octoslack

octoslack is a tool for transforming HTTP requests from any webhook into Slack messages.

Usage

flowchart TB
    src[Some webhook source] -- POST https://octoslack.example.com/services/XXX/YYY --- payload[JSON payload]
    subgraph "octoslack.example.com"
    payload[JSON payload] -- "Transform payload by octoslack" --- spayload[JSON payload for Slack]
    end
    spayload[JSON payload for Slack] -- POST https://hooks.slack.com/services/XXX/YYY --> Slack[Slack Incoming Webhook endpoint]

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0. Requirements

• Slack Incoming Webhook URL ( https://hooks.slack.com/services/XXX/YYY )

1. Setup config.yml

Describe the settings for transforming/forwarding/dropping HTTP requests from the target webhook.

In particular, octoslack targets GitHub repository webhooks, so it parses the X-GitHub-Event header ( to github_event ).

# config.yml
requests:
  -
    condition: github_event == 'discussion' && payload.action == 'created'
    action: transform
    transform:
      blocks:
        - type: section
          text:
            type: mrkdwn
            text: 'Discussion created by {{ payload.user.login }}'
        - type: section
          text:
            type: mrkdwn
            text: '{{ quote(payload.discussion.body) }}'
  -
    condition: github_event == 'ping'
    action: forward

2. Start octoslack server

Start the octoslack server and make the server accessible from the Internet.

$ octoslack server -c config.yml -p 8080

If you want to use a Docker image and start the server using the config file in the GitHub repository, you can run the following.

$ docker container run -it --rm --name octoslack-server \
  -e OCTOSLACK_CONFIG=github://k1LoW/octoslack/testdata/config.yml \
  -e OCTOSLACK_PORT=8080 \
  -e GITHUB_TOKEN \ # use GITHUB_TOKEN for getting config.yml from GitHub repository
  -p 8080:8080 \
  ghcr.io/k1low/octoslack:latest

Here, assume it is published as https://octoslack.example.com.

3. Set Slack Incoming webhook URL by changing the host to octoslack.example.com

Change the host of the Slack Incoming webhook URL to octoslack.example.com.

https://hooks.slack..com/services/XXX/YYY -> https://octoslack.example.com/services/XXX/YYY

And set it as the destination URL.

4. Webhook event fired

HTTP requests are

• transformed into requests that Slack can read through octoslack.
• forwarded directly to Slack.
• dropped.

flowchart TB
    src[GitHub Webhooks] -- POST https://octoslack.example.com/services/XXX/YYY --- payload[JSON payload]
    subgraph "octoslack.example.com"
    payload[JSON payload] -- "Transform payload by octoslack" --- spayload[JSON payload for Slack]
    end
    spayload[JSON payload for Slack] -- POST https://hooks.slack.com/services/XXX/YYY --> Slack[Slack Incoming Webhook endpoint]

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Drop all requests that do not match the conditions.

Actions selectable for the request ( action: )

transform

Transform into requests that Slack can read through octoslack.

forward

Forward request directly to Slack.

drop

Drop request.

Expression evaluation engine

octoslack has embedded expr-lang/expr as the evaluation engine for the expression.

It can be used in requests.[*].condition: and requests.[*].transform:.

See Language Definition.

Built-in functions

• quote ... Quote all lines.
• shorten_lines ... Shorten the number of lines.
• shorten_lines_md ... Shorten the number of lines considering Slack markdown syntax.
• string ... cast.ToString

Available variables

Variable name	Type	Description
method	string	Method of HTTP request
headers	object	Headers of HTTP request
path	string	Path of HTTP request
payload	object	Payload of HTTP request
github_event	string	Value of X-GitHub-Event header

Option

$ octoslack server -h
start server.

Usage:
  octoslack server [flags]

Flags:
  -c, --config string   config path (default "octoslack.yml")     # env: OCTOSLACK_CONFIG
  -h, --help            help for server
  -p, --port uint       listen port (default 8080)                # env: OCTOSLACK_PORT
  -d, --update-config-interval string   interval to update config # env: OCTOSLACK_UPDATE_CONFIG_INTERVAL
      --verbose         show verbose log                          # env: OCTOSLACK_VERBOSE
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