lnworker.try_force_closing: changed to not be async (and renamed)

This is to ensure that the channel is "immediately" set to FORCE_CLOSING.
(previously it took at least one event loop iteration)

electrum/lnpeer.py

@@ -1052,7 +1052,7 @@ class Peer(Logger):
             fut.set_exception(RemoteMisbehaving("remote ahead of us"))
         elif we_are_ahead:
             self.logger.warning(f"channel_reestablish ({chan.get_id_for_log()}): we are ahead of remote! trying to force-close.")
-            asyncio.ensure_future(self.lnworker.try_force_closing(chan.channel_id))
+            self.lnworker.schedule_force_closing(chan.channel_id)
             fut.set_exception(RemoteMisbehaving("we are ahead of remote"))
         else:
             # all good
@@ -1382,7 +1382,7 @@ class Peer(Logger):
         self.logger.info(f"on_update_fail_malformed_htlc. chan {chan.get_id_for_log()}. "
                          f"htlc_id {htlc_id}. failure_code={failure_code}")
         if failure_code & OnionFailureCodeMetaFlag.BADONION == 0:
-            asyncio.ensure_future(self.lnworker.try_force_closing(chan.channel_id))
+            self.lnworker.schedule_force_closing(chan.channel_id)
             raise RemoteMisbehaving(f"received update_fail_malformed_htlc with unexpected failure code: {failure_code}")
         reason = OnionRoutingFailure(code=failure_code, data=payload["sha256_of_onion"])
         chan.receive_fail_htlc(htlc_id, error_bytes=None, reason=reason)
@@ -1404,7 +1404,7 @@ class Peer(Logger):
         if chan.get_state() != ChannelState.OPEN:
             raise RemoteMisbehaving(f"received update_add_htlc while chan.get_state() != OPEN. state was {chan.get_state()!r}")
         if cltv_expiry > bitcoin.NLOCKTIME_BLOCKHEIGHT_MAX:
-            asyncio.ensure_future(self.lnworker.try_force_closing(chan.channel_id))
+            self.lnworker.schedule_force_closing(chan.channel_id)
             raise RemoteMisbehaving(f"received update_add_htlc with cltv_expiry > BLOCKHEIGHT_MAX. value was {cltv_expiry}")
         # add htlc
         chan.receive_htlc(htlc, onion_packet)

electrum/lnworker.py

@@ -966,7 +966,7 @@ class LNWallet(LNWorker):
 
         if chan.get_state() == ChannelState.OPEN and chan.should_be_closed_due_to_expiring_htlcs(self.network.get_local_height()):
             self.logger.info(f"force-closing due to expiring htlcs")
-            await self.try_force_closing(chan.channel_id)
+            await self.schedule_force_closing(chan.channel_id)
 
         elif chan.get_state() == ChannelState.FUNDED:
             peer = self._peers.get(chan.node_id)
@@ -2109,16 +2109,21 @@ class LNWallet(LNWorker):
         """Force-close the channel. Network-related exceptions are propagated to the caller.
         (automatic rebroadcasts will be scheduled)
         """
+        # note: as we are async, it can take a few event loop iterations between the caller
+        #       "calling us" and us getting to run, and we only set the channel state now:
         tx = self._force_close_channel(chan_id)
         await self.network.broadcast_transaction(tx)
         return tx.txid()
 
-    async def try_force_closing(self, chan_id: bytes) -> None:
-        """Force-close the channel. Network-related exceptions are suppressed.
+    def schedule_force_closing(self, chan_id: bytes) -> 'asyncio.Task[None]':
+        """Schedules a task to force-close the channel and returns it.
+        Network-related exceptions are suppressed.
         (automatic rebroadcasts will be scheduled)
+        Note: this method is intentionally not async so that callers have a guarantee
+              that the channel state is set immediately.
         """
         tx = self._force_close_channel(chan_id)
-        await self.network.try_broadcasting(tx, 'force-close')
+        return asyncio.create_task(self.network.try_broadcasting(tx, 'force-close'))
 
     def remove_channel(self, chan_id):
         chan = self.channels[chan_id]

electrum/tests/test_lnpeer.py

@@ -231,7 +231,7 @@ class MockLNWallet(Logger, NetworkRetryManager[LNPeerAddr]):
     pay_to_node = LNWallet.pay_to_node
     pay_invoice = LNWallet.pay_invoice
     force_close_channel = LNWallet.force_close_channel
-    try_force_closing = LNWallet.try_force_closing
+    schedule_force_closing = LNWallet.schedule_force_closing
     get_first_timestamp = lambda self: 0
     on_peer_successfully_established = LNWallet.on_peer_successfully_established
     get_channel_by_id = LNWallet.get_channel_by_id