A very simple crawler
=====================

This is a fork of [crawl](https://git.autistici.org/ale/crawl) with changes
which make crawl more amenable to serve as a drop-in replacement for
[wpull](https://github.com/ArchiveTeam/wpull)/[grab-site](https://github.com/ArchiveTeam/grab-site).
Notable changes include:

* dramatically reduce memory usage; (temporarily) write responses to
  the filesystem rather than pass data around in memory buffers
* --bind, support making outbound requests from a particular interface
* --resume, directory containing the crawl state to continue from
* infinite recursion depth by default
* set User-Agent fingerprint to Firefox on Windows to look more like
  a browser
* store crawl contents in a dated directory
* update ignore regex set per updates to
  [ArchiveBot](https://github.com/ArchiveTeam/ArchiveBot)
* max default WARC size 100 MB -> 5 GB
* record assembled seed URLs to seed_urls file

This tool can crawl a bunch of URLs for HTML content, and save the
results in a nice WARC file. It has little control over its traffic,
save for a limit on concurrent outbound requests. An external tool
like `trickle` can be used to limit bandwidth.

Its main purpose is to quickly and efficiently save websites for
archival purposes.

The *crawl* tool saves its state in a database, so it can be safely
interrupted and restarted without issues.

# Installation

Assuming you have a proper [Go](https://golang.org/) environment setup,
you can install this package by running:

    $ go install git.jordan.im/crawl/cmd/crawl@latest

This should install the *crawl* binary in your $GOPATH/bin directory.

# Usage

Just run *crawl* by passing the URLs of the websites you want to crawl
as arguments on the command line:

    $ crawl http://example.com/

By default, the tool will store the output WARC file and its own
temporary crawl database in a newly-created directory.

The crawling scope is controlled with a set of overlapping checks:

* URL scheme must be one of *http* or *https*
* URL must have one of the seeds as a prefix (an eventual *www.*
  prefix is implicitly ignored)
* maximum crawling depth can be controlled with the *--depth* option
* resources related to a page (CSS, JS, etc) will always be fetched,
  even if on external domains, unless the *--exclude-related* option
  is specified

If the program is interrupted, running it again with the same command
line from the same directory will cause it to resume crawling from
where it stopped when a previous crawl state directory is passed with
*--resume*. At the end of a successful crawl, the temporary crawl
database will be removed (unless you specify the *--keep* option, for
debugging purposes).

It is possible to tell the crawler to exclude URLs matching specific
regex patterns by using the *--exclude* or *--exclude-from-file*
options. These option may be repeated multiple times. The crawler
comes with its own builtin set of URI regular expressions meant to
avoid calendars, admin panels of common CMS applications, and other
well-known pitfalls. This list is sourced from the
[ArchiveBot](https://github.com/ArchiveTeam/ArchiveBot) project.

If you're running a larger crawl, the tool can be told to rotate the
output WARC files when they reach a certain size (100MB by default,
controlled by the *--output-max-size* flag.

## Limitations

Like most crawlers, this one has a number of limitations:

* it completely ignores *robots.txt*. You can make such policy
  decisions yourself by turning the robots.txt into a list of patterns
  to be used with *--exclude-from-file*.
* it does not embed a Javascript engine, so Javascript-rendered
  elements will not be detected.
* CSS parsing is limited (uses regular expressions), so some *url()*
  resources might not be detected.
* it expects reasonably well-formed HTML, so it may fail to extract
  links from particularly broken pages.
* support for \<object\> and \<video\> tags is limited.

# Contact

Send bugs and patches to me@jordan.im.