PHP's file_get_contents() sometimes returns zero bytes / false

Question

We build a PHP script to cache images on the hard drive (ext4) of a server (Debian Wheezy with SELinux, Apache, PHP 5.3.26).

Something like the following code is used:

$data = "...";
$file = "cached_foo_1234.jpg"; 
if (!is_file($file)) file_put_contents($file, $data);

Later in the script, the same file is opened for reading:

$content = file_get_contents($file);

Despite the right data on the hard drive, sometimes $content is empty turing the time the file is written to the file system. The function filesize() shows the same behavior.

There are no errors in any log files (audit, php, etc). Placing clearstatcache() on top of file_get_contents() or locking the file with LOCK_EX in file_put_contents() does not help. The script is accessed a lot in parallel with the same file name. Apache returns existing cached images as well directly without PHP.

I guess file locking should avoid empty returns while the file is written.

Why do we get zero bytes when we try to read the file from the file system?

Answer 1

Came across this problem and found that it is caused if a file name contains a disallowed character and becomes invalid.

To remove invalid filename characters use:

$bad = array_merge(
    array_map('chr', range(0,31)),
    array("<", ">", ":", '"', "/", "\\", "|", "?", "*"));
$result = str_replace($bad, "", $filename);

Filename practice

Answer 2

Use curl, and check for ignoring to verify for SSL: curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false);