Require gossip_queries in LNWallet (follow-up f83d2d9fee)

- workaround lnd bug https://github.com/lightningnetwork/lnd/issues/3651
 - also reduces bandwidth usage

electrum/lnpeer.py

@@ -256,6 +256,8 @@ class Peer(Logger):
         self.gossip_queue.put_nowait(('channel_update', payload))
 
     def maybe_save_remote_update(self, payload):
+        if not self.channels:
+            return
         for chan in self.channels.values():
             if chan.short_channel_id == payload['short_channel_id']:
                 chan.set_remote_update(payload['raw'])
@@ -265,7 +267,14 @@ class Peer(Logger):
             # Save (some bounded number of) orphan channel updates for later
             # as it might be for our own direct channel with this peer
             # (and we might not yet know the short channel id for that)
+            # Background: this code is here to deal with a bug in LND,
+            # see https://github.com/lightningnetwork/lnd/issues/3651
+            # and https://github.com/lightningnetwork/lightning-rfc/pull/657
+            # This code assumes gossip_queries is set. BOLT7: "if the
+            # gossip_queries feature is negotiated, [a node] MUST NOT
+            # send gossip it did not generate itself"
             short_channel_id = ShortChannelID(payload['short_channel_id'])
+            self.logger.info(f'received orphan channel update {short_channel_id}')
             self.orphan_channel_updates[short_channel_id] = payload
             while len(self.orphan_channel_updates) > 25:
                 self.orphan_channel_updates.popitem(last=False)

electrum/lnworker.py

@@ -554,6 +554,9 @@ class LNWallet(LNWorker):
         self.lnrater: LNRater = None
         self.features |= LnFeatures.OPTION_DATA_LOSS_PROTECT_REQ
         self.features |= LnFeatures.OPTION_STATIC_REMOTEKEY_REQ
+        # we do not want to receive unrequested gossip (see lnpeer.maybe_save_remote_update)
+        self.features |= LnFeatures.GOSSIP_QUERIES_REQ
+
         self.payments = self.db.get_dict('lightning_payments')     # RHASH -> amount, direction, is_paid  # FIXME amt should be msat
         self.preimages = self.db.get_dict('lightning_preimages')   # RHASH -> preimage
         # note: this sweep_address is only used as fallback; as it might result in address-reuse