*Intro*
crawl.py: A QtWebKit based web crawler that is designed to click on 
everything, even things in iframes, for a list of links and to a certain depth, 
with the goal of investigating distribution of malware via advertising 
networks. While it can crawl through all links on a set of pages, it includes 
optimizations to reduce crawling time. Fully headless, but based on a real web 
browser (WebKit) so it actually renders the page as a user would see it and 
properly evaluates JavaScript (in theory).

get-links.py: A QtWebKit based link scraper for a single page.

*Usage*
To run:
python crawl.py <link depth> <domain with http://>

Results come back as:
<depth> <site visited> <site's parent>

Example:
$ python crawl.py 2 http://example.com
0 http://example.com None
1 http://www.icann.org/ http://example.com
2 http://gsa.icann.org/search?access=p&client=icann&proxystylesheet=icann&output=xml_no_dtd&site=icann&q=&proxycustom=%3CADVANCED/%3E http://www.icann.org/
2 http://twitter.com/icann/ http://www.icann.org/
2 http://blog.icann.org http://www.icann.org/
2 http://meetings.icann.org http://www.icann.org/
2 http://hostedjobs.openhire.com/epostings/submit.cfm?fuseaction=app.allpositions&company_id=16025&version=1 http://www.icann.org/
2 http://www.root-dnssec.org/ http://www.icann.org/
2 http://svsf40.icann.org/ http://www.icann.org/
2 http://www.iana.org http://www.icann.org/
2 http://www.atlarge.icann.org http://www.icann.org/
2 http://aso.icann.org/ http://www.icann.org/
2 http://ccnso.icann.org http://www.icann.org/
2 http://gac.icann.org/ http://www.icann.org/
2 http://gnso.icann.org http://www.icann.org/
2 http://www.internic.net/whois.html http://www.icann.org/

*Crawler class*
To create a Crawler object, use this:
Crawler(url_list, max_depth, dots=True, skip_same_domain=False, debug=False)

where url_list is a list of url strings you want to crawl, and max_depth is the
click depths you're interested in. Crawling results are stored as a list of 
results (Crawler.results), each element of which contains a single URL's crawl
tree.

There are some options inside the Crawler class for configuring output:
- dots=True: turn on some status dots to indicate that progress is occuring. 
- skip_same_domain=True: skips links to the same domain as the current page.
- debug=True: as expected, provides some extra debug verbosity (exactly what depends on the revision you're using!)

There are two key functions in the Crawler class:
- process(url, ttl=10, log=False, strip_dupes=True, debug=False, round_two=False)
This function extracts all the urls that are available for a user to click on a
single page. This includes links on the page itself, as well as those contained
in any iframes on the page. Because iframes can contain other iframes, 
redirects, etc, we use the ttl field to prevent gettting lost in a particularly
nasty iframe. If log=True, we log the (prettified) HTML we pulled in to a file.
strip_dupes=True means we remove duplicate links from the result set. round_two
is a marker for handling links inside iframes: think of it as a finishing move.

- crawl(url):
This starts a crawl at a particular URL. It basically builds a crawl tree using
process() and stores it in the results list.  

*Earl class*
The results list of a crawler is a list of Earl objects. Each Earl is a node of 
a crawl tree. It has four attributes:
- value: the URL of this node of the crawl tree
- depth: the click depth we were at when we discovered it
- parent: the Earl of the page on which on which this URL was discovered
- children[]: a list of Earls of URLs which were reached form this page

There is one function, show(). Earl.show() prints a crawl tree, as shown in
the example output above.

*Acks*
QtWebKit code taken from here:
http://blog.sitescraper.net/2010/06/scraping-javascript-webpages-in-python.html

*Author*
Shaddi Hasan (shaddi@berkeley.edu)
March 2011