util.stanza: Add method for extracting a single attribute value Sometimes you only care about a single attribute, but the child tag itself may be optional, leading to needing `tag and tag.attr.foo` or `stanza:find("tag@foo")`. The `:find()` method is fairly complex, so avoiding it for this kind of simpler use case is a win.

author: Kim Alvefur <zash@zash.se>
date: Wed, 17 Aug 2022 19:04:30 +0200
parent: 12589:39ae08180c81
child: 12960:31b22cc221b5
--- a/plugins/mod_pubsub/pubsub.lib.lua	Mon Aug 15 16:35:14 2022 +0200
+++ b/plugins/mod_pubsub/pubsub.lib.lua	Wed Aug 17 19:04:30 2022 +0200
@@ -678,8 +678,7 @@
 function handlers.set_retract(origin, stanza, retract, service)
 	local node, notify = retract.attr.node, retract.attr.notify;
 	notify = (notify == "1") or (notify == "true");
-	local item = retract:get_child("item");
-	local id = item and item.attr.id
+	local id = retract:get_child_attr("item", nil, "id");
 	if not (node and id) then
 		origin.send(pubsub_error_reply(stanza, node and "item-not-found" or "nodeid-required"));
 		return true;