channeld: send shutdown_complete even if reestablish_only.

This lets us transition (with a few supporting changes) to closingd,
which will happily let them mutual close with us.

We already handle the case where this mutual close is redundant (for
packet loss), so this is easy.

Signed-off-by: Rusty Russell <[email protected]>
Changelog-Added: Protocol: We will now reestablish and negotiate mutual close on channels we've already closed (great if peer has lost their database).

Author: rustyrussell

channeld/channeld.c

@@ -918,6 +918,15 @@ static void maybe_send_shutdown(struct peer *peer)
 	billboard_update(peer);
 }
 
+static void send_shutdown_complete(struct peer *peer)
+{
+	/* Now we can tell master shutdown is complete. */
+	wire_sync_write(MASTER_FD,
+			take(towire_channeld_shutdown_complete(NULL, peer->pps)));
+	per_peer_state_fdpass_send(MASTER_FD, peer->pps);
+	close(MASTER_FD);
+}
+
 /* This queues other traffic from the fd until we get reply. */
 static u8 *master_wait_sync_reply(const tal_t *ctx,
 				  struct peer *peer,
@@ -2929,10 +2938,17 @@ static void peer_reconnect(struct peer *peer,
 #endif /* EXPERIMENTAL_FEATURES */
 
 	/* Now stop, we've been polite long enough. */
-	if (reestablish_only)
+	if (reestablish_only) {
+		/* If we were successfully closing, we still go to closingd. */
+		if (shutdown_complete(peer)) {
+			send_shutdown_complete(peer);
+			daemon_shutdown();
+			exit(0);
+		}
 		peer_failed_err(peer->pps,
 				&peer->channel_id,
 				"Channel is already closed");
+	}
 
 	/* Corner case: we didn't send shutdown before because update_add_htlc
 	 * pending, but now they're cleared by restart, and we're actually
@@ -3594,15 +3610,6 @@ static void init_channel(struct peer *peer)
 	billboard_update(peer);
 }
 
-static void send_shutdown_complete(struct peer *peer)
-{
-	/* Now we can tell master shutdown is complete. */
-	wire_sync_write(MASTER_FD,
-			take(towire_channeld_shutdown_complete(NULL, peer->pps)));
-	per_peer_state_fdpass_send(MASTER_FD, peer->pps);
-	close(MASTER_FD);
-}
-
 static void try_read_gossip_store(struct peer *peer)
 {
 	u8 *msg = gossip_store_next(tmpctx, peer->pps);

lightningd/channel_control.c

@@ -318,7 +318,8 @@ static void peer_start_closingd_after_shutdown(struct channel *channel,
 	peer_start_closingd(channel, pps);
 
 	/* We might have reconnected, so already be here. */
-	if (channel->state != CLOSINGD_SIGEXCHANGE)
+	if (!channel_closed(channel)
+	    && channel->state != CLOSINGD_SIGEXCHANGE)
 		channel_set_state(channel,
 				  CHANNELD_SHUTTING_DOWN,
 				  CLOSINGD_SIGEXCHANGE,

lightningd/closing_control.c

@@ -145,7 +145,7 @@ static void peer_closing_complete(struct channel *channel, const u8 *msg)
 	channel_set_billboard(channel, false, NULL);
 
 	/* Retransmission only, ignore closing. */
-	if (channel->state == CLOSINGD_COMPLETE)
+	if (channel_closed(channel))
 		return;
 
 	/* Channel gets dropped to chain cooperatively. */

tests/test_closing.py

@@ -2786,7 +2786,6 @@ def test_htlc_rexmit_while_closing(node_factory, executor):
     fut2.result(TIMEOUT)
 
 
-@pytest.mark.xfail(strict=True)
 @pytest.mark.openchannel('v1')
 @pytest.mark.developer("needs dev_disconnect")
 def test_you_forgot_closed_channel(node_factory, executor):