gossipd: dev-set-max-scids-encode-size to artificially force "full" replies.

We cap each reply at a single one, which forces the code into our
recursion logic.

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

gossipd/gossip.c

@@ -101,6 +101,10 @@ HTABLE_DEFINE_TYPE(struct important_peerid,
 		   important_peerid_eq,
 		   important_peerid_map);
 
+#if DEVELOPER
+static u32 max_scids_encode_bytes = -1U;
+#endif
+
 struct daemon {
 	/* Who am I? */
 	struct pubkey id;
@@ -439,6 +443,10 @@ static void encode_add_short_channel_id(u8 **encoded,
 
 static bool encode_short_channel_ids_end(u8 **encoded, size_t max_bytes)
 {
+#if DEVELOPER
+	if (tal_len(*encoded) > max_scids_encode_bytes)
+		return false;
+#endif
 	return tal_len(*encoded) <= max_bytes;
 }
 
@@ -2291,6 +2299,17 @@ fail:
 								      NULL)));
 	goto out;
 }
+
+static struct io_plan *dev_set_max_scids_encode_size(struct io_conn *conn,
+						     struct daemon *daemon,
+						     const u8 *msg)
+{
+	if (!fromwire_gossip_dev_set_max_scids_encode_size(msg,
+							   &max_scids_encode_bytes))
+		master_badmsg(WIRE_GOSSIP_DEV_SET_MAX_SCIDS_ENCODE_SIZE, msg);
+
+	return daemon_conn_read_next(conn, &daemon->master);
+}
 #endif /* DEVELOPER */
 
 static int make_listen_fd(int domain, void *addr, socklen_t len, bool mayfail)
@@ -3518,11 +3537,15 @@ static struct io_plan *recv_req(struct io_conn *conn, struct daemon_conn *master
 	case WIRE_GOSSIP_QUERY_CHANNEL_RANGE:
 		return query_channel_range(conn, daemon, daemon->master.msg_in);
 
+	case WIRE_GOSSIP_DEV_SET_MAX_SCIDS_ENCODE_SIZE:
+		return dev_set_max_scids_encode_size(conn, daemon,
+						     daemon->master.msg_in);
 #else
 	case WIRE_GOSSIP_PING:
 	case WIRE_GOSSIP_QUERY_SCIDS:
 	case WIRE_GOSSIP_SEND_TIMESTAMP_FILTER:
 	case WIRE_GOSSIP_QUERY_CHANNEL_RANGE:
+	case WIRE_GOSSIP_DEV_SET_MAX_SCIDS_ENCODE_SIZE:
 		break;
 #endif /* !DEVELOPER */
 
@@ -3581,7 +3604,6 @@ int main(int argc, char *argv[])
 	timers_init(&daemon->timers, time_mono());
 	daemon->broadcast_interval = 30000;
 	daemon->last_announce_timestamp = 0;
-
 	/* stdin == control */
 	daemon_conn_init(daemon, &daemon->master, STDIN_FILENO, recv_req,
 			 master_gone);

gossipd/gossip_wire.csv

@@ -186,6 +186,10 @@ gossip_query_channel_range_reply,,final_complete,bool
 gossip_query_channel_range_reply,,num,u16
 gossip_query_channel_range_reply,,scids,num*struct short_channel_id
 
+# Set artificial maximum reply_channel_range size.  Master->gossipd
+gossip_dev_set_max_scids_encode_size,3030
+gossip_dev_set_max_scids_encode_size,,max,u32
+
 # Given a short_channel_id, return the endpoints
 gossip_resolve_channel_request,3009
 gossip_resolve_channel_request,,channel_id,struct short_channel_id

lightningd/gossip_control.c

@@ -139,6 +139,7 @@ static unsigned gossip_msg(struct subd *gossip, const u8 *msg, const int *fds)
 	case WIRE_GOSSIP_QUERY_SCIDS:
 	case WIRE_GOSSIP_QUERY_CHANNEL_RANGE:
 	case WIRE_GOSSIP_SEND_TIMESTAMP_FILTER:
+	case WIRE_GOSSIP_DEV_SET_MAX_SCIDS_ENCODE_SIZE:
 	case WIRE_GOSSIPCTL_PEER_DISCONNECT:
 	case WIRE_GOSSIPCTL_PEER_IMPORTANT:
 	case WIRE_GOSSIPCTL_PEER_DISCONNECTED:
@@ -761,4 +762,37 @@ static const struct json_command dev_query_channel_range_command = {
 	"Query {peerid} for short_channel_ids for {first} block + {num} blocks"
 };
 AUTODATA(json_command, &dev_query_channel_range_command);
+
+static void json_dev_set_max_scids_encode_size(struct command *cmd,
+					       const char *buffer,
+					       const jsmntok_t *params)
+{
+	u8 *msg;
+	jsmntok_t *maxtok;
+	u32 max;
+
+	if (!json_get_params(cmd, buffer, params,
+			     "max", &maxtok,
+			     NULL)) {
+		return;
+	}
+
+	if (!json_tok_number(buffer, maxtok, &max)) {
+		command_fail(cmd, JSONRPC2_INVALID_PARAMS,
+			     "max must be a number");
+		return;
+	}
+
+	msg = towire_gossip_dev_set_max_scids_encode_size(NULL, max);
+	subd_send_msg(cmd->ld->gossip, take(msg));
+
+	command_success(cmd, null_response(cmd));
+}
+
+static const struct json_command dev_set_max_scids_encode_size = {
+	"dev-set-max-scids-encode-size",
+	json_dev_set_max_scids_encode_size,
+	"Set {max} bytes of short_channel_ids per reply_channel_range"
+};
+AUTODATA(json_command, &dev_set_max_scids_encode_size);
 #endif /* DEVELOPER */

tests/test_lightningd.py

@@ -2714,6 +2714,21 @@ class LightningDTests(BaseLightningDTests):
         assert ret['final_complete']
         assert len(ret['short_channel_ids']) == 0
 
+        # Make l2 split reply into two.
+        l2.rpc.dev_set_max_scids_encode_size(max=9)
+        ret = l1.rpc.dev_query_channel_range(id=l2.info['id'],
+                                             first=0,
+                                             num=1000000)
+
+        # It should definitely have split
+        assert ret['final_first_block'] != 0 or ret['final_num_blocks'] != 1000000
+        assert ret['final_complete']
+        assert len(ret['short_channel_ids']) == 2
+        assert ret['short_channel_ids'][0] == scid12
+        assert ret['short_channel_ids'][1] == scid23
+
+        l2.daemon.wait_for_log('queue_channel_ranges full: splitting')
+
     @unittest.skipIf(not DEVELOPER, "needs DEVELOPER=1")
     def test_query_short_channel_id(self):
         l1 = self.node_factory.get_node(options={'log-level': 'io'})