private async Task CopyToAsyncCore(Stream destination, int bufferSize, CancellationToken cancellationToken)
{
// Synchronize async operations as does Read/WriteAsync.
await LazyEnsureAsyncActiveSemaphoreInitialized().WaitAsync().ConfigureAwait(false);
try
{
int readBytes = _readLen - _readPos;
Debug.Assert(readBytes >= 0, $"Expected a non-negative number of bytes in buffer, got {readBytes}");
if (readBytes > 0)
{
// If there's any read data in the buffer, write it all to the destination stream.
Debug.Assert(_writePos == 0, "Write buffer must be empty if there's data in the read buffer");
await destination.WriteAsync(_buffer, _readPos, readBytes, cancellationToken).ConfigureAwait(false);
_readPos = _readLen = 0;
}
else if (_writePos > 0)
{
// If there's write data in the buffer, flush it back to the underlying stream, as does ReadAsync.
await FlushWriteAsync(cancellationToken).ConfigureAwait(false);
}
// Our buffer is now clear. Copy data directly from the source stream to the destination stream.
await _stream.CopyToAsync(destination, bufferSize, cancellationToken).ConfigureAwait(false);
}
finally { _asyncActiveSemaphore.Release(); }
}
} // class BufferedStream
