How can my Slack-using BotFramework bot ignore messages on all channels except direct?

I know this seems like it's been asked before - but I understand that you can figure out that someone's talking on a Slack channel by inspecting activity.Conversation.IsGroup - I'm using this successfully.

This is fine as long as the channel has more than two members! But there's an annoying edge case where newly-created channels, say, or channels just containing two members, have to experience the bot trying to respond to all messages there, until at least 3 members are added to the channel.

Has anyone figured out a handy way to detect this? I inspected the Activity JSON for both a message to the app/bot user directly and a message to a channel, but there's no obvious way of being able to distinguish a channel message from a direct-to-bot-user message.

Solution

If I remember well, there is a difference in Slack in the naming between a channel and a direct messaging: this difference can be seen in the Conversation.Id field:

Examples:

for a channel: il will look like Bxxxxxxxx:Tyyyyyyyy:Czzzzzzzz
for a direct messaging between you and people A: Bxxxxxxxx:Tyyyyyyyy:Daaaaaaaa
for a direct messaging with several people: Bxxxxxxxx:Tyyyyyyyy:Gbbbbbbbb

Where:

Bxxxxxxxx is your bot Slack's ID
Tyyyyyyyy is your Slack's workspace ID
Czzzzzzzz is the current channel Slack's ID (visible in the url when using web version of Slack)

You will be able to detect your case by checking the conversation ID