private static void ReadCore <T>(ref JsonReaderState readerState, bool isFinalBlock, ReadOnlySpan <byte> buffer, ref DdbEntityReadStack readStack) where T : class
{
var ddbReader = new DdbReader(buffer, isFinalBlock, ref readerState, ref readStack)
{
State = { ReadAhead = !isFinalBlock, BytesConsumed = 0 }
};
ReadCore <T>(ref ddbReader);
readerState = ddbReader.JsonReaderValue.CurrentState;
readStack = ddbReader.State;
}
public static async ValueTask <ReadResult <TEntity> > ReadAsync <TEntity>(Stream utf8Json, DdbClassInfo classInfo, DynamoDbContextMetadata metadata, bool returnCrc, int defaultBufferSize = DefaultBufferSize, CancellationToken cancellationToken = default)
where TEntity : class
{
var readerState = new JsonReaderState();
var readStack = new DdbEntityReadStack(DdbEntityReadStack.DefaultStackLength, metadata);
try
{
readStack.GetCurrent().ClassInfo ??= classInfo;
var buffer = ArrayPool <byte> .Shared.Rent(defaultBufferSize);
var clearMax = 0;
try
{
var bytesInBuffer = 0;
uint crc = 0;
var isFirstBlock = true;
while (true)
{
var isFinalBlock = false;
while (true)
{
var bytesRead = await utf8Json.ReadAsync(new Memory <byte>(buffer, bytesInBuffer, buffer.Length - bytesInBuffer), cancellationToken).ConfigureAwait(false);
if (bytesRead == 0)
{
isFinalBlock = true;
break;
}
if (returnCrc)
{
crc = Crc32Algorithm.Append(crc, buffer, bytesInBuffer, bytesRead);
}
bytesInBuffer += bytesRead;
if (bytesInBuffer == buffer.Length)
{
break;
}
}
if (bytesInBuffer > clearMax)
{
clearMax = bytesInBuffer;
}
readStack.UseFastPath = isFirstBlock && isFinalBlock;
readStack.Buffer = buffer;
readStack.BufferStart = 0;
readStack.BufferLength = bytesInBuffer;
ReadCore <TEntity>(ref readerState, isFinalBlock, new ReadOnlySpan <byte>(buffer, 0, bytesInBuffer), ref readStack);
var bytesConsumed = (int)readStack.BytesConsumed;
bytesInBuffer -= bytesConsumed;
if (isFinalBlock)
{
break;
}
// Check if we need to shift or expand the buffer because there wasn't enough data to complete deserialization.
if ((uint)bytesInBuffer > ((uint)buffer.Length / 2))
{
// We have less than half the buffer available, double the buffer size.
byte[] dest = ArrayPool <byte> .Shared.Rent((buffer.Length < (int.MaxValue / 2))?buffer.Length * 2 : int.MaxValue);
// Copy the unprocessed data to the new buffer while shifting the processed bytes.
Buffer.BlockCopy(buffer, bytesConsumed, dest, 0, bytesInBuffer);
new Span <byte>(buffer, 0, clearMax).Clear();
ArrayPool <byte> .Shared.Return(buffer);
clearMax = bytesInBuffer;
buffer = dest;
}
else if (bytesInBuffer != 0)
{
// Shift the processed bytes to the beginning of buffer to make more room.
Buffer.BlockCopy(buffer, bytesConsumed, buffer, 0, bytesInBuffer);
}
isFirstBlock = false;
}
return(new ReadResult <TEntity>((TEntity)readStack.GetCurrent().ReturnValue !, crc));
}
finally
{
new Span <byte>(buffer, 0, clearMax).Clear();
ArrayPool <byte> .Shared.Return(buffer);
}
}
finally
{
readStack.Dispose();
}
}