Twitter self-hosted image service/url shortener

index.php

<?
// Twitter self-hosted image service/url shortener by Ryan Petrich
// Installation:
// 1. Paste this script into the top of your HTTP root's index.php (rename index.html to index.php if it doesn't exist)
// 2. Add the following to your HTTP root's .htaccess file (create .htaccess if it doesn't exist):
//     ErrorDocument 404 /index.php
// 3. Create a "s" subfolder and give it 777 permissions
// 4. Add the following as the custom URL for URL shortening in Twitter for iPhone's settings:
//     http://yourdomain.com/?d=%@&p=password
// 5. Add the following as the custom URL for Image service:
//     http://yourdomain.com/?password

$password = 'password';

function genRandomString($length) {
    $characters = '0123456789abcdefghijklmnopqrstuvwxyz';
    $string = '';
    for ($p = 0; $p < $length; $p++) {
        $string .= $characters[mt_rand(0, strlen($characters))];
    }
    return $string;
}

function randomFileName() {
	$filename = genRandomString(4);
	while (file_exists("s/$filename.url") || file_exists("s/$filename.png") || file_exists("s/$filename.jpg"))
		$filename = genRandomString(5);
	return $filename;
}

if (($_GET['p'] == $password) && isset($_GET['d']) && ($_GET['d'] != '%@')) {
	// Shortening a URL
	$filename = randomFileName();
	$fh = fopen("s/$filename.url", 'w') or die("can't open file");
	fwrite($fh, $_GET['d']);
	fclose($fh);
	echo 'http://'.$_SERVER['SERVER_NAME'].'/'.$filename;
	exit();
}
$url = $_SERVER['REQUEST_URI'];
if ($url == "/?$password") {
	// Uploading media
	$filetype = $_FILES['media']['type'];
	if ($filetype == 'image/png')
		$filetype = '.png';
	else if ($filetype == 'image/jpeg')
		$filetype = '.jpg';
	else
		die('bad filetype');
	$filename = randomFileName();
	move_uploaded_file($_FILES['media']['tmp_name'], 's/'.$filename.$filetype);
	echo '<mediaurl>http://'.$_SERVER['SERVER_NAME'].'/'.$filename.'</mediaurl>';
	exit();
}

if (strpos($url, '.') == false) {
	$url = substr($url, 1);
	// Shortened URL
	if (file_exists("s/$url.url")) {
		$contents = file("s/$url.url");
		header('HTTP/1.1 301 Moved Permanently'); 
		header('Location: '.$contents[0]);
		exit();
	}
	// Uploaded media (PNG)
	if (file_exists("s/$url.png")) {
		header('Content-Type: image/png');
		header('Content-Length: ' . filesize("s/$url.png"));
		ob_clean();
		flush();
		readfile("s/$url.png");
		exit();
	}
	// Uploaded media (JPEG)
	if (file_exists("s/$url.jpg")) {
		header('Content-Type: image/jpeg');
		header('Content-Length: ' . filesize("s/$url.jpg"));
		ob_clean();
		flush();
		readfile("s/$url.jpg");
		exit();
	}
}
?>