well you do have a point here, but … to get rid of over-eager javascripts I MUST modify the document before the browser sees it (if this was what you mean, that is). The JS interpreters embedded in various browsers will always *pre-process* all inline JS, so any changes after loading the full document will get dismissed. (Trust me, I had to go through all this first to realize that my attempts were fruitless :))

The binary input stream’s readBytes() method is just a string of bytes… you *could* parse it–and manipulate it–but there are too many potential problems.

Don’t try to parse until the download is complete. Let’s say the stream comes in two parts… You can’t create a parse-able document from that. You’ll have unclosed tags, parts of multi-byte characters, etc.

By the way… in all honesty, it’s probably better to modify the document after it has loaded. Delaying document loading is definitely unexpected behaviour.

thanks for your reply, and your sample code. However, you’re one step ahead :)

I’m still in onDataAvailable():
var data = binaryInputStream.readBytes(count);

At first, I’ll need the step how to get the binaryInputStream to something better parseable.

What you *could* try doing is not passing things on down the listener chain until the very end. Do your processing on the completed string/page and then pass the modified version on to the other listeners.

To perform normal DOM methods, you can load the content into a virtual iframe:

function createDoc (htmlText) {
_iframe.docShell.allowJavascript = false;
_iframe.docShell.allowAuth = false;
_iframe.docShell.allowPlugins = false;
_iframe.docShell.allowMetaRedirects = false;
_iframe.docShell.allowSubframes = false;
_iframe.docShell.allowImages = false;

var doc = _iframe.contentDocument;
var strip = /([\s\S]*?)< \/html>/i;
if (strip.test(htmlText)) {
doc.getElementsByTagName(”html”)[0].innerHTML = strip.exec(htmlText)[1];
}

return doc;
}

And then just get the content back out again when you want to pass it on to the next listener

this is a great site. I have to bookmark this one now as Honza has closed the comments section (for no obvious reason, whatsoever!)
Well then.

I wonder why you need a BINARY input stream for all that?
Supposed I want to use this code as a basis to transform a web page “on the fly” before the browser can get hold of it, e. g. to remove over-eager javascripts or even only a few JS _lines_.

Supposed too that the stream is nothing but HTML+JS, it would be great to be able to use a DOM function like getElementsByTagName() to get some nodes *before* the browser can do anything with the page.
AFAIK this is not possible with a binary input stream.

So am I doomed to use the BIS or can I also use a sort of “character input stream”?

Good catch. I had fixed this bug in PirateQuesting several months back but obviously I’d forgotten to update this blog entry.

Needed to add:


if (typeof Cc == "undefined") {
var Cc = Components.classes;
}
if (typeof Ci == "undefined") {
var Ci = Components.interfaces;
}


to the httpRequestObserver methods as they operate in a different scope than TracingListener. Firebug’s const values were still valid though and the oversight was missed in testing.

Tnx for this article. I got my extension to listen in on XHR request using this code but I have a problem, the code only works if firebug is installed! Without firebug the onStart, onDataAvailable and onStopRequest all get value as ‘undefined’ for their request parameter(i didn’t check for other parameters). But whenever firebug is also installed in the browser the request value gets passed and everything works.

Can you pls let me how i can fix this?

tnx
Harini

piratequesting is an add-on I made for the browser game at http://www.piratequest.net. You can download the add-on at pq.ashita.org and test it out. Unfortunately I haven’t updated it in a while and it is no longer compatible with the current version of Firefox. If you turn off version compatibility checking it works just fine.

Best regards.