One of the big problems I’ve run into as a WordPress plugin developer is the diversity of PHP installations. Simply stating you only support PHP5 and greater is insufficient to ensure compatibility. Things you may take for granted in your development environment may be missing or worse, partially functional. I’ve decided to document a few of the bigger “gotchas” I’ve run into so future WordPress hackers will have a starting point for investigating problems.

Minimum PHP Version

One easy way to reduce compatibility confusion is specifying a minimum version of PHP for your WordPress plugin or widget. To do so you can use PHP’s version_compare function:

if(version_compare(PHP_VERSION, '5.0.0','<')) {
	die(sprintf('You are currently running PHP version %s and you must have at least PHP 5.0.x', PHP_VERSION));
}

Take a look at the version_compare documentation for more information.

PHP Modules

The biggest single thing to remember is that any module for PHP is optional. If you want to require something like curl, that’s great, but be aware that some non-trivial percentage of your potential users may not have it. Still want to use that module? Test for its presence during the instantiation of your plugin and die if it’s not present. This will prevent users from being able to successfully install your “broken” product if they don’t have the proper requirements.

Sometimes you’ll find yourself using functions you think are core to PHP like “mime_content_type”. This is not the case. In fact, I have frequently run into PHP installations that have no MIME detection facilities at all. Consider writing a fallback for suffix detection¹ in addition to coding for mime_content_type and the finfo_* methods.

Safe Mode and Related Problems

Another common issue is safe_mode and open_basedir. These flags enforce certain security restrictions (must have the same group as PHP when writing to a directory, can’t open files beneath the basedir, et cetera). However, they also impact some modules. For instance, using curl you can’t use CURLOPT_FOLLOWLOCATION. This will trigger the error “CURLOPT_FOLLOWLOCATION cannot be activated when in safe_mode or an open_basedir is set”.

Network Communication

I’ve already talked a bit about the curl module, but you may also be tempted to use file_get_contents() assuming allow_url_fopen is enabled. This is very frequently untrue in shared hosting environments. Luckily, you don’t need to rely on curl or allow_url_fopen or write your own fsockopen() wrapper class. Instead, WordPress has integrated Snoopy into the core. Invoking it to fetch just the contents of a URL could not be easier!

require_once( ABSPATH . 'wp-includes/class-snoopy.php');
$snoopy = new Snoopy();
$result = $snoopy->fetch($url);
if($result) {
	$response = $snoopy->results;
}

Just hit up Google for the class docs to learn everything Snoopy can do for you.

There are many more where these came from, so drop your problems and solutions in the comments!