htlcswitch: avoid leaking peer interface from link

Here we notice that the only use of the Peer call on the link is
to find out what the peer's pubkey is. To avoid leaking handles to
IO actions outside the interface we reduce the surface area to
just return the peer's public key.

htlcswitch/switch.go

@@ -1147,7 +1147,7 @@ func (s *Switch) handlePacketForward(packet *htlcPacket) error {
 
 			return s.failAddPacket(packet, linkError)
 		}
-		targetPeerKey := targetLink.Peer().PubKey()
+		targetPeerKey := targetLink.PeerPubKey()
 		interfaceLinks, _ := s.getLinks(targetPeerKey)
 		s.indexMtx.RUnlock()
 
@@ -1810,9 +1810,9 @@ out:
 			}
 			s.indexMtx.RUnlock()
 
-			peerPub := link.Peer().PubKey()
+			peerPub := link.PeerPubKey()
 			log.Debugf("Requesting local channel close: peer=%v, "+
-				"chan_id=%x", link.Peer(), chanID[:])
+				"chan_id=%x", link.PeerPubKey(), chanID[:])
 
 			go s.cfg.LocalChannelClose(peerPub[:], req)
 
@@ -2335,7 +2335,7 @@ func (s *Switch) addLiveLink(link ChannelLink) {
 
 	// Next we'll add the link to the interface index so we can
 	// quickly look up all the channels for a particular node.
-	peerPub := link.Peer().PubKey()
+	peerPub := link.PeerPubKey()
 	if _, ok := s.interfaceIndex[peerPub]; !ok {
 		s.interfaceIndex[peerPub] = make(map[lnwire.ChannelID]ChannelLink)
 	}
@@ -2610,7 +2610,7 @@ func (s *Switch) removeLink(chanID lnwire.ChannelID) ChannelLink {
 
 	// If the link has been added to the peer index, then we'll move to
 	// delete the entry within the index.
-	peerPub := link.Peer().PubKey()
+	peerPub := link.PeerPubKey()
 	if peerIndex, ok := s.interfaceIndex[peerPub]; ok {
 		delete(peerIndex, link.ChanID())