plugin: Remove added JSON-RPC methods if a plugin gets killed

Removes the method from the dispatch table, leaving a NULL entry
currently.

Signed-off-by: Christian Decker <@cdecker>

lightningd/jsonrpc.c

@@ -347,11 +347,12 @@ static const struct json_command *find_cmd(const struct jsonrpc *rpc,
 {
 	struct json_command **commands = rpc->commands;
 
-	/* commands[i]->name can be NULL in test code. */
-	for (size_t i=0; i<tal_count(commands); i++)
-          if (commands[i]->name &&
-              json_tok_streq(buffer, tok, commands[i]->name))
-            return commands[i];
+	/* commands[i] can be NULL if the plugin that registered it
+	 * was killed, commands[i]->name can be NULL in test code. */
+	for (size_t i = 0; i < tal_count(commands); i++)
+		if (commands[i] && commands[i]->name &&
+		    json_tok_streq(buffer, tok, commands[i]->name))
+			return commands[i];
 	return NULL;
 }
 
@@ -738,6 +739,18 @@ bool jsonrpc_command_add(struct jsonrpc *rpc, struct json_command *command)
 	return true;
 }
 
+void jsonrpc_command_remove(struct jsonrpc *rpc, const char *method)
+{
+	// FIXME: Currently leaves NULL entries in the table, if we
+	// restart plugins we should shift them out.
+	for (size_t i=0; i<tal_count(rpc->commands); i++) {
+		struct json_command *cmd = rpc->commands[i];
+		if (cmd && streq(cmd->name, method)) {
+			rpc->commands[i] = tal_free(cmd);
+		}
+	}
+}
+
 struct jsonrpc *jsonrpc_new(const tal_t *ctx, struct lightningd *ld)
 {
 	struct jsonrpc *jsonrpc = tal(ctx, struct jsonrpc);

lightningd/jsonrpc.h

@@ -117,5 +117,13 @@ void jsonrpc_listen(struct jsonrpc *rpc, struct lightningd *ld);
  */
 bool jsonrpc_command_add(struct jsonrpc *rpc, struct json_command *command);
 
+/**
+ * Remove a command/method from the JSON-RPC.
+ *
+ * Used to dynamically remove a `struct json_command` from the
+ * JSON-RPC dispatch table by its name.
+ */
+void jsonrpc_command_remove(struct jsonrpc *rpc, const char *method);
+
 AUTODATA_TYPE(json_command, struct json_command);
 #endif /* LIGHTNING_LIGHTNINGD_JSONRPC_H */

lightningd/lightningd.c

@@ -781,6 +781,8 @@ int main(int argc, char *argv[])
 
 	shutdown_subdaemons(ld);
 
+	tal_free(ld->plugins);
+
 	/* Clean up the JSON-RPC. This needs to happen in a DB transaction since
 	 * it might actually be touching the DB in some destructors, e.g.,
 	 * unreserving UTXOs (see #1737) */
@@ -788,7 +790,6 @@ int main(int argc, char *argv[])
 	tal_free(ld->jsonrpc);
 	db_commit_transaction(ld->wallet->db);
 
-	tal_free(ld->plugins);
 	remove(ld->pidfile);
 
 	/* FIXME: pay can have children off tmpctx which unlink from

lightningd/plugin.c

@@ -118,6 +118,8 @@ static void plugin_kill(struct plugin *plugin, char *msg)
 	plugin->stop = true;
 	io_wake(plugin);
 	kill(plugin->pid, SIGKILL);
+	list_del(&plugin->list);
+	tal_free(plugin);
 }
 
 /**
@@ -384,8 +386,10 @@ static bool plugin_opts_add(const struct plugin_request *req)
 	return true;
 }
 
-static void plugin_rpcmethod_destroy(struct json_command *cmd)
+static void plugin_rpcmethod_destroy(struct json_command *cmd,
+				     struct jsonrpc *rpc)
 {
+	jsonrpc_command_remove(rpc, cmd->name);
 }
 
 static void plugin_rpcmethod_dispatch(struct command *cmd, const char *buffer,
@@ -448,7 +452,7 @@ static bool plugin_rpcmethod_add(struct plugin *plugin, const char *buffer,
 
 	cmd->deprecated = false;
 	cmd->dispatch = plugin_rpcmethod_dispatch;
-	tal_add_destructor(cmd, plugin_rpcmethod_destroy);
+	tal_add_destructor2(cmd, plugin_rpcmethod_destroy, plugin->plugins->rpc);
 	if (!jsonrpc_command_add(plugin->plugins->rpc, cmd)) {
 		log_broken(plugin->log,
 			   "Could not register method \"%s\", a method with "