/// <remarks>
/// Parses via Sequence, but doesn't ever need to copy bytes. Puts onus on Utf8JsonReader to be fast with Sequence.
/// </remarks>
public static async Task <T> ParseNoCopyAsync <T, TParser>(Stream stream, CancellationToken cancellationToken)
where TParser : IJsonParser <T>, new()
{
ArrayPool <byte> pool = ArrayPool <byte> .Shared;
int rentSize = 4096;
MyBuffer firstBuffer, lastBuffer;
int fill = 0, consumed = 0;
bool done = false;
firstBuffer = lastBuffer = new MyBuffer(pool.Rent(rentSize), 0);
var readerState = new JsonReaderState();
var parser = new TParser();
while (true)
{
if (!done)
{
if (fill == lastBuffer.Memory.Length)
{
rentSize = Math.Min(65536, rentSize * 3 / 2);
var newLastBuffer = new MyBuffer(pool.Rent(rentSize), lastBuffer.RunningIndex + lastBuffer.Memory.Length);
lastBuffer.SetNext(newLastBuffer);
lastBuffer = newLastBuffer;
fill = 0;
}
int read = await stream.ReadAsync(lastBuffer.WritableMemory.AsMemory(fill), cancellationToken).ConfigureAwait(false);
fill += read;
done = read == 0;
}
if (!DoReadSync())
{
if (done)
{
throw new Exception("unexpected end of document.");
}
}
else
{
return(parser.FinalValue);
}
}
bool DoReadSync()
{
var availableSequence = new ReadOnlySequence <byte>(firstBuffer, consumed, lastBuffer, fill);
var reader = new Utf8JsonReader(availableSequence, done, readerState);
bool res = parser.TryContinueParse(ref reader);
long newConsumed = reader.BytesConsumed;
while (newConsumed != 0)
{
int left = (firstBuffer == lastBuffer ? fill : firstBuffer.Memory.Length) - consumed;
int take = (int)Math.Min(left, newConsumed);
consumed += take;
newConsumed -= take;
if (consumed == firstBuffer.Memory.Length)
{
consumed = 0;
if (firstBuffer != lastBuffer)
{
pool.Return(firstBuffer.WritableMemory);
firstBuffer = (MyBuffer)firstBuffer.Next;
}
else
{
fill = 0;
}
}
}
readerState = reader.CurrentState;
return(res);
}
}
