Category Archives: Browsers

A Better IE 5.5 and 6 PNG Fix

I should have posted this here prior to now, but as you can probably tell … .. I don’t post to this blog very often. During the implementation of the new flixn.com site we decided to use PNG alpha transparency to some extent. During the course of implementation existing IE5.5/6 PNG hacks were deemed to be wholly inadequate for our needs. So, I took some time to reimplement the core PNG hack as an .htc (IE CSS Behavior) and layer in some additional hacks on top to support css repeat and positioning.

Get the code: [HERE]

Original post follows:

So there I was in the wake of an unexpected and tragic steamroller accident involving the entirety of the production design staff… “Wait, you mean I have to cut and implement all the new Flixn.com designs? Me? Well, ok, this shouldn’t be too hard. I’ll just slice each element out with alpha transparency preserved in PNG’s, then layer them using CSS just like they are in Photoshop.”

“Wait, wait. What do you mean that won’t work?”

Back in reality, the lack of true support for PNG alpha transparency in Internet Explorer 5.5 and 6 has been nipping at us and many others for at least 4 or 5 years now. Given that browsers that are fully supporting are in the 70%+ market share range, we decided that it was time to come up with a proper “fix” that would allow our alpha transparent PNG’s to degrade gracefully on now effectively “legacy” versions of IE.

Many web developers out there will be familiar with the prevalent “.htc” file behavior fix targeted at this problem. There are certainly other ways to approach a solution, but we tend to like this one for a number of reasons, perhaps the biggest being: It will invalidate otherwise valid CSS. This may seem a bit crazy, but a fix (hack) is a fix (hack) and as a boundary pushing web developer, one probably shouldn’t be left to forget that.

The IE behavior/.htc fix that has been around for a number of years has some pretty staggering limitations when used on anything resembling a complex layout – so staggering, in fact, that it’s easier to just say what it gets right: images in img tags, and non-repeating (non-tiled) background images aligned to the top left of their container. Perhaps this isn’t a problem if you design the page with this in mind, but it certainly won’t suffice in making a crazy-alpha-png’d-layout degrade gracefully on IE 5.5/6.

For our from-scratch implementation, we started with a page cut and structured as we desired and validated the presentation in IE7, Firefox2+ and Safari 3+, then implemented our own behavior/htc hack to correct all the regressions that we could find in earlier versions of IE. What we ended up with was something that was capable of not only preserving the status-quo in IE PNG hacks. We also bring to the table full support for the CSS properties background-position (for labeled, pixel and percentage offsets) and background-repeat (for values of repeat, no-repeat, repeat-x and repeat-y). The only thing we don’t do is support the use of these two properties together. We’ll leave that for someone else… or maybe a future weekend hacking session.

PowerDNS / PostgreSQL & Web Interfaces 2

After a bit of eat and drink, as well as a half hour of zOMG why is this not werking!?!?! (iptables), Supermaster/Superslave is operating famously. It seems to “just work”. No complaints thus far, which is, well… highly unusual for me to put it lightly.


Feb 03 05:35:55 Received NOTIFY for flixn.com from 72.232.239.130 for which we are not authoritative
Feb 03 05:35:55 Created new slave zone 'flixn.com' from supermaster 72.232.239.130, queued axfr
Feb 03 05:35:55 gpgsql Connection succesful
Feb 03 05:35:55 No serial for 'flixn.com' found - zone is missing?
Feb 03 05:35:55 AXFR started for 'flixn.com', transaction started
Feb 03 05:35:55 AXFR done for 'flixn.com', zone committed

PowerDNS / PostgreSQL & Web Interfaces

http://evilcode.net/sjg/infernal/PowerDNS/SCHEMA/

I have been looking at PowerDNS for a while now, and after regular confirmation that it is in fact performing extremely admirably over at DreamHost I decided that it was time to deploy it.

While PowerDNS is the least braindead DNS server I have ever come across, there were a couple of things that I was not 100% happy with, at least in terms of coupling it to a web frontend.

  • SOA records are stored space-delimited. This would hardly be a problem except that our serial is stored here. In its defense, PowerDNS has an alternate method of handling serials that is probably better in most circumstances. Hardly, but we would still have to break it apart and put it back together again to edit the minimum (default in practice) TTL, etc.
  • Record types are stored textually. Even when implemented as an enumerated value this still violates DRY, as you must re-state these values in your frontend code.
  • Everything must be represented fully qualified. This = FAIL from a normalization perspective.

Here I have come up with a somewhat optimal schema from the point of view of my web interface, and I have tied it to PowerDNS’s preferred table structure via domain logic. This could have been handled in other ways of course, but I tend to like this one for a number of reasons.

  • First, the alternative is to add custom queries to the PowerDNS configuration file to make it understand whatever schema we might have in place, PowerDNS actually makes this very easy.
  • Another alternative would be to use dynamic (normal) views.

On to the benefits, some being quite minor.

  • Querying against serialized views will have performance benefits versus the above two options, this of course has to be weighed against the cost of maintaining the views.
  • As mentioned, PowerDNS has two methods of handling serials, either in the SOA record, which we are keeping up to date with our domain logic. Alternatively PowerDNS will scan each record for you to find the most recently updated (if you maintain change_date). The former should logically be more performant, so we have implemented that option. This could have been handled either way in the domain logic, but most importantly we aren’t relying on our web frontend to keep our serials up to date.
  • Most importantly, namely for debuggability, data on master’s and slave’s “looks the same”.

To get you rolling your PowerDNS configuration file need not be any more complicated than this:


launch=gpgsql
gpgsql-host=hostname
gpgsql-user=powerdns
gpgsql-password=password
gpgsql-dbname=pdnstest
daemon=yes

I haven’t tried slaving yet, but I suspect it will work without a hitch. Will update here when I do and when this rolls out.

ActionScript

This week I decided to toy with ActionScript/Flash a bit (for the first time, really). I’m using the FlashDevelop IDE, so it’s all free goodness, no shelling out $500 to Adobe. Anyway, I wrote an MP3 player that is devoid of any sort of flash user interface, completely controllable through JavaScript. It’s a mere 162 lines of ActionScript and weighs in at 2071 bytes as an swf. It supports a wide range of operations, load, play, pause, stop, setvolume, getvolume, ispaused, getpauseoffset, getcurrentfile, getduration, getposition, getbytesloaded, getbytestotal, getid3, as well as a number of asynchronous JavaScript callbacks (notifications) on various events, loadcomplete, playcomplete and id3found. You can see it in action with possibly the simplest UI possible here: http://evilcode.net/sjg/player/.

The real question that I am trying to answer for myself is, does eliminating the flash user interface somehow make it [flash] more palatable?

PHP/AJAX file upload with progress bar, part 3

Part 1, Part 2

I pulled this back out over the weekend and did a little work on it. The backend code is now totally functional, however I would consider it to be alpha quality. It just needs to be wrapped in a UI now, check it out and let me know what you think. Try the demo with JavaScript enabled first, once the upload completes you will see the result is a mash-up that looks like PHP’s $_REQUEST/$_FILES. Hit the resulting url again within 60 seconds and you will see the status side of things (Using a GET request, you don’t want to re-post the form data). Total bytes, bytes received, percent complete. Try it again with JavaScript disabled and behold the standard php handler.

Source
Demo

PHP/AJAX file upload with progress bar, part 2

I made some good progress on implementing the server side of things as outlined in my prior post on this subject, but I got lazy as usual. I simply haven’t gotten around to finishing this up, so I decided to throw the code up and make a post about it in the hopes that someone will either badger me into completing it, or find some of what is already there useful. The code as of now implements what could be a reasonably useful (python asyn* inspired) set of utility classes for writing socket applications in PHP. Not that anyone would ever want to do anything like that, of course.

http://evilprojects.com/hacks/

PHP/AJAX file upload with progress bar

Over the past couple of days I have been pondering adding some file upload functionality to the form classes I have been using for a bit over a year now. History repeats itself, again, time spent pondering instead of just getting on with the nitty gritty means I start thinking about ideal functionality. So, as I pondered how to go about sanely handling file uploads features started coming to mind, and one of them just wouldn’t go away. A semi-realtime inline file upload progress indicator. Well, that doesn’t sound so hard.

I spent some time with Google doing the requisite research to find that there are a number of stumbling blocks. The first being client-side, when a browser window/frame is busy pushing a file or files up the pipe, it seems that it is just that, busy. Which makes it a bit difficult to talk it into displaying updates. This seems to be pretty easily solved by pushing the file upload through a hidden iframe referenced by the target attribute on the form.

That certainly isn’t where the problems end. As luck would have it, not only is the browser happy to be working against us, so is PHP, in more ways than one.

When the execution unit handling the upload gets hit with the POST, it would seem that it likes to make itself busy as well. Ok, so no way to get the status of the file upload from the thread/process actually handling the upload. Apparently there are some patches against PHP to rectify this situation, but until they get committed and see a release they are unusable for most people. I am all for gratuitously hacking my own PHP install, but it seemed like there must be a better way.

I then stumbled across another method. Scan the upload_tmp_dir (PHP INI variable) for files of a known naming scheme, looking for the one with the latest timestamp. The current size of this file could be pushed back to the browser so that it could calculate the upload progress. This method is also not without its glaring faults. The probability of a race condition is too high for any kind of production use. Oh wait, scratch that, I’m starting to sound like a PHP developer, let me rephrase… There is an unavoidable possibility of a race condition, so this method cannot be used. Well… Wait a minute, there is an upload_tmp_dir variable. Why don’t we just generate some kind of unique form id to be passed back to us when we get the POST, then it should be possible to create a directory to have PHP put the file(s) in of a known name, eliminating our race, no? I suppose upload_tmp_dir being read-only is a bit of a stumbling block with that idea, considering we already decided hacks to the PHP source were out. Not to mention PHP probably isn’t going to let us set the variable before it gets busy processing that form data anyway.

Google led me to a couple more resources for accomplishing this throughout the course of my research, but they all involved an external non-PHP script to handle the upload and drop status information somewhere accessible. Unacceptable I say! There must be a way to do it with PHP alone!

I have theorized a method, implementation forthcoming. Here is a brief summary. Have an onSubmit handler frob a PHP script and retrieve a URL to apply to the action property of the form, said PHP script will have just launched a PHP-based very simple webserver. This webserver’s sole purpose in life is to eat POST’s and parse multipart form data. This same PHP script will update an accessible location with the status of the upload. The hidden iframe trick gets used to free up the window with the form in it. This window can now pull upload status via XMLHttpRequest and update a progress bar accordingly. This method also has the benefit of being able to degrade gracefully in the event that JavaScript is unavailable on the client. The default action URL can be implemented as a standard file upload handler.