A high performance web crawler / scraper in Elixir, with worker pooling and rate limiting via OPQ.

• Crawl assets (javascript, css and images).
• Save to disk.
• Hook for scraping content.
• Restrict crawlable domains, paths or content types.
• Limit concurrent crawlers.
• Limit rate of crawling.
• Set the maximum crawl depth.
• Set timeouts.
• Set retries strategy.
• Set crawler's user agent.
• Manually pause/resume/stop the crawler.

See Hex documentation.

Below is a very high level architecture diagram demonstrating how Crawler works.

Crawler.crawl("http://elixir-lang.org", max_depths: 2)

There are several ways to access the crawled page data:

1. Use Crawler.Store
2. Tap into the registry(?) Crawler.Store.DB
3. Use your own scraper
4. If the :save_to option is set, pages will be saved to disk in addition to the above mentioned places
5. Provide your own custom parser and manage how data is stored and accessed yourself

It is possible to swap in your custom logic as shown in the configurations section. Your custom modules need to conform to their respective behaviours:

See Crawler.Fetcher.Retrier.

Crawler uses ElixirRetry's exponential backoff strategy by default.

defmodule CustomRetrier do
  @behaviour Crawler.Fetcher.Retrier.Spec
end

See Crawler.Fetcher.UrlFilter.

defmodule CustomUrlFilter do
  @behaviour Crawler.Fetcher.UrlFilter.Spec
end

See Crawler.Scraper.

defmodule CustomScraper do
  @behaviour Crawler.Scraper.Spec
end

See Crawler.Parser.

defmodule CustomParser do
  @behaviour Crawler.Parser.Spec
end

See Crawler.Fetcher.Modifier.

defmodule CustomModifier do
  @behaviour Crawler.Fetcher.Modifier.Spec
end

Crawler provides pause/1, resume/1 and stop/1, see below.

{:ok, opts} = Crawler.crawl("https://elixir-lang.org")

Crawler.running?(opts) # => true

Crawler.pause(opts)

Crawler.running?(opts) # => false

Crawler.resume(opts)

Crawler.running?(opts) # => true

Crawler.stop(opts)

Crawler.running?(opts) # => false

Please note that when pausing Crawler, you would need to set a large enough :timeout (or even set it to :infinity) otherwise parser would timeout due to unprocessed links.

It is possible to start multiple crawlers sharing the same queue.

{:ok, queue} = OPQ.init(worker: Crawler.Dispatcher.Worker, workers: 2)

Crawler.crawl("https://elixir-lang.org", queue: queue)
Crawler.crawl("https://github.com", queue: queue)

Crawler.Store.all_urls() # => ["https://elixir-lang.org", "https://google.com", ...]

This example performs a Google search, then scrapes the results to find Github projects and output their name and description.

See the source code.

You can run the example by cloning the repo and run the command:

mix run -e "Crawler.Example.GoogleSearch.run()"

Please see https://hexdocs.pm/crawler.

Please see CHANGELOG.md.

Copyright (c) 2016 Fred Wu

This work is free. You can redistribute it and/or modify it under the terms of the MIT License.