lightningd: fix similar race in `stop`.

Tested by putting a sleep in the rpc_command hook.

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

lightningd/jsonrpc.c

@@ -192,10 +192,17 @@ static struct command_result *json_stop(struct command *cmd,
 	if (!param(cmd, buffer, params, NULL))
 		return command_param_failed();
 
-	/* This can't have closed yet! */
-	cmd->ld->stop_conn = cmd->jcon->conn;
 	log_unusual(cmd->ld->log, "JSON-RPC shutdown");
 
+	/* With rpc_command_hook, jcon might have closed in the meantime! */
+	if (!cmd->jcon) {
+		/* Return us to toplevel lightningd.c */
+		io_break(cmd->ld);
+		return command_still_pending(cmd);
+	}
+
+	cmd->ld->stop_conn = cmd->jcon->conn;
+
 	/* This is the one place where result is a literal string. */
 	jout = json_out_new(tmpctx);
 	json_out_start(jout, NULL, '{');

lightningd/lightningd.c

@@ -1021,12 +1021,13 @@ int main(int argc, char *argv[])
 	assert(io_loop_ret == ld);
 	ld->state = LD_STATE_SHUTDOWN;
 
+	stop_fd = -1;
+	stop_response = NULL;
+
 	/* Were we exited via `lightningd_exit`?  */
 	if (ld->exit_code) {
 		exit_code = *ld->exit_code;
-		stop_fd = -1;
-		stop_response = NULL;
-	} else {
+	} else if (ld->stop_conn) {
 		/* Keep this fd around, to write final response at the end. */
 		stop_fd = io_conn_fd(ld->stop_conn);
 		io_close_taken_fd(ld->stop_conn);