Crowbar: scrape javascript-generated pages via Gecko and REST!

Careful with buzzwords on that one…from the extremely clever hacks department, Stefano strikes again with crowbar, a RESTish page-scraping component based on the Gecko rendering engine.

As a first proof of concept, scraping crowbar’s test page, where some content is generated via javascript, works just fine.

Using a non-javascript scraper gets you the raw page, obviously (you lame crawler!):

$ curl -s http://simile.mit.edu/crowbar/test.html
<html>
<head>
<script>
function init() {
document.getElementById("message").innerHTML = "Hi Crowbar!";
}
</script>
</head>
<body onload="init()">
<h1 id="message">Hi lame crawler</h1>
</body>
</html>

Using crowbar as a proxy, the page is rendered using the Gecko engine (called via a simple XULRunner app), exactly as a a client browser would do (of course – it is the same client browser engine that Firefox would use):

$ curl -s --data "url=http://simile.mit.edu/crowbar/test.html" http://127.0.0.1:10000/  | xml fo -s 2
<?xml version="1.0"?>
<html>
<-- (stuff added by crowbar for its test page omitted)... -->
<HEAD>
<SCRIPT>
function init() {
document.getElementById("message").innerHTML = "Hi Crowbar!";
}
</SCRIPT>
</HEAD>
<BODY onload="init()">
<H1 id="message">Hi Crowbar!</H1>
</BODY>
</html>

Note the use of XMLStarlet to format the resulting document: as it’s a DOM dump from Gecko, the output is well-formed in all cases.

The only thing missing seems to be the encoding declaration in the XML output: crawling http://www.perdu.com for example (one of my favorite references on the Web), didn’t work produce parsable XML as the XML output is serialized using the iso-8859-1 encoding (at least here on my macosx system), but the XML declaration doesn’t mention this.

The code is at http://simile.mit.edu/repository/crowbar/trunk/ and can be installed directly under XULRunner.

Very clever! This will take some polishing of course, but if you need to index or analyze javascript-generated content (automated testing anyone?), there’s no better way than getting it straight from the browser horse’s mouth!

Update: the brand new Crowbar web site has more info.

One Response to Crowbar: scrape javascript-generated pages via Gecko and REST!

  1. argv says:

    Check out HTMLUnit

    And don’t forget xvfb:

    We can send HTTP commands to a headless Firefox and sniff the rendered html as it comes through the wire.

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