Enter chimera

This is a follow up article to Enhanced Web Scraping in Node.js

Enter Chimera, the other kind of phantom

I was inspired by PhantomJS and wanted something similar, but could be run inside of the nodejs environment, without calling out to an external process. PhantomJS is run as an external process that users can run under any language, however one must create a fancy glue wrapper so that development isn’t impaired. I created something that does exactly what phantomjs is capable of doing, except in a full js environment, called Chimera.

There are similar “glues” like phantomjs-node that integrate phantomjs by spawning a process, and processing the stdout stream, but it is limited by what can be done via the command line of phantomjs. If you really want direct api access to the browser, the best way is via direct integration.

PhantomJS merely invokes QtWebkit behind the scenes, and provides an api layer that allows users to move the mouse, take a screenshot, execute js code, etc. In Chimera, we are doing essentially the same thing, except that QtWebkit runs in the same node process, and control flow is governed by libuv and QMutex. There should be very little lag time between node and webkit as we’ve implemented it using the same async-style code that everyone is already accustomed with in node.

Since this is a true browser, one can actually play youtube videos, move the mouse cursor around, etc – anything that you could do in your chrome browser, you can do here. For fast web scraping, there’s nothing better than running an actual headless browser window.

If you’re installing via npm, you can easily install it like this:

npm install chimera

It does take quite a bit of time to download because it includes precompiled binaries for macosx, linux 32bit, and linux 64bit. Each binary contains everything needed to run chimera including parts of the Qt toolkit.

An example is the best way to show how easy this is using chimera: (coffeescript shown below)

Chimera = require('chimera').Chimera
c = new Chimera()
c.perform
  url: "http://digg.com"
  locals:
    username: myUsername
    password: myPassword
  run: (callback) ->
    setTimeout( ->
      if jQuery('a.modal-close-inline').length > 0
        jQuery('a.modal-close-inline').click()
        jQuery('#modal-login').click()
        setTimeout( ->
          jQuery('#ident').val(username)
          jQuery('#password').val(password)
          pos = jQuery('#login-button').offset()
          chimera.sendEvent("click", pos.left + 10, pos.top + 10)
        , 500)
      else
        setTimeout( ->
          callback(null, "success")
        , 1000)
    , 1000)
  callback: (err, result) ->
    console.log('capture screen shot')
    c.capture("screenshot.png")
    cookies = c.cookies()
    c.close()

Note that this example may not work anymore as digg.com has completely redone their site. This example code belongs in a single file that you’d run using something like “node example.js”.

Let’s break it down

Chimera includes all parts of the code to run inside and outside the browser. The “run” property specifies a function that will run inside the browser, where the first argument is a callback function that should be called when you want to return back to node.

The callback property is a function that will be executed immediately when we pass the control flow back to node. (minimum example shown below)

Chimera = require('chimera').Chimera
c = new Chimera()
c.perform
  url: "http://digg.com"
  locals:
    username: myUsername
    password: myPassword
  run: (callback) ->
    alert('I run inside the browser!')
    callback(null, "success")
  callback: (err, result) ->
    console.log("I'm back inside nodejs")

Since the browser does not run under the same js execution environment as node does, you cannot use variables defined in your current closure. The only way to pass variables into the browser is by making use of the “locals” property. Each property defined in here will appear as a local variable inside the run method.

Extracting & setting cookies

One of the interesting things about chimera is the ability to extract and assign cookies to the browser. We can assign cookies to our chimera instance so that when the browser is run, it starts with a given state. For example, we might first extract the cookies in our callback using the chimera.cookies() method in code that looks like this:

c = new Chimera()
c.perform
  url: "http://digg.com"
  run: (callback) ->
    // add login code here
    callback(null, "success")
  callback: (err, result) ->
    console.log("here are the cookies")
    console.log(c.cookies())

Then we can assign the cookies in a completely new browser window like this:

cookies = "session_id=94d4d4bca3da9f7dc916e16c49363a9c5fd026178ead6cb35747471c994da8c3; expires=Wed, 30-May-2012 02:24:27 GMT; domain=.digg.com; path=/"
c = new Chimera(cookies: cookies)
c.perform
  url: "http://digg.com"
  run: (callback) ->
    // we should already be logged in!
    callback(null, "success")
  callback: (err, result) ->
    console.log("done")

Published: August 13 2012

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