Script to get nsIWebProgressListener state names from state codes

This is totally Mozilla specific and probably will not make any sense to anyone not involved with Mozilla code.

So in Mozilla there is an interface named nsIWebProgressListener which can be used to get notifications about any web progress -- a page load in simple terms. So these notifications are sent to us by calling our onStateChange methods. One of the parameters passed is the state of the request. This is a hex code. Memorizing all the hex codes is insane. So to log the states I wrote a small, dumb, script.

I wanted to put it somewhere on the internet, instead of a file on my disk, and hence this blog post. Here is the script to convert nsIWebProgressListener state hex codes to state names. A simple lookup function, but handy for logging

var flagNames = [
"STATE_START",
"STATE_REDIRECTING",
"STATE_TRANSFERRING",
"STATE_NEGOTIATING",
"STATE_STOP",
"STATE_IS_REQUEST",
"STATE_IS_DOCUMENT",
"STATE_IS_NETWORK",
"STATE_IS_WINDOW",
"STATE_RESTORING"
]

var flagValues = [
0x00000001,
0x00000002,
0x00000004,
0x00000008,
0x00000010,
0x00010000,
0x00020000,
0x00040000,
0x00080000,
0x01000000
]

function splitFlags(aFlag) {
var states = ""
for(var i in flagValues)
{
if(aFlag & flagValues[i])
{
    states+= flagNames[i] + "\n";
}
}
return states;
}

That's it.

Mozilla Developer Network (MDN) survey -- My inputs

I just finished the MDN survey and here is what I said in that last box which was put there for the people like us to pen down our rants. ;-)

• Project documentation needs improvement. It has improved and is improving, but a lot still needs to be done specifically about the oldest lines of code.
• I hear from some of the core developers that there are lots of hacks which make the code not entirely predictable. These need to be removed and replaced by proper, reliable code. Again the cleaning is going on, am just saying that it is really important so that there is some sort of SLA based on which people can develop applications.
• Consolidation of the content on MDC and MozEdu so that we can have a "The Mozilla Book", which any beginner can go through and dive into Mozilla related development -- either the platform or the browser or the add-ons or anything.
• Finally, making various Mozilla components available in the form of easily pluggable library modules and step by step guides telling us how to use them.

I do not know if any of this is useful to anyone else in the community, but for me, these appeared to be very important based on my association with Moziila for about 2.5 years now.

Getting the size of an already loaded page (from cache) in a Firefox extension.

Today this question came up in the IRC (moznet, #extdev). One of the add-on developers wanted to get the size of the page, either bytes or number of characters. The most obvious thing that came to my mind was progress listeners for definitive answers or the content length from the channel for not so critical scenario. But then he said he wants it for an already loaded page. And he further said that the information is already there somewhere as it is shown by the Page Info dialog (Right Click on a web page and select View Page Info). He was indeed right. Somebody in the code is already going through the trouble of calculating the data size and we can just re-use that. And I immediately started the quest to find that out.

As usual to figure out any browser component I opened up DOM Inspector. That tool is improving, which was against my earlier perception (Sorry Shawn Wilsher), though the highlighting part is still screwed up. Nevertheless, locating that particular label "Size" and the textbox in front of it containing the value was not difficult at all. I got the "id" of the textbox containing the size value. (Its "sizetext" :) ).

Next it was MXR (http://mxr.moziila.org/) in action. I did a text search for the id and got a bunch of results, one of which was pageInfo.js with this entry : line 489 -- setItemValue("sizetext", sizeText); . It is here. The very line made it apparent that it is the place where the value is being set and hence it is the place from where I can get to know how the value is being calculated.

Once I saw the code it was very clear and straight forward and pretty simple also. We have the URL. From the URL we get the cache entry for that URL. (Every cache entry has a key and that key is the URL - so neat). We try to get the cache entry from the HTTP Session first and if that fails we try FTP Session. The cache entry has the size as an attribute on itself, so its just getting that attribute value. DONE.

I am not sure how this will behave if we have disabled every type of cache. AFAIK, there will still be some in-memory cache as long as the page is still loaded. Probably good enough.

That was the end of a small but interesting quest. :-)

An official full-fledged Firefox Add-ons dev guide

Having done a little work on Mozilla Firefox and extensions for it I have always felt the lack of an official, step by step document for extension development. I do accept that there are a lot of resources available on the internet. Innumerable number of blogs and tutorials explaining the process step by step. But most of them become outdated with newer versions of Firefox and the authors are not really keen about updating the info. That is why an official tutorial or guide from Mozilla itself would be the right thing. It will make sure the contents in the guide are up-to-date and worth reading for developing an extension for the currently available version of Firefox.

There are documents for extension development on MDC like the various links present at: https://developer.mozilla.org/en/Extensions but it was either scattered or pretty brief in most places though it did touch most parts of extension development. Nevertheless a wholesome "official" guide was needed and here it is now. I went through the guide and as the blog post says it is still in BETA with a lot of "TO-DO" tags in there. In spite of that it is very much usable. Do visit it and post back your feedback to make it a much better guide.

Add-ons Blog » Blog Archive » Firefox Add-ons Developer Guide (beta release) - Calling all Add-on Developers!

Lets hope we will have more and more quality extensions now. :-)