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Creating a simple URL shortening service

Published: Andreas Wiebe, 03 February 2010 - 00:50

Environment:

PHP
Apache with mod_rewrite enabled
MySQL

Requirements:

Separate domain with a short name

Overview

In the last few years URL shortening services have been popping up everywhere. While there are several advantages to using these types of services there are also potential pitfalls:

The service closes
The service activates a “doorway page” forcing an additional click for users to get through but allowing advertising for the service
The service activates an IFRAME, effectively stealing “link-juice” (i.e. Digg.com)
The service is used in spam email causing spam filters to automatically block any email with the services domain

For more information on possible issues with URL shortening see our article on EndUserThoughts.com: http://www.enduserthoughts.com/archives/16

Depending on your needs you may want or need to setup your own simple URL shortening service, it’s easy and shouldn’t take longer than 30 minutes to create. We’re only going to cover the basics here, depending on your needs you may choose to add more functionality like statistics gathering for example.

For this service you will need a domain with a very short domain-name, preferably this should be something recognizable as connected to your primary domain. Unfortunately for us, eug.ca and eug.com were taken so we’re using our toolset domain, m0m.ca, to run our service. If you don’t already have one, take a look at the available top-level domains out there, there are several two-letter TLD’s available (http://en.wikipedia.org/wiki/List_of_Internet_top-level_domains).

For our service we’ll base the shortened URL tag (or key) on the unique id of the database entry as opposed to the URL itself, this way the tag will always be unique and as short as possible. To keep the tag even shorter, we’ll change the unique id to a different base (base 36) using php’s built-in function base_convert. Note that it’s possible to convert the id with base 62 but this makes the tags case-sensitive which we don’t recommend.

Warning:

The service we describe in this guide is stripped-down for simplicity and is not intended for running a large multi-user or mission-critical service.

Notes:

To keep things simple, this guide will not cover security and authentication to the service
It’s always better to avoid using a shortening service if at all possible as they obscure the destination of the URL and create more traffic to DNS servers. The only real uses we’ve encountered are for Twitter and mobile devices, everything else should use a normal URL.

The pieces

The Backend - For the URL forwarding there are 3 components we need to build:

1)The database to store URL’s and keys

2)An .htaccess file with mod-rewrite commands

3)An index.php file

The Frontend - For URL shortening there are 2 components:

1)new_url.php

2)url_store.php

Backend:

The database

You need to have a MySQL database setup, in our example the DB Is named ‘url_tool’.

For our service we need to store the following information:

1)ID as required Auto-incrementing integer

2)The full URL as required varchar

3)The shortened url tag as required varchar

4)The title of the document being redirected to as optional varchar

5)The posters IP address as required Integer

The SQL to create this table:

CREATE TABLE `url_tool`.`short` (

`id` int(10) unsigned NOT NULL AUTO_INCREMENT,

`url_full` varchar(2083) NOT NULL,

`url_key` varchar(10) NOT NULL,

`title` varchar(100) DEFAULT NULL,

`posterip` int(10) unsigned NOT NULL,

PRIMARY KEY (`id`),

KEY `urlkey` (`url_key`)

) ENGINE=InnoDB AUTO_INCREMENT=0;

The .htaccess file

We want our URL’s to be as short as possible, that means we need to eliminate URL variables. For example, we want our URL’s to look like this “example.com/1234” instead of “example.com/?id=1234”. To accomplish this, we’re going to use the mod_rewrite module of Apache.

Create a file in your root directory called .htaccess
Put the following text into your .htaccess file:

Options +FollowSymLinks

RewriteEngine On

RewriteRule ^([0-9A-Za-z]+)/?$ index.php?key=$1 [L]

The index.php file

The index.php file will process any request made to your shortening service and redirect the user to the proper URL, if the page is called without a shortened url tag we’ll redirect to the new URL form

Create a file in your root directory called index.php
Put the following text into your index.php file:

<?php

if (isset($_GET['key']))

{

$DB['host'] = ' '; //Your DB Host

$DB['user'] = ' '; //Your DB Username

$DB['pass'] = ' '; //Your DB Password

$DB['database'] = ' '; //Your DB name

if (!@mysql_connect($DB['host'],$DB['user'],$DB['pass']))

    die("<h3>Critical Error: Could not connect to DB</h3>");

if (!@mysql_select_db($DB['database']))

    die("<h3>Critical Error: Could not select DB</h3>");

    $mykey=mysql_real_escape_string($_GET['key']);

$query="SELECT url_full FROM shrunk WHERE url_key='$mykey'";

    $result=mysql_query($query);

    if ($result === false)

    {

      header('Location: error.php');

    }

    elseif(mysql_num_rows($result)>0)

    {

      $thekey=mysql_fetch_assoc($result);

      $fullurl=$thekey['url_full'];

      header('Location: '.$fullurl);

    }

    else

    {

      header('Location: error.php');

    }

}

else

{

header('Location: new_url.php');

}

?>

The Frontend:

The frontend is where you (or other users) enter a URL to be shortened, it consists of a simple form and a separate file to process data entered on the form and insert it into the database we created earlier.

new_url.php

The new_url.php file contains the form where you will enter the URL to be shortened

Create a file new_url.php in your root directory
Put the following text in your new_url.php file:

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

<head>

    <meta content="text/html; charset=ISO-8859-1" http-equiv="content-type">

    <title>Shorten URL</title>

</head>

<body>

    <form method="post" action="url_store.php" name="createurl">

      <fieldset>

      URL to shorten: <input name="url" value="http://" size="80">

      <br>

      Title (optional):<input size="80">

      <br>

      <input type="submit">

      </fieldset>

    </form>

</body>

</html>

url_store.php

The url_store.php file stores the data and displays the shortened URL to the user

Create a file url_store.php in your root directory
Put the following text in your url_store.php file:

<?php

/**

*--url_store.php

*- Receives: URL & Description (title)

*- Processes

*--- Get current pk value

*--- Short URL Key = Convert base of (pk value+1)

*--- Insert DB: short url key, description, user IP address

*- Displays: serviceurl/+shortkey

*/

if(isset($_POST["url"]) && $_POST["url"]!='http://')

{

$DB['host'] = ' '; //Your DB Host

$DB['user'] = ' '; //Your DB Username

$DB['pass'] = ' '; //Your DB Password

$DB['database'] = ' '; //Your DB name

if (!@mysql_connect($DB['host'],$DB['user'],$DB['pass']))

    die("<h3>Critical Error: Could not connect to DB</h3>");

if (!@mysql_select_db($DB['database']))

    die("<h3>Critical Error: Could not select DB</h3>");

$userIP=getenv("REMOTE_ADDR");

$longurl= mysql_real_escape_string($_POST["url"]);

isset($_POST["urlTitle"])==TRUE ? $title= mysql_real_escape_string($_POST["urlTitle"]) : $TITLE="";

    //-- Double-check that the url has not already been shortened, if it has return the original key and exit

    //--- Potential improvement: check if the passed title is different, if it is update the DB

    $query = "SELECT url_key FROM shrunk WHERE url_full='$longurl'";

    $result=mysql_query($query);

    $row = mysql_fetch_array($result);

    if(mysql_num_rows(mysql_query($query)))

      $shorten=$row['url_key']; //-- URL has already been shortened

    else

    {

    //-- Get the last used id value from the DB

    //--- Note: There are other ways to accomplish this

      $query = "SELECT id FROM shrunk ORDER BY id DESC LIMIT 1";

      $result=mysql_query($query);

      $row = mysql_fetch_array($result);

      $last_id=$row['id'];

      $last_id++; //increment ID by one

      $shorten=base_convert($last_id,10,36); //The juice, converts the base from 10 (integer) to 36 (1-9,a-z)

    //-- Double-check that key does not already exist, fail with prejudice if it does

      $query = "SELECT id FROM shrunk WHERE url_key = '$shorten'";

      if(mysql_num_rows(mysql_query($query)))

        die ("<h1>FATAL ERROR</h1><p>The shortkey already exists</p>");

    //-- Insert the new key into the DB

      $insert="INSERT INTO shrunk (url_full,url_key,title,posterip) VALUES('$longurl','$shorten','$title',INET_ATON('$userIP'))";

      $result=mysql_query($insert) or die(mysql_error());

    }

print "Your short-url is: <a href=\"$shorten\">http://m0m.ca/$shorten</a>";

}

else //If someone tries to access this script without at least the URL post variable set, send them to the form...

header("Location: new_url.php");

?>

That’s all there is to it.

More Information

Don’t want to build your own, want more features out of the box? Take a look at the phurl project http://code.google.com/p/phurl/
Enduserguides.com uses a modified version of this service and has it integrated directly into the CMS (MODx) as a plugin. If you would like to know how we did that please let us know and we’ll put a guide together.
There are several public URL shortening services available including:
- tinyurl.com
- bit.ly
- is.gd
- tr.im