Simple, PHP-based bookmark system so you can save internet pages. Uses HTTP Digest for Auth and PDO-SQLite extension (built-in).

bookmarked.php

<?php

// Place the DB files outside of the public web directory so people don't download it!
define('DB', 'links.sq3');

// Number of seconds a user must wait to post another link (false to disable)
define('WAIT', false);

// Should we enforce IP checking? (false to disable)
define('IP_CHECK', false);

// Auth password (false to disable)
define('PASSWORD', 'mybookmarks');

/**
 * Map paths to callbacks objects/closures
 *
 * @see https://gist.github.com/Xeoncross/5357205
 * @param string $path
 * @param mixed $closure
 * @return mixed
 */
function route($path, $closure = null)
{
	static $routes = array();
 
	if($closure) return $routes[$path] = $closure;
 
	foreach($routes as $route => $closure) {
		if(preg_match("~^$route$~", $path, $match)) {
			return call_user_func_array($closure, $match);
		}
	}
}

/**
 * HTTP Digest Auth is a lot better than plain HTTP Auth since
 * the password is not transfered in the clear
 */
function hmac_http_auth($password, $realm = "Simple Bookmark")
{
	if( ! empty($_SERVER['PHP_AUTH_DIGEST']))
	{
		// Decode the data the client gave us
		$default = array('nounce', 'nc', 'cnounce', 'qop', 'username', 'uri', 'response');
		preg_match_all('~(\w+)="?([^",]+)"?~', $_SERVER['PHP_AUTH_DIGEST'], $matches);
		$data = array_combine($matches[1] + $default, $matches[2]);
 
		// Generate the valid response
		$A1 = md5($data['username'] . ':' . $realm . ':' . $password);
		$A2 = md5(getenv('REQUEST_METHOD').':'.$data['uri']);
		$valid_response = md5($A1.':'.$data['nonce'].':'.$data['nc'].':'.$data['cnonce'].':'.$data['qop'].':'.$A2);
 
		// Compare with what was sent
		if($data['response'] === $valid_response)
		{
			return $data['username'];
		}
	}
 
	// Failed, or haven't been prompted yet
	header('HTTP/1.1 401 Unauthorized');
	header('WWW-Authenticate: Digest realm="' . $realm.
		'",qop="auth",nonce="' . uniqid() . '",opaque="' . md5($realm) . '"');
	exit();
}


function db($args = array(PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION))
{
	static $db;
	$db = $db ?: (new PDO('sqlite:' . DB, 0, 0, $args));
	return $db;
}

function query($sql, $params = NULL)
{
	$s = db()->prepare($sql);
	$s->execute(array_values((array) $params));
	return $s;
}

function insert($table, $data)
{
	query("INSERT INTO $table(" . join(',', array_keys($data)) . ')VALUES('
		. str_repeat('?,', count($data)-1). '?)', $data);
	return db()->lastInsertId();
}

function update($table, $data, $value)
{
	return query("UPDATE $table SET ". join('`=?,`', array_keys($data))
		. "=?WHERE i=?", $data + array($value))->rowCount();
}

function delete($table, $field, $value)
{
	return query("DELETE FROM $table WHERE $field = ?", $value)->rowCount();
}

function filter($string)
{
	return htmlspecialchars(trim(@iconv('UTF-8', 'UTF-8//TRANSLIT//IGNORE', $string)));
}

function lastLinkByIP($ip)
{
	return query('SELECT created FROM links WHERE ip = ?', array($ip))->fetchColumn();
}

/* @todo
function limitPerDay($ip, $start, $end)
{
	return query('SELECT count(created) FROM links WHERE ip = ? AND created BETWEEN ? AND ?', array($ip, $start, $end))->fetchColumn();
}
*/

function getLinkID($url)
{
	return query('SELECT id FROM links WHERE url = ?', array($url))->fetchColumn();
}

function getLink($id)
{
	return query('SELECT id,title,url,host FROM links WHERE id = ?', array($id))->fetch();
}

function getRecentLinks($limit = 20, $offset = 0)
{
	return query('SELECT id,title,description,url,host FROM links ORDER BY created DESC LIMIT ' . $limit);
}

function getHTMLMeta($html)
{
	libxml_use_internal_errors(true);
	$doc = new DOMDocument();
	$doc->loadHTML($html);
	$xpath = new DOMXPath($doc);
	return array(
		@$xpath->query('//head/title')->item(0)->nodeValue,
		@$xpath->query('/html/head/meta[@name="description"]/@content')->item(0)->value
	);
}

function getURL($url)
{
	// First try to use cURL
	if(function_exists('curl_init')) {
		$ch = curl_init($url);
		curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
		curl_setopt($ch, CURLOPT_USERAGENT, 'Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.13) Gecko/20080311 Firefox/2.0.0.13');
		$content = curl_exec($ch);
		curl_close($ch);
		return $content;
	}

	// file_get_contents will follow redirects as of 5.3.2 http://php.net/manual/en/context.http.php
	return file_get_contents($url);
}

/*
 * Start of Application Logic
 */

// Create database if it does not exist
if( ! is_file(DB)) {

	query('CREATE TABLE "links" (
		id INTEGER PRIMARY KEY,
		url TEXT,
		host TEXT,
		user TEXT,
		title TEXT,
		description TEXT,
		html, TEXT,
		ip TEXT,
		created INTEGER
	)');
}

header('Content-Type: text/html; charset="UTF-8"');

$user = null;

// If we require passwords
if(PASSWORD) {
	$user = hmac_http_auth(PASSWORD);
}

define('USER', $user);

/*
 * Page routes
 */

// Home page
route('/', function($path)
{
	if(isset($_GET['url'])) {
		
		$url = substr($_GET['url'], 0, 200);

		if( ! filter_var($url, FILTER_VALIDATE_URL)) {
			//dump($url, $path);
			die('Invalid ?url=... passed: ' . $url);
		}

		if( ! ($host = parse_url($_GET['url'], PHP_URL_HOST))) {
			die('Invalid ?url=... passed: ' . $url);
		}

		// Does this URL already exist? Re-use the ID
		$id = getLinkID($url);

		if( ! $id) {

			$ip = getenv('REMOTE_ADDR');

			// If we have rate-limiting on
			if(WAIT) {
				$ts = (int) lastLinkByIP($ip);

				if($ts AND $ts < (time() - WAIT)) {
					die('You can only post one link every ' . WAIT . ' seconds');
				}
			}

			// Anti-spam bot check
			if(IP_CHECK AND $ip != '127.0.0.1') {
				if(checkdnsrr(join('.',array_reverse(explode('.',$ip))).".opm.tornevall.org","A")) {
					die('Your IP is blacklisted as a bot');
				}
			}
		
			// If we can't load the page, then the server must be down
			if( ! ($html = getURL($url))) {
				die('Unable to get ?url=... passed: ' . $url);
			}

			list($title, $description) = getHTMLMeta($html);
			
			$id = insert('links', array(
				'ip' => $ip,
				'url' => $url,
				'host' => $host,
				'user' => USER,
				'title' => filter($title),
				'description' => filter($description),
				'html' => filter($html),
				'created' => time()
			));

		}

		// 307 Temporary Redirect
		$slug = base_convert($id, 10, 32);
		header("Location: /$slug", 0, 307);
		exit($slug);
	}

	?>
	<!doctype html>
	<html>
		<head>
			<meta charset="utf-8"/>
			<title>Simple URL Shortener</title>
			<style type="text/css">
				body { font: 1em/1.4em serif, georgia; }
				a { text-decoration: none; }
				a:hover { text-decoration: underline; }
				h1 { font-weight: normal;}
				div { margin: 1em auto; max-width: 700px;}
				p { padding: 0; margin: 0;}
				li { padding-bottom: 1em;}
			</style>
		</head>
		<body lang="en">
			<div>
				<h1>Simple URL shortener</h1>
				<p>
				<a href="javascript:location.href='http://<?php print getenv('HTTP_HOST'); ?>/?url='+encodeURIComponent(location.href)+'&title='+encodeURIComponent(document.title);">
					Bookmarklet (drag to your browser)
				</a>
				</p>
				<p>Recently people saved:</p>
				<ul>
				<?php
				foreach(getRecentLinks(80) as $link) {
					$slug = base_convert($link['id'], 10, 32);
					print '<li><span><a href="' . $link['url'] . '" rel="nofollow">' . $link['title'] . "</a>";
					print ' (<a href="/' . $slug . '+">' . $slug . "</a>)</span>\n";
					print '<p>' . $link['description'] . "</p></li>\n";
				} ?>
				</ul>
			</div>
		</body>
	</html>
	<?php
});

// A page link
route('/(\w+)(\+?)', function($path, $slug, $info = false)
{
	if($id = base_convert($slug, 32, 10)) {

		if($link = getLink($id)) {

			// Show extra info?
			if($info) { ?>

				<script>
					link_refresh=window.setTimeout(function(){window.location.href='<?php print $link['url']; ?>'},4000);
				</script>
				<noscript>
					<meta http-equiv="refresh" content="4; url=<?php print $link['url']; ?>" />
				</noscript>
				Redirecting you to... <a href="<?php print $link['url']; ?>"><?php print $link['title']; ?></a>
				<br><br>
				(<i>You can check Google to see if there is a problem with 
				<a href="http://www.google.com/safebrowsing/diagnostic?site=<?php print $link['url']; ?>">
					<?php print $link['url']; ?>
				</a></i>)

				<?php /*
				<br>
				<pre>
					<?php print $link['html']; ?>
				</pre>
				*/
				?>

			<?php } else {

				// 301 Moved Permanently
				header('Location: ' . $link['url'], 0, 301);
				var_dump($link);

			}

			exit();
		}
	}

	print 'Unknown Link ID';
});


// Catch all fun
route('.+', function($path)
{
	header("HTTP/1.0 404 Not Found");
	header('Location: /', 0, 301);
	exit();
});

route(parse_url(getenv('REQUEST_URI'), PHP_URL_PATH));