Fail to convert base64 string when using TryFromBase64String

February 6, 2024

I receive a Guid as a base64 string. By using the Convert.FromBase64String(b64), the conversion is working well, then I try to use the Convert.TryFromBase64String(b64) but in that case, the method return false and my byte array stays empty

var dataString = "kADs1tnSQ+2ehpdtUAK/Jg==";
// output: d6ec0090-d2d9-ed43-9e86-976d5002bf26
Console.WriteLine(new Guid(Convert.FromBase64String(dataString)));

Span<byte> bytes = new();
bool success = Convert.TryFromBase64String(dataString, bytes, out int _);

// output: False, then FormatException
Console.WriteLine(success);
Console.WriteLine(new Guid(success ? bytes : Convert.FromHexString(dataString)));

I guess my problem is with the initialization of the Span, because if I use new byte[16], it is working, but is it safe to write it using a fixed size of 16?

>Solution :

You should provide bytes with allocated space, e.g.

// 16 bytes to store parsed GUID
byte[] bytes = new byte[16];

bool success = Convert.TryFromBase64String(dataString, bytes, out int _);

Similar, if you want to use Span:

// Span of the array which allocates 16 bytes to store GUID
var bytes = new byte[16].AsSpan();

bool success = Convert.TryFromBase64String(dataString, bytes, out int _);