Simple Web Server file throttle sending via PHP. (Low bandwidth emulation)

.htaccess

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^(.+\.(?:jpg|jpeg|gif|png))$ /throttle.php?$1 [L]
</IfModule>

throttle.php

<?php
if (!empty($_SERVER['REDIRECT_QUERY_STRING']) AND $filepath = $_SERVER['REDIRECT_QUERY_STRING'] AND is_file($filepath))
{
    if ($mime = detect_mime($filepath))
    {
        header("Content-type: $mime");
        srand(time());
        $sleep = rand(0, 1);
        sleep($sleep);

        echo file_get_contents($filepath);
    }
    else
    {
        fallback();
    }
}
else
{
    fallback();
}

function fallback()
{
    header("Location: {$_SERVER['REDIRECT_QUERY_STRING']}");
    exit;
}

function detect_mime($filepath)
{
    if(function_exists('mime_content_type'))
    {
        return mime_content_type($filepath);
    }

    $filename = basename($filepath);
    $extension = array_pop(explode('.', $filename));

    switch($extension)
    {
            case "js":
                return "application/x-javascript";
            case "json":
                return "application/json";
            case "jpg":
            case "jpeg":
            case "jpe":
                return "image/jpg";
            case "png":
				return "image/png";
            case "gif":
				return "image/gif";
            case "css":
                return "text/css";
            case "xml":
                return "application/xml";
            case "doc":
            case "docx":
                return "application/msword";
            case "xls":
            case "xlt":
            case "xlm":
            case "xld":
            case "xla":
            case "xlc":
            case "xlw":
            case "xll":
                return "application/vnd.ms-excel";
            case "ppt":
            case "pps":
                return "application/vnd.ms-powerpoint";
            case "rtf":
                return "application/rtf";
            case "pdf":
                return "application/pdf";
            case "html":
            case "htm":
            case "php":
                return "text/html";
            case "txt":
                return "text/plain";
            case "mpeg":
            case "mpg":
            case "mpe":
                return "video/mpeg";
            case "mp3":
                return "audio/mpeg3";
            case "wav":
                return "audio/wav";
            case "aiff":
            case "aif":
                return "audio/aiff";
            case "avi":
                return "video/msvideo";
            case "wmv":
                return "video/x-ms-wmv";
            case "mov":
                return "video/quicktime";
            case "zip":
                return "application/zip";
            case "tar":
                return "application/x-tar";
            case "swf":
                return "application/x-shockwave-flash";
    }
}