huginn/app/models/agents/http_status_agent.rb

require 'time_tracker'

module Agents
  class HttpStatusAgent < Agent
    include WebRequestConcern
    include FormConfigurable

    can_dry_run!
    can_order_created_events!

    default_schedule "every_12h"

    form_configurable :url
    form_configurable :disable_redirect_follow, type: :boolean
    form_configurable :changes_only, type: :boolean
    form_configurable :headers_to_save

    description <<~MD
      The HttpStatusAgent will check a url and emit the resulting HTTP status code with the time that it waited for a reply. Additionally, it will optionally emit the value of one or more specified headers.

      Specify a `Url` and the Http Status Agent will produce an event with the HTTP status code. If you specify one or more `Headers to save` (comma-delimited) as well, that header or headers' value(s) will be included in the event.

      The `disable redirect follow` option causes the Agent to not follow HTTP redirects. For example, setting this to `true` will cause an agent that receives a 301 redirect to `http://yahoo.com` to return a status of 301 instead of following the redirect and returning 200.

      The `changes only` option causes the Agent to report an event only when the status changes. If set to false, an event will be created for every check.  If set to true, an event will only be created when the status changes (like if your site goes from 200 to 500).
    MD

    event_description <<~MD
      Events will have the following fields:

          {
            "url": "...",
            "status": "...",
            "elapsed_time": "...",
            "headers": {
              "...": "..."
            }
          }
    MD

    def working?
      memory['last_status'].to_i > 0
    end

    def default_options
      {
        'url' => "http://google.com",
        'disable_redirect_follow' => "true",
      }
    end

    def validate_options
      errors.add(:base, "a url must be specified") unless options['url'].present?
    end

    def header_array(str)
      (str || '').split(',').map(&:strip)
    end

    def check
      check_this_url interpolated[:url], header_array(interpolated[:headers_to_save])
    end

    def receive(incoming_events)
      incoming_events.each do |event|
        interpolate_with(event) do
          check_this_url interpolated[:url],
                         header_array(interpolated[:headers_to_save])
        end
      end
    end

    private

    def check_this_url(url, local_headers)
      # Track time
      measured_result = TimeTracker.track { ping(url) }

      current_status = measured_result.result ? measured_result.status.to_s : ''
      return if options['changes_only'] == 'true' && current_status == memory['last_status'].to_s

      payload = { 'url' => url, 'response_received' => false, 'elapsed_time' => measured_result.elapsed_time }

      # Deal with failures
      if measured_result.result
        final_url = boolify(interpolated['disable_redirect_follow']) ? url : measured_result.result.env.url.to_s
        payload.merge!({ 'final_url' => final_url, 'redirected' => (url != final_url), 'response_received' => true,
                         'status' => current_status })
        # Deal with headers
        if local_headers.present?
          header_results = local_headers.each_with_object({}) { |header, hash|
            hash[header] = measured_result.result.headers[header]
          }
          payload.merge!({ 'headers' => header_results })
        end
        create_event(payload:)
        memory['last_status'] = measured_result.status.to_s
      else
        create_event(payload:)
        memory['last_status'] = nil
      end
    end

    def ping(url)
      result = faraday.get url
      result.status > 0 ? result : nil
    rescue StandardError
      nil
    end
  end
end