Slackbot unable to join private channel with `conversations.join`

[adrielklein]

Description

Hello I am running into a problem that is preventing my slackbot from joining private channels (AKA groups).

So I made sure to add the groups:write scope upon initializing the app, but for whatever reason when i call conversations.join I am faced with the following error:

method_not_supported_for_channel_type

I would have assumed that since I contain the proper scope, then my app should be able to join the private channel. Any suggestions on how to successfully join the private channel? Am I perhaps missing another scope?

Here's some of my code for reference:

const expressReceiver = new ExpressReceiver({
  processBeforeResponse: true,
  signingSecret: process.env.SLACK_SIGNING_SECRET,
  clientId: process.env.SLACK_CLIENT_ID,
  clientSecret: process.env.SLACK_CLIENT_SECRET,
  stateSecret: "my-secret",
  scopes: [
    "chat:write",
    "commands",
    "channels:join",
    "reactions:write",
    "groups:write",
  ],
  installationStore: {
    ...
  },
});

What type of issue is this? (place an x in one of the [ ])

• bug
• enhancement (feature request)
• question
• documentation related
• example code related
• testing related
• discussion

Requirements (place an x in each of the [ ])

• I've read and understood the Contributing guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've searched for any related issues and avoided creating a duplicate issue.

---

Bug Report

Reproducible in:

package version:

{
  "name": "party-poll-v2",
  "version": "1.0.0",
  "main": "index.js",
  "license": "MIT",
  "dependencies": {
    "@slack/bolt": "^3.12.1",
    "@slack/oauth": "^2.5.4",
    "@vendia/serverless-express": "^4.10.1",
    "axios": "^1.1.3",
    "querystring": "^0.2.1"
  },
  "devDependencies": {
    "serverless-dotenv-plugin": "^4.0.2",
    "serverless-offline": "^10.0.2"
  }
}

node version:
v14.20.1
OS version(s):
macOS Big Sur 11.6.8 (20G730)

Steps to reproduce:

1. To to slackbot website
2. Select "Add to Slack"
3. Authorize
4. Try running a party poll command, i.e. /partypoll "What is your favorite color?" red blue green in a private channel

Expected result:

User sees slackbot respond and post a poll as a message to the channel

Actual result:

User's command disappears. User sees message /partypoll failed with the error "dispatch_failed"

Express server fails with the following error:

{
  code: "slack_webapi_platform_error",
  data: {
    ok: false,
    error: "method_not_supported_for_channel_type",
    response_metadata: {
      scopes: [
        "chat:write",
        "commands",
        "channels:join",
        "reactions:write",
        "groups:write",
      ],
      acceptedScopes: ["channels:join"],
    },
  },
}

[srajiang]

Hey @adrielklein - that's an intentional design decision here and the error message is pretty descriptive. For context, only existing members of private channels can add other members, and that goes for both regular slack users as well as apps with the permissions to groups:write. With that scope you can create a new private channel with your app and add other members to that, but existing private channels where the bot isn't the owner cannot be joined from the outside.

I'm not entirely sure what your use case would be, but perhaps creating a new private channel is an option here?

[adrielklein]

@srajiang gotcha, so the problem here is that let's say a user tries to create a poll with the slash command in a private channel (or a DM for that manner). Currently they will just get back the dispatch_failed error message which is a poor user experience for the person issuing the command.

I'm trying to find a solution where I at least show the user a helpful error message such as "/partypoll command cannot be used in a private channel or DM, please use the poll only in public channels", however it's a chicken and egg problem since I will not be able to show the user that error message since the app is not allowed to post messages into a private channel.

Yes, I could create a new private channel and create a poll there, but I believe that would be too cumbersome especially if the user wants to create multiple polls.

So there's no way possible for my slackbot to post any type of message (or even error message) to display to the user that they must use the command in public channels only?

[seratch]

@adrielklein

So there's no way possible for my slackbot to post any type of message (or even error message) to display to the user that they must use the command in public channels only?

For slash command patterns, you can use ack() method to send a simple reply to the command. This method works everywhere including the DMs/private channels where your app is not allowed to post a message using chat.postMessage API.

app.command("/partypoll", async ({ ack, body }) => {
  if (isMemberOfChannel(body)) {
    // post a message in the channel
  } else {
    // tell the end-user what to do next
    await ack("/partypoll command cannot be used in a private channel or DM, please use the poll only in public channels.");
  }
});

[adrielklein]

@seratch that's a great idea, however I'm wondering how isMemberOfChannel would work because as far as I'm aware there is no information in body that specifies whether or not the slackbot is a member of that channel.

On top of that, I don't see any data in body that indicates whether or not the channel is public, private, or a DM.

The only solution I can see to solving this would be a bit more complex where the slackbot calls conversations.list earlier to get all the information about every channel in the workspace and create a map. On subsequent calls for users to create polls, we'd do a lookup in this map based on channel_id to determine if the channel is public, private, or a DM to determine how to proceed.

Clearly that would be a lot more effort and complexity that I'm trying to avoid. Do you know if there's any other data in body that can be used to determine either if the slackbot is already a member of the channel or if the channel is public?

[adrielklein]

ah just doing a bit more research on this and perhaps I can just use conversations.info after I get back the channelId to determine if it's public or not

[adrielklein]

ah just doing a bit more research on this and perhaps I can just use conversations.info after I get back the channelId to determine if it's public or not

Turns out I tried this but getting channel_not_found even though I verified that I successfully passed in the valid channelId of the private channel.

For the records I've also added the required scopes for conversations.info

    "channels:read",
    "groups:read",
    "mpim:read",
    "im:read",

[adrielklein]

So for the record, I was able to find a solution by using conversations.list to determine if the conversation is public or not:

app.command("/partypoll", async ({ ack, say, body, client }) => {
  const conversationListResponse = await client.conversations.list();
  const isPublicChannel =
    conversationListResponse.channels.filter(
      (channel) => channel.id === body.channel_id
    ).length > 0;
  if (isPublicChannel) {
    ack();
    await client.conversations.join({
      channel: body.channel_id,
    });
    await createPoll(body.text, say, client);
  } else {
    ack(
      "/partypoll cannot be used in a private channel or DM at this time. Please use the poll only in public channels."
    );
  }
});

I'm still curious though about the conversations.join method and limitations to joining the private channel in the first place to create the poll there. In fact, I was looking into other polling apps like Simple Poll and discovered that that app is able to join create polls in private channels seamlessly, so I'm just wondering how it's possible for them to do this given the road block I initially faced with my bot joining a private channel via method_not_supported_for_channel_type.

However, I'm going to table that for since thanks to both of your help I was able to successfully to create the poll to public channels and show private error messages (via ack) for private channels, DMs, and multiple DMs.

Thanks again for your help 🙏 . Will close now.

[kyrylolvov]

So the only way to have the App in private channel, is to create a fresh channel with it already in it?

I tried to manually adding App to private channel, but conversations.join still fails.

[kyrylolvov]

So the only way to have the App in private channel, is to create a fresh channel with it already in it?

I tried to manually adding App to private channel, but conversations.join still fails.

@srajiang