Extension:EmbedScript

work in progress, related to Extension:EmbedSandbox



Designed to sandbox scripts from the local wiki by inserting them into an iframe hosted from a separate domain. Scripts from the wiki can thus run without being able to access the hosting wiki's JavaScript contexts, making them (in theory) as secure as linking to a third-party site.


 * Live samples on labs: http://embed-demo.wmflabs.org/wiki/Main_Page
 * MediaWiki extension code: https://github.com/brion/EmbedScript (todo)
 * Sandbox page: https://github.com/brion/EmbedScriptSandbox

Basic protocol

 * Host opens with the sandbox page's URL
 * Sandbox initializes self, jQuery
 * Host sees 'load' event on iframe
 * Host posts message to sandbox: {action: 'load', code: '...js source...', args: ['...string...', ...]}
 * Sandbox makes the 'args' parameter available as 'sandbox.args' in script's local context
 * Sandbox executes the JavaScript code in its local context

postMessage details
Send JSON-serialized strings of object maps, prefixed with 'mediawiki.embedscript:'

Host verifies the sandbox's messages by the origin window and the prefix. Sandbox verifies the host's messages by the origin window and the prefix.

Security
Security is enforced by the browser's same-origin controls. As such, protection against malicious code can only be ensured by using a sandbox page hosted on a separate domain.

Remember that the code will have full capability to do anything the browser allows in an iframe, including loading foreign scripts or sending all data passed into it to an evil web site!

HTTPS is recommended for loading the sandbox page; the real sandbox page will never send data passed to it on to any server, but a malicious MitM one might.

Wiki-side usage
...JS code...



Optional parameters:
 * width - defaults to 640
 * height - defaults to 480
 * src - to load script source from a wiki page instead of contents
 * fallback - fallback content if JS unavailable (NYI)

Width and height default to 640x480

File access
tbd

Libraries
Currently the extension can load a single wiki page via the 'src' parameter, replacing the provided text.

It could be useful to make code libraries available; eg to combine several scripts together so we can include, say, jQuery or the Raphael.js graphics library for some uses but skip them when they're not needed.

When loading multiple items on a single page, it may also be useful to load source dynamically, so common files only need to be loaded once.

Consider related Gadget issues.

Limitations
Some features such as WebWorkers for background processing require additional scripts in the sandbox's contexts, so probably won't be possible.

The /Mandelbrot set example could benefit from one or two worker threads, but instead makes do by using setTimeout to break processing into chunks without blocking the UI thread for too long.

Examples

 * /Mandelbrot set
 * /Pythagorean theorem