//
// Helpers
//
internal static OutputSpanStream Stream(int size, int pad = 0)
{
var s = new OutputSpanStream(new byte[size + pad]);
for (var i = 0; i < pad; i++)
{
s.WriteByte(0xCC);
}
return(s);
}
public override int Read(byte[] buffer, int offset, int count)
{
// Start new block
if (_blockMac == null)
{
_blockMac = _baseStream.ReadExact(32);
// To avoid allocations we read into the cache buffer since it's unused at this point and parse from it
_baseStream.ReadExact(_buffer, 0, 4);
_blockSize = BitConverter.ToInt32(_buffer, 0);
// End of stream
if (_blockSize == 0)
{
return(0);
}
_blockReadPointer = 0;
_bufferActualSize = 0;
_bufferReadPointer = 0;
// Start the MAC calculation for the new block
_hmac = new HMACSHA256(Util.ComputeBlockHmacKey(_hmacKey, _blockIndex));
// To avoid allocation we write into the cache buffer and then use it for hashing
var forHashing = new OutputSpanStream(_buffer);
forHashing.WriteUInt64(_blockIndex);
forHashing.WriteInt32(_blockSize);
_hmac.TransformBlock(_buffer, 0, forHashing.Position, null, 0);
}
// Read next piece into the buffer
if (_bufferReadPointer >= _bufferActualSize)
{
var toRead = Math.Min(_buffer.Length, _blockSize - _blockReadPointer);
_bufferActualSize = _baseStream.Read(_buffer, 0, toRead);
_bufferReadPointer = 0;
// Hash the read portion
_hmac.TransformBlock(_buffer, 0, _bufferActualSize, null, 0);
}
var toCopy = Math.Min(count, _bufferActualSize - _bufferReadPointer);
Array.Copy(_buffer, _bufferReadPointer, buffer, offset, toCopy);
_bufferReadPointer += toCopy;
_blockReadPointer += toCopy;
// End of block
if (_blockReadPointer >= _blockSize)
{
// Finalize MAC
_hmac.TransformFinalBlock(Array.Empty <byte>(), 0, 0);
var storedMac = _blockMac;
var computedMac = _hmac.Hash;
_blockIndex++;
_blockMac = null;
_hmac.Dispose();
_hmac = null;
if (!Crypto.AreEqual(storedMac, computedMac))
{
throw new InternalErrorException("Corrupted, block MAC doesn't match");
}
}
return(toCopy);
}
