Introduction

Here is a set of functions to shorten GUIDs in C# and PHP.

Background

GUIDs are a very useful tool for your web and application developers, but a little bit verbose.

The small function below lets you shave 30% off the guid string size while keeping the entire data.

This is not rocket science, I use the standard: Base64 with URL and Filename Safe Alphabet (RFC 4648 'base64url' encoding) without the end padding.

How does it work.

A normal guid uses the characters '0' to '9', 'A' to 'F'. This is a range of 16 different characters. It also have generally 4 dashes that contain no data.

Fortunately, we can use more characters.

This algorithm uses the characters '0' to '9', 'a' to 'z', 'A' to 'Z' and also '-' et '_'. This is a range of 64 characters.

Using a range of 64 different characters, to store 128 bits we only need a string of length 22.

Therefore a shortGuid is 22 characters long

Using the Code

The ToShortString method produces a short string like this one: U1ZBOzMa-0eV_4gFv965cQ

String shortString = someGuid.ToShortString();

Then the ParseShortGuid:

Guid parsedGuid =  ParseShortGuid("U1ZBOzMa-0eV_4gFv965cQ"); 

The Main C# Functions

private static string ToShortGuid(this Guid newGuid)
{
    string modifiedBase64 = Convert.ToBase64String(newGuid.ToByteArray())
        .Replace('+', '-').Replace('/', '_') // avoid invalid URL characters
        .Substring(0, 22);
    return modifiedBase64;
}

private static Guid ParseShortGuid(string shortGuid)
{
    string base64 = shortGuid.Replace('-', '+').Replace('_', '/') + "==";
    Byte[] bytes = Convert.FromBase64String(base64);
    return new Guid(bytes);
} 

The Main PHP Functions

These are the equivalent functions in PHP.

function ParseShortGuid($a)
{
   $a=str_replace('_','/',str_replace('-','+',$a))."==";
   $a=base64_decode($a);
   if ($a==false || strlen($a)<16) return NULL;
   $a= bin2hex($a);
   $a = substr($a,6,2).substr($a,4,2).substr($a,2,2).substr($a,0,2)
      .'-'.substr($a,10,2).substr($a,8,2)
      .'-'.substr($a,14,2).substr($a,12,2)
      .'-'.substr($a,16,4)
      .'-'.substr($a,20,12);
   return $a;
}    

ToShortGuid uses the hex2bin function if you have a recent PHP but will fallback if it is not available.

function ToShortGuid($a)
{
   $a=str_replace('-','',str_replace('{','',str_replace('}','',$a)));
   $a = substr($a,6,2).substr($a,4,2).substr($a,2,2).substr($a,0,2)
     .substr($a,10,2).substr($a,8,2)
     .substr($a,14,2).substr($a,12,2)
     .substr($a,16,4)
     .substr($a,20,12);
   if(function_exists('hex2bin')) $a= hex2bin($a);
   else
   {
      $bin = '';
      for ($i = 0; $i < strlen($a); $i += 2) {
        $bin .= chr(hexdec($a{$i}.$a{($i + 1)}));
      }
      $a = $bin;
   }
   $a=base64_encode($a);
   $a=str_replace('/','_',str_replace('+','-',$a));
   $a=substr($a,0,22);
   return $a;
}      

Points of Interest

It would be nice to post other languages.