private static async Task <(MemoryStream output, IMS2SizeHeader size)> InternalGetEncryptionStreamAsync(Stream input, long inputSize, IBufferedCipher cipher, long headerSize)
{
byte[] inputBytes = new byte[inputSize];
int read = await input.ReadAsync(inputBytes, 0, (int)inputSize).ConfigureAwait(false);
if (inputSize != read)
{
throw new EndOfStreamException();
}
using var msInput = new MemoryStream(inputBytes);
using var cs = new CipherStream(msInput, cipher, null);
using var ms = new MemoryStream();
var output = new MemoryStream();
await cs.CopyToAsync(ms).ConfigureAwait(false);
var data = ms.ToArray();
var encoder = new Base64Encoder();
encoder.Encode(data, 0, data.Length, output);
var header = new MS2SizeHeader(output.Length, inputSize, headerSize);
output.Position = 0;
return(output, header);
}