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.

This module implements the [Server
Optimization](https://xmpp.org/extensions/xep-0410.html#serveroptimization)
part of [XEP-0410: MUC Self-Ping]

# Usage

The module is loaded on MUC components:

```lua
Component "muc.example.com" "muc"
modules_enabled = {
    "muc_ping";
}
```

# Configuration

No options.

# Compatibility

It should work with Prosody up until 0.10.x.

Prosody 0.11.x and trunk natively supports XEP-0410 so this module is **not** needed.