gossipd: make sure to mark node_announcement dying if we fast-path remove last channel.

Normally, channels are marked dying, the 12 blocks later, removed.
But for local channels, we can access any spliced channel already, so
we remove them immediately from our local gossip.  This left a hole in
our logic, if that channel was the last one keeping a
node_announcement alive.

Solution is to unify with the "moved node_announcement" path.

Signed-off-by: Rusty Russell <[email protected]>

Author: rustyrussell

gossipd/gossmap_manage.c

@@ -243,7 +243,7 @@ static bool all_node_channels_dying(struct gossmap *gossmap,
  * - Suppress future lookups in case we receive another channel_update.
  * - Put deleted tombstone in gossip_store.
  * - Mark records deleted in gossip_store.
- * - See if node_announcement(s) need to be removed, or moved.
+ * - See if node_announcement(s) need to be removed, marked dying, or moved.
  */
 static void remove_channel(struct gossmap_manage *gm,
 			   struct gossmap *gossmap,
@@ -272,8 +272,6 @@ static void remove_channel(struct gossmap_manage *gm,
 	/* Check for node_announcements which should no longer be there */
 	for (int dir = 0; dir < 2; dir++) {
 		struct gossmap_node *node;
-		const u8 *nannounce;
-		u32 timestamp;
 		u64 offset;
 
 		node = gossmap_nth_node(gossmap, chan, dir);
@@ -289,18 +287,26 @@ static void remove_channel(struct gossmap_manage *gm,
 		}
 
 		/* Maybe this was the last channel_announcement which preceeded node_announcement? */
-		if (chan->cann_off > node->nann_off)
-			continue;
-
-		if (any_cannounce_preceeds_offset(gossmap, node, chan, node->nann_off))
-			continue;
+		if (chan->cann_off < node->nann_off
+		    && any_cannounce_preceeds_offset(gossmap, node, chan, node->nann_off)) {
+			const u8 *nannounce;
+			u32 timestamp;
 
-		/* To maintain order, delete and re-add node_announcement */
-		nannounce = gossmap_node_get_announce(tmpctx, gossmap, node);
-		timestamp = gossip_store_get_timestamp(gm->daemon->gs, node->nann_off);
+			/* To maintain order, delete and re-add node_announcement */
+			nannounce = gossmap_node_get_announce(tmpctx, gossmap, node);
+			timestamp = gossip_store_get_timestamp(gm->daemon->gs, node->nann_off);
 
-		gossip_store_del(gm->daemon->gs, node->nann_off, WIRE_NODE_ANNOUNCEMENT);
-		offset = gossip_store_add(gm->daemon->gs, nannounce, timestamp);
+			gossip_store_del(gm->daemon->gs, node->nann_off, WIRE_NODE_ANNOUNCEMENT);
+			offset = gossip_store_add(gm->daemon->gs, nannounce, timestamp);
+		} else {
+			/* Are all remaining channels dying but we weren't?
+			 * Can happen if we removed this channel immediately
+			 * for our own channels, without marking them
+			 * dying. */
+			if (gossmap_chan_is_dying(gossmap, chan))
+				continue;
+			offset = node->nann_off;
+		}
 
 		/* Be sure to set DYING flag when we move (ignore current
 		 * channel, we haven't reloaded gossmap yet!) */