message migration from mattermost to slack

mattermost_to_slack.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
import json
import pprint
import csv

if __name__ == '__main__':
    with open('./bulk.csv', 'w') as csvf:
        writer = csv.writer(csvf, lineterminator='\n', quoting=csv.QUOTE_ALL)
        with open('./bulk.json', 'r') as f:
            i = 0
            while True:
                line = f.readline()
                if not line:
                    break
                i+=1
                data = json.loads(line)
                if data.has_key('post') and data['post'].has_key('channel'):# and data['post']['channel'] == 'off-topic':
                    #from IPython.terminal import embed; ipshell=embed.InteractiveShellEmbed(config=embed.load_default_config())(local_ns=locals())
                    writer.writerow([data['post']['create_at']/1000, data['post']['channel'], data['post']['user'], data['post']['message'].encode('utf-8')])

change data['post']['create_at'] to data['post']['create_at']/1000 as mattermost export timestamp in millisecond otherwise slack will give (undetailed) error faling the import.

Can you provide more detail on which export tool should I use to create the input file for this script?

https://docs.mattermost.com/administration/bulk-export.html

Any chance one could modify this to include threads?

i dont use mattermost now. fork is welcome