identify: Don't filter addr if remote is neither public nor private (#…

…2820)

Updates the filterAddrs logic to no-op if the address is neither public nor private.

This fixes an issue in mocknet that assigns each node an address in the IPv6 discard prefix space. That doesn't interact well with this logic in identify.

The issue mocknet hits is that it filters out all received listen addresses and then doesn't remember any address for the peer.

p2p/protocol/identify/id.go

@@ -831,7 +831,7 @@ func (ids *idService) consumeMessage(mes *pb.Identify, c network.Conn, isPush bo
 	ids.Host.Peerstore().UpdateAddrs(p, peerstore.TempAddrTTL, 0)
 	ids.addrMu.Unlock()
 
-	log.Debugf("%s received listen addrs for %s: %s", c.LocalPeer(), c.RemotePeer(), lmaddrs)
+	log.Debugf("%s received listen addrs for %s: %s", c.LocalPeer(), c.RemotePeer(), addrs)
 
 	// get protocol versions
 	pv := mes.GetProtocolVersion()
@@ -1064,18 +1064,23 @@ func (nn *netNotifiee) Disconnected(_ network.Network, c network.Conn) {
 func (nn *netNotifiee) Listen(n network.Network, a ma.Multiaddr)      {}
 func (nn *netNotifiee) ListenClose(n network.Network, a ma.Multiaddr) {}
 
-// filterAddrs filters the address slice based on the remove multiaddr:
-// * if it's a localhost address, no filtering is applied
-// * if it's a local network address, all localhost addresses are filtered out
-// * if it's a public address, all localhost and local network addresses are filtered out
+// filterAddrs filters the address slice based on the remote multiaddr:
+//   - if it's a localhost address, no filtering is applied
+//   - if it's a private network address, all localhost addresses are filtered out
+//   - if it's a public address, all non-public addresses are filtered out
+//   - if none of the above, (e.g. discard prefix), no filtering is applied.
+//     We can't do anything meaningful here so we do nothing.
 func filterAddrs(addrs []ma.Multiaddr, remote ma.Multiaddr) []ma.Multiaddr {
-	if manet.IsIPLoopback(remote) {
+	switch {
+	case manet.IsIPLoopback(remote):
 		return addrs
-	}
-	if manet.IsPrivateAddr(remote) {
+	case manet.IsPrivateAddr(remote):
 		return ma.FilterAddrs(addrs, func(a ma.Multiaddr) bool { return !manet.IsIPLoopback(a) })
+	case manet.IsPublicAddr(remote):
+		return ma.FilterAddrs(addrs, manet.IsPublicAddr)
+	default:
+		return addrs
 	}
-	return ma.FilterAddrs(addrs, manet.IsPublicAddr)
 }
 
 func trimHostAddrList(addrs []ma.Multiaddr, maxSize int) []ma.Multiaddr {