Robin Knight Robin Knight - 5 months ago 36
PHP Question

PHP random URL names (short URL)

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?

Answer

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

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