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• Convert GUIDs to a Shorter Textual Representation and Back

  Friday, January 13, 2023

  English .NET

  6 Comments

  The shortest textual representation of a GUID available out-of-the-box is with ToString("N"), which will create a string of 32 characters, e.g.:

  b91d07b8826e4233ba40142603cff7ef

  If you have several GUIDs next to each other, e.g., in columns in an Excel file, they can take up a considerable amount of space. For my use case (Excel export/import of data from/to an application), hiding the columns was not an option, as I needed to be able to take a look at the GUIDs. Not for the actual value, just to notice differences and patterns in the data.

  Behind the scenes, a GUID consists of 128 bits. Converting the bits to a (case-insensitive) hex number as done with ToString("N")  leaves some room for improvement. The usual choice for a better conversion from binary to text is base64 encoding, which is described in https://datatracker.ietf.org/doc/html/rfc4648#section-4. This encoding creates text that consists of case-sensitive letters, digits, and only a few special characters (more on that later).

  The .NET framework offers the functions Convert.ToBase64String() and Convert.FromBase64String(), so implementing the conversion is straightforward.

  Details worth noting

  • The result of Convert.ToBase64String(someGuid.ToByteArray()) is a string that always ends on two padding characters (“==”). These can be removed and added back later for a conversion into the other direction.
  • The base64 encoding uses the characters “+” and “/”. Depending on your scenario, this may cause issues, so replacing them with different characters is an option. In my case, I did not feel comfortable having arithmetic operators around in Excel, even though they do not cause trouble unless a cell value starts with “=”. This is why my code uses the characters “_” and “$” instead.

  The code

  I wrote a helper class with two functions and published it on https://github.com/RWeigelt/ShortGuidHelperDemo

  The following code

  var originalGuid = Guid.NewGuid();
  Console.WriteLine($"From GUID   : {originalGuid:N}");
  
  var shortId=ShortGuidHelper.GetShortId(originalGuid);
  Console.WriteLine($"To short ID : {shortId}");
  
  var recreatedGuid=ShortGuidHelper.GetGuid(shortId);
  Console.WriteLine($"Back to GUID: {recreatedGuid:N}");
  

  results in output similar to this:

  From GUID   : b91d07b8826e4233ba40142603cff7ef
  To short ID : uAcduW6CM0K6QBQmA8$37w
  Back to GUID: b91d07b8826e4233ba40142603cff7ef

  Ten characters saved for one GUID may not be much, but with several GUIDs next to each other, it still adds up.