# HG changeset patch
# User Kim Alvefur <zash@zash.se>
# Date 1629631379 -7200
# Node ID 8231774f5bfd8091b2cb883d7f57c8891f852974
# Parent  44af84178cead47ba2169722fdba3958e3bc959f
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.

diff -r 44af84178cea -r 8231774f5bfd mod_cloud_notify_encrypted/mod_cloud_notify_encrypted.lua
--- a/mod_cloud_notify_encrypted/mod_cloud_notify_encrypted.lua	Sun Aug 22 10:46:31 2021 +0100
+++ b/mod_cloud_notify_encrypted/mod_cloud_notify_encrypted.lua	Sun Aug 22 13:22:59 2021 +0200
@@ -1,5 +1,6 @@
 local array = require "util.array";
 local base64 = require "util.encodings".base64;
+local valid_utf8 = require "util.encodings".utf8.valid;
 local ciphers = require "openssl.cipher";
 local jid = require "util.jid";
 local json = require "util.json";
@@ -78,6 +79,9 @@
 		body = original_stanza:get_child_text("body");
 		if body and #body > 255 then
 			body = body:sub(1, 255);
+			if not valid_utf8(body) then
+				body = body:gsub("[\194-\244][\128-\191]*$", "");
+			end
 		end
 	end