After I released uploadprogress 1.0.0 some days ago and finally declared it as stable, it's time to write that blogpost about some of the limitations and caveats one has to know.

The post links to a demo and answers a few different questions on issues such as:

• Running it on other modules than mod_php on Apache ( like fastcgi)
• Checking if files are too big
• The position and content of UPLOAD_IDENTIFIER within the form is important
• Why not use $_SESSION for the info?
• It segfaults, when I don't include UPLOAD_IDENTIFIER

See the PECL page for the extension for more information.

The uploadprogress extension for PHP never really worked on Windows and since I don't have a Windows development environment I could never do a proper analysis of the problem. Until this week, when Tomas Holusa sent me an email telling me about some VCWD_RENAME problems on Windows.

A patch that was submitted a while back confirmed the issue and a new patch was written and submitted to take care of the problem. You can try out the new extension on Windows with either the normal Wind32 build or Win32 nts build.

The blog post was voted up on reddit, and the server got slammed. So slammed, in fact, that it was unusable for a few hours while I investigated the problem. I didn't know the post was on reddit, but I knew I was getting some traffic.

He spent some time trying to get the Apache server to finally die off and give him back his machine, at least enough to get a feel for what was going on. Part of his problem was not having APC installed like he thought and the other part - WordPress. While friendly on the outside, it's apparently somewhat lacking on the inside.

This current tirade stems from implementing a file upload progress meter in PHP5. Yes, PHP5.2 has some hook, and there's a PECL extension. [...] I realize this is partially a PHP issue I'm ranting about, but it's ultimately a hacky workaround to a basic piece of functionality that browsers should support.

He mentions an example where he basically directly asked a member of the IE team about it. It wasn't greeted seriously and still hasn't managed to be included in most of the popular browsers of today.

Given that uploading huge files can be tedious for impatient users, it is important to provide them positive feedback to keep them from giving up and going away.

Fortunately, PHP V5.2's new hooks into the file upload process allow us to show users in real time what is happening with their uploads. In this article, we will create a progress bar using PHP V5.2 for our users (see Download for source code).

They talk about what "hooks" are to explain how things work together before getting into the setup of the sample app. They chose to go with WAMP for their examples, but it can be easily adapted to any other flavor of *AMP setup of your choosing.

They set up a default upload box inside of a normal form the user can upload a file with. The real magic happens on the backend when the "Upload" button is hit. Via a handy call to the apc_fetch function, we can determine how far along the file is in the upload. This is relayed back to the script when their "Start me up!" link is clicked and a progress bar is advanced as the file is uploaded.

Since I wanted to use this upload progress meter extension under PHP 4, I had to find an alternative solution. I decided to port the patch that adds hooks to monitor upload progress to make it run under PHP 4.

These two patches work for different versions:

• PHP 4.3.11
• PHP 4.4.4

• an example of a plugin using COMET to generate the progress bar
• the upload progress meter for the PHP 5 series
• and a Windows version of the same.

This progess meter is based on the yahoo user interface library and alternative php cache (APC). You will need both of these for it to display properly. PHP 5.2.0 or higher is also required. (I have written a previous article on alternative PHP cache here).

He gives a brief overview of how things work (including the php.ini setting to make it happen) and has a screenshot of the resulting output. You can check out the demo here or just grab the source and jump right in.

Frank Kromann applied some patches yesterday to the PECL sources of the uploadprogress extension to make it compile under Windows (almost the same as by SteveH provided in a comment of my post yesterday). Therefore, thanks to the pecl4win site, a compiled dll is now already available. Get it here (untested by me..)

He also mentions some documentation that was asked about concerning the package (and the patches), but notes that he "can't promise anything any time soon".

After some tweaking, code improvements and remote code execution vulnerability fixes, I finally put the uploadprogress extension into PECL.

Windows users might be out of luck for a while though, since Christian's not pursuing binaries for the package. However, the source is there, and anyone is more than welcome to try...

Showing a real progress bar when uploading large files is an often requested (and quite informative) feature, which is not easily doable with the way the upload handling works in PHP. There is a patch available for PHP 4.4 and 5.0, which made it nevertheless possible, but some php core files itself needed to be patched for that.

He notes, however, that a new sort of patch for the same thing has just been committed to the PHP_5_2 branch, making the previous patch a thing of the past. It's completely new and you can check out the code here or the svnweb here.