Sunday, 29 May 2011

Writing a basic php5 extension

I wanted to put formatter into a php extension because the CorCodeDemo currently has to write the CorCode and CorTex returned by the server to temporary files because formatter is currently a C commandline tool, and the CorTex and CorCode responses are too long to be commandline arguments. Also making formatter directly accessible from within php will effectively make it a replacement for XSLT, which is my intention.

The trouble with "hello world" as a php extension

I followed the instructions at but there were several problems. Documenting them might help others.

The first gotcha I discovered was that you're supposed to build php from the latest sources and install that on your system. This is actually quite dangerous on a Linux system because doing so invalidates the version installed by the package manager. The default deb package on Ubuntu puts files here, there and everywhere, and making the source code build put everything in exactly the same places is rather difficult and would destroy the package manager information about php. On the other hand, putting it elsewhere gives you two versions and the actual one invoked depends on the order directories are searched. The main problem this leads to is that building an extension in any version other than the one it is run in will prevent the extension from loading. My original php version was 5.3.2, which is what my server is still using. The latest version is currently 5.3.6, which became my commandline version. I didn't want to delete the old version because I had spent some effort installing and configuring it with xdebug, mysql and xslt.

The second gotcha was that the commandline php.ini file is not the same as the one used by the web server. On my system the apache2 one is in /etc/php5/apache2 and the commandline one is in /etc/php5/cli. You really must check the following:

  1. that the extension_dir used during execution is the one you put your extension in
  2. that the php.ini file that loads your extension is the one actually being used by php on the commandline (or server)

You can check the php.ini file by invoking on the commandline:

php -i | grep php.ini

And the extension_dir similarly:

php -i | grep extension_dir

Like me you'll probably be surprised by what it says. But match them up, and match the compile and the execution versions and it will work. Remember though, that the server will use a different php.ini file, and a different extension_dir. The best way around this dilemma is to download the same version of the source as is currently installed on your system, and build with that.

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