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.

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 "https://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, handler: :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 handler
parse is invoked. In the parse handler, 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 a handler.

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
• driver
• delay
• headers
• cookies
• threads
• middleware
• proxy
• blacklist
• whitelist

Headers

class MyScraper < Vessel::Cargo
  headers "Content-Type" => "text/plain",
          "Referer" => "http://example.com"
end

Headful mode

You can disable headless mode by passing driver_options settings:

MyScraper.run(driver_options: { headless: false })

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.