XULRunner is a bit intolerant in its chrome.manifest files when it comes to jarred chrome versus flat chrome. For example, I filed bug 295023 because I typically build with flat chrome, and the sample app insisted that its chrome was jarred.

There’s actually a simple, undocumented way to avoid this problem. You force the build process to use a particular chrome format just for your XUL application. If you want to force jarred chrome, add this line to your Makefile.in file, after the autoconf.mk line:

MOZ_CHROME_FILE_FORMAT = jar

That’s it. The build process will take that, and override the user’s default setting. Alternatively, if you insist on flat chrome:

MOZ_CHROME_FILE_FORMAT = flat

XULRunner apps should use one of these settings for any Makefile.in tied to their chrome.manifest. Of course, it’s not a nice thing to do in a traditional SeaMonkey application, where jar.mn rules. In this case, you’re forcing your choice format on the developer building

. If you can use jar.mn instead of chrome.manifest, please do.

Say you have a document <root xmlns="https://weblogs.mozillazine.org/weirdal/namespaces/root/"/>. Your default namespace has no prefix for DOM XPath to look up. So if you try to do this:

  var resolver = document.createNSResolver();
var result = document.evaluate("//root", document, resolver,
Components.interfaces.nsIDOMXPathResult.ANY_UNORDERED_NODE_TYPE, null);
alert("Node: " + result.singleNodeValue + "\n");

It’s not going to work. You can’t get to it using Mozilla’s default namespace resolver. Instead, you have to create your own:

  var resolver = {
lookupNamespaceURI: function lookup(aPrefix) {
if (aPrefix == "default") {
return document.documentElement.namespaceURI;
}
}
}
var result = document.evaluate("//default:root", document, resolver,
Components.interfaces.nsIDOMXPathResult.ANY_UNORDERED_NODE_TYPE, null);
alert("Node: " + result.singleNodeValue + "\n");

That will alert a node instead of throwing an exception. It’d really, really be nice if Mozilla’s native XPathNSResolver was smart enough to actually give you a default prefix. Of course, to do that in any sane way, you’d probably have to add a matching lookupPrefix() method, so that if you fed lookupPrefix() a default namespace URI, it would spit back a prefix you could use with your xpath evaluation.

It took me several hours to figure this out, and then only with the help of a devmo-linked tutorial on XPath basics. I want to file a bug on this, but I’m not sure the bug would be valid. If it were valid, I’d fix it myself in a matter of minutes. (It’s worth noting the DOM 3 XPath spec is a Working Group Note, so we’re not under any obligations whatsoever to not do anything to the native resolver.)

UPDATE: Err, I spoke too soon about a matter of minutes, before writing any code on it. If I have <root xmlns="https://weblogs.mozillazine.org/weirdal/namespaces/root/"><real xmlns=https://weblogs.mozillazine.org/weirdal/namespaces/real/"/></root>, then I’m a wee bit hosed at real. I need to work out a JS-based solution first.

UPDATE 2 Hm. “//xmlns:root” seems to work just fine

. I remembered something about default namespaces. An attribute xmlns=”foo” has a namespaceURI of “http://www.w3.org/2000/xmlns/”, not null. So that works, and actually fits my needs perfectly. Nothing to see here, move along.

UPDATE 3 I realized about an hour ago that the xmlns: prefix in XPath only covers the namespace URI of the resolver’s initializing node; other nodes with different default namespaces are still lost. Plus, XPath is the wrong solution for the problem I had in mind anyway. Back to the drawing board…

After two very long days of coding and one bug patch, I’ve almost succeeded in the third approach to the string contents as files problem.

My tests prove I can feed JS strings through a XPCOM service, a special protocol handler and a corresponding nsIChannel implementation into the browser. Most of it was heavily inspired by the data: protocol handler and channel implementation.

The only detail left unresolved is the handling of hash targets for XBL… a crucial weakness. (I’ve gotten HTML hash targets working.) The hash targets are part of the URL, but they’re not getting recognized. This makes the protocol slightly better than data:.

There has to be some way to make this work

. I just have no idea what it is. I’ve not seen any evidence of it in the protocol / channel pairs.

UPDATE: As far as I can tell, the problem is actually upstream of my code. My onStartRequest() and onDataAvailable methods get called normally, but my onStopRequest() doesn’t get called until I decide to move on to another page or close the window. The HTML page through my virtual: protocol does call onStopRequest with a status of 0. So this is probably something nutty in XBL.

UPDATE 2 Nope, it landed squarely back in my face. I’d filed bug 306217, and debugging led bz, biesi and I through a long series of hoops. Eventually, biesi guessed (correctly) that I should’ve closed the output stream.

But with that fixed, I can declare my virtual: protocol handler operational. Not optimal, but operational.

I’m hitting a conceptual problem in Verbosio’s development

. Say the user is editing a XUL document, one sprinkled throughout with URL’s: scripts, overlays, DTD’s, stylesheets, you name it. Most of these point to files which presumably don’t exist yet (for example, chrome://package/content/file.xml). So how do you load all these files from JavaScript strings, so the user can preview the changes he’s making without saving?

I have at the moment four ideas, none of them very nice:

1. data: URI’s

   Basically, I feed it the content-type, then a comma, then the contents of the string as the second argument. The two disadvantages I know of are (a) URI’s are supposed to be short, and data: might be abusing that, and (b) data: URI’s don’t support hash targets (#foo). That means they’re useless for pointing within the document to a specific ID attribute (XBL depends on that pretty heavily, and (X)HTML likes it).

2. file:///userHomeDir/cache/path/to/file

   This means saving the file in a cached form to the local file system. This is probably the simplest, but it involves reading and writing to the file system repeatedly. (Every time the user changes to the document or a file depending on it, most likely.) It also doesn’t allow for granting chrome privileges that easily (though I suppose I could set CAPS security policies as needed). In case you’re wondering, this is %APPDATA%/(appName) in Windows, not …/dist/bin/anything.

3. virtual:protocol:///path/to/file

   This would mean creating a bunch of XPCOM components, starting with protocol handlers and channels. This is unfamiliar ground for me, but it would run fast and not abuse the system.

4. Hack the system to attempt reading from a JS source first.

   Something like this is very likely to destabilize the GRE running this chrome application, and would probably involve a lot of the same work as the previous idea. It’s just not feasible.

I really, really need some help here. If left to my own devices, I will go with the second route. I would welcome implementations, except for the data: system. I’d also welcome other ideas to solving this problem.

Assuming jslib gets a fix for a perceived bustage in fileUtils.js soon, here’s some code I whipped up for grabbing files from chrome, either jarred or flat:

  const fUtils = new FileUtils();
var localPath = fUtils.chromeToPath(sourceURI);
var isJarRE = /^jar:(file:\/\/\/.*\.jar)!\/(.*)/.exec(localPath);
var fileAsString = "";
if (isJarRE) {
include(jslib_zip);
var jarPath = fUtils.urlToPath(isJarRE[1]);
var jarFile = new File(jarPath);
var jarContents = new Zip(jarPath);
jarContents.open();
fileAsString = jarContents.readEntry(isJarRE[2]);
jarContents.close();
} else {
var fileObj = new File(localPath);
fileObj.open("r");
fileAsString = fileObj.read();
fileObj.close();
}

This assumes you’ve loaded chrome://jslib/content/jslib.js and chrome://jslib/content/io/io.js already.

On a side note, I’ve finished the first step of the 34-step Verbosio smoketest

. This code above was needed to make sure I did things right.

Javadoc-style comments are wonderful. Doxygen uses them to generate on-the-fly documentation. They describe properties, methods, arguments of methods, return values, etc. To compilers and interpreters, they’re just comments. So why can’t we do that for XBL?

For most XML languages, it wouldn’t make any sense. But XBL-implemented properties, methods, and event handlers are perfect for javadoc’ing, with XML-style comments.

Instead of:

/**
* Function description.
*
* @param firstArg The first argument.
*
* @return Boolean true if the first argument is a number, false otherwise.
*/

We could have:

<!--
- Function description.
-
- @param firstArg The first argument.
-
- @return Boolean true if the first argument is a number, false otherwise.
-->

I would love to see Doxygen modified to provide support for this. I would love to see Mozilla’s toolkit(s) use this style of commenting to document the widgets. I would love to see this style used in whatever xulwidgets project I’ll launch.

I’d also like your opinions. A little XML commenting in bindings never hurt (except in bindings’ content, where it hurts a little). Is this the right style, and is it worth doing?

UPDATE: Okay, how about variation 1:

<!--
/**
* Function description.
*
* @param firstArg The first argument 
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*
* @return Boolean true if the first argument is a number, false otherwise.
*/
-->

This follows the old commenting style, and embeds it in XML comments. Or, variation 2, suggested by Nico:

<!--*
- Function description.
-
- @param firstArg The first argument.
-
- @return Boolean true if the first argument is a number, false otherwise.
-->

This one takes less characters, and still has a special format to identify the comment to a system like doxygen. I personally prefer #2, as the javadoc comment then remains adjacent to the method, instead of wrapped in another comment.

LXR Filename Reference Search
If you install this script, visit http://lxr.mozilla.org/seamonkey/source/mailnews/base/resources/content/messenger.xul
and observe the breadcrumbs (mozilla / mailnews / base ..

. )

You guys rock, you know that? I posted the test request an hour ago, and already I have enough conclusive evidence to file a bug.
Here’s the situation.
I’m developing a XBL binding to do what Venkman (ye handy dandy JavaScript Debugger) does with floating panes, except it won’t create new windows every time. So, I want to use global toolkit icons for the various pieces of the widget. I would use the Close.gif image I asked you about to hide a pane from the user.
In SeaMonkey for Windows, chrome://global/skin/icons/close.gif works. It doesn’t work for Mozilla Firefox 1.0.6 (WinXP). The URL I gave you, with a capital C, works for both SeaMonkey and Firefox.
This sort of discrepancy is not good for developers. I’m actually surprised both worked in SeaMonkey. But I needed to know if it would work across the board… and you’ve proven that it won’t.
I don’t want to spend my whole time creating theme-specific stylesheets. Global is global is global. I’m filing a bug very shortly on this. I’m not filing because Close.gif doesn’t work..

. I’m filing because I don’t have a consistent choice to rely on.
Thanks, everyone!
UPDATE: I’ve filed Bug 303974 based on your feedback. Anyone want a “good first bug” to create a patch for?

Please load chrome://global/skin/icons/Close.gif into your browser, exactly as typed.
I just need a quick test on the following platforms to see if the X renders:

Legend:

• +: Yes, it rendered
• -: Blank screen
• ?: Disagreement from testers’ comments

Please comment

. I am hoping the community can help me fill in the blanks, so I know whether I need to file a bug or not.
(Note: I got the icon on WinXP, SeaMonkey and Firefox 1.0.6.)
UPDATE: Enough already. Comments closed.

I’m thinking we really should have a mozdev project for useful XUL widgets, written in XBL. Somewhat like JSLib, but for XUL

.
I’ve put out several widgets before, and I continue to work on new ideas.
Who else wants a bigger toolkit? I’ve got so many ideas, easy to do in XBL, for additional bindings. Who has their own custom widgets to contribute?
P.S. The Open Source Convention is a blast.