MUC: Add initial hats support (broadcast only) Based on the currently-deferred XEP-0317. The protocol differs a little (because XEP-0317 is incomplete), therefore currently we use a custom namespace. The plan is to update and finish XEP-0317.

author: Matthew Wild <mwild1@gmail.com>
date: Wed, 18 Mar 2020 17:42:56 +0000
child: 10714:9ecad2304297
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/plugins/muc/hats.lib.lua	Wed Mar 18 17:42:56 2020 +0000
@@ -0,0 +1,23 @@
+local st = require "util.stanza";
+
+local xmlns_hats = "xmpp:prosody.im/protocol/hats:1";
+
+module:hook("muc-broadcast-presence", function (event)
+	-- Strip any hats claimed by the client (to prevent spoofing)
+	event.stanza:remove_children("hats", xmlns_hats);
+
+	local aff_data = event.room:get_affiliation_data(event.occupant.bare_jid);
+	local hats = aff_data and aff_data.hats;
+	if not hats then return; end
+	local hats_el;
+	for hat_id, hat_data in pairs(hats) do
+		if hat_data.active then
+			if not hats_el then
+				hats_el = st.stanza("hats", { xmlns = xmlns_hats });
+			end
+			hats_el:tag("hat", { uri = hat_id, title = hat_data.title }):up();
+		end
+	end
+	if not hats_el then return; end
+	event.stanza:add_direct_child(hats_el);
+end);