September, 2009 browsing by month


Asynchronous PHP with wget

Wednesday, September 23rd, 2009

I have a site where there’s a cache of a bunch of tracks (music site) and there are instances when a user does something and I need to rebuild that cache. The rebuilding takes a good five or ten seconds and will only become slower as we get more tracks so having the user wait while I do that is no longer feasible. I have a script that does a periodic rebuild (every fifteen min) but I’ve found that users don’t understand that their changes were accepted when they don’t show up for several minutes. It has to rebuild on demand but asynchronously. That way you get their changes applied pretty quickly but don’t have to wait on it.

I tried googling for asynchronous php solutions but couldn’t get anything to actually work. Brent accepted this answer but I had no luck with that. It would make the call but it wouldn’t do it asynchronously. I always had to wait for the thing to finish.

Some people suggested using the command line to run php and make the call that way but I couldn’t do that because of some architectural crap. I came up with this beauty though:
exec('wget -O /dev/null -o /dev/null -qb --no-cache --post-data=foo=bar');
and it works perfectly. You can call a script on any server (not just your own like with php) and it runs in the background and discards the output quietly. Just one line and forget it.

Naturally, this only works on Linux servers with wget installed. Sorry windows folks

jQuery document.body is null error

Wednesday, September 23rd, 2009

I had a little “fun” with jQuery where it was giving me a “document.body is null” error…or sometimes it wouldn’t say anything but would just quietly fail. After some investigating, I made an interesting discovery about jQuery’s data() function.

I was chaining calls to data, like'foo', foo).data('bar', bar);

which generally works fine but apparently if foo is undefined, an error is thrown and the whole thing dies. If bar is undefined, it’s no problem, but something about trying to call data() with an undefined value breaks jQuery’s ability to make any further chained calls to that element.

The easiest solution I found is just dropping in a little
if (!foo) foo = null;'foo', foo).data('bar', bar);

And then everything works!

WP Post Thumbnail IE Error

Monday, September 14th, 2009

I just finished rebuilding and used WordPress for the whole thing which was a new experience for me. I hadn’t done any real work customizing before and it’s a really interesting design. The documentation isn’t quite what I’d like it to be but I was able to figure out everything eventually.

One particularly vexing issue was with the plug-in WP Post Thumbnail which gives you a ridiculously convenient way to add thumbnails to each post (Note that I intentionally linked to the older version because I like the interface a lot better). When you add/edit a post, you can upload an image right there and crop/scale it to different, configurable dimensions before adding it to the post. It was perfect for what I needed it for except the admin didn’t work in IE.

When IE tries to load a post edit page with WP Post Thumbnail enabled, it gives the very helpful:

Webpage error details
User Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; .NET CLR 1.1.4322)
Timestamp: Mon, 14 Sep 2009 23:23:31 UTC
Message: Invalid argument.
Line: 12
Char: 12949
Code: 0

If you track down character 12,949 on line 12, it’s jQuery code that I believe is several functions inside an attr call. However what the exact problem is at that point eludes me. It’s trying to set variable[zIndex] = null; and I fail to see an invalid argument in that.

Now IE8 actually has a pretty nice js debugger but apparently it can’t stack trace code that was dynamically added to the page using jQuery.load, which of course this was, so I couldn’t see what has actually making the attr call. All I could figure out to do was put alert() messages all over all the dynamically loaded files and I eventually tracked it the offending call to this line in plugins/wp-post-thumbnail/wppt_repository.php:

I soon discovered that any call to imgAreaSelect threw the same error.

Looking for the source to that function, I found it within the imgAreaSelect Library which came with WP Post Thumbnail. The version that came with WP Post Thumbnail is v0.5.1 but if you go the imgAreaSelect site, you can get v0.9.1 (as of this writing).

Download the new imgAreaSelect code, unzip it, drop the .min.js file in your plugins/wp-post-thumbnail/js folder, add the css of your choice to plugins/wp-post-thumbnail/css/wppt-admin.css (if you choose the animated one, copy the images into your css folder too), and lastly, update plugins/wp-post-thumbnail/wppt.php’s wppt_js() function to have the correct path to your new imgAreaSelect js file. Presto! WP Post Thumbnail will be fully functional in IE.

At least that fixed it for me 😛