lightningd: don't populate local alias if NULL, have the caller do it.

We were populating local aliases for stub channels, which means putting them in
the htable and thus risking that we could try to route through them.

Instead, NULL means "caller will populate", and for the other cases make the
caller specify the real scid.

We opencode channel_set_random_local_alias, since there's only one caller now.

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

Author: rustyrussell

lightningd/channel.c

@@ -268,16 +268,6 @@ static void chanmap_add(struct lightningd *ld,
 	tal_add_destructor2(scc, destroy_scid_to_channel, ld);
 }
 
-static void channel_set_random_local_alias(struct channel *channel)
-{
-	assert(channel->alias[LOCAL] == NULL);
-	channel->alias[LOCAL] = tal(channel, struct short_channel_id);
-	*channel->alias[LOCAL] = random_scid();
-	/* We don't check for uniqueness.  We would crash on a clash, but your machine is
-	 * probably broken beyond repair if it gets two equal 64 bit numbers */
-	chanmap_add(channel->peer->ld, channel, *channel->alias[LOCAL]);
-}
-
 void channel_set_scid(struct channel *channel, const struct short_channel_id *new_scid)
 {
 	struct lightningd *ld = channel->peer->ld;
@@ -355,8 +345,12 @@ struct channel *new_unsaved_channel(struct peer *peer,
 		= CLOSING_FEE_NEGOTIATION_STEP_UNIT_PERCENTAGE;
 	channel->shutdown_wrong_funding = NULL;
 	channel->closing_feerate_range = NULL;
-	channel->alias[REMOTE] = channel->alias[LOCAL] = NULL;
-	channel_set_random_local_alias(channel);
+	channel->alias[REMOTE] = NULL;
+	channel->alias[LOCAL] = tal(channel, struct short_channel_id);
+	*channel->alias[LOCAL] = random_scid();
+	/* We don't check for uniqueness.  We would crash on a clash, but your machine is
+	 * probably broken beyond repair if it gets two equal 64 bit numbers */
+	chanmap_add(channel->peer->ld, channel, *channel->alias[LOCAL]);
 
 	channel->shutdown_scriptpubkey[REMOTE] = NULL;
 	channel->last_was_revoke = false;
@@ -611,15 +605,12 @@ struct channel *new_channel(struct peer *peer, u64 dbid,
 	/* All these possible short_channel_id variants go in the lookup table! */
 	if (channel->scid)
 		chanmap_add(peer->ld, channel, *channel->scid);
+	/* This is always set, *EXCEPT* for stub channels! */
 	if (channel->alias[LOCAL])
 		chanmap_add(peer->ld, channel, *channel->alias[LOCAL]);
 	for (size_t i = 0; i < tal_count(channel->old_scids); i++)
 		chanmap_add(peer->ld, channel, channel->old_scids[i]);
 
-	/* We always make sure this is set (historical channels from db might not) */
-	if (!channel->alias[LOCAL])
-		channel_set_random_local_alias(channel);
-
 	channel->alias[REMOTE] = tal_steal(channel, alias_remote);  /* Haven't gotten one yet. */
 	channel->cid = *cid;
 	channel->our_msat = our_msat;

lightningd/opening_control.c

@@ -110,6 +110,7 @@ wallet_commit_channel(struct lightningd *ld,
 	struct timeabs timestamp;
 	struct channel_stats zero_channel_stats;
 	enum addrtype addrtype;
+	struct short_channel_id local_alias;
 
 	/* We can't have any payments yet */
 	memset(&zero_channel_stats, 0, sizeof(zero_channel_stats));
@@ -172,6 +173,8 @@ wallet_commit_channel(struct lightningd *ld,
 	else
 		static_remotekey_start = 0x7FFFFFFFFFFFFFFF;
 
+	local_alias = random_scid();
+
 	channel = new_channel(uc->peer, uc->dbid,
 			      NULL, /* No shachain yet */
 			      CHANNELD_AWAITING_LOCKIN,
@@ -190,7 +193,7 @@ wallet_commit_channel(struct lightningd *ld,
 			      false, /* !remote_channel_ready */
 			      NULL, /* no scid yet */
 			      NULL, /* no old scids */
-			      NULL, /* assign random local alias */
+			      &local_alias, /* random local alias */
 			      NULL, /* They haven't told us an alias yet */
 			      cid,
 			      /* The three arguments below are msatoshi_to_us,
@@ -1621,11 +1624,14 @@ static struct channel *stub_chan(struct command *cmd,
 			      &zero_channel_stats,
 			      tal_arr(NULL, struct channel_state_change *, 0));
 
-	/* We fill in scid manually here, so it doesn't go in the hash table! */
+	/* We fill in scid & local alias manually here, so it doesn't go in the hash table! */
 	channel->scid = tal(cmd, struct short_channel_id);
 	/*To indicate this is an stub channel we keep it's scid to 1x1x1.*/
 	if (!mk_short_channel_id(channel->scid, 1, 1, 1))
                 fatal("Failed to make short channel 1x1x1!");
+	/* Every channel is assumed to have a non-NULL local alias */
+	channel->alias[LOCAL] = tal(channel, struct short_channel_id);
+	*channel->alias[LOCAL] = *channel->scid;
 
 	/* We don't want to gossip about this, ever. */
 	channel->channel_gossip = tal_free(channel->channel_gossip);