Mattermost to Slack Migration

This is a Node.js script to reformat Mattermost export data into Slack JSON format. This script supports Direct Messages, Group Messages, Public Channels, and Private Channels. See Limitations section for what is not supported.

Prerequisites

• Node Version Manager (NVM) or Node v20 installed.
• Familiarity with Command Line

Overview

The general process is as follows:

1. Generate Mattermost export using Mattermost bulk export tool
2. Copy emojis from Mattermost server.
3. Process Mattermost data and generate export folder
4. Upload Emojis to Slack Admin (using a bulk import browser add-on is handy!)
5. Zip the export folder and import to Slack

Initial Setup

Generating Mattermost Export

1. On the Mattermost server, generate your export using the Mattermost command line tool:

   mmctl export create --no-attachments

2. Once this is complete, copy the zip from the server and extract the contents.
3. Move the import.jsonl into the root of this project.

Emojis

1. Copy the contents of your emoji directory found in the Mattermost uploads directory on the server into this project at /emoji

Environment Variables

1. Copy .env.sample to .env and update values as necessary

Running the Script

1. Ensure your node version: nvm install or nvm use
2. Run the following: npm run build
3. An export directory with the timestamp will be created in the export directory
4. Zip this directory (i.e. export-{timestamp}) and proceed with data import using the Slack UI (see documentation)

*Note: In addition to the export-{timestamp} directory, channel-admins-{timestamp}.json and data-map--{timestamp}.json are created for reference only. These files are not needed during the Slack Import.

Options

If you are intending to filter data before/after a certain date, you can pass a unix timestamp:

npm run build -- after=1715294431037

Slack Import Issues

• Direct upload of Zip to Slack failed even though file size was under 2GB
• Slack upload tool instructs that Google Drive can be linked, but documentation says it cannot. Ultimately uploading Zip to Dropbox and linking is what worked for us.

Limitations

• This script does not import file attachments / file uploads from Mattermost
• Reactions to top-level messages – this seemed to be a bug with the Mattermost export leaving this data out as opposed to this script actually handling it.