mod_cloud_notify_encrypted: Ensure body substring remains valid UTF-8 The `body:sub()` call risks splitting the string in the middle of a multi-byte UTF-8 sequence. This should have been caught by util.stanza validation, but that would have caused some havoc, at the very least causing the notification to not be sent. There have been no reports of this happening. Likely because this module isn't widely deployed among users with languages that use many longer UTF-8 sequences. The util.encodings.utf8.valid() function is O(n) where only the last sequence really needs to be checked, but it's in C and expected to be fast.

local st = require "util.stanza";

local omemo_namespace_prefix = "eu.siacs.conversations.axolotl."

module:hook("iq/bare/http://jabber.org/protocol/pubsub:pubsub", function (event)
	local origin, stanza = event.origin, event.stanza;

	local node = stanza.tags[1].tags[1].attr.node;
	if node and node:sub(1, #omemo_namespace_prefix) == omemo_namespace_prefix then
		origin.send(st.error_reply(stanza, "cancel", "item-not-found", "OMEMO is disabled"));
		return true;
	end
end, 10);