Hacking ActiveResource::Connection for Shopify API in order to read HTTP response header 'http_x_shopify_api_call_limit'. Simply require this code after your gems have been loaded. Caveat emptor: This hack modifies a private method of AR::Connection; H

ShopifyAPICallLimit.rb

class ActiveResource::Connection
  # HACK 1:  Add an attr_reader for response
  attr_reader :response
  
  def request(method, path, *arguments)
    result = ActiveSupport::Notifications.instrument("request.active_resource") do |payload|
      payload[:method]      = method
      payload[:request_uri] = "#{site.scheme}://#{site.host}:#{site.port}#{path}"
      payload[:result]      = http.send(method, path, *arguments)
    end  
    # HACK 2:  Save response to instance var @response  
    @response = handle_response(result)
  rescue Timeout::Error => e
    raise TimeoutError.new(e.message)
  rescue OpenSSL::SSL::SSLError => e
    raise SSLError.new(e.message)
  end  
end


module ShopifyAPI
  # Takes form num_requests_executed/max_requests
  # Eg: 101/3000
  CALL_LIMIT_HEADER_PARAM = 'http_x_shopify_api_call_limit'
  
  class << self
    ##
    # How many more API calls can I make?
    #
    def available_calls    
      call_limit - call_count
    end

    ##
    # Have I reached my API call limit?
    #
    def maxed_out?
      call_limit == call_count
    end

    ##
    # How many total API calls can I make?
    # @return Integer
    #
    def call_limit
      @api_call_limit ||= api_call_limit_param.pop.to_i
    end

    ##
    # How many API calls have I made?
    # @return Integer
    def call_count
      api_call_limit_param.shift.to_i
    end

    def api_call_limit_param
      response[CALL_LIMIT_HEADER_PARAM].split('/')
    end

    def response
      Shop.current unless ActiveResource::Base.connection.response
      ActiveResource::Base.connection.response
    end
  end  
end