mod_mam_smart_retention

Description

This module removes messages from the archive after they have been delivered to one or all of the user’s clients.

Background

The first module for allowing clients to “catch up” with messages that were received while they were offline was mod_offline. Due to the design of that protocol, offline messages could only be delivered to a single client before the server deleted them.

The newer XEP-0313 protocol, implemented by mod_mam, allows servers to cache messages for a configurable retention period. This allows clients to synchronize with the user’s incoming and outgoing messages, providing a more flexible “catch up” protocol that is compatible with multiple devices.

The ideal retention period is long enough for all devices to catch up, but not too long (increased storage and processing requirements on the server, metadata accumulation, etc.).

This module takes a middle approach. If successful delivery of messages is known, then they can be removed from the message archive before the global retention period.

Caveats

To work properly, this module expects clients that:

• Always use XEP-0198 Stream Management
• Always use XEP-0386 Bind 2
• Always query the archive using XEP-0313 during login, synchronizing all messages in order (oldest to newest).

If clients do not fit these requirements, you may get unusual results (including, in the worst case, expiring messages which have not been delivered).

Note also that cleanup of delivered messages is scheduled daily. This means that even with the "one" strategy and no minimum retention time set, messages are not removed immediately upon delivery, but only after the next cleanup task runs.

Configuration

Just load this module on a host that also has mod_mam. For example:

modules_enabled = {
  ...
  "mam";
  "mam_smart_retention";
  ...
}

You can then set the following options:

smart_retention_strategy

Can be "one" (default) or "all", depending on whether you want to expire messages that have been delivered to at least one client, or wait until all known clients have received them.

smart_retention_min

An optional minimum amount of time to keep messages for, even if they have already been delivered to clients.

Compatibility

Requires Prosody trunk, commit 8fb7408ded73 or later. Not compatible with Prosody 13.0 or earlier.

sudo prosodyctl install --server=https://modules.prosody.im/rocks/ mod_mam_smart_retention