How can a Slack bot detect a direct message vs a message in a channel?

Question

TL;DR: Via the Slack APIs, how can I differentiate between a message in a channel vs a direct message?

I have a working Slack bot using the RTM API, let's call it Edi. And it works great as long as all commands start with "@edi"; e.g. "@edi help". It currently responses to any channel it's a member of and direct messages. However, I'd like to update the bot so that when it's a direct message, there won't be a need to start a command with "@edi"; e.g. "@edi help" in a channel, but "help" in a direct message. I don't see anything specific to differentiate between the two, but I did try using the channel.info endpoint and counting the number of people in "members"; however, this method only works on public channel. For private channels and direct messages, the endpoint returns an "channel_not_found" error.

Thanks in advance.

Answer 1

I talked to James at Slack and he gave me a simply way to determine if a message is a DM or not; if a channel ID begins with a:

• C, it's a public channel
• D, it's a DM with the user
• G, it's either a private channel or multi-person DM

However, these values aren't set in stone and could change at some point, or be added to.

So if that syntax goes away, another way to detect a DM to use both channels.info and groups.info. If they both return “false” for the “ok” field, then you know it’s a DM.

Note:

• channels.info is for public channels only
• groups.info is for private channels and multi-person DMs only

Bonus info: Once you detect a that a message is a DM, use either the user ID or channel ID and search for it in the results of im.list; if you find it, then you’ll know it’s a DM to the bot.

• “id” from im.list is the channel ID
• “user” from im.list is the user ID from the person DM’ing with the bot
• You don’t pass in the bot’s user ID, because it’s extracted from the token

Answer 2

Slack have added Conversations API some time ago. You should use it to differentiate between PM/channel instead of relying on prefix.

From Conversations API documentation:

Each channel has a unique-to-the-team ID that begins with a single letter prefix, either C, G, or D. When a channel is shared across teams (see Developing for Shared Channels), the prefix of the channel ID may be changed, e.g. a private channel with ID G0987654321 may become ID C0987654321.

This is one reason you should use the conversations methods instead of the previous API methods! You cannot rely on a private shared channel's unique ID remaining constant during its entire lifetime.

Get conversation info using conversations.info method and check is_im flag. is_im == true means that the conversation is a direct message between two distinguished individuals or a user and a bot.