How to build a URL shortener with PHP?

If you've ever shared a link on your social media, you've probably noticed how long and illegible it is. Using a link shortener not only simplifies link sharing but also makes them easier to read. It is interesting to know that the length of a URL or the characters used in it affect the validity of that URL; You may share a secure, hassle-free link, but its length and illegibility make people skeptical and wonder if they can click it or if they can share it. On the other hand, a link that is short and readable will automatically be valid.

In this article, we will teach you how to make a URL shortener in PHP.

Requirements:

To understand this tutorial, you need to be familiar with the web development process and have a good knowledge of PHP and MySQL.

• Create a table in the database:

We will use the database to control and handle redirection based on shortened links. The following SQL code creates the short_urls table in the MySQL database. We will use this table to store URL information; This information will include LONG URL, SHORT CODE, HITS and record creation time.

CREATE TABLE `short_urls` (
 `id` int(11) NOT NULL AUTO_INCREMENT,
 `long_url` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
 `short_code` varchar(25) COLLATE utf8_unicode_ci NOT NULL,
 `hits` int(11) NOT NULL,
 `created` datetime NOT NULL,
 PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

• Shortener Library (Shortener.class.php):

The link shortening class allows you to create short URLs using programming methods, PHP and MySQL. This class uses the PDO Extension to work with the MySQL database, so a PDO object instance is required to set up the Shortener class.

Our static variables will be:

• chars: Characters allowed for short links (character groups are separated by |)
• table: Database table for storing URL information and short links.
• checkUrlExists: Set to TRUE to check if there is a long URL.
• codeLength: The length of the short URL characters.

The list of our functions will be as follows:

• construct: Sets the reference and timing of the PDO object.
• urlToShortCode: Validate URL and create short links.
• validateUrlFormat: To evaluate the URL format
• verifyUrlExists: Checks the presence or absence of links using cURL in PHP.
• urlExistsInDB: Checks if there is a long URL in the database. Returns the short link if present; otherwise returns the FALSE value.
• createShortCode: Create a shortcode for long URLs and insert long URLs and short links in the database.
• generateRandomString: Create a random string (shortcode) with the characters specified in the chars variable.
• insertUrlInDB: Enter the URL information into the database using PDO Extension and MySQL and return the row ID.
• shortCodeToUrl: Convert shortcode to long URL and enter the number of hits in the database.
• validateShortCode: Validates short links based on authorized characters.
• getUrlFromDB: Receives the link based on a short URL from the database.
• incrementCounter: Increases the number of URL hits in the database for a specific record.

<?php
/** 
 * Class to create short URLs and decode shortened URLs
 * 
 * @author www.maryam-hajireza.ir 
 * @copyright Copyright (c) 2021, www.maryam-hajireza.ir
 * @url https://www.maryam-hajireza.ir
 */ 
class Shortener
{
    protected static $chars = "abcdfghjkmnpqrstvwxyz|ABCDFGHJKLMNPQRSTVWXYZ|0123456789";
    protected static $table = "short_urls";
    protected static $checkUrlExists = false;
    protected static $codeLength = 7;

    protected $pdo;
    protected $timestamp;

    public function __construct(PDO $pdo){
        $this->pdo = $pdo;
        $this->timestamp = date("Y-m-d H:i:s");
    }

    public function urlToShortCode($url){
        if(empty($url)){
            throw new Exception("No URL was supplied.");
        }

        if($this->validateUrlFormat($url) == false){
            throw new Exception("URL does not have a valid format.");
        }

        if(self::$checkUrlExists){
            if (!$this->verifyUrlExists($url)){
                throw new Exception("URL does not appear to exist.");
            }
        }

        $shortCode = $this->urlExistsInDB($url);
        if($shortCode == false){
            $shortCode = $this->createShortCode($url);
        }

        return $shortCode;
    }

    protected function validateUrlFormat($url){
        return filter_var($url, FILTER_VALIDATE_URL, FILTER_FLAG_HOST_REQUIRED);
    }

    protected function verifyUrlExists($url){
        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL, $url);
        curl_setopt($ch, CURLOPT_NOBODY, true);
        curl_setopt($ch,  CURLOPT_RETURNTRANSFER, true);
        curl_exec($ch);
        $response = curl_getinfo($ch, CURLINFO_HTTP_CODE);
        curl_close($ch);

        return (!empty($response) && $response != 404);
    }

    protected function urlExistsInDB($url){
        $query = "SELECT short_code FROM ".self::$table." WHERE long_url = :long_url LIMIT 1";
        $stmt = $this->pdo->prepare($query);
        $params = array(
            "long_url" => $url
        );
        $stmt->execute($params);

        $result = $stmt->fetch();
        return (empty($result)) ? false : $result["short_code"];
    }

    protected function createShortCode($url){
        $shortCode = $this->generateRandomString(self::$codeLength);
        $id = $this->insertUrlInDB($url, $shortCode);
        return $shortCode;
    }
    
    protected function generateRandomString($length = 6){
        $sets = explode('|', self::$chars);
        $all = '';
        $randString = '';
        foreach($sets as $set){
            $randString .= $set[array_rand(str_split($set))];
            $all .= $set;
        }
        $all = str_split($all);
        for($i = 0; $i < $length - count($sets); $i++){
            $randString .= $all[array_rand($all)];
        }
        $randString = str_shuffle($randString);
        return $randString;
    }

    protected function insertUrlInDB($url, $code){
        $query = "INSERT INTO ".self::$table." (long_url, short_code, created) VALUES (:long_url, :short_code, :timestamp)";
        $stmnt = $this->pdo->prepare($query);
        $params = array(
            "long_url" => $url,
            "short_code" => $code,
            "timestamp" => $this->timestamp
        );
        $stmnt->execute($params);

        return $this->pdo->lastInsertId();
    }
    
    public function shortCodeToUrl($code, $increment = true){
        if(empty($code)) {
            throw new Exception("No short code was supplied.");
        }

        if($this->validateShortCode($code) == false){
            throw new Exception("Short code does not have a valid format.");
        }

        $urlRow = $this->getUrlFromDB($code);
        if(empty($urlRow)){
            throw new Exception("Short code does not appear to exist.");
        }

        if($increment == true){
            $this->incrementCounter($urlRow["id"]);
        }

        return $urlRow["long_url"];
    }

    protected function validateShortCode($code){
        $rawChars = str_replace('|', '', self::$chars);
        return preg_match("|[".$rawChars."]+|", $code);
    }

    protected function getUrlFromDB($code){
        $query = "SELECT id, long_url FROM ".self::$table." WHERE short_code = :short_code LIMIT 1";
        $stmt = $this->pdo->prepare($query);
        $params=array(
            "short_code" => $code
        );
        $stmt->execute($params);

        $result = $stmt->fetch();
        return (empty($result)) ? false : $result;
    }

    protected function incrementCounter($id){
        $query = "UPDATE ".self::$table." SET hits = hits + 1 WHERE id = :id";
        $stmt = $this->pdo->prepare($query);
        $params = array(
            "id" => $id
        );
        $stmt->execute($params);
    }
}

• Database configuration (dbConfig.php):

In the dbConfig.php file, the PDO is used to select and transfer to the database. The information you need to specify ARE:

dbHost: Database host
dbUsername: Database username
dbPassword: Database password
dbName: The name of the database

<?php
// Database configuration
$dbHost     = "localhost";
$dbUsername = "root";
$dbPassword = "root";
$dbName     = "codexworld";

// Create database connection
try{
    $db = new PDO("mysql:host=$dbHost;dbname=$dbName", $dbUsername, $dbPassword);
}catch(PDOException $e){
    echo "Connection failed: " . $e->getMessage();
}

• Create short URL with PHP

The following command will create a short link using the Shortener class.

// Include database configuration file
require_once 'dbConfig.php';

// Include URL Shortener library file
require_once 'Shortener.class.php';

// Initialize Shortener class and pass PDO object
$shortener = new Shortener($db);

// Long URL
$longURL = 'https://www.maryam-hajireza.ir/tutorials/php/';

// Prefix of the short URL 
$shortURL_Prefix = 'https://xyz.com/'; // with URL rewrite
$shortURL_Prefix = 'https://xyz.com/?c='; // without URL rewrite

try{
    // Get short code of the URL
    $shortCode = $shortener->urlToShortCode($longURL);
    
    // Create short URL
    $shortURL = $shortURL_Prefix.$shortCode;
    
    // Display short URL
    echo 'Short URL: '.$shortURL;
}catch(Exception $e){
    // Display error
    echo $e->getMessage();
}

• Redirect to long URL

The following code manages redirection from short URL to main URL.

// Include database configuration file
require_once 'dbConfig.php';

// Include URL Shortener library file
require_once 'Shortener.class.php';

// Initialize Shortener class and pass PDO object
$shortener = new Shortener($db);

// Retrieve short code from URL
$shortCode = $_GET["c"];

try{
    // Get URL by short code
    $url = $shortener->shortCodeToUrl($shortCode);
    
    // Redirect to the original URL
    header("Location: ".$url);
    exit;
}catch(Exception $e){
    // Display error
    echo $e->getMessage();
}

• Rewrite URL with HTACCESS

If you want to make the URL user-friendly, use HTACCESS with RewriteRule. With mod_rewrite, you can shorten the URL length and make it easier to share.

Create an .htaccess file and add the following code.

<IfModule mod_rewrite.c>
   RewriteEngine On
   RewriteCond %{REQUEST_FILENAME} !-f
   RewriteCond %{REQUEST_FILENAME} !-d
   RewriteRule ^([a-zA-Z0-9]+)/?$ redirect.php?c=$1 [L] 
</IfModule>

Conclusion:

This Shortener class helps you to easily shorten your URLs using PHP. You can use this library to create link shorteners.