How to get the Slack DM channel ID of the Slack App - slack-api

Question

I have created a simple Slack App app where the only purpose is to send a message to a channel. I understand that there is the conversations.list API to list all public channels to get the correct ID.
However, as a first step, I just want to send the message to the app channel itself. If I use the D... ID it works as expected. No invite by the channel is needed. But how do I get this ID? conversations.list only returns publich channels, but no the app channel itself.

Answer 1

In Slack, there is no such thing as an app's channel. There is a DM channel between every user and your app/bot. In these terms, to send a DM message from your app/bot to the user, you need to know ID of this user and specify it as a channel argument of the postMessage API request.

Answer 2

The ability to pass a Slack user ID as channel is somewhat unique to chat.postMessage. If you try this with other API methods which expect a channel ID only (conversations.info), you'll get "error": "channel_not_found". The docs state:
Begin a conversation in a user's App Home
Start a conversation with users in your App Home.
With the chat:write scope enabled, call chat.postMessage and pass a user's ID (U0G9QF9C6) as the value of channel to post to that user's App Home channel. You can use their direct message channel ID (as found with im.open, for instance) instead.
Source: https://api.slack.com/methods/chat.postMessage#app_home
Note: The above behavior assumes you're using the bot token. If you provide the user token instead, you'll make the user DM themselves.
Now, if you *do* need to get a user's App Home channel ID for use outside of chat.postMessage, keep reading... Here are three ways to do it, each with their own shortcomings:
1. chat.postMessage
Well, it's worth mentioning that if you are going to use chat.postMessage, it returns the resolved channel ID in its response: "channel": "D01234ABCDE". You can save this for later use.
2. conversations.open
The API method im.open referenced in the docs above has been renamed to conversations.open, which can be used to obtain the user's App Home channel ID:
Use the user token, and set users to the app bot ID, or
Use the bot token, and set users to the user ID.
Though, I've observed some weirdness with conversations.open, which may or may not be a dealbreaker for you:
It requires stronger OAuth permission scopes than ones required to initiate a private DM with a user than chat.postMessage (a bot token with chat:write is insufficient), and
It behaves strangely with respect to the "open state" of a conversation. For example...
I tested this method with a user token.
The user for that token already had a DM channel with the app! (Doesn't that mean the conversation is already open?)
Strangely, the first response had is_opened: false (and subsequent responses had is_opened: true).
3. app_home_opened
The event app_home_opened fires when the user opens your App Home. If you handle this event, you can save the channel in the event payload on your server and use it later, obviating the need to later call conversations.open.
Since the event only occurs if and when the user opens your app's App Home, this approach is more of an optimization than a standalone solution.
4. A better way...?
Due to the drawbacks outlines above, if anyone knows a better way of getting the App Home channel ID for a Slack user, please, comment on this answer!

Answer 3

You can get the channel ID of the app channel through the GUI if you:
navigate to a message in the channel
go to the more actions men
select copy link
The channel ID will be the string following archives/ eg:
{myorg}.slack.com/archives/{channel_ID}
Using this approach would work for any channel in the slack app, though it's unlikely to be the best approach since it's manual vs something more programmatic.