identify: only record observed addresses that match an address we're announcing

This is should prevent us from, e.g., announcing relay addresses _just_ because
a peer tells us we're reachable through a relay.

Author: Stebalien

p2p/protocol/identify/id.go

@@ -240,6 +240,11 @@ func (ids *IDService) consumeMessage(mes *pb.Identify, c inet.Conn) {
 
 	// NOTE: Do not add `c.RemoteMultiaddr()` to the peerstore if the remote
 	// peer doesn't tell us to do so. Otherwise, we'll advertise it.
+	//
+	// This can cause an "addr-splosion" issue where the network will slowly
+	// gossip and collect observed but unadvertised addresses. Given a NAT
+	// that picks random source ports, this can cause DHT nodes to collect
+	// many undialable addresses for other peers.
 
 	// Extend the TTLs on the known (probably) good addresses.
 	// Taking the lock ensures that we don't concurrently process a disconnect.
@@ -415,6 +420,11 @@ func (ids *IDService) consumeObservedAddress(observed []byte, c inet.Conn) {
 		return
 	}
 
+	if !HasConsistentTransport(maddr, ids.Host.Addrs()) {
+		log.Debugf("ignoring observed multiaddr that doesn't match the transports of any addresses we're announcing", c.RemoteMultiaddr())
+		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.observedAddrs.Add(maddr, c.LocalMultiaddr(), c.RemoteMultiaddr(),