Slack Gateway: An HTTP gateway for posting to Slack

With a single HTTP request, you can post a message, creating the channel first if it doesn't exist and invite people and groups.

What can it do?

Runs as a server, listening for an HTTP request. Upon receipt of a message, the gateway:

• creates the given Slack channel if it doesn't exist
• ensures a list of users (or user groups) are in the channel (if not - invites them)
• posts the message to the channel

This removes the complexity of orchestrating many Slack API calls behind a simple endpoint.

Examples

Using Slack format

Send a message to a channel:

curl http://localhost:8080/messages/raw \
    --header "Content-Type: application/json" \
    --data '{"channel":"general", text":"Hello World!"}'

Send a message with attachments:

curl http://localhost:8080/messages/raw \
    --header "Content-Type: application/json" \
    --data '{"channel":"general", text":"Hello World!","attachments":[{"text":"More info","color":"#33ee33"}]}'

Using simple key-value format

If you don't want to compose the JSON yourself, you can use a simpler, but slightly more limited, key-value format instead.

Send a message to a channel:

curl http://localhost:8080/messages/text \
    --data 'channel=general' \
    --data 'text=Hello%20World!'

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Getting started

Overview

• As a Slack admin, create a Slack app, add the required scopes (see below) and install it to your workspace
• Set environment variables
• Run!

Starting the server

If you'd like to run Slack Gateway yourself as a Docker container, you can do the following:

docker run -d \
    --env SLACK_USER_TOKEN="CHANGEME" \
    --env SLACK_CHANNEL_MEMBERS="jsmith,mjones" \
    --publish 8080:8080 \
    outofcoffee/slack-gateway

Note: See the Environment variables section for the available configuration settings.

Usage

You can send messages to Slack Gateway using either the Slack format, or a simpler key-value format.

Using Slack format

Send a message to a channel:

curl http://localhost:8080/messages/raw \
    --header "Content-Type: application/json" \
    --data '{"channel":"general", text":"Hello World!"}'

Send a message with attachments:

curl http://localhost:8080/messages/raw \
    --header "Content-Type: application/json" \
    --data '{"channel":"general", text":"Hello World!","attachments":[{"text":"More info","color":"#33ee33"}]}'

For more information on the Slack post message format, see https://api.slack.com/

Using simple key-value format

If you don't want to compose the JSON yourself, you can use a simpler, but slightly more limited, key-value format instead.

Send a message to a channel:

curl http://localhost:8080/messages/text \
    --data 'channel=general' \
    --data 'text=Hello%20World!'

Send a message as an attachment:

curl http://localhost:8080/messages/text \
    --data 'channel=general' \
    --data 'text=Hello%20World!' \
    --data 'title=Attachment' \
    --data 'attachment=true' \
    --data 'color=00ff00'

The example above will send the text message as an attachment, with a particular colour and title.

The available options for the key-value format are:

Key	Required	Type	Purpose
channel	Yes	String	Channel name
text	Yes, unless additional message keys used	String	Literal message text
attachment	No	Boolean	Whether to send in attachment mode
title	No	String	Attachment title
color	No	String	Attachment color
author_name	No	String	Attachment author name
title_link	No	String	Attachment title link URL
footer	No	String	Attachment footer text
footer_icon	No	String	Attachment footer icon URL
Additional message keys	No, unless text is empty	String	See below

Additional message keys

When using the key-value format, any additional keys are appended to the text message. For example:

curl http://localhost:8080/messages/text \
    --data 'channel=general' \
    --data 'key_one=foo' \
    --data 'key_two=bar' \
    --data 'key_three=baz'

This will result in message text such as the following:

key one: *foo* | key two: *bar* | key three: *baz*

Note that underscores in key names are replaced with spaces, and the values are emboldened.

Setting the channel type

You can specify the channel type as public or private. This will be used when creating channels, or posting messages.

Set the channel_type query parameter in the HTTP request, or use the DEFAULT_CREATE_CHANNEL_TYPE environment variable.

Valid values:

• private
• public

Example using the query parameter:

curl http://localhost:8080/messages/text \
   --data 'channel=some-private-channel' \
   --data 'text=Hello%20world' \
   --data 'channel_type=private'

Creating a Slack app

As a Slack admin, create a Slack app: https://api.slack.com/apps/new

Add a bot user in the 'Bot Users' section:

https://api.slack.com/apps/<your app ID>/bots

Add the required scopes in the 'OAuth & Permissions' section:

https://api.slack.com/apps/<your app ID>/oauth

The scopes are:

chat:write:bot
channels:read
channels:write
groups:read
groups:write
users:read
usergroups:read

Don't forget to save changes after adding scopes.

Install your app to your workspace. This will generate two tokens.

Copy the 'OAuth Access Token' and set it as the SLACK_USER_TOKEN. It should look like this:

xoxp-123456789012-123456789012-123456789012-abcdef1234567890abcdef1234567890

Copy the 'Bot User OAuth Access Token' and set it as the SLACK_BOT_TOKEN. It should look like this:

xoxb-123456789012-123456789012-abcdef1234567890abcdef1234567890

Don't forget to invite your app to any existing private channels, using:

/invite @YourAppName

Slack doesn't permit apps to post to channels unless they have permissions.

---

Build

If instead you wish to build and run locally, you can run:

./gradlew installDist
docker-compose build

Once built, set the environment variables in docker-compose.yml. See the Environment variables section.

Then run with:

docker-compose up

If you change anything, don't forget to rebuild before running again.

Environment variables

Configure the bot using the following environment variables.

Basic variables

• SLACK_BOT_TOKEN - required to post to channels not containing the user who created the user token
• SLACK_USER_TOKEN - must have the right permission scopes (see 'Creating a Slack app' in this document)
• SLACK_CHANNEL_MEMBERS - users to invite to channels e.g. "janesmith,bob" (comma separated; default empty)
• SLACK_CHANNEL_GROUPS - user groups to invite to channels e.g. "devteam" (comma separated; default empty)

Advanced variables

• HTTP_BIND_PORT (default 8080)
• HTTP_BIND_HOST (default 0.0.0.0)
• SLACK_CACHE_SECONDS - period to cache Slack objects like users and user groups (default 300)
• DEFAULT_CREATE_CHANNEL_TYPE (default 'private') - the default channel type to create if none is specified in the request

Contributing

• Pull requests are welcome.
• PRs should target the develop branch.
• Please run ktlint against the code first ;-)

Author

Pete Cornish (outofcoffee@gmail.com)