plugin: Add listconfigs stub for the --plugin option

lightningd/options.c

@@ -971,7 +971,7 @@ static void add_config(struct lightningd *ld,
 			if (ld->proxyaddr)
 				answer = fmt_wireaddr(name0, ld->proxyaddr);
 		} else if (opt->cb_arg == (void *)opt_add_plugin) {
-			/* FIXME: Actually add the plugin options */
+			json_add_opt_plugins(response, ld->plugins);
 #if DEVELOPER
 		} else if (strstarts(name, "dev-")) {
 			/* Ignore dev settings */

lightningd/plugin.c

@@ -2,6 +2,8 @@
 
 #include <ccan/list/list.h>
 #include <ccan/tal/str/str.h>
+#include <lightningd/json.h>
+#include <unistd.h>
 
 struct plugin {
 	int stdin, stdout;
@@ -33,3 +35,16 @@ void plugin_register(struct plugins *plugins, const char* path TAKES)
 void plugins_init(struct plugins *plugins)
 {
 }
+
+void json_add_opt_plugins(struct json_stream *response,
+			  const struct plugins *plugins)
+{
+	struct plugin *p;
+	json_object_start(response, "plugin");
+	for (size_t i=0; i<tal_count(plugins->plugins); i++) {
+		p = plugins->plugins[i];
+		json_object_start(response, p->cmd);
+		json_object_end(response);
+	}
+	json_object_end(response);
+}

lightningd/plugin.h

@@ -3,6 +3,7 @@
 #include "config.h"
 #include <ccan/take/take.h>
 #include <ccan/tal/tal.h>
+#include <lightningd/jsonrpc.h>
 
 /**
  * A collection of plugins, and some associated information.
@@ -35,4 +36,13 @@ void plugins_init(struct plugins *plugins);
  */
 void plugin_register(struct plugins *plugins, const char* path TAKES);
 
+/**
+ * Add the plugin option and their respective options to listconfigs.
+ *
+ * This adds a dict that maps the plugin name to a dict of configuration options
+ * for the corresponding plugins.
+ */
+void json_add_opt_plugins(struct json_stream *response,
+			  const struct plugins *plugins);
+
 #endif /* LIGHTNING_LIGHTNINGD_PLUGIN_H */