--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mod_muc_restrict_media/mod_muc_restrict_media.lua	Tue Nov 23 17:14:25 2021 +0000
@@ -0,0 +1,68 @@
+module:depends"muc";
+
+local restrict_by_default = not module:get_option_boolean("muc_room_default_restrict_media", true);
+
+local function should_restrict_media(room)
+	local restrict_media = room._data.restrict_media;
+	if restrict_media == nil then
+		restrict_media = restrict_by_default;
+	end
+	return restrict_media;
+end
+
+module:hook("muc-config-form", function(event)
+	local room, form = event.room, event.form;
+	table.insert(form, {
+		name = "{xmpp:prosody.im}muc#roomconfig_unaffiliated_media",
+		type = "boolean",
+		label = "Display inline media (images, etc.) from non-members",
+		value = not should_restrict_media(room),
+	});
+end);
+
+module:hook("muc-config-submitted", function(event)
+	local room, fields, changed = event.room, event.fields, event.changed;
+	local new_restrict_media = not fields["{xmpp:prosody.im}muc#roomconfig_unaffiliated_media"];
+	if new_restrict_media ~= should_restrict_media(room) then
+		if new_restrict_media == restrict_by_default(room) then
+			room._data.restrict_media = nil;
+		else
+			room._data.restrict_media = new_restrict_media;
+		end
+		if type(changed) == "table" then
+			changed["{xmpp:prosody.im}muc#roomconfig_unaffiliated_media"] = true;
+		else
+			event.changed = true;
+		end
+	end
+end);
+
+module:hook("muc-disco#info", function (event)
+	local room, form, formdata = event.room, event.form, event.formdata;
+
+	local allow_unaffiliated_media = not should_restrict_media(room);
+	table.insert(form, {
+		name = "{xmpp:prosody.im}muc#roomconfig_unaffiliated_media",
+	});
+	formdata["{xmpp:prosody.im}muc#roomconfig_unaffiliated_media"] = allow_unaffiliated_media;
+end);
+
+local function filter_media_tags(tag)
+	local xmlns = tag.attr.xmlns;
+	if xmlns == "jabber:x:oob" then
+		return nil;
+	elseif xmlns == "urn:xmpp:reference:0" then
+		if tag:get_child("media-sharing", "urn:xmpp:sims:1") then
+			return nil;
+		end
+	end
+	return tag;
+end
+
+module:hook("muc-occupant-groupchat", function (event)
+	local stanza = event.stanza;
+	if stanza.attr.type ~= "groupchat" then return; end
+	if should_restrict_media(event.room) then
+		stanza:maptags(filter_media_tags);
+	end
+end, 20);