vessel

Vessel - high-level web crawling framework

Fast as Chrome, dead simple and yet extendable.

It is Ruby high-level web crawling framework based on Ferrum for extracting the data you need from websites. It can be used in a wide range of scenarios, like data mining, monitoring or historical archival. For automated testing we recommend Cuprite.

Thanks to Evrone design team. Read about Vessel & other projects supported by Evrone here.

Install

Add this to your Gemfile:

gem "vessel"

A look around

In order to show you how Vessel works we are going to crawl together famous quotes website:

require "json"
require "vessel"

class QuotesToScrapeCom < Vessel::Cargo
  domain "quotes.toscrape.com"
  start_urls "http://quotes.toscrape.com/tag/humor/"

  def parse
    css("div.quote").each do |quote|
      yield({
        author: quote.at_xpath("span/small").text,
        text: quote.at_css("span.text").text
      })
    end

    if next_page = at_xpath("//li[@class='next']/a[@href]")
      url = absolute_url(next_page.attribute(:href))
      yield request(url: url, method: :parse)
    end
  end
end

quotes = []
QuotesToScrapeCom.run { |q| quotes << q }
puts JSON.generate(quotes)

Save this to quotes.rb file and run bundle exec ruby quotes.rb > quotes.json. When this finishes you will have a list of the quotes in JSON format in the quotes.json file.

How it all works? First Vessel using Ferrum spawns Chrome which goes to one or more urls in start_urls, in our case it's only one. After Chrome reports back that page is loaded with all the resources it needs the first default callback parse is invoked. In the parse callback, we loop through the quote elements using a CSS Selector, yield a Hash with the extracted quote text and author and look for a link to the next page and schedule another request using the same parse method as callback.

Notice that all requests are scheduled and handled concurrently. We use thread pool to work with all your requests with one page per core by default or add threads max: n to a class. If you yield more than one request Ruby will send them to Chrome which will load pages in parallel. Thus crawler is lightweight and speedy.

Settings

• domain
• start_urls
• delay
• timeout
• threads
• middleware

Selectors

• at_css
• css
• at_xpath
• xpath

Middleware

To be continued

License

The gem is available as open source under the terms of the MIT License.