gossipd: don't request channel_updates if we're being spammed.

It's simple: if we wouldn't accept the timestamp we see, don't put
the channel in the stale_scid_map.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

gossipd/routing.c

@@ -45,19 +45,24 @@ struct pending_node_announce {
 #define TOKENS_PER_MSG 24
 #define TOKEN_MAX (24 * 4)
 
-static bool ratelimit(const struct routing_state *rstate,
-		      u8 *tokens, u32 prev_timestamp, u32 new_timestamp)
+static u8 update_tokens(const struct routing_state *rstate,
+			u8 tokens, u32 prev_timestamp, u32 new_timestamp)
 {
-	u64 num_tokens;
+	u64 num_tokens = tokens;
 
 	assert(new_timestamp >= prev_timestamp);
 
-	/* First, top up tokens, avoiding overflow. */
-	num_tokens = *tokens + ((new_timestamp - prev_timestamp)
+	num_tokens += ((new_timestamp - prev_timestamp)
 		       / GOSSIP_TOKEN_TIME(rstate->dev_fast_gossip));
 	if (num_tokens > TOKEN_MAX)
 		num_tokens = TOKEN_MAX;
-	*tokens = num_tokens;
+	return num_tokens;
+}
+
+static bool ratelimit(const struct routing_state *rstate,
+		      u8 *tokens, u32 prev_timestamp, u32 new_timestamp)
+{
+	*tokens = update_tokens(rstate, *tokens, prev_timestamp, new_timestamp);
 
 	/* Now, if we can afford it, pass this message. */
 	if (*tokens >= TOKENS_PER_MSG) {
@@ -2191,6 +2196,14 @@ bool routing_add_channel_update(struct routing_state *rstate,
 	return true;
 }
 
+bool would_ratelimit_cupdate(struct routing_state *rstate,
+			     const struct half_chan *hc,
+			     u32 timestamp)
+{
+	return update_tokens(rstate, hc->tokens, hc->bcast.timestamp, timestamp)
+		>= TOKENS_PER_MSG;
+}
+
 static const struct node_id *get_channel_owner(struct routing_state *rstate,
 					       const struct short_channel_id *scid,
 					       int direction)

gossipd/routing.h

@@ -483,6 +483,11 @@ static inline struct local_chan *is_local_chan(struct routing_state *rstate,
 	return local_chan_map_get(&rstate->local_chan_map, &chan->scid);
 }
 
+/* Would we ratelimit a channel_update with this timestamp? */
+bool would_ratelimit_cupdate(struct routing_state *rstate,
+			     const struct half_chan *hc,
+			     u32 timestamp);
+
 /* Because we can have millions of channels, and we only want a local_disable
  * flag on ones connected to us, we keep a separate hashtable for that flag.
  */

gossipd/seeker.c

@@ -528,15 +528,19 @@ static void peer_gossip_probe_nannounces(struct seeker *seeker)
 }
 
 /* They have update with this timestamp: do we want it? */
-static bool want_update(u32 timestamp, const struct half_chan *hc)
+static bool want_update(struct seeker *seeker,
+			u32 timestamp, const struct half_chan *hc)
 {
 	if (!is_halfchan_defined(hc))
 		return timestamp != 0;
 
-	return timestamp > hc->bcast.timestamp;
+	if (timestamp <= hc->bcast.timestamp)
+		return false;
+
+	return !would_ratelimit_cupdate(seeker->daemon->rstate, hc, timestamp);
 }
 
-/* They gave us timestamps.  Do we need updated versions? */
+/* They gave us timestamps.  Do we want updated versions? */
 static void check_timestamps(struct seeker *seeker,
 			     struct chan *c,
 			     const struct channel_update_timestamps *ts)
@@ -552,9 +556,9 @@ static void check_timestamps(struct seeker *seeker,
 	 *    for `node_id_2`, or 0 if there was no `channel_update` from that
 	 *    node.
 	 */
-	if (want_update(ts->timestamp_node_id_1, &c->half[0]))
+	if (want_update(seeker, ts->timestamp_node_id_1, &c->half[0]))
 		query_flag |= SCID_QF_UPDATE1;
-	if (want_update(ts->timestamp_node_id_2, &c->half[1]))
+	if (want_update(seeker, ts->timestamp_node_id_2, &c->half[1]))
 		query_flag |= SCID_QF_UPDATE2;
 
 	if (!query_flag)

gossipd/test/run-next_block_range.c

@@ -52,6 +52,11 @@ void status_failed(enum status_failreason code UNNEEDED,
 void status_fmt(enum log_level level UNNEEDED, const char *fmt UNNEEDED, ...)
 
 { fprintf(stderr, "status_fmt called!\n"); abort(); }
+/* Generated stub for would_ratelimit_cupdate */
+bool would_ratelimit_cupdate(struct routing_state *rstate UNNEEDED,
+			     const struct half_chan *hc UNNEEDED,
+			     u32 timestamp UNNEEDED)
+{ fprintf(stderr, "would_ratelimit_cupdate called!\n"); abort(); }
 /* AUTOGENERATED MOCKS END */
 
 static void test_block_range(struct seeker *seeker,