Resumable PHP Upload

<?php
    set_time_limit(0);
    header('Content-Type: text/html; charset=utf-8');
    header('Accept-Ranges: bytes');

    $file_name = base64_decode( strtr($_POST["file_name"], '-_,', '+/=') );
    if ( $file_name !== "" )
    {
        $file_handle      = fopen("/full/path/$file_name", "a+");
        $php_input_handle = fopen("php://input", "r");

        while ( $data_chunk = fread($php_input_handle, 4096) )
        {
            fwrite($file_handle, $data_chunk, strlen($data_chunk));
        }

        fclose($file_handle);
        fclose($php_input_handle);
    }
?>