From 450d78ad67dc6fd1aed48ec7c5b140d0ff54ef77 Mon Sep 17 00:00:00 2001
From: Rusty Russell <rusty@rustcorp.com.au>
Date: Sun, 11 Feb 2024 21:02:41 +1030
Subject: [PATCH] gossipd: set dying flag on node_announcement when all
 channels are dying.

This avoids us gossiping about nodes which don't have live channels.

Interstingly, we previously tested that we *did* gossip such node
announcements, and now we fix that test.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
---
 gossipd/gossmap_manage.c | 31 +++++++++++++++++++++++++++++++
 tests/test_gossip.py     |  4 ++--
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/gossipd/gossmap_manage.c b/gossipd/gossmap_manage.c
index e540eb009..309fbb8b3 100644
--- a/gossipd/gossmap_manage.c
+++ b/gossipd/gossmap_manage.c
@@ -220,6 +220,17 @@ static bool any_cannounce_preceeds_offset(struct gossmap *gossmap,
 	return false;
 }
 
+/* Are all channels associated with this node dying? */
+static bool all_node_channels_dying(struct gossmap *gossmap, const struct gossmap_node *n)
+{
+	for (size_t i = 0; i < n->num_chans; i++) {
+		const struct gossmap_chan *c = gossmap_nth_chan(gossmap, n, i, NULL);
+		if (!gossmap_chan_is_dying(gossmap, c))
+			return false;
+	}
+	return true;
+}
+
 /* To actually remove a channel:
  * - Suppress future lookups in case we receive another channel_update.
  * - Put deleted tombstone in gossip_store.
@@ -1161,6 +1172,26 @@ void gossmap_manage_channel_spent(struct gossmap_manage *gm,
 				      GOSSIP_STORE_DYING_BIT,
 				      WIRE_CHANNEL_UPDATE);
 	}
+
+	/* If all channels associated with either node are dying, node_announcement is dying
+	   too (so we don't broadcast) */
+	for (int dir = 0; dir < 2; dir++) {
+		struct gossmap_node *n = gossmap_nth_node(gossmap, chan, dir);
+
+		if (!gossmap_node_announced(n))
+			continue;
+
+		/* Don't get confused if a node has a channel with self! */
+		if (dir == 1 && n == gossmap_nth_node(gossmap, chan, 0))
+			continue;
+
+		if (all_node_channels_dying(gossmap, n)) {
+			gossip_store_set_flag(gm->daemon->gs,
+					      n->nann_off,
+					      GOSSIP_STORE_DYING_BIT,
+					      WIRE_NODE_ANNOUNCEMENT);
+		}
+	}
 }
 
 struct gossmap *gossmap_manage_get_gossmap(struct gossmap_manage *gm)
diff --git a/tests/test_gossip.py b/tests/test_gossip.py
index 5c61bfa77..1d1e6d2c3 100644
--- a/tests/test_gossip.py
+++ b/tests/test_gossip.py
@@ -1960,9 +1960,9 @@ def test_gossip_not_dying(node_factory, bitcoind):
 
     l1.daemon.wait_for_log("closing soon due to the funding outpoint being spent")
 
-    # We won't gossip the dead channel any more (but we still propagate node_announcement).  But connectd is not explicitly synced, so wait for "a bit".
+    # We won't gossip the dead channel any more, nor the node_announcements.  But connectd is not explicitly synced, so wait for "a bit".
     time.sleep(1)
-    assert len(get_gossip(l1)) == 2
+    assert get_gossip(l1) == []
 
 
 def test_dump_own_gossip(node_factory):