Propagate exceptions raise by force_close to the GUI.

Define 'try_force_closing' for cases where we do not
want exceptions to be raised.

electrum/lnchannel.py

@@ -98,6 +98,7 @@ state_transitions = [
     (cs.OPEN, cs.CLOSED),
     (cs.CLOSING, cs.CLOSING), # if we reestablish
     (cs.CLOSING, cs.CLOSED),
+    (cs.FORCE_CLOSING, cs.FORCE_CLOSING), # allow multiple attempts
     (cs.FORCE_CLOSING, cs.CLOSED),
     (cs.FORCE_CLOSING, cs.REDEEMED),
     (cs.CLOSED, cs.REDEEMED),

electrum/lnpeer.py

@@ -869,11 +869,11 @@ class Peer(Logger):
             return
         elif we_are_ahead:
             self.logger.warning(f"channel_reestablish ({chan.get_id_for_log()}): we are ahead of remote! trying to force-close.")
-            await self.lnworker.force_close_channel(chan_id)
+            await self.lnworker.try_force_closing(chan_id)
             return
         elif self.lnworker.wallet.is_lightning_backup():
             self.logger.warning(f"channel_reestablish ({chan.get_id_for_log()}): force-closing because we are a recent backup")
-            await self.lnworker.force_close_channel(chan_id)
+            await self.lnworker.try_force_closing(chan_id)
             return
 
         chan.peer_state = peer_states.GOOD
@@ -1106,7 +1106,7 @@ class Peer(Logger):
         if chan.get_state() != channel_states.OPEN:
             raise RemoteMisbehaving(f"received update_add_htlc while chan.get_state() != OPEN. state was {chan.get_state()}")
         if cltv_expiry > bitcoin.NLOCKTIME_BLOCKHEIGHT_MAX:
-            asyncio.ensure_future(self.lnworker.force_close_channel(channel_id))
+            asyncio.ensure_future(self.lnworker.try_force_closing(channel_id))
             raise RemoteMisbehaving(f"received update_add_htlc with cltv_expiry > BLOCKHEIGHT_MAX. value was {cltv_expiry}")
         # add htlc
         htlc = UpdateAddHtlc(

electrum/lnworker.py

@@ -732,7 +732,7 @@ class LNWallet(LNWorker):
 
         if chan.get_state() == channel_states.OPEN and self.should_channel_be_closed_due_to_expiring_htlcs(chan):
             self.logger.info(f"force-closing due to expiring htlcs")
-            await self.force_close_channel(chan.channel_id)
+            await self.try_force_closing(chan.channel_id)
             return
 
         if chan.get_state() == channel_states.OPENING:
@@ -1297,11 +1297,19 @@ class LNWallet(LNWorker):
         return await peer.close_channel(chan_id)
 
     async def force_close_channel(self, chan_id):
+        # returns txid or raises
+        chan = self.channels[chan_id]
+        tx = chan.force_close_tx()
+        txid = await self.network.broadcast_transaction(tx)
+        chan.set_state(channel_states.FORCE_CLOSING)
+        return txid
+
+    async def try_force_closing(self, chan_id):
+        # fails silently but sets the state, so that we will retry later
         chan = self.channels[chan_id]
         tx = chan.force_close_tx()
         chan.set_state(channel_states.FORCE_CLOSING)
         await self.network.try_broadcasting(tx, 'force-close')
-        return tx.txid()
 
     def remove_channel(self, chan_id):
         chan = self.channels[chan_id]