PR Check

Monitors Slack for messages that refer to a Pull Request. When that Pull Request is approved, adds a reaction emoji to each of the messages that mentioned it.

How it works

Slack sends a POST to the service's /slack endpoint any time a github.com URL is mentioned. The service records that mention as Pull Request URL, the Slack channel the message was posted in, and the timestamp of the message (which is Slack's unique identifier).
GitHub sends a POST to the service's /github endpoint any time a Pull Request is approved. The service records the Pull Request URL as an approval.
The system makes an API call to Slack to add a reaction emoji to each mention of an approved Pull Request.

Note that steps 1 and 2 can happen in any order, and both will trigger step 3.

Development requirements

Install serverless globally

npm install -g serverless

Install the serverless plugins

yarn install

Install the ruby gems

bundle install --standalone --path vendor/bundle

You also need to have a Docker daemon running if you attempt to deploy. The first deploy may take a long time as the Docker image used to compile native gems is downloaded.

Deployment

Make sure you follow the instructions for Initial Deployment Configuration below, if the app has not been setup in Slack or Github yet.

You must specify a Slack OAuth token via SLACK_TOKEN environment variable when deploying. The token must have access to add reactions to messages.

SLACK_TOKEN=12345 serverless deploy --stage production

Initial Deployment Configuration

Configure Slack

Go to Slack to create a new application

In the Create a Slack App dialog:

App Name: pr_check

Development Slack Workspace:

On the App Settings page, go to OAuth & Permissions

Scroll down to User Token Scopes and add:

reactions:write # under Reactions
links:read      # under Unfurls

Click Save Changes

Scroll to the top of the page and click Install App to Workspace

You will see the OAuth approval page confirming you want to grant the permissions to the app. Click Authorize.

You should now see an OAuth Access Token at the top of the page. This is the value you need to set in the SLACK_TOKEN environment variable when you deploy.

Deploy the app:

SLACK_TOKEN=yourtoken serverless deploy -s production

When the deploy finishes, the output will contain a list of endpoints. Copy the URL that ends with slack.

Back in the Slack app settings page, go to Basic Information
Click Add features and functionality
Click Event Subscriptions
Click to Enable Events
Paste in the URL from the deploy that ends with slack
Click Add Workspace Event, choose link_shared
At the bottom of the page under App Unfurl Domains, click Add Domain
Enter github.com and click Done
Click Save Changes

Configure Github

Open Github, go to Organization settings or settings for an individual Repository

Go to Webhooks

Click Add Webhook

In Payload URL, enter the endpoint from the deploy output that ends in github

Change the Content type to application/json

Enter a Secret. We will eventually use this value to verify the hook validity.

For "which events" choose "Let me select individual events"

Uncheck Pushes

Check "Pull request reviews".

This should be the only event checked.

Click Add Webhook button

Github will send a test ping (click on the webhook to see the Recent Deliveries)

The service is now ready, watching for pull request mentions and approvals.

twmills / pr-check