p2p/proto/identify: use observed listen addrs

This commit finally makes use of the sent observed addrs.
If the connection's local address is from one of our
listen addrs, then the remote's observed addr is its
natted mapping, which is useful to us. For now, we add
it directly to our address book. (a future commit should
make addressbook addresses expire)

protocol/identify/id.go

@@ -163,7 +163,9 @@ func (ids *IDService) consumeMessage(mes *pb.Identify, c inet.Conn) {
 	p := c.RemotePeer()
 
 	// mes.Protocols
+
 	// mes.ObservedAddr
+	ids.consumeObservedAddress(mes.GetObservedAddr(), c)
 
 	// mes.ListenAddrs
 	laddrs := mes.GetListenAddrs()
@@ -208,3 +210,44 @@ func (ids *IDService) IdentifyWait(c inet.Conn) <-chan struct{} {
 	close(ch)
 	return ch
 }
+
+func (ids *IDService) consumeObservedAddress(observed []byte, c inet.Conn) {
+	if observed == nil {
+		return
+	}
+
+	maddr, err := ma.NewMultiaddrBytes(observed)
+	if err != nil {
+		log.Debugf("error parsing received observed addr for %s: %s", c, err)
+		return
+	}
+
+	// we should only use ObservedAddr when our connection's LocalAddr is one
+	// of our ListenAddrs. If we Dial out using an ephemeral addr, knowing that
+	// address's external mapping is not very useful because the port will not be
+	// the same as the listen addr.
+	ifaceaddrs, err := ids.Host.Network().InterfaceListenAddresses()
+	if err != nil {
+		log.Infof("failed to get interface listen addrs", err)
+		return
+	}
+
+	log.Debugf("identify identifying observed multiaddr: %s %s", c.LocalMultiaddr(), ifaceaddrs)
+	if !addrInAddrs(c.LocalMultiaddr(), ifaceaddrs) {
+		// not in our list
+		return
+	}
+
+	// ok! we have the observed version of one of our ListenAddresses!
+	log.Debugf("added own observed listen addr: %s --> %s", c.LocalMultiaddr(), maddr)
+	ids.Host.Peerstore().AddAddress(ids.Host.ID(), maddr)
+}
+
+func addrInAddrs(a ma.Multiaddr, as []ma.Multiaddr) bool {
+	for _, b := range as {
+		if a.Equal(b) {
+			return true
+		}
+	}
+	return false
+}