file_exists and paths that include relative paths ("/../") - php

Question

When I use file_get_contents on a path like /a/path/to/a/../file.php, it gets the content just fine. If I call file_exists first (or is_file or realpath), the return values indicate that the file does not exist. What seems to be the issue?
Edit: Here is some additional information condensed from comments to answers:
I am running Mac OS X 10.9 with php 5.5.6, so safe mode should not be an issue (it was removed in version 5.4)
I tried clearing the file cash by calling clearstatcache(true, $dir1)
The file in question is 362 bytes in size, but I reproduced this issue with several different files in a medley of locations.
open_basedir is commented out in the php.ini
The file is local (the first file I tried was in the same directory as the script)
The issue exists in the command line (phpUnit) and in the browser.
The permissions on the file in questions are -rwxrwxrwx (I sudo-chmod-777ed the file)
This is a code snippet that creates the behavior:
$dir1 = '/a/path/to/a/../file.php';
$dir2 = '/a/path/to/file.php';
echo "File content dir1:\n";
echo file_get_contents($dir1);
echo "\ndir1 exists: ".(int)file_exists($dir1);
echo "\n\nFile content dir2:\n";
echo file_get_contents($dir2);
echo "\ndir2 exists: ".(int)file_exists($dir2);
the output is:
File content dir1:
The actual content of the file. I promise!
dir1 exists: 0
File content dir2:
The actual content of the file. I promise!
dir2 exists: 1

Answer 1

It sounds like you have safe mode turned on and are attempting to access a file that PHP would consider unsafe when running in safe mode. From the manual:
Warning
This function returns FALSE for files inaccessible due to safe mode restrictions. However these files still can be included if they are located in safe_mode_include_dir.
EDIT: You can also reproduce this behavior if /a/path/to/a/ is not a real path. For example:
<?php
$dir1 = '/realDir/realDir2/filetoinclude.php';
echo "File content dir1:\n";
echo file_get_contents($dir1); // outputs file contents
echo "\ndir1 exists: ".(int)file_exists($dir1); // outputs 1
$dir2 = '/realDir/realDir2/realDir3/../filetoinclude.php';
echo "\n\nFile content dir2:\n";
echo file_get_contents($dir2); // outputs file contents
echo "\ndir2 exists: ".(int)file_exists($dir2); // outputs 1
$dir3 = '/realDir/realDir2/NotARealDirectory/../filetoinclude.php';
echo "\n\nFile content dir3:\n";
echo file_get_contents($dir3); // outputs file contents
echo "\ndir3 exists: ".(int)file_exists($dir3); // outputs 0
This is because file_exists needs to traverse the entire path, literally, so it looks for the missing directory and fails. I'm not sure exactly what file_get_contents does that is different, and I can't find much on Google, but it clearly does some parsing of the path that is different from what file_exists does.

Answer 2

I am providing the workaround that I developed with a regex, if others have this same issue. I hate to be using this hack, and I still don't understand why I am having this issue, but hopefully someone will come up with an actual solution.
Before calling file_exists I now call this function:
function resolve($path) {
$regex = "/(.?)(\/[^\/]*\/\.\.)(.*)/";
$result = preg_replace($regex, "$1$3", $path);
if ($result != $path) {
$result = resolve($result);
}
return $result;
}