15 Feb 2012

So I recently had to generate a bunch of files with contents from a database. Since we’re already using Symfony2 and Doctrine I opted for implementing this in PHP as a Symfony Command, instead of using another language.

I wrote PHP templates for the files and called them from my Command like this and wrote the return value to a file.

function renderTemplate( $template, $parameter )
{
 ob_start();
 extract($parameter);
 include $template;
 return ob_get_clean();
}

Files started to get big real fast and I soon encountered the following:

zend__mm_buffer corruption

Well I could’ve changed my buffer size in the php.ini locally, but our admin would’ve never allowed it on the production servers. So that was no option.

I checked the manual to see if ob_start allowed for a callback and indeed it did. Sadly the callback is only called on every flush of the cache. The only way I know of flushing the cache are the ob_get_clean and similar functions, which activate after everything is done :(. So that wouldn’t work.

The manual mentioned more parameters for the ob_start, so I checked them. It took me a bit of looking around and I reread the manual a few times before I finally found the text explaining the chunk size. They couldnt’ve hidden the darn thing any better.

Anyway my code then looked like this

function renderTemplateToFile( $template, $parameter )
{
	ob_start('mycallback',2);
	extract($parameter);
	include $template;
	ob_get_clean();
}

function mycallback($text)
{
	file_put_contents('file.out', $text, FILE_APPEND);
}

This didn’t work. It took me a bit of figuring out, but there seem to be two problems here. - The Callback should always return a string - if you don’t asign a variable to the output of ob_get_clean the callback won’t get fired. At least not on all the time on all systems. Seems I had a typo in one of my statements, which caused this unusual behavior

The result of this was the following class, which of course can still be further improved:

class TemplateToFileRenderer
{
	protected $_params = array();
	protected $_filename = null;
	public function setParameter( $params )
	{
		$this->_params = $params;
		return $this;
	}
	public function setFilename( $filename )
	{
		$this->_filename = $filename;
		return $this;
	}
	public function render( $template )
	{
		$this->resetFile();
		ob_start( array($this, 'writeBuffer'), 2 );
		extract($this->_params);
		include_once($template);
		ob_get_clean();
	}
	private function resetFile()
	{
		@unlink($this->_filename);
		touch($this->_filename);
	}
	public function writeBuffer( $text )
	{
		file_put_contents($this->_filename, $text, FILE_APPEND);
		return '';
	}
}