pytest: test dropping transient connections.

Requires a hack to exhaust connectd fds and make us close a transient.

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

connectd/connectd.c

@@ -436,6 +436,10 @@ void close_random_connection(struct daemon *daemon)
 		if (!c->transient)
 			continue;
 
+		/* This could be the one caller is trying right now */
+		if (!c->conn)
+			continue;
+
 		status_debug("due to stress, closing transient connect attempt to %s",
 			     fmt_node_id(tmpctx, &c->id));
 		/* This tells destructor why it was closed */
@@ -1979,6 +1983,12 @@ static char *fd_mode_str(int fd)
 static void dev_report_fds(struct daemon *daemon, const u8 *msg)
 {
 	bool found_chr_fd = false;
+
+	/* Not only would this get upset with all the /dev/null,
+	 * our symbol code fails if it can't open files */
+	if (daemon->dev_exhausted_fds)
+		return;
+
 	for (int fd = 3; fd < 4096; fd++) {
 		bool listener;
 		const struct io_conn *c;
@@ -2035,6 +2045,19 @@ static void dev_report_fds(struct daemon *daemon, const u8 *msg)
 	}
 }
 
+static void dev_exhaust_fds(struct daemon *daemon, const u8 *msg)
+{
+	int fd;
+
+	while ((fd = open("/dev/null", O_RDONLY)) >= 0);
+	if (errno != EMFILE)
+		status_failed(STATUS_FAIL_INTERNAL_ERROR, "dev_exhaust_fds got %s",
+			      strerror(errno));
+
+	status_unusual("dev_exhaust_fds: expect failures");
+	daemon->dev_exhausted_fds = true;
+}
+
 static struct io_plan *recv_peer_connect_subd(struct io_conn *conn,
 					      const u8 *msg,
 					      int fd,
@@ -2116,6 +2139,12 @@ static struct io_plan *recv_req(struct io_conn *conn,
 			goto out;
 		}
 		/* Fall thru */
+	case WIRE_CONNECTD_DEV_EXHAUST_FDS:
+		if (daemon->developer) {
+			dev_exhaust_fds(daemon, msg);
+			goto out;
+		}
+		/* Fall thru */
 	/* We send these, we don't receive them */
 	case WIRE_CONNECTD_INIT_REPLY:
 	case WIRE_CONNECTD_ACTIVATE_REPLY:
@@ -2210,6 +2239,7 @@ int main(int argc, char *argv[])
 	daemon->shutting_down = false;
 	daemon->dev_suppress_gossip = false;
 	daemon->custom_msgs = NULL;
+	daemon->dev_exhausted_fds = false;
 
 	/* stdin == control */
 	daemon->master = daemon_conn_new(daemon, STDIN_FILENO, recv_req, NULL,

connectd/connectd.h

@@ -264,6 +264,8 @@ struct daemon {
 	bool dev_suppress_gossip;
 	/* dev_disconnect file */
 	int dev_disconnect_fd;
+	/* Did we exhaust fds?  If so, skip dev_report_fds */
+	bool dev_exhausted_fds;
 };
 
 /* Called by io_tor_connect once it has a connection out. */

connectd/connectd_wire.csv

@@ -163,3 +163,5 @@ msgtype,connectd_start_shutdown_reply,2131
 # master -> connect: stop sending gossip.
 msgtype,connectd_dev_suppress_gossip,2032
 
+# master -> connect: waste all your fds.
+msgtype,connectd_dev_exhaust_fds,2036

lightningd/connect_control.c

@@ -611,6 +611,7 @@ static unsigned connectd_msg(struct subd *connectd, const u8 *msg, const int *fd
 	case WIRE_CONNECTD_CUSTOMMSG_OUT:
 	case WIRE_CONNECTD_START_SHUTDOWN:
 	case WIRE_CONNECTD_SET_CUSTOMMSGS:
+	case WIRE_CONNECTD_DEV_EXHAUST_FDS:
 	/* This is a reply, so never gets through to here. */
 	case WIRE_CONNECTD_INIT_REPLY:
 	case WIRE_CONNECTD_ACTIVATE_REPLY:
@@ -932,3 +933,26 @@ static const struct json_command dev_report_fds = {
 	.dev_only = true,
 };
 AUTODATA(json_command, &dev_report_fds);
+
+static struct command_result *json_dev_connectd_exhaust_fds(struct command *cmd,
+							    const char *buffer,
+							    const jsmntok_t *obj UNNEEDED,
+							    const jsmntok_t *params)
+{
+	if (!param(cmd, buffer, params, NULL))
+		return command_param_failed();
+
+	subd_send_msg(cmd->ld->connectd,
+		      take(towire_connectd_dev_exhaust_fds(NULL)));
+
+	return command_success(cmd, json_stream_success(cmd));
+}
+
+static const struct json_command dev_connectd_exhaust_fds = {
+	"dev-connectd-exhaust-fds",
+	"developer",
+	json_dev_connectd_exhaust_fds,
+	"Make connectd run out of file descriptors",
+	.dev_only = true,
+};
+AUTODATA(json_command, &dev_connectd_exhaust_fds);

tests/test_connection.py

@@ -4596,3 +4596,24 @@ def test_wss_proxy(node_factory):
         msg = lconn.read_message()
         if int.from_bytes(msg[0:2], 'big') == 19:
             break
+
+
+def test_connect_transient(node_factory):
+    l1, l2, l3, l4 = node_factory.get_nodes(4, opts={'may_reconnect': True})
+
+    # This is not transient, because they have a channel
+    node_factory.join_nodes([l1, l2])
+
+    # Make sure it reconnects once it has a channel.
+    l1.rpc.disconnect(l2.info['id'], force=True)
+    l1.rpc.connect(l2.info['id'], 'localhost', l2.port)
+
+    # This has no channel, and thus is a transient.
+    l1.rpc.connect(l3.info['id'], 'localhost', l3.port)
+
+    l1.rpc.dev_connectd_exhaust_fds()
+
+    # Connecting to l4 will discard connection to l3!
+    l1.rpc.connect(l4.info['id'], 'localhost', l4.port)
+    assert l1.rpc.listpeers(l3.info['id'])['peers'] == []
+    assert l1.daemon.is_in_log(fr"due to stress, randomly closing peer {l3.info['id']} \(score 0\)")