lightningd/plugin.c: Add important plugins, which if they terminate, lightningd also terminates.

Changelog-Added: New option `--important-plugin` loads a plugin is so important that if it dies, `lightningd` will exit rather than continue.  You can still `--disable-plugin` it, however, which trumps `--important-plugin` and it will not be started at all.

doc/lightningd-config.5

@@ -534,10 +534,11 @@ add multiple directories\.
 
 
  \fBclear-plugins\fR
-This option clears all \fIplugin\fR and \fIplugin-dir\fR options preceeding it,
+This option clears all \fIplugin\fR, \fIimportant-plugin\fR, and \fIplugin-dir\fR options
+preceeding it,
 including the default built-in plugin directory\. You can still add
-\fIplugin-dir\fR and \fIplugin\fR options following this and they will have the
-normal effect\.
+\fIplugin-dir\fR, \fIplugin\fR, and \fIimportant-plugin\fR options following this
+and they will have the normal effect\.
 
 
  \fBdisable-plugin\fR=\fIPLUGIN\fR
@@ -547,6 +548,16 @@ be loaded at startup, whatever directory it is in\.  This option is useful for
 disabling a single plugin inside a directory\.  You can still explicitly
 load plugins which have been disabled, using \fBlightning-plugin\fR(7) \fBstart\fR\.
 
+
+ \fBimportant-plugin\fR=\fIPLUGIN\fR
+Speciy a plugin to run as part of C-lightning\.
+This can be specified multiple times to add multiple plugins\.
+Plugins specified via this option are considered so important, that if the
+plugin stops for any reason (including via \fBlightning-plugin\fR(7) \fBstop\fR),
+C-lightning will also stop running\.
+This way, you can monitor crashes of important plugins by simply monitoring
+if C-lightning terminates\.
+
 .SH BUGS
 
 You should report bugs on our github issues page, and maybe submit a fix

doc/lightningd-config.5.md

@@ -439,10 +439,11 @@ loaded. *DIRECTORY* must exist; this can be specified multiple times to
 add multiple directories.
 
  **clear-plugins**
-This option clears all *plugin* and *plugin-dir* options preceeding it,
+This option clears all *plugin*, *important-plugin*, and *plugin-dir* options
+preceeding it,
 including the default built-in plugin directory. You can still add
-*plugin-dir* and *plugin* options following this and they will have the
-normal effect.
+*plugin-dir*, *plugin*, and *important-plugin* options following this
+and they will have the normal effect.
 
  **disable-plugin**=*PLUGIN*
 If *PLUGIN* contains a /, plugins with the same path as *PLUGIN* will
@@ -451,6 +452,15 @@ be loaded at startup, whatever directory it is in.  This option is useful for
 disabling a single plugin inside a directory.  You can still explicitly
 load plugins which have been disabled, using lightning-plugin(7) `start`.
 
+ **important-plugin**=*PLUGIN*
+Speciy a plugin to run as part of C-lightning.
+This can be specified multiple times to add multiple plugins.
+Plugins specified via this option are considered so important, that if the
+plugin stops for any reason (including via lightning-plugin(7) `stop`),
+C-lightning will also stop running.
+This way, you can monitor crashes of important plugins by simply monitoring
+if C-lightning terminates.
+
 BUGS
 ----
 

lightningd/options.c

@@ -348,7 +348,7 @@ static char *opt_add_plugin(const char *arg, struct lightningd *ld)
 		log_info(ld->log, "%s: disabled via disable-plugin", arg);
 		return NULL;
 	}
-	plugin_register(ld->plugins, arg, NULL);
+	plugin_register(ld->plugins, arg, NULL, false);
 	return NULL;
 }
 
@@ -369,6 +369,16 @@ static char *opt_clear_plugins(struct lightningd *ld)
 	return NULL;
 }
 
+static char *opt_important_plugin(const char *arg, struct lightningd *ld)
+{
+	if (plugin_blacklisted(ld->plugins, arg)) {
+		log_info(ld->log, "%s: disabled via disable-plugin", arg);
+		return NULL;
+	}
+	plugin_register(ld->plugins, arg, NULL, true);
+	return NULL;
+}
+
 /* Prompt the user to enter a password, from which will be derived the key used
  * for `hsm_secret` encryption.
  * The algorithm used to derive the key is Argon2(id), to which libsodium
@@ -771,6 +781,10 @@ static void register_opts(struct lightningd *ld)
 			       NULL, ld,
 			       "Disable a particular plugin by filename/name");
 
+	opt_register_early_arg("--important-plugin", opt_important_plugin,
+			       NULL, ld,
+			       "Add an important plugin to be run (can be used multiple times). Die if the plugin dies.");
+
 	/* Early, as it suppresses DNS lookups from cmdline too. */
 	opt_register_early_arg("--always-use-proxy",
 			       opt_set_bool_arg, opt_show_bool,
@@ -1278,6 +1292,9 @@ static void add_config(struct lightningd *ld,
 			json_add_opt_log_levels(response, ld->log);
 		} else if (opt->cb_arg == (void *)opt_disable_plugin) {
 			json_add_opt_disable_plugins(response, ld->plugins);
+		} else if (opt->cb_arg == (void *)opt_important_plugin) {
+			/* Do nothing, this is already handled by
+			 * opt_add_plugin.  */
 		} else if (opt->cb_arg == (void *)opt_add_plugin_dir
 			   || opt->cb_arg == (void *)plugin_opt_set
 			   || opt->cb_arg == (void *)plugin_opt_flag_set) {

lightningd/plugin.c

@@ -53,6 +53,7 @@ struct plugins *plugins_new(const tal_t *ctx, struct log_book *log_book,
 	p->startup = true;
 	p->json_cmds = tal_arr(p, struct command *, 0);
 	p->blacklist = tal_arr(p, const char *, 0);
+	p->shutdown = false;
 	uintmap_init(&p->pending_requests);
 	memleak_add_helper(p, memleak_help_pending_requests);
 
@@ -62,6 +63,9 @@ struct plugins *plugins_new(const tal_t *ctx, struct log_book *log_book,
 void plugins_free(struct plugins *plugins)
 {
 	struct plugin *p;
+
+	plugins->shutdown = true;
+
 	/* Plugins are usually the unit of allocation, and they are internally
 	 * consistent, so let's free each plugin first. */
 	while (!list_empty(&plugins->plugins)) {
@@ -105,6 +109,7 @@ struct command_result *plugin_register_all_complete(struct lightningd *ld,
 static void destroy_plugin(struct plugin *p)
 {
 	struct plugin_rpccall *call;
+
 	plugin_hook_unregister_all(p);
 	list_del(&p->list);
 
@@ -118,10 +123,23 @@ static void destroy_plugin(struct plugin *p)
 	/* Don't call this if we're still parsing options! */
 	if (p->plugin_state != UNCONFIGURED)
 		check_plugins_resolved(p->plugins);
+
+	/* If we are shutting down, do not continue to checking if
+	 * the dying plugin is important.  */
+	if (p->plugins->shutdown)
+		return;
+
+	/* Now check if the dying plugin is important.  */
+	if (p->important) {
+		log_broken(p->log,
+			   "Plugin marked as important, "
+			   "shutting down lightningd!");
+		lightningd_exit(p->plugins->ld, 1);
+	}
 }
 
 struct plugin *plugin_register(struct plugins *plugins, const char* path TAKES,
-			       struct command *start_cmd)
+			       struct command *start_cmd, bool important)
 {
 	struct plugin *p, *p_temp;
 
@@ -130,6 +148,9 @@ struct plugin *plugin_register(struct plugins *plugins, const char* path TAKES,
 		if (streq(path, p_temp->cmd)) {
 			if (taken(path))
 				tal_free(path);
+		 	/* If added as "important", upgrade to "important".  */
+			if (important)
+				p_temp->important = true;
 			return NULL;
 		}
 	}
@@ -153,6 +174,8 @@ struct plugin *plugin_register(struct plugins *plugins, const char* path TAKES,
 	list_add_tail(&plugins->plugins, &p->list);
 	tal_add_destructor(p, destroy_plugin);
 	list_head_init(&p->pending_rpccalls);
+
+	p->important = important;
 	return p;
 }
 
@@ -186,6 +209,8 @@ void plugin_blacklist(struct plugins *plugins, const char *name)
 			log_info(plugins->log, "%s: disabled via disable-plugin",
 				 p->cmd);
 			list_del_from(&plugins->plugins, &p->list);
+			/* disable-plugin overrides important-plugin.  */
+			p->important = false;
 			tal_free(p);
 		}
 	}
@@ -1188,7 +1213,7 @@ char *add_plugin_dir(struct plugins *plugins, const char *dir, bool error_ok)
 			log_info(plugins->log, "%s: disabled via disable-plugin",
 				 fullpath);
 		} else {
-			p = plugin_register(plugins, fullpath, NULL);
+			p = plugin_register(plugins, fullpath, NULL, false);
 			if (!p && !error_ok)
 				return tal_fmt(NULL, "Failed to register %s: %s",
 				               fullpath, strerror(errno));
@@ -1396,24 +1421,35 @@ void plugins_config(struct plugins *plugins)
 	plugins->startup = false;
 }
 
-void json_add_opt_plugins(struct json_stream *response,
-			  const struct plugins *plugins)
+/** json_add_opt_plugins_array
+ *
+ * @brief add a named array of plugins to the given response,
+ * depending on whether it is important or not important.
+ *
+ * @param response - the `json_stream` to write into.
+ * @param name - the field name of the array.
+ * @param plugins - the plugins object to query.
+ * @param important - match the `important` setting of the
+ * plugins to be added.
+ */
+static
+void json_add_opt_plugins_array(struct json_stream *response,
+				const char *name,
+				const struct plugins *plugins,
+				bool important)
 {
 	struct plugin *p;
-	struct plugin_opt *opt;
 	const char *plugin_name;
+	struct plugin_opt *opt;
 	const char *opt_name;
 
-	/* DEPRECATED: duplicated JSON "plugin" entries */
-	if (deprecated_apis) {
-		list_for_each(&plugins->plugins, p, list) {
-			json_add_string(response, "plugin", p->cmd);
-		}
-	}
-
 	/* we output 'plugins' and their options as an array of substructures */
-	json_array_start(response, "plugins");
+	json_array_start(response, name);
 	list_for_each(&plugins->plugins, p, list) {
+		/* Skip if not matching.  */
+		if (p->important != important)
+			continue;
+
 		json_object_start(response, NULL);
 		json_add_string(response, "path", p->cmd);
 
@@ -1444,6 +1480,23 @@ void json_add_opt_plugins(struct json_stream *response,
 	json_array_end(response);
 }
 
+void json_add_opt_plugins(struct json_stream *response,
+			  const struct plugins *plugins)
+{
+	struct plugin *p;
+
+	json_add_opt_plugins_array(response, "plugins", plugins, false);
+	json_add_opt_plugins_array(response, "important-plugins", plugins, true);
+
+	/* DEPRECATED: duplicated JSON "plugin" entries */
+	if (deprecated_apis) {
+		list_for_each(&plugins->plugins, p, list) {
+			json_add_string(response, p->important ? "important-plugin" : "plugin", p->cmd);
+		}
+	}
+
+}
+
 void json_add_opt_disable_plugins(struct json_stream *response,
 				  const struct plugins *plugins)
 {
@@ -1546,7 +1599,6 @@ static void mark_plugin_destroyed(const struct plugin *unused,
 	pd->plugin = NULL;
 }
 
-
 struct plugin_destroyed *plugin_detect_destruction(const struct plugin *plugin)
 {
 	struct plugin_destroyed *pd = tal(NULL, struct plugin_destroyed);

lightningd/plugin.h

@@ -79,6 +79,10 @@ struct plugin {
 	/* An array of currently pending RPC method calls, to be killed if the
 	 * plugin exits. */
 	struct list_head pending_rpccalls;
+
+	/* If set, the plugin is so important that if it terminates early,
+	 * C-lightning should terminate as well.  */
+	bool important;
 };
 
 /**
@@ -103,6 +107,9 @@ struct plugins {
 
 	/* Blacklist of plugins from --disable-plugin */
 	const char **blacklist;
+
+	/* Whether we are shutting down (`plugins_free` is called) */
+	bool shutdown;
 };
 
 /* The value of a plugin option, which can have different types.
@@ -175,13 +182,15 @@ void plugins_free(struct plugins *plugins);
  * @param plugins: Plugin context
  * @param path: The path of the executable for this plugin
  * @param start_cmd: The optional JSON command which caused this.
+ * @param important: The plugin is important.
  *
  * If @start_cmd, then plugin_cmd_killed or plugin_cmd_succeeded will be called
  * on it eventually.
  */
 struct plugin *plugin_register(struct plugins *plugins,
 			       const char* path TAKES,
-			       struct command *start_cmd);
+			       struct command *start_cmd,
+			       bool important);
 
 /**
  * Returns true if the provided name matches a plugin command

lightningd/plugin_control.c

@@ -58,7 +58,7 @@ struct command_result *plugin_cmd_all_complete(struct plugins *plugins,
 static struct command_result *
 plugin_dynamic_start(struct command *cmd, const char *plugin_path)
 {
-	struct plugin *p = plugin_register(cmd->ld->plugins, plugin_path, cmd);
+	struct plugin *p = plugin_register(cmd->ld->plugins, plugin_path, cmd, false);
 	const char *err;
 
 	if (!p)

tests/test_misc.py

@@ -833,7 +833,7 @@ def test_listconfigs(node_factory, bitcoind, chainparams):
 
     # Test one at a time.
     for c in configs.keys():
-        if c.startswith('#') or c.startswith('plugins'):
+        if c.startswith('#') or c.startswith('plugins') or c == 'important-plugins':
             continue
         oneconfig = l1.rpc.listconfigs(config=c)
         assert(oneconfig[c] == configs[c])