lightningd: have plugin_send_getmanifest return an error string.

This way the caller doesn't have to "know" that it should use strerror().

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

lightningd/plugin.c

@@ -1224,7 +1224,7 @@ void plugins_add_default_dir(struct plugins *plugins)
 	}
 }
 
-bool plugin_send_getmanifest(struct plugin *p)
+const char *plugin_send_getmanifest(struct plugin *p)
 {
 	char **cmd;
 	int stdin, stdout;
@@ -1242,7 +1242,7 @@ bool plugin_send_getmanifest(struct plugin *p)
 		cmd[1] = "--debugger";
 	p->pid = pipecmdarr(&stdin, &stdout, &pipecmd_preserve, cmd);
 	if (p->pid == -1)
-		return false;
+		return tal_fmt(p, "opening pipe: %s", strerror(errno));
 
 	log_debug(p->plugins->log, "started(%u) %s", p->pid, p->cmd);
 	p->buffer = tal_arr(p, char, 64);
@@ -1268,7 +1268,7 @@ bool plugin_send_getmanifest(struct plugin *p)
 				       plugin_manifest_timeout, p);
 	}
 
-	return true;
+	return NULL;
 }
 
 bool plugins_send_getmanifest(struct plugins *plugins)
@@ -1278,9 +1278,12 @@ bool plugins_send_getmanifest(struct plugins *plugins)
 
 	/* Spawn the plugin processes before entering the io_loop */
 	list_for_each_safe(&plugins->plugins, p, next, list) {
+		const char *err;
+
 		if (p->plugin_state != UNCONFIGURED)
 			continue;
-		if (plugin_send_getmanifest(p)) {
+		err = plugin_send_getmanifest(p);
+		if (!err) {
 			sent = true;
 			continue;
 		}

lightningd/plugin.h

@@ -196,8 +196,10 @@ bool plugin_remove(struct plugins *plugins, const char *name);
 
 /**
  * Kick of initialization of a plugin.
+ *
+ * Returns error string, or NULL.
  */
-bool plugin_send_getmanifest(struct plugin *p);
+const char *plugin_send_getmanifest(struct plugin *p);
 
 /**
  * Kick of initialization of all plugins which need it/

lightningd/plugin_control.c

@@ -59,6 +59,7 @@ 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);
+	const char *err;
 
 	if (!p)
 		return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
@@ -66,10 +67,11 @@ plugin_dynamic_start(struct command *cmd, const char *plugin_path)
 				    plugin_path);
 
 	/* This will come back via plugin_cmd_killed or plugin_cmd_succeeded */
-	if (!plugin_send_getmanifest(p))
+	err = plugin_send_getmanifest(p);
+	if (err)
 		return command_fail(cmd, PLUGIN_ERROR,
-				    "%s: failed to open: %s",
+				    "%s: %s",
-				    plugin_path, strerror(errno));
+				    plugin_path, err);
 
 	return command_still_pending(cmd);
 }