Monitor software version changes with Huginn

Huginn is a great piece of software, but the documentation is … a bit sparse. Especially when it comes to details of the agents. I’m going to blog about a couple more more examples in the future.

For another project I’m using Leaflet, a JavaScript library for rendering maps in a browser. New versions are released occasionally, and I want to know when it’s time to update the project website. Huginn can do that.

This needs three agents:

• Http Status Agent
• Event Formatting Agent
• Email Agent

Checking for new versions: Http Status Agent

This agent is used to periodically check the website and see if there is a new released version.

In this case I’m using the GitHub repository as source, and there the latest link. The Releases page has a Latest release link (https://github.com/Leaflet/Leaflet/releases), which is a redirect to the actual version (currently: https://github.com/Leaflet/Leaflet/releases/tag/v1.7.1).

The Huginn agent is configured as follow:

• Schedule: pick one, I’m using a weekly time
• Keep events: I keep events around for 7 days, for debugging purposes
• Url: https://github.com/Leaflet/Leaflet/releases/latest
• Disable redirect follow: False
• Changes only: True

By disabling Disable redirect follow the agent will follow the redirect, and provide the final link in final_url. And by enabling Changes only this agent is only emitting events when something changes - a new version is released.

Formatting the data: Event Formatting Agent

The incoming data from the Http Status Agent looks like this:

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{
  "url": "https://github.com/Leaflet/Leaflet/releases/latest",
  "response_received": true,
  "elapsed_time": 0.5510568432509899,
  "final_url": "https://github.com/Leaflet/Leaflet/releases/tag/v1.7.1",
  "redirected": true,
  "status": "200"
}

What I need is the version information after tag/. The Formatting Agent can do that using the matchers. As source specify the output from the Http Status Agent above. As Options the following

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{
  "instructions": {
    "agent": "{{agent.type}}",
    "version_regexp_data": "{{version}}",
    "version_string": "{{version.1}}"
  },
  "matchers": [
    {
      "path": "{{final_url}}",
      "regexp": ".+tag.(.+)",
      "to": "version"
    }
  ],
  "mode": "merge"
}

The matchers will extract everything after tag/ using a regexp, and store the information in version. The instructions creates new variables using the data from the match.

Notify: Email Agent

As input use the output from the Event Formatting Agent. I’m using the following options:

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{
  "subject": "Leaflet version change: {{version_string}}",
  "expected_receive_period_in_days": "365",
  "content_type": "text/html",
  "body": "<br/>New Leaflet version: {{version_string}}"
}

This creates a short email, with the new version information included.