What regular expression could I use to validate a blob container name?

Question

I'd like to validate that a blob container name is valid before attempting to create it. Is there an existing regular expression I could use? See here for the naming rules: http://msdn.microsoft.com/en-us/library/dd135715.aspx

Answer 1

Try this:

^([a-z]|\d){1}([a-z]|-|\d){1,61}([a-z]|\d){1}$

or you can use this function:

internal static bool IsBlobContainerNameValid(string name)
    {
      if (name.Equals("$root"))
      { 
        return true; 
      }
      string validBlobContainerNameRegex = @"^([a-z]|\d){1}([a-z]|-|\d){1,61}([a-z]|\d){1}$";
      Regex reg = new Regex(validBlobContainerNameRegex);
      if (reg.IsMatch(name))
      {
        return true;
      }
      return false;
    }

Hope this helps

Thanks

Gaurav Mantri

Cerebrata Software

http://www.cerebrata.com

Answer 2

I think this is not enough.

The code above do not handle the fact a dash character must be immediately preceded and followed by a letter or number.

For example, the following string will be returned as a correct container name whereas it should not : "a--b"

 

Therefore, I recommend to use this code:

/// <summary>Checks that containerName is a valid DNS name, as requested by Azure</summary>
    public static bool IsContainerNameValid(string containerName)
    {
      return (Regex.IsMatch(containerName, @"(^([a-z]|\d))((-([a-z]|\d)|([a-z]|\d))+)$") 
        && (3 <= containerName.Length) && (containerName.Length <= 63));
    }

Matthieu Durut

Lokad

http://www.lokad.com

 

Answer 3

It turns out that neither of the previous two answers are correct.  Regular expressions are really tricky to get "correct". :)  You can test this regular expression carefully using your favorite regular expression tool (RegEx Buddy, RegEx Coach, etc.)

// Container names must be valid DNS names, and must conform to these rules:
// * Container names must start with a letter or number, and can contain only letters, numbers, and the dash (-) character.
// * Every dash (-) character must be immediately preceded and followed by a letter or number; consecutive dashes are not permitted in container names.
// * All letters in a container name must be lowercase.
// * Container names must be from 3 through 63 characters long.

// $root is a special container that can exist at the root level and is always valid.
if (containerName.Equals("$root"))
 return; 

if (!Regex.IsMatch(containerName, @"^[a-z0-9](([a-z0-9\-[^\-])){1,61}[a-z0-9]$"))
 throw new Exception("Invalid container name);

Answer 4

I realise that this is a year too late, but I was recently performing the same check and came across this page!

I think that in order to ensure that you can match the dashes correctly, you need to use a "zero-width positive lookahead" - (?=x) syntax.

I think this RegEx should work:

^(([a-z\d]((-(?=[a-z\d]))|([a-z\d])){2,62})|(\$root))$

 

I have combined the check for the $root container name.

The regex uses grouping and the positive look ahead.

It matches either a [letter or number] as the first match, this must then be followed by (EITHER (a dash followed by a [letter or number]) OR ([a letter or number])) - it MUST have at least two matches of this to a maximum of 62, giving 63 total characters.