public async Task <MqttBasePacket> ReceivePacketAsync(TimeSpan timeout, CancellationToken cancellationToken)
{
var input = Connection.Transport.Input;
try
{
while (!cancellationToken.IsCancellationRequested)
{
ReadResult readResult;
var readTask = input.ReadAsync(cancellationToken);
if (readTask.IsCompleted)
{
readResult = readTask.Result;
}
else
{
readResult = await readTask.ConfigureAwait(false);
}
var buffer = readResult.Buffer;
var consumed = buffer.Start;
var observed = buffer.Start;
try
{
if (!buffer.IsEmpty)
{
if (PacketSerializer.TryDeserialize(buffer, out var packet, out consumed, out observed))
{
return(packet);
}
else
{
// we did receive something but the message is not yet complete
ReadingPacketStarted?.Invoke(this, EventArgs.Empty);
}
}
else if (readResult.IsCompleted)
{
throw new MqttCommunicationException("Connection Aborted");
}
}
finally
{
// The buffer was sliced up to where it was consumed, so we can just advance to the start.
// We mark examined as buffer.End so that if we didn't receive a full frame, we'll wait for more data
// before yielding the read again.
input.AdvanceTo(consumed, observed);
}
}
private async Task <ReceivedMqttPacket> ReceiveAsync(CancellationToken cancellationToken)
{
var fixedHeader = await MqttPacketReader.ReadFixedHeaderAsync(_channel, _fixedHeaderBuffer, _singleByteBuffer, cancellationToken).ConfigureAwait(false);
try
{
ReadingPacketStarted?.Invoke(this, EventArgs.Empty);
if (fixedHeader.RemainingLength == 0)
{
return(new ReceivedMqttPacket(fixedHeader.Flags, null));
}
var body = new byte[fixedHeader.RemainingLength];
var bodyOffset = 0;
var chunkSize = Math.Min(ReadBufferSize, fixedHeader.RemainingLength);
do
{
var bytesLeft = body.Length - bodyOffset;
if (chunkSize > bytesLeft)
{
chunkSize = bytesLeft;
}
#if WINDOWS_UWP
var readBytes = await _channel.ReadAsync(body, bodyOffset, chunkSize, cancellationToken).ConfigureAwait(false);
#else
// async/await is not used to avoid the overhead of context switches. We assume that the reamining data
// has been sent from the sender directly after the initial bytes.
//var readBytes = _channel.ReadAsync(body, bodyOffset, chunkSize, cancellationToken).ConfigureAwait(false).GetAwaiter().GetResult();
var readBytes = AsyncContext.Run(async() => await _channel.ReadAsync(body, bodyOffset, chunkSize, cancellationToken).ConfigureAwait(false));
#endif
cancellationToken.ThrowIfCancellationRequested();
ExceptionHelper.ThrowIfGracefulSocketClose(readBytes);
bodyOffset += readBytes;
} while (bodyOffset < body.Length);
return(new ReceivedMqttPacket(fixedHeader.Flags, new MqttPacketBodyReader(body, 0, body.Length)));
}
finally
{
ReadingPacketCompleted?.Invoke(this, EventArgs.Empty);
}
}
private async Task <MqttReceivedPacket> ReceiveAsync(CancellationToken cancellationToken)
{
var fixedHeader = await MqttPacketReader.ReadFixedHeaderAsync(_channel, _fixedHeaderBuffer, _singleByteBuffer, cancellationToken).ConfigureAwait(false);
try
{
ReadingPacketStarted?.Invoke(this, EventArgs.Empty);
if (fixedHeader.RemainingLength == 0)
{
return(new MqttReceivedPacket(fixedHeader.Flags, null));
}
var body = new byte[fixedHeader.RemainingLength];
var bodyOffset = 0;
var chunkSize = Math.Min(ReadBufferSize, fixedHeader.RemainingLength);
do
{
var bytesLeft = body.Length - bodyOffset;
if (chunkSize > bytesLeft)
{
chunkSize = bytesLeft;
}
//async/await不用于避免上下文切换的开销。我们假设扩孔数据已从发件人直接发送到初始字节之后。
var readBytes = _channel.ReadAsync(body, bodyOffset, chunkSize, cancellationToken).ConfigureAwait(false).GetAwaiter().GetResult();
cancellationToken.ThrowIfCancellationRequested();
ExceptionHelper.ThrowIfGracefulSocketClose(readBytes);
bodyOffset += readBytes;
} while (bodyOffset < body.Length);
return(new MqttReceivedPacket(fixedHeader.Flags, new MqttPacketBodyReader(body, 0, body.Length)));
}
finally
{
ReadingPacketCompleted?.Invoke(this, EventArgs.Empty);
}
}
