Merge pull request #8814 from SomberNight/202401_lnpeer_chan_reest

lnpeer.reestablish_channel: fix some timing issues for dataloss case

electrum/gui/qt/channels_list.py

@@ -119,9 +119,6 @@ class ChannelsList(MyTreeView):
     def on_channel_closed(self, txid):
         self.main_window.show_error('Channel closed' + '\n' + txid)
 
-    def on_request_sent(self, b):
-        self.main_window.show_message(_('Request sent'))
-
     def on_failure(self, exc_info):
         type_, e, tb = exc_info
         traceback.print_tb(tb)
@@ -137,7 +134,7 @@ class ChannelsList(MyTreeView):
         on_success = self.on_channel_closed
         def task():
             return self.network.run_from_another_thread(coro)
-        WaitingDialog(self, 'please wait..', task, on_success, self.on_failure)
+        WaitingDialog(self, _('Please wait...'), task, on_success, self.on_failure)
 
     def force_close(self, channel_id):
         self.save_backup = True
@@ -161,7 +158,7 @@ class ChannelsList(MyTreeView):
         def task():
             coro = self.lnworker.force_close_channel(channel_id)
             return self.network.run_from_another_thread(coro)
-        WaitingDialog(self, 'please wait..', task, self.on_channel_closed, self.on_failure)
+        WaitingDialog(self, _('Please wait...'), task, self.on_channel_closed, self.on_failure)
 
     def remove_channel(self, channel_id):
         if self.main_window.question(_('Are you sure you want to delete this channel? This will purge associated transactions from your wallet history.')):
@@ -191,7 +188,9 @@ class ChannelsList(MyTreeView):
         def task():
             coro = self.lnworker.request_force_close(channel_id)
             return self.network.run_from_another_thread(coro)
-        WaitingDialog(self, 'please wait..', task, self.on_request_sent, self.on_failure)
+        def on_done(b):
+            self.main_window.show_message(_('Request scheduled'))
+        WaitingDialog(self, _('Please wait...'), task, on_done, self.on_failure)
 
     def set_frozen(self, chan, *, for_sending, value):
         if not self.lnworker.uses_trampoline() or self.lnworker.is_trampoline_peer(chan.node_id):

electrum/lnchannel.py

@@ -140,6 +140,7 @@ state_transitions = [
     (cs.OPEN,     cs.WE_ARE_TOXIC),
     (cs.SHUTDOWN, cs.WE_ARE_TOXIC),
     (cs.REQUESTED_FCLOSE, cs.WE_ARE_TOXIC),
+    (cs.WE_ARE_TOXIC, cs.WE_ARE_TOXIC),
     #
     (cs.FORCE_CLOSING, cs.FORCE_CLOSING),  # allow multiple attempts
     (cs.FORCE_CLOSING, cs.CLOSED),
@@ -1015,6 +1016,8 @@ class Channel(AbstractChannel):
     def should_try_to_reestablish_peer(self) -> bool:
         if self.peer_state != PeerState.DISCONNECTED:
             return False
+        if self.should_request_force_close:
+            return True
         return ChannelState.PREOPENING < self._state < ChannelState.CLOSING
 
     def get_funding_address(self):
@@ -1629,6 +1632,8 @@ class Channel(AbstractChannel):
             if not self.has_unsettled_htlcs():
                 ret.append(ChanCloseOption.COOP_CLOSE)
                 ret.append(ChanCloseOption.REQUEST_REMOTE_FCLOSE)
+        if self.get_state() == ChannelState.WE_ARE_TOXIC:
+            ret.append(ChanCloseOption.REQUEST_REMOTE_FCLOSE)
         if not self.is_closed() or self.get_state() == ChannelState.REQUESTED_FCLOSE:
             ret.append(ChanCloseOption.LOCAL_FCLOSE)
         assert not (self.get_state() == ChannelState.WE_ARE_TOXIC and ChanCloseOption.LOCAL_FCLOSE in ret), "local force-close unsafe if we are toxic"

electrum/lnpeer.py

@@ -1113,6 +1113,7 @@ class Peer(Logger):
     async def request_force_close(self, channel_id: bytes):
         """Try to trigger the remote peer to force-close."""
         await self.initialized
+        self.logger.info(f"trying to get remote peer to force-close chan {channel_id.hex()}")
         # First, we intentionally send a "channel_reestablish" msg with an old state.
         # Many nodes (but not all) automatically force-close when seeing this.
         latest_point = secret_to_pubkey(42) # we need a valid point (BOLT2)
@@ -1146,7 +1147,11 @@ class Peer(Logger):
             self.logger.info(f"tried to force-close channel {chan.get_id_for_log()} "
                              f"but close option is not allowed. {chan.get_state()=!r}")
 
-    def on_channel_reestablish(self, chan, msg):
+    def on_channel_reestablish(self, chan: Channel, msg):
+        # Note: it is critical for this message handler to block processing of further messages,
+        #       until this msg is processed. If we are behind (lost state), and send chan_reest to the remote,
+        #       when the remote realizes we are behind, they might send an "error" message - but the spec mandates
+        #       they send chan_reest first. If we processed the error first, we might force-close and lose money!
         their_next_local_ctn = msg["next_commitment_number"]
         their_oldest_unrevoked_remote_ctn = msg["next_revocation_number"]
         their_local_pcp = msg.get("my_current_per_commitment_point")
@@ -1230,40 +1235,23 @@ class Peer(Logger):
             self.lnworker.save_channel(chan)
             chan.peer_state = PeerState.BAD
             # raise after we send channel_reestablish, so the remote can realize they are ahead
-            fut.set_exception(RemoteMisbehaving("remote ahead of us"))
+            # FIXME what if we have multiple chans with peer? timing...
+            fut.set_exception(GracefulDisconnect("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.")
             self.schedule_force_closing(chan.channel_id)
-            fut.set_exception(RemoteMisbehaving("we are ahead of remote"))
+            # FIXME what if we have multiple chans with peer? timing...
+            fut.set_exception(GracefulDisconnect("we are ahead of remote"))
         else:
             # all good
             fut.set_result((we_must_resend_revoke_and_ack, their_next_local_ctn))
 
-    async def reestablish_channel(self, chan: Channel):
-        await self.initialized
+    def _send_channel_reestablish(self, chan: Channel):
+        assert self.is_initialized()
         chan_id = chan.channel_id
-        if chan.should_request_force_close:
-            chan.set_state(ChannelState.REQUESTED_FCLOSE)
-            await self.request_force_close(chan_id)
-            chan.should_request_force_close = False
-            return
-        assert ChannelState.PREOPENING < chan.get_state() < ChannelState.FORCE_CLOSING
-        if chan.peer_state != PeerState.DISCONNECTED:
-            self.logger.info(
-                f'reestablish_channel was called but channel {chan.get_id_for_log()} '
-                f'already in peer_state {chan.peer_state!r}')
-            return
-        chan.peer_state = PeerState.REESTABLISHING
-        util.trigger_callback('channel', self.lnworker.wallet, chan)
         # ctns
-        oldest_unrevoked_local_ctn = chan.get_oldest_unrevoked_ctn(LOCAL)
-        latest_local_ctn = chan.get_latest_ctn(LOCAL)
         next_local_ctn = chan.get_next_ctn(LOCAL)
         oldest_unrevoked_remote_ctn = chan.get_oldest_unrevoked_ctn(REMOTE)
-        latest_remote_ctn = chan.get_latest_ctn(REMOTE)
-        next_remote_ctn = chan.get_next_ctn(REMOTE)
-        # BOLT-02: "A node [...] upon disconnection [...] MUST reverse any uncommitted updates sent by the other side"
-        chan.hm.discard_unsigned_remote_updates()
         # send message
         assert chan.is_static_remotekey_enabled()
         latest_secret, latest_point = chan.get_secret_and_point(LOCAL, 0)
@@ -1284,6 +1272,46 @@ class Peer(Logger):
             f'(next_local_ctn={next_local_ctn}, '
             f'oldest_unrevoked_remote_ctn={oldest_unrevoked_remote_ctn})')
 
+    async def reestablish_channel(self, chan: Channel):
+        await self.initialized
+        chan_id = chan.channel_id
+        if chan.should_request_force_close:
+            if chan.get_state() != ChannelState.WE_ARE_TOXIC:
+                chan.set_state(ChannelState.REQUESTED_FCLOSE)
+            await self.request_force_close(chan_id)
+            chan.should_request_force_close = False
+            return
+        if chan.get_state() == ChannelState.WE_ARE_TOXIC:
+            # Depending on timing, the remote might not know we are behind.
+            # We should let them know, so that they force-close.
+            # We do "request force-close" with ctn=0, instead of leaking our actual ctns,
+            # to decrease the remote's confidence of actual data loss on our part.
+            await self.request_force_close(chan_id)
+            return
+        if chan.get_state() == ChannelState.FORCE_CLOSING:
+            # We likely got here because we found out that we are ahead (i.e. remote lost state).
+            # Depending on timing, the remote might not know they are behind.
+            # We should let them know:
+            self._send_channel_reestablish(chan)
+            return
+        # if we get here, we will try to do a proper reestablish
+        if not (ChannelState.PREOPENING < chan.get_state() < ChannelState.FORCE_CLOSING):
+            raise Exception(f"unexpected {chan.get_state()=} for reestablish")
+        if chan.peer_state != PeerState.DISCONNECTED:
+            self.logger.info(
+                f'reestablish_channel was called but channel {chan.get_id_for_log()} '
+                f'already in peer_state {chan.peer_state!r}')
+            return
+        chan.peer_state = PeerState.REESTABLISHING
+        util.trigger_callback('channel', self.lnworker.wallet, chan)
+        # ctns
+        oldest_unrevoked_local_ctn = chan.get_oldest_unrevoked_ctn(LOCAL)
+        next_local_ctn = chan.get_next_ctn(LOCAL)
+        oldest_unrevoked_remote_ctn = chan.get_oldest_unrevoked_ctn(REMOTE)
+        # BOLT-02: "A node [...] upon disconnection [...] MUST reverse any uncommitted updates sent by the other side"
+        chan.hm.discard_unsigned_remote_updates()
+        # send message
+        self._send_channel_reestablish(chan)
         # wait until we receive their channel_reestablish
         fut = self.channel_reestablish_msg[chan_id]
         await fut

electrum/lnworker.py

@@ -2904,9 +2904,8 @@ class LNWallet(LNWorker):
                 if self._can_retry_addr(peer, urgent=True):
                     await self._add_peer(peer.host, peer.port, peer.pubkey)
             for chan in self.channels.values():
-                if chan.is_closed():
-                    continue
                 # reestablish
+                # note: we delegate filtering out uninteresting chans to this:
                 if not chan.should_try_to_reestablish_peer():
                     continue
                 peer = self._peers.get(chan.node_id, None)
@@ -2961,10 +2960,9 @@ class LNWallet(LNWorker):
         if channel_id in self.channels:
             chan = self.channels[channel_id]
             peer = self._peers.get(chan.node_id)
-            if not peer:
-                raise Exception('Peer not found')
             chan.should_request_force_close = True
-            peer.close_and_cleanup()
+            if peer:
+                peer.close_and_cleanup()  # to force a reconnect
         elif connect_str:
             peer = await self.add_peer(connect_str)
             await peer.request_force_close(channel_id)

electrum/tests/test_lnpeer.py

@@ -566,30 +566,50 @@ class TestPeerDirect(TestPeer):
             await gath
 
     async def test_reestablish_with_old_state(self):
-        random_seed = os.urandom(32)
-        alice_channel, bob_channel = create_test_channels(random_seed=random_seed)
-        alice_channel_0, bob_channel_0 = create_test_channels(random_seed=random_seed)  # these are identical
-        p1, p2, w1, w2, _q1, _q2 = self.prepare_peers(alice_channel, bob_channel)
-        lnaddr, pay_req = self.prepare_invoice(w2)
-        async def pay():
-            result, log = await w1.pay_invoice(pay_req)
-            self.assertEqual(result, True)
-            gath.cancel()
-        gath = asyncio.gather(pay(), p1._message_loop(), p2._message_loop(), p1.htlc_switch(), p2.htlc_switch())
-        with self.assertRaises(asyncio.CancelledError):
-            await gath
-        p1, p2, w1, w2, _q1, _q2 = self.prepare_peers(alice_channel_0, bob_channel)
-        for chan in (alice_channel_0, bob_channel):
-            chan.peer_state = PeerState.DISCONNECTED
-        async def reestablish():
-            await asyncio.gather(
-                p1.reestablish_channel(alice_channel_0),
-                p2.reestablish_channel(bob_channel))
-        gath = asyncio.gather(reestablish(), p1._message_loop(), p2._message_loop(), p1.htlc_switch(), p2.htlc_switch())
-        with self.assertRaises(lnutil.RemoteMisbehaving):
-            await gath
-        self.assertEqual(alice_channel_0.peer_state, PeerState.BAD)
-        self.assertEqual(bob_channel._state, ChannelState.FORCE_CLOSING)
+        async def f(alice_slow: bool, bob_slow: bool):
+            random_seed = os.urandom(32)
+            alice_channel, bob_channel = create_test_channels(random_seed=random_seed)
+            alice_channel_0, bob_channel_0 = create_test_channels(random_seed=random_seed)  # these are identical
+            p1, p2, w1, w2, _q1, _q2 = self.prepare_peers(alice_channel, bob_channel)
+            lnaddr, pay_req = self.prepare_invoice(w2)
+            async def pay():
+                result, log = await w1.pay_invoice(pay_req)
+                self.assertEqual(result, True)
+                gath.cancel()
+            gath = asyncio.gather(pay(), p1._message_loop(), p2._message_loop(), p1.htlc_switch(), p2.htlc_switch())
+            with self.assertRaises(asyncio.CancelledError):
+                await gath
+            p1, p2, w1, w2, _q1, _q2 = self.prepare_peers(alice_channel_0, bob_channel)
+            for chan in (alice_channel_0, bob_channel):
+                chan.peer_state = PeerState.DISCONNECTED
+
+            async def alice_sends_reest():
+                if alice_slow: await asyncio.sleep(0.05)
+                await p1.reestablish_channel(alice_channel_0)
+            async def bob_sends_reest():
+                if bob_slow: await asyncio.sleep(0.05)
+                await p2.reestablish_channel(bob_channel)
+
+            with self.assertRaises(GracefulDisconnect):
+                async with OldTaskGroup() as group:
+                    await group.spawn(p1._message_loop())
+                    await group.spawn(p1.htlc_switch())
+                    await group.spawn(p2._message_loop())
+                    await group.spawn(p2.htlc_switch())
+                    await group.spawn(alice_sends_reest)
+                    await group.spawn(bob_sends_reest)
+            self.assertEqual(alice_channel_0.peer_state, PeerState.BAD)
+            self.assertEqual(alice_channel_0._state, ChannelState.WE_ARE_TOXIC)
+            self.assertEqual(bob_channel._state, ChannelState.FORCE_CLOSING)
+
+        with self.subTest(msg="both fast"):
+            # FIXME: we want to test the case where both Alice and Bob sends channel-reestablish before
+            #        receiving what the other sent. This is not a reliable way to do that...
+            await f(alice_slow=False, bob_slow=False)
+        with self.subTest(msg="alice is slow"):
+            await f(alice_slow=True, bob_slow=False)
+        with self.subTest(msg="bob is slow"):
+            await f(alice_slow=False, bob_slow=True)
 
     @staticmethod
     def _send_fake_htlc(peer: Peer, chan: Channel) -> UpdateAddHtlc: