How to Detect When File Uploads Exceed PHP\'s `post_max_size` Limit?

Handling File Uploads Exceeding PHP's post_max_size

When handling file uploads with PHP, exceeding the post_max_size limit can pose a challenge. Unlike upload_max_filesize, which returns a file size of 0 for oversized files, post_max_size may cause your script to fail silently without any error message.

How to Detect File Size Limit Errors

1. Check for Empty Superglobals:

According to the PHP documentation, if the post data exceeds post_max_size, the $_POST and $_FILES superglobals will be empty. You can detect this by passing a query parameter to the form that will only be set when $_POST is non-empty.

if (isset($_GET['processed'])) {
    // Perform file upload processing
} else {
    // Display blank form
}

2. Compare with $_SERVER['CONTENT_LENGTH']:

Another approach is to compare the CONTENT_LENGTH header, which includes not only the file data but also multipart sequences, with the post_max_size setting.

if ($_SERVER['CONTENT_LENGTH'] > ini_get('post_max_size')) {
    // Error handling for oversized file
}

Note: These methods allow you to detect oversized files without PHP generating an error. However, it's important to adjust these settings in your php.ini file to prevent potential security issues or performance degradation due to large files.

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