PHP random URL names (short URL)

Question

After using sites like JSFiddle I noticed that they auto generate a random and unique URL made up of various upper and lower case characters.

We could benefit from this for our booking pages. How is it done?

Melantha

Answer 1

This is not random, there based of the ID of your database record.

How it works:

basically you have a string that is unique but it can be decrypted to represent a number, you should look at it as a short encryption / decryption.

You have a function that would take an unique ID and then it creates a Unique 'short string' from that id, and then you can reverse the process to get the unique id from the short string.

Here's a snipped I have found of a website:

function alphaID($in, $to_num = false, $pad_up = false, $passKey = null)
{
    $index = "abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    if ($passKey !== null)
    {
        /* Although this function's purpose is to just make the
        * ID short - and not so much secure,
        * with this patch by Simon Franz (http://blog.snaky.org/)
        * you can optionally supply a password to make it harder
        * to calculate the corresponding numeric ID */

        for ($n = 0; $n<strlen($index); $n++)
        {
            $i[] = substr( $index,$n ,1);
        }

        $passhash = hash('sha256',$passKey);

        $passhash = (strlen($passhash) < strlen($index)) ? hash('sha512',$passKey) : $passhash;

        for ($n=0; $n < strlen($index); $n++)
        {
            $p[] =  substr($passhash, $n ,1);
        }

        array_multisort($p,  SORT_DESC, $i);
        $index = implode($i);
    }

    $base  = strlen($index);

    if ($to_num)
    {
        // Digital number  <<--  alphabet letter code
        $in  = strrev($in);
        $out = 0;
        $len = strlen($in) - 1;

        for ($t = 0; $t <= $len; $t++)
        {
            $bcpow = bcpow($base, $len - $t);
            $out   = $out + strpos($index, substr($in, $t, 1)) * $bcpow;
        }

        if (is_numeric($pad_up))
        {
            $pad_up--;
            if ($pad_up > 0)
            {
                $out -= pow($base, $pad_up);
            }
        }
        $out = sprintf('%F', $out);
        $out = substr($out, 0, strpos($out, '.'));
    }
    else
    {
        // Digital number  -->>  alphabet letter code
        if (is_numeric($pad_up))
        {
            $pad_up--;
            if ($pad_up > 0)
            {
                $in += pow($base, $pad_up);
            }
        }

        $out = "";
        for ($t = floor(log($in, $base)); $t >= 0; $t--)
        {
            $bcp = bcpow($base, $t);
            $a   = floor($in / $bcp) % $base;
            $out = $out . substr($index, $a, 1);
            $in  = $in - ($a * $bcp);
        }
        $out = strrev($out); // reverse
    }
    return $out;
}

Example

alphaID(9007199254740989);   //-> PpQXn7COf
alphaID('PpQXn7COf', true);  //-> 9007199254740989

there's a link to the script here: https://github.com/kvz/deprecated/blob/kvzlib/php/functions/alphaID.inc.php

Galvanic

Answer 2

Use the uniqid() function if you just want a random id of a specified length or use the md5() hash of your long url if you need something repeatable. (output always the same for a given input). Creating a short URL service using PHP and MySQL gives a good rundown of how to put it all together.

Aluminiferous

Answer 3

It is very simple.

Your URL is something like:

www.example.com/in/here/RANDOMPART

You rewrite www.example.com/in/here/* to a script of your choice. In this script you can get the requested URI with the globals and you can split it and use the part after the last /. This is your RANDOMPART. yust check it against your Database or whatever.

To create such an URL you simply have to add something behind www.example.com/in/here/. You could generate a nice hopefully unique string with md5(uniqid(rand(), true)).

Do not forget to save this string in a Database or whatever.

I hope that helps.

Spirituous

Answer 4

Something along these lines:

<?php
  $url_length = rand(10,20); //generate a random number between 10 and 20 for the length   of the URL
  $url = array($url_length);
  for($i=0; $i < $url_length; $i++)
  {
     $char = 0;
     while($char < 65 OR $char > 122 OR ($char > 91 AND $char < 97))
     {
       $char = rand(65,122);
     }
     $url[] = chr($char);
  }
  print_r($url);
?>

Note this is partially psuedo code. This creates a URL with a random length (somewhere between 10 and 20), and populates each character with a random ASCII code that cooresponds to a letter in the alphabet. There are a few "junk" characters between the upper and lower case letters in the ASCII table, so this will reroll a random number until a valid ASCII number is generated.

This assumes you are storing this URL in a database. To ensure that this string is unique, you need to check to see if it exists yet in the database. If not, then add it and you're fine. If it exists, then redo the process again until you get a unique string.

Es

Answer 5

You could simply create an array of all potential characters then randomly pick out however many you want and return them as the URL "code"?

$arr = array('a','b','c','d');
$count = count($arr) - 1;
$str = $arr[rand(0, $coun)].$arr[rand(0, $coun)];

Hobo

But this could lead to duplicate strings (though not very likely). – Vacillatory

Does that matter? The only thing you'd need to do is check to make sure it is unique by some method (such as DB lookup, if stored that way). – Hobo