Base64Encoding.UsingSpanBase64

Base64Encoding.UsingSpanBase64.cs

public static string UsingSpanBase64(Guid oid, params string[] input)
{
    var totalUtf8Bytes = 36; // GUID.Format(D) = 36 bytes
    for (int i = 0; i < input.Length; i++)
    {
        totalUtf8Bytes += Encoding.UTF8.GetByteCount(input[i]);
    }

    Span<byte> resultSpan = stackalloc byte[Base64.GetMaxEncodedToUtf8Length(totalUtf8Bytes)];
    if (!Utf8Formatter.TryFormat(oid, resultSpan, out int writtenBytes) || writtenBytes != 36)
    {
        throw new ArithmeticException();
    }

    for (int i = 0; i < input.Length; i++)
    {
        var ixs = EncodingHelper.GetUtf8Bytes(input[i].AsSpan(), resultSpan.Slice(writtenBytes));
        writtenBytes += ixs;
    }

    OperationStatus status = Base64.EncodeToUtf8InPlace(resultSpan, totalUtf8Bytes, out int base64Written);
    if (status != OperationStatus.Done)
    {
        throw new ArithmeticException();
    }

    var base64String = EncodingHelper.GetUrlSafeString(resultSpan.Slice(0, base64Written));
    return base64String;
}