The input is not a valid Base-64 string

Question

Facing issue for FromBase64String method.

The input is not a valid Base-64 string as it contains a non-base 64 character, more than two padding characters, or an illegal character among the padding characters.

Tried replacing - to +

var bytes = Convert.FromBase64String(id);
id = "59216167-f9c0-4b1b-b1db-1babd1209f10@ABC"

Expected result is string should be converted to an equivalent 8-bit unsigned integer array.

Answer 1

It's not a Base64 encoded string. It's a Guid. You can read it into a byte array like this

var bytearray = new Guid("59216167-f9c0-4b1b-b1db-1babd1209f10").ToByteArray();

Answer 2

The input is not a valid Base-64 string

The exact reason you are getting this type of error is because it's not a valid Base64 string, instead as already mentioned, it's a Guid; and not a valid Guid at that.

First you can check if you even have a valid Base64 string by trying to convert it.

public static bool StringIsBase64(string myString)
{
   Span<byte> buffer = new Span<byte>(new byte[myString.Length]);
   return Convert.TryFromBase64String(myString, buffer , out int bytesParsed);
}

Now if you call this function and it succeeds, then we would assume you do have a valid Base64 string, otherwise a conversion error would occur.

Your call can now look like this:

 string id = "59216167-f9c0-4b1b-b1db-1babd1209f10@ABC";
 var bytes;
 if (StringIsBase64(id))
 {
    bytes = Convert.FromBase64String(id);
 } 

Something else I would like to address that none of the other answers addressed, is the input is not valid for even a Guid. A GUID is a 128-bit integer (16 bytes) and that string isn't valid.

You actually would receive the error:

Guid should contain 32 digits with 4 dashes (xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx)

The characters @ABC at the end of the string are causing this, if these are removed then we have an actual valid Guid.