underpainting

underpainting

Render HTML on the server that's supposed to be rendered on the client.

Why

From what I can tell it's still not possible to get decent search results for applications rendered entirely on the client. Google's fetch & render in webmaster tools seems to run JavaScript perfectly well, but the crawler itself must not be doing the same thing. Please correct me if I'm mistaken and / or just doing it rong!

Prerender is a nice idea for solving the problem, but it seems overly complex and ran my server OOM so I hacked this up instead.

How

BYO Chromium, talk to it using the remote debugging protocol.

• Optionally pass a custom _ready_check_ expression by passing it in the querystring, hex encoded. Defaults to document.querySelector('title').textContent.
• Optionally pass a custom _ready_check_interval_ to indicate how frequently the _ready_check_ should be tested. Specified in milliseconds. Defaults to 100.
• Optionally pass _strip_js_ to indicate you would like all script tags removed from responses. Defaults to false.

Example

$ node index.js &
$ curl http://unicodes.jessetane.com                       # empty dom
$ curl http://localhost:8080/http://unicodes.jessetane.com # dom with stuff

Configuration

Enviroment variables you can set. Sane (hopefully) defaults are provided but you will probably need to adjust them.

CHROME_{HOST,PORT}

Defaults are localhost and 9222 respectively.

CHROME_OWNER

Defaults to true (but can be set to 'false') and implies that any existing tabs should be closed at start up.

MAX_WORKERS

You probably want to limit the number of tabs you have open at any given time depending on the resources you have available. Defaults to 5.

TIMEOUT

The number of milliseconds workers are allowed to spend processing a request is capped. Defaults to 5000.

Notes

Installing / running Chrome headlessly on Ubuntu

$ apt-get install xvfb chromium-browser
$ xvfb-run chromium-browser --remote-debugging-port=9222
$ # or a slightly more customized example:
# xvfb-run --server-args='-screen 0, 1024x768x16' chromium-browser --start-maximized --no-first-run --disable-gpu --remote-debugging-port=9222

Running Chrome (with debugging enabled) on OS X

$ /Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome --remote-debugging-port=9222

Disabling image loading

To disable image loading for all users, you can create a Chrome policy setting:

{
  "DefaultImagesSetting": 2
}

License

Public domain