			// check whether port mapping is enabled
+			if _, nat, err := upnp.client.GetNATRSIPStatus(); err != nil || !nat {
+				return
+			}
+			out <- upnp
+			found = true
+		})
+	}
+	if !found {
+		out <- nil
+	}
+}