Crawler

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

Features

• 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.

Architecture

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

Usage

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

Configurations

Custom Modules

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:

Retrier

See Crawler.Fetcher.Retrier.

Crawler uses ElixirRetry's exponential backoff strategy by default.

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

URL Filter

See Crawler.Fetcher.UrlFilter.

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

Scraper

See Crawler.Scraper.

defmodule CustomScraper do
  @behaviour Crawler.Scraper.Spec
end

Parser

See Crawler.Parser.

defmodule CustomParser do
  @behaviour Crawler.Parser.Spec
end

Modifier

See Crawler.Fetcher.Modifier.

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

Pause / Resume / Stop Crawler

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

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

Crawler.pause(opts)

Crawler.resume(opts)

Crawler.stop(opts)

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.

API Reference

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

Changelog

Please see CHANGELOG.md.

License

Licensed under MIT.