plugin: Make unannounced notification topics no longer fatal

Since plugins will start sending them soon, and they are likely to get
it wrong sometimes, be a bit more lenient, warn them in the logs
instead and then make sure it doesn't accidentally work anyway.

lightningd/plugin.c

@@ -464,33 +464,22 @@ static const char *plugin_notification_handle(struct plugin *plugin,
 
 	methname = json_strdup(tmpctx, plugin->buffer, methtok);
 
-	if (notifications_have_topic(plugin->plugins, methname)) {
-
 	if (!plugin_notification_allowed(plugin, methname)) {
-			log_unusual(
+		log_unusual(plugin->log,
-			    plugin->log,
 			    "Plugin attempted to send a notification to topic "
 			    "\"%s\" it hasn't declared in its manifest, not "
 			    "forwarding to subscribers.",
 			    methname);
-			return NULL;
+	} else if (notifications_have_topic(plugin->plugins, methname)) {
-		} else {
-
 		n = jsonrpc_notification_start(NULL, methname);
 		json_add_string(n->stream, "origin", plugin->shortname);
-			json_add_tok(n->stream, "payload", paramstok,
+		json_add_tok(n->stream, "payload", paramstok, plugin->buffer);
-				     plugin->buffer);
 		jsonrpc_notification_end(n);
 
 		plugins_notify(plugin->plugins, take(n));
+	}
 	return NULL;
 }
-	} else {
-		return tal_fmt(plugin, "Unknown notification method %.*s",
-			       json_tok_full_len(methtok),
-			       json_tok_full(plugin->buffer, methtok));
-	}
-}
 
 /* Returns the error string, or NULL */
 static const char *plugin_response_handle(struct plugin *plugin,

tests/plugins/custom_notifications.py

@@ -17,5 +17,19 @@ def emit(plugin):
     plugin.notify("custom", "Hello world")
 
 
+@plugin.method("faulty-emit")
+def faulty_emit(plugin):
+    """Emit a simple string notification to topic "custom"
+    """
+    plugin.notify("ididntannouncethis", "Hello world")
+
+
+@plugin.subscribe("ididntannouncethis")
+def on_faulty_emit(origin, payload, **kwargs):
+    """We should never receive this as it gets dropped.
+    """
+    plugin.log("Got the ididntannouncethis event")
+
+
 plugin.add_notification_topic("custom")
 plugin.run()

tests/test_plugin.py

@@ -2411,3 +2411,15 @@ def test_custom_notification_topics(node_factory):
     l1 = node_factory.get_node(options={'plugin': plugin})
     l1.rpc.emit()
     l1.daemon.wait_for_log(r'Got a custom notification Hello world')
+
+    # And now make sure that we drop unannounced notifications
+    l1.rpc.faulty_emit()
+    l1.daemon.wait_for_log(
+        r"Plugin attempted to send a notification to topic .* not forwarding"
+    )
+    time.sleep(1)
+    assert not l1.daemon.is_in_log(r'Got the ididntannouncethis event')
+
+    # The plugin just dist what previously was a fatal mistake (emit
+    # an unknown notification), make sure we didn't kill it.
+    assert 'custom_notifications.py' in [p['name'] for p in l1.rpc.listconfigs()['plugins']]