Flash player API for browser extension

Question

let's say we have a P2P multi-player Flash based game hosted on a website. Would it be possible to create a browser extension that would listen to what is going on within the Flash application? For example, I would like to know when a player connects to a room, gets kicked or banned, or simply leaves by himself. I'm sorry this is not really a specific question but I need a direction to start. Thanks in advance!

Answer 1

I can see a few ways to communicate between Flash and a browser plugin.

One is to open a socket to a server running on the local machine. Because of the security sandbox, this may not be the easiest approach, but if feasible, it is of course probably the one to go for because you've already got your socket-handling code written, and listening/writing to a additional socket isn't terribly complicated. For this approach, you just need your plugin to start listening on a socket, and get the flash applet to connect to it.

Another way might be to try something with passing messages in cookies. Pretty sure this would just cause much grief, though.

Another way, and I suspect this may turn out to be the easier path, is to communicate between Flash and JavaScript using the ExternalInterface class, then from JavaScript to the plugin. Adobe's IntrovertIM example should get you started if you can find a copy on the web.

In Flash, create two functions, a jsToSwf(command:String, args:Array<String>):Dynamic function, to handle incoming messages from JS that are sent to that callback, and a swfToJs(command:String, args:Array<String> = null):Dynamic function, which calls flash.external.ExternalInterface.call("swfToJs", command, args);.

To set it up, you need to do something like:

if (flash.external.ExternalInterface.available) {
  flash.external.ExternalInterface.addCallback("jsToSwf", jsToSwf);
  swfToJs("IS JS READY?");
}

(The two parameters to addCallback are what the function is called in JS, and what it's called in Flash. They don't have to be the same thing, but it sort of makes sense that they do)

In JS, you need the same functions: function swfToJs(command, params) accepts commands and parameter lists from Flash; and jsToSwf(command, params) calls getSwf("Furcadia").jsToSwf(command, params);.

getSwf("name") should probably be something like:

/** Get ref to specified SWF file.
// Unfortunately, document.getElementById() doesn't
// work well with Flash Player/ExternalInterface. */
function getSwf(movieName) {
    result = '';
    if (navigator.appName.indexOf("Microsoft") != -1) {
        result = window[movieName];
    } else {
        result = document[movieName];
    }
    return result;
}

The only fiddly bit there is that you need to do a little handshake to make sure everyone's listening. So when you have Flash ready, it calls swfToJs("IS JS READY?"); then the JS side, on getting that command, replies with jsToSwf("JS IS READY!"); then on getting that, Flash confirms receipt with swfToJs("FLASH IS READY!"); and both sides set a flag saying they're now clear to send any commands they like.

So, you've now got Flash talking with JS. But how does JS talk with a browser extension? And, do you mean extension, or add-on, since there's a difference! Well, that becomes a whole 'nother can of worms, since you didn't specify which browser.

Every browser handles things differently. For example, Mozilla has port.emit()/port.on() and the older postMessage() as APIs for JS to communicate with add-ons.

Still, I think ExternalInterface lets us reduce a hard question (Flash-to-external-code comms) to a much simpler question (Js-to-external-code comms).