Running out of memory always on the same line - php

Question

First of all, I am not looking for an answer saying "Check your PHP memory limit" or "You need to add more memory" or these kind of stuff ... I am on a dedicated machine, with 8GB of RAMS; 512MB of it is the memory limit. I always get an out of memory error on one single line :
To clarify: This part of the code belongs to Joomla! CMS.
function get($id, $group, $checkTime){
$data = false;
$path = $this->_getFilePath($id, $group);
$this->_setExpire($id, $group);
if (file_exists($path)) {
$data = file_get_contents($path);
if($data) {
// Remove the initial die() statement
$data = preg_replace('/^.*\n/', '', $data); // Out of memory here
}
}
return $data;
}
This is a part of Joomla's caching ... This function read the cache file and remove the first line which block direct access to the files and return the rest of the data.
As you can see the line uses a preg_replace to remove the first line in the cache file which is always :
<?php die("Access Denied"); ?>
My question is, it seems to me as a simple process (removing the first line from the file content) could it consume a lot of memory if the initial $data is huge? if so, what's the best way to work around that issue? I don't mind having the cache files without that die() line I can take of security and block direct access to the cache files.
Am I wrong?
UPDATE
As suggested by posts, regex seems to create more problems than solving them. I've tried:
echo memory_get_usage() . "\n";
after the regex then tried the same statement using substr(). The difference is very slight in memory usage. Almost nothing.
That's for your contributions, I am still trying to find out why this happen.

Answer 1

Use substr to avoid the memory hungry preg_replace() , like this:
$data = substr($data, strpos($data, '?>') + 3);
As a general advice don't use regular expressions if you can do the same task by using other string/array functions, regular expression functions are slower and consume more memory than the core string/array functions.
This is explicitly warned in PHP docs too, see some examples:
http://www.php.net/manual/en/function.preg-match.php#refsect1-function.preg-match-notes
http://www.php.net/manual/en/function.preg-split.php#refsect1-function.preg-split-notes

Answer 2

don't use a string function to replace something in a huge string. You can cycle through the lines of a file and just break after you have found what your looking for.
check the PHP docs here:
http://php.net/manual/en/function.fgets.php
basically what #cbuckley just said :p

Answer 3

If You just want to remove the first line of a file and return the rest, you should make use of file:
$lines = file($path);
array_shift($lines);
$data = implode("\n", $lines);

Answer 4

In stead of using file_get_contents() that gets the entire file at once, which can be too big to run regexps on, you should use fopen() in combination with fgets() (http://php.net/fgets). This function gets the file line by line.
You can then choose to do a regexp on a specific line. Or in your case just skip the entire line.
So in stead of:
$data = file_get_contents($path);
if($data) {
// Remove the initial die() statement
$data = preg_replace('/^.*\n/', '', $data); // Out of memory here
}
try this:
$fileHandler = fopen($path,'r');
$lineNumber = 0;
while (($line = fgets($fileHandler)) !== false) {
if($lineNumber++ != 0) { // Skip the initial die() statement
$data .= $line; // or maybe echo out $line directly so $data doesn't take up too much memory as well.
}
}

Answer 5

I suggest you use this in the file including the cached files:
define('INCLUDESALLOW', 1);
and in the file that will be included:
if( !defined('INCLUDESALLOW') ) die("Access Denied");
Then just use include instead of file_get_contents. This would run PHP code in the included though, not 100% sure if that is what you need.

Answer 6

There times that you will use more memory than the 8 MB php has allotted. If your unable to use less memory by making your code more efficient, you might have to increase your available memory. This can be done in two ways.
The limit can be set to a global default in php.ini:
memory_limit = 32M
Or you can override it in your script like this:
<?php
ini_set('memory_limit', '64M');
...
For more on PHP memory limit you can see This SO question or ini.memory-limit.