modify firefox response (addon)

bootstrap.js

/////// START - DO NOT EDIT
var {classes: Cc, interfaces: Ci, results: Cr, Constructor: CC, utils: Cu} = Components;
Cu.import('resource://gre/modules/Services.jsm');

var BinaryInputStream = CC('@mozilla.org/binaryinputstream;1', 'nsIBinaryInputStream', 'setInputStream');
var BinaryOutputStream = CC('@mozilla.org/binaryoutputstream;1', 'nsIBinaryOutputStream', 'setOutputStream');
var StorageStream = CC('@mozilla.org/storagestream;1', 'nsIStorageStream', 'init');

function TracingListener() {
	this.receivedChunks = []; // array for incoming data. holds chunks as they come, onStopRequest we join these junks to get the full source
	this.responseBody; // we'll set this to the 
	this.responseStatusCode;

	this.deferredDone = {
		promise: null,
		resolve: null,
		reject: null
	};
	this.deferredDone.promise = new Promise(function(resolve, reject) {
		this.resolve = resolve;
		this.reject = reject;
	}.bind(this.deferredDone));
	Object.freeze(this.deferredDone);
	this.promiseDone = this.deferredDone.promise;
}
TracingListener.prototype = {
	onDataAvailable: function(aRequest, aContext, aInputStream, aOffset, aCount) {
		var iStream = new BinaryInputStream(aInputStream) // binaryaInputStream
		//var sStream = new StorageStream(8192, aCount, null); // storageStream // not sure why its 8192 but thats how eveyrone is doing it, we should ask why
		//var oStream = new BinaryOutputStream(sStream.getOutputStream(0)); // binaryOutputStream

		// Copy received data as they come.
		var data = iStream.readBytes(aCount);
		this.receivedChunks.push(data);

		//oStream.writeBytes(data, aCount);
		
		//this.originalListener.onDataAvailable(aRequest, aContext, sStream.newInputStream(0), aOffset, aCount);
	},
	onStartRequest: function(aRequest, aContext) {
		this.originalListener.onStartRequest(aRequest, aContext);
	},
	onStopRequest: function(aRequest, aContext, aStatusCode) {
		this.responseBody = this.receivedChunks.join("");
		this.responseBody = this.responseBody.replace(/Yelp/g,'Melp');

		var sStream = new StorageStream(8192, this.responseBody.length, null);
		var oStream = new BinaryOutputStream(sStream.getOutputStream(0));
		oStream.writeBytes(this.responseBody, this.responseBody.length);
		this.originalListener.onDataAvailable(aRequest, aContext, sStream.newInputStream(0), 0, this.responseBody.length);

		delete this.receivedChunks;
		this.responseStatus = aStatusCode;
		this.originalListener.onStopRequest(aRequest, aContext, aStatusCode);

		this.deferredDone.resolve();
	},
	QueryInterface: function(aIID) {
		if (aIID.equals(Ci.nsIStreamListener) || aIID.equals(Ci.nsISupports)) {
			return this;
		}
		throw Cr.NS_NOINTERFACE;
	}
};

var httpResponseObserver = {
	observe: function(aSubject, aTopic, aData) {
		var newListener = new TracingListener();
		aSubject.QueryInterface(Ci.nsITraceableChannel);
		newListener.originalListener = aSubject.setNewListener(newListener);
/////// END - DO NOT EDIT
		newListener.promiseDone.then(
			function() {
				// no error happened
				console.log('yay response done:', newListener.responseBody);
			},
			function(aReason) {
				// promise was rejected, right now i didnt set up rejection, but i should listen to on abort or bade status code then reject maybe
			}
		).catch(
			function(aCatch) {
				console.error('something went wrong, a typo by dev probably:', aCatch);
			}
		);
	}
};

Services.obs.addObserver(httpResponseObserver, 'http-on-examine-response', false);
// Services.obs.removeObserver(httpResponseObserver, 'http-on-examine-response'); // call this when you dont want to listen anymore