Qwicap 1.4a4 and 1.3.3 Released

Qwicap 1.4a4 and 1.3.3 have been released. The change history has all the details fit to print, but the main motivation behind the 1.4a4 release was to make available a fix for a race condition during session tear-down that's been in the Qwicap code base more-or-less forever. Originally, its effects were of little importance—mostly some exceptions showing-up in the logs—and it wasn't at all clear how the problems came about. With 1.4's support for dynamically generated downloadables, those effects started to have an actual impact by sometimes preventing access to the downloadables in the final page of the session. Fortunately, that made the nature of the problem more obvious and led to this bug fix.

Another old bug (or inadequately developed feature) was in the Qwicap.goodbye method which is the method that sends an application's final page to the user. The bug was that the method didn't inform Qwicap that the application was shutting-down, so Qwicap did nothing to help the application shutdown. Which was fine, for applications that invoked goodbye and gracefully returned their way back to, and out of, their main method, but those that didn't could inadvertently persist in the delusion that they were still operating normally by calling a variety of Qwicap methods that should have no role in, and could delay, the shutdown of an application (retrieving user input, sending pages to the user, etc.). Now that goodbye informs Qwicap that the application is shutting down, those methods that shouldn't be used during shutdown will throw a QwicapSessionDeathException when invoked, in order to help the application along in its shutdown activities. (By the way, QwicapSessionDeathException now includes a message that states why the session is dead, or dying.)

In addition, some enhancements have been made since 1.4a0, including: the addition of the Qwicap.getFloat method; moving the Downloadable class into the public API; changing all of the XML attribute manipulation methods to accept arbitrary objects as attribute values; and various improvements to the Javadocs. In addition, the Hunt The Wumpus example application has had its game logic further debugged, and it has been extended to support larger maps, upon request. The extra "config" page that allows larger maps to be specified, also provides a long-overdue example of Qwicap features like the high-level form manipulation API, while further illustrating how multi-page applications function.

Qwicap 1.3.3

Qwicap 1.3.3 was created by back-porting the bug fixes and minor enhancements that have accumulated in the 1.4 branch as of version 1.4a4. So, that race condition is gone, Qwicap.goodbye is beefed-up, Qwicap.getFloat exists, XML attribute values can be specified as arbitrary objects, QwicapSessionDeathExceptions are more informative, Qwicap.convertSubmitButtonsToInputs has had its documentation substantially expanded, various Context methods that didn't need to be public have been removed from the public API, the XML tag hierarchy validator includes document names in any exceptions it throws, all subclasses of Markup now include getMutable and getImmutable methods, the Context.getFile and Context.getExistingFile methods have been documented at long last, some useless code has been removed, and the Javadocs have suffered various improvements. Also, its version of Hunt The Wumpus received a bug fix, and therefore sucks less than it traditionally has done.

Which Reminds Me

While trying to implement the large map generator for the Qwicap 1.4a4 version of Hunt The Wumpus, I was frustrated for quite a while by my inability to come up with a simple implementation for the generator. The generator had a conceptually simple job to do, so it seemed the implementation should be simple, too. We all know such things frequently don't work out that way, but it was bugging me all the same. At one point, I considered using a cellular automaton to generate a hexagon-based map, and that sent me off to Wolfram's A New Kind of Science (NKS) pages, which was more convenient than winching down my copy of the book from its shelf and finding a spot for it on my desk. What I stumbled upon in doing so was WolframTones, a site that generates music using Wolfram's one-dimensional cellular automata. I found it very impressive, and a welcome demonstration of Wolfram's NKS ideas in an easily appreciated, real-world application - which is the sort of thing I regretted the absence of in the NKS book.

My only complaint with WolframTones is that it limits its compositions to thirty seconds. Ideally, it'd be possible to generate arbitrarily long compositions. What I wonder about long compositions is this: Will they seem to hold-together as well as the thirty-second ones usually do? Or does one's brain eventually reject a longer composition due to the extended lack of the sort of patterns designed into music by human intelligences? This would probably be more of an issue with some types of music than others; in particular, some flavors of jazz might not be a problem. And if it's not a problem for some types of music, what does that tell us about music, and will this eventually result in, say, a music generator box for use in stores that will continuously compose and play new music to save the stores the cost of playing background music that someone owns? As background music, shortcomings in the compositions would be masked by the lack of attention being paid to them. Which is fine for customers passing through, but what about the staff that has to hear the stuff all day? Will they eventually hunt down and destroy the box to save themselves? Or would it work well enough that it wouldn't drive people nuts, and, in fact, would periodically produce something really catchy? With every composition produced by an automaton chosen randomly from a set of around 4 billion possible automata, and with no direct access to the box to ask it to save its state, one would end-up in the frustrating situation of hearing a great song that no one had ever heard before, and knowing that you'd never, ever hear it again. That might promote some useful contemplation of the transitory nature of life, but I think, for the most part, it would just be a new way of pissing people off. Technology is great for that.

Qwicap Feature Summary

I've never succinctly described the features of the Qwicap web application API in one place. I'd assumed most of them would be obvious from reading the introductory documents, but that was probably a mistake on several levels. For one thing, without having been given a good reason to care, who's going to bother with the introductory documents? For another, my colleagues at UT Austin have been exposed to Qwicap for years, and I doubt that they're aware of a lot of these features. So here goes:

• Pure Java
• Open Source
• Designed for Developers, Unapologetically
• Discards the CGI Model
• Very Rich State, Totally Automatic
• Developer-Friendly APIs
• Security: Automatically Prevents Replay Attacks
• Security: Automatically Prevents Cross-Site Scripting Attacks
• Markup Integrity: Completely Standards Compliant
• Markup Integrity: Automatic HTML Encoding & Decoding
• Markup Integrity: Automatic Integrity Checking
• Automatic Input Verification, Error Messages and User Correction Requests
• Transparent File Uploads
• Transparent File Downloads
• High-Level XHTML Form Manipulation API
• Custom XML Engine - Fast and convenient, with thread-safe, fine-grained caching.
• Zero JavaScript
• No Metadata, No Configuration Files
• Simplified Web Application Deployment
• Not a Framework - It fits into your code, rather than vice versa.

For more details, start with the version of that list that includes explanatory text. If that doesn't frighten you off, there's plenty more reading material on the Qwicap site. If you have any questions, drop me a line.

And Now For Something Completely Different....

Those familiar with Christopher Alexander's work—most famously his book "A Pattern Language", which was frequently referenced by Richard P. Gabriel in his book "Patterns of Software"—may find interesting Alexander's response to criticism of his more recent work, "The Nature of Order, Book One". (Thanks to Carfree Times for the pointer.)

Oh, and a bit of computation and UT Austin history.... While going through the Austin History Center's archives a few weeks back, I came across the 1958 memo announcing the appointment of the first director of UT's Computation Center. (My first job with The University was in the Comp. Center, and I've never left.) One thing I found interesting about the memo is the reference to our big iron of the day, the IBM 650. (Thankfully, unlike most computer companies, IBM has not forgotten its old models.) Among other things, that beast could do 138,000 logical operations per minute. And you have to love that magnetic drum - echoes of Atanasoff & Berry. Also interesting is the fact that, 47 years later, Dr. Young is still at The University, in our Computer Science department.

Qwicap 1.4a0 Released

A holiday week's worth of coding has advanced Qwicap 1.4 from a scrap of dusty paper with a feature list scrawled across it, to an alpha-test release. As befits an alpha release, it is not feature complete, but it is stable and useful, and lays the groundwork for the rest of what I want to accomplish with 1.4.

The noteworthy new features in Qwicap 1.4a0 are:

• Support for dynamically generated downloads - Generate your downloadable material any way you like, convert it to a byte array, and invoke the new Qwicap.addDownloadable method with a name, and an optional MIME type. It returns a unique URI for the downloadable, which you embed in your page markup wherever you wish. Downloadables automatically become eligible for garbage collection when the page they were first used in ceases to be "in play". (In other words, when the method that manages that page ceases to be in the call chain.)
• Input is now accepted from links ("a href" and "area href"), so you don't have to use forms exclusively, anymore. Combine this feature with the support for dynamically generated downloads, and things like dynamic graphics with corresponding client-side image maps become simple to implement. (The revised version of the Hunt The Wumpus example application demonstrates just such a map.)
• Simplified deployment - Most applications can now use a generic "web.xml" file, as seen in the revised example apps. Qwicap will automatically discover the entry-point of your application code at runtime, and will also handle serving-out any web pages, style sheets, etc. that would otherwise be inaccessible due to the default servlet url path being "/". This means one less thing to learn/remember, and also keeps the URLs for your web applications pleasantly short.

Major features remaining to be implemented in version 1.4 include internationalization, and asynchronous prompts. The former represents unfamiliar ground for me, but it seems clear that there should be some way for developers to alter the default input-validation error messages that Qwicap automatically adds to web pages. Given Qwicap's facility with XML files, I'm inclined to have it retrieve those messages from a language-specific XML file. What I haven't wrapped my head around yet is how to cope with the various permutations of those messages, like pluralization. Perhaps a language-specific class is in order - a method could be invoked on it that is specific to particular problem (bad integer input, for instance), and the code could supply whatever markup it wished in response (it could be loaded from a language-specific XML file, or produced by any other means convenient to the international developer).

I have a much better handle on the idea of asynchronous prompts (my favorite would-be feature in 1.4), but the implementation details to be considered are numerous, and, in some cases, rather non-trivial. The idea, however, is simple enough: instead of blocking until user input arrives, as the current Qwicap.prompt methods do, an asynchronous prompt would be non-blocking, and would therefore allow the web application to continue processing after sending a page to the user. The page would presumably be set to refresh periodically, and would thereby receive status updates until the server had concluded its processing, at wich point the client and server become synchronized once again. Equivalent (or fancier) functionality can be created in many web application schemes already, but Qwicap's asynchronous prompts should be vastly simpler for developers to comprehend, use, and support, while also being more predictable/dependable in as much as the code remains strictly server-side.

Barring another week of holiday materializing out of thin air, I don't know when I'll have a chance to make headway on these outstanding features. (Things are busy at the office, and our current and pending web applications don't have a compelling need for either of those features.) Nonetheless, I would value insights on internationalization in the mean time. And anyone who can put a sexy interface on the new Hunt The Wumpus example would be appreciated. (At present its interface is pleasantly minimal and clean, but doesn't exactly manage to catch one's eye.)