Clear All Slack Channel Messages

This app clears all messages from a Slack channel with a simple slash command. Once invoked, it will delete 40 messages per minute from the channel it is invoked in until the channel has no messages left or the command is cancelled by running /cmd clear cancel.

For security, you can restrict who can trigger this command by setting an variable with authorized Slack user ids.

Deployment is simple - all you need to do is press the install button to get started!

Note: You must have sufficient permissions in your Slack workspace to clear messages posted by an admin or owner.

How It Works

This Source contains two endpoints:

functions/events/slack/command/clear.js, which responds to an incoming Slack command (invoked as /cmd clear) and marks a Slack channel for clearing.
functions/events/scheduler/minutely.js, which runs every minute using the Autocode scheduler and deletes up to 40 messages using the slack.messages.destroy API.

Slack has a rate limit of around 50 requests per minute around the message deletion API, and running the deletion process minutely and deleting messages in batches allows your app to respect this limit.

When you run /cmd clear, your app will store the channel_id and user_id from the incoming slack.command event using the utils.kv API and update you with an ephemeral message created with the slack.messages.ephemeral API:

await lib.utils.kv['@0.1.16'].set({
  key: `__clearedSlackChannelData:${context.service.identifier}__`,
  value: `${event.channel_id},${event.user_id}`
});
return lib.slack.messages['@0.6.1'].ephemeral.create({
  channelId: event.channel_id,
  userId: event.user_id,
  text: `Clearing channel <#${event.channel_id}>...`,
  attachments: [{
    text: `This app will run once a minute until it has deleted all the messages it can`
  }, {
    text: `You can run */cmd clear cancel* to stop this process`
  }]
});

Once these keys are set, the Autocode scheduler will trigger minutely.js every minute, first retrieving a list of all messages in the channel with the slack.channels.messages.list API:

let messages = await lib.slack.channels['@0.7.2'].messages.list({
  channel: '#' + channel.name
});

And then clearing the messages from the channel, keeping track of which failures are retryable:

console.log(`About to clear ${messages.length} messages from #${channel.name}...`);

let deletionResults = await async.mapLimit(messages, 2, async (message) => {
  try {
    await lib.slack.messages['@0.6.1'].destroy({
      id: clearedChannelId,
      ts: message.ts,
      as_user: true
    });
    return {
      successful: true
    };
  } catch (e) {
    return {
      successful: false,
      retryable: e.message && e.message.indexOf('ratelimited') !== -1
    };
  }
});

Once no more messages remain in the channel or all failures are not retryable, the app clears the key and sends a final ephemeral message.

You can preemptively stop the clearing process by running /cmd clear cancel. This will clear the values stored in utils.kv and stop the scheduled endpoint handler from deleting further messages in the channel.

Restricting Access

If you'd like to limit access to your command to certain users, open functions/events/slack/command/clear.js in the Autocode editor. This file contains the code that runs in response to the slash command. Add the Slack user ids of users you would like to allow to the SLACK_USER_ID_ALLOWLIST array on line 3. You can modify the entries on this list by changing the code and redeploying your app.

Note: If you do not add any user ids here, this command will be usable by anyone in your workspace. You can find the ids of users in your workspace by viewing their profile and pressing the More button in the pane, then retrieving the member ID in the menu that appears.

That's it!

Thanks for checking out this Source! Follow the Autocode team on Twitter @AutocodeHQ for updates. If you have any questions, please join our community Slack channel - you can get an invite from under the community tab in the topbar of this page.