Another Mattermost to Matrix bridge

This project can do 2 things:

1. Automate migrating from Mattermost team to Matrix (back up [from Mattermost] and restore [to Matrix])

2. Bridge Matrix spaces <-> Mattermost teams

Essentially, this is a backfill bridge to Matrix, except you have to run part 1 and part 2 separately, if you wish to use backfill.

Instructions to use

You don't need a bot account or admin access on the Mattermost side to use this bridge (you can authenticate with either token or user/password). On the Matrix side you need to be able to register an application service.

1. Copy config.sample.yaml to config.yaml and edit with your own settings.

Important Note: If you wish to migrate messages and use this as a bridge as well, please leave enable_bridge: false. You can set it to true after you finish message migration and before you start the bridge.

2. Export your Mattermost data using the helper script: export_from_mattermost/download_everything.sh. For more info about specific things that you can export, see export_from_mattermost/README.md,

3. Generate a Matrix registration file using python generate_registration.py, which will be called registration.yaml but you can rename.

4. Register it to your homeserver, for instance https://docs.mau.fi/bridges/general/registering-appservices.html. If you are running Synapse you can copy the registration file to a new directory /etc/matrix-synapse/appservices and then edit your Synapse config to add the application service, like this:

app_service_config_files:
 - /etc/matrix-synapse/appservices/mattermost_migration.yaml

5. Run the import script import_to_matrix/import_all_teams.py. Alternatively, you may wish to import only some teams or channels, e.g. import_to_matrix/import_team.py sipb or import_to_matrix/import_channel.py 3g5jnmyzzi8a9pcksonnraxzgy, with the team name or channel ID, respectively.

6. If all you wish is to migrate your messages, once that's done, you can revert the changes you made to your Synapse config.yaml or conf.d, since it is a good idea to revoke unused credentials.

7. If you wish to use the bridge, you should change enable_bridge: true in the config, and re-regenerate the registration file, then edit the file in Synapse's config, then restart Syanpse. The URL field at the bottom will change.

8. You can now start bridge.py and keep it always running (e.g. through a systemd unit) to use the bridge.

How to bridge private channels?

To bridge a private channel, all you need is to add the bot to the private channel. If you wish to backfill, manually run:

$ cd export_from_mattermost
$ python export_channel.py [channel ID on mattermost]
$ cd ..
$ python import_to_matrix/import_channel.py [channel ID]

If the channel gets created before you run the import, set matrix -> skip_existing to false on config.yaml, or remove the aliases from the existing channel so the bot doesn't see it. Then, run the import script again.

However, currently it will be bridged as a public channel on Matrix, so anyone who knows the link can join. You can set it to invite-only if the membership will not change. Private channels are still WIP.

What's supported

This program aims to preserve as much as possible fidelity from Mattermost to Matrix

• User display name and profile picture changes
• Mattermost team -> Matrix space (public channels only)
• Rich text messages (most but not all Markdown features)
• Images and other attachments
• Joins/leaves
• Header/purpose changes -> Matrix topic changes (with customizable behavior)
• Reactions (on Matrix->Mattermost the bot will react on the Matrix user's behalf, and only adding reactions is supported)
• Replies and threads (with customizable behavior, since Mattermost conflates them)
• Channel name changes -> Matrix room name changes
• Webhooks (but messages of type slack_webhook are only partially supported)
• Pinned messages (only fully supported on backfill)
• Typing notifications (Mattermost->Matrix only)
• Edits
• Deletions

What's currently not supported

Because I didn't/haven't implemented them (PRs are welcome):

• Private channels or DMs
• During backfill, edited messages are not marked as edited on Matrix
• Full slack-webhook support (rendering author and all fields)
• Webhooks with profile pictures
• Some Markdown features
  • Lists without any newline between any preceding text and the start of the list
  • Inline emojis (#15)
  • LaTeX
  • Mentions
• Pinning a Mattermost message from Matrix (#16)
• Some emoji reactions may not work due to emoji variation selectors (#17)
• Presence / online status
• Deleting Mattermost messages from Matrix when they have attachments
• Room name changes, or other team changes

Due to platform differences:

• Custom reactions (not yet supported by Matrix, bridged as the name of the reaction)

• Reacting with arbitrary strings (not supported by Mattermost)

• Typing notifications from Matrix->Mattermost (that would require creating ghost users on the Mattermost side too like https://github.com/dalcde/matrix-appservice-mattermost does)

• Note that when you delete a message on Mattermost, all of its children get deleted too. So if you delete the root of a thread on Matrix, its children will be visible on Matrix but will be gone on Mattermost.