/// <summary>
/// Enables efficiently reading a stream using <see cref="PipeReader"/>.
/// </summary>
/// <param name="stream">The stream to read from using a pipe.</param>
/// <param name="sizeHint">A hint at the size of messages that are commonly transferred. Use 0 for a commonly reasonable default.</param>
/// <param name="pipeOptions">Optional pipe options to use.</param>
/// <param name="disposeWhenReaderCompleted">A task which, when complete, signals that this method should dispose of the <paramref name="stream"/>.</param>
/// <param name="cancellationToken">A cancellation token that aborts reading from the <paramref name="stream"/>.</param>
/// <returns>A <see cref="PipeReader"/>.</returns>
/// <remarks>
/// When the caller invokes <see cref="PipeReader.Complete(Exception)"/> on the result value,
/// this leads to the associated <see cref="PipeWriter.Complete(Exception)"/> to be automatically called as well.
/// </remarks>
private static PipeReader UsePipeReader(this Stream stream, int sizeHint = 0, PipeOptions?pipeOptions = null, Task?disposeWhenReaderCompleted = null, CancellationToken cancellationToken = default)
{
Requires.NotNull(stream, nameof(stream));
Requires.Argument(stream.CanRead, nameof(stream), "Stream must be readable.");
var pipe = new Pipe(pipeOptions ?? PipeOptions.Default);
// Notice when the pipe reader isn't listening any more, and terminate our loop that reads from the stream.
// OBSOLETE API USAGE NOTICE: If at some point we need to stop relying on PipeWriter.OnReaderCompleted (since it is deprecated and may be removed later),
// we can return a decorated PipeReader that calls us from its Complete method directly.
var combinedTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
#pragma warning disable CS0618 // Type or member is obsolete
pipe.Writer.OnReaderCompleted(
(ex, state) =>
{
try
{
((CancellationTokenSource)state !).Cancel();
}
catch (AggregateException cancelException)
{
// .NET Core may throw this when canceling async I/O (https://github.com/dotnet/runtime/issues/39902).
// Just swallow it. We've canceled what we intended to.
cancelException.Handle(x => x is ObjectDisposedException);
}
},
combinedTokenSource);
// When this argument is provided, it provides a means to ensure we don't hang while reading from an I/O pipe
// that doesn't respect the CancellationToken. Disposing a Stream while reading is a means to terminate the ReadAsync operation.
if (disposeWhenReaderCompleted is object)
{
disposeWhenReaderCompleted.ContinueWith(
(_, s1) =>
{
var tuple = (Tuple <Pipe, Stream>)s1 !;
tuple.Item1.Writer.OnReaderCompleted((ex, s2) => ((Stream)s2 !).Dispose(), tuple.Item2);
},
Tuple.Create(pipe, stream),
cancellationToken,
TaskContinuationOptions.ExecuteSynchronously,
TaskScheduler.Default).Forget();
}
#pragma warning restore CS0618 // Type or member is obsolete
Task.Run(async delegate
{
while (!combinedTokenSource.Token.IsCancellationRequested)
{
Memory <byte> memory = pipe.Writer.GetMemory(sizeHint);
try
{
int bytesRead = await stream.ReadAsync(memory, combinedTokenSource.Token).ConfigureAwait(false);
if (bytesRead == 0)
{
break;
}
pipe.Writer.Advance(bytesRead);
}
catch (OperationCanceledException)
{
break;
}
catch (ObjectDisposedException)
{
break;
}
catch (Exception ex)
{
// Propagate the exception to the reader.
await pipe.Writer.CompleteAsync(ex).ConfigureAwait(false);
return;
}
FlushResult result = await pipe.Writer.FlushAsync().ConfigureAwait(false);
if (result.IsCompleted)
{
break;
}
}
// Tell the PipeReader that there's no more data coming
await pipe.Writer.CompleteAsync().ConfigureAwait(false);
}).Forget();
return(pipe.Reader);
}
/// <summary>
/// Initializes a new instance of the <see cref="MultiplexingStream"/> class.
/// </summary>
/// <param name="stream">The stream to multiplex multiple channels over. Use <see cref="FullDuplexStream.Splice(Stream, Stream)"/> if you have distinct input/output streams.</param>
/// <param name="options">Options to define behavior for the multiplexing stream.</param>
/// <param name="cancellationToken">A cancellation token.</param>
/// <returns>The multiplexing stream, once the handshake is complete.</returns>
/// <exception cref="EndOfStreamException">Thrown if the remote end disconnects before the handshake is complete.</exception>
public static async Task <MultiplexingStream> CreateAsync(Stream stream, Options options, CancellationToken cancellationToken = default)
{
Requires.NotNull(stream, nameof(stream));
Requires.Argument(stream.CanRead, nameof(stream), "Stream must be readable.");
Requires.Argument(stream.CanWrite, nameof(stream), "Stream must be writable.");
options = options ?? new Options();
// Send the protocol magic number, and a random GUID to establish even/odd assignments.
var randomSendBuffer = Guid.NewGuid().ToByteArray();
var sendBuffer = new byte[ProtocolMagicNumber.Length + randomSendBuffer.Length];
Array.Copy(ProtocolMagicNumber, sendBuffer, ProtocolMagicNumber.Length);
Array.Copy(randomSendBuffer, 0, sendBuffer, ProtocolMagicNumber.Length, randomSendBuffer.Length);
Task writeTask = stream.WriteAsync(sendBuffer, 0, sendBuffer.Length);
Task flushTask = stream.FlushAsync(cancellationToken);
var recvBuffer = new byte[sendBuffer.Length];
await ReadToFillAsync(stream, recvBuffer, throwOnEmpty : true, cancellationToken).ConfigureAwait(false);
// Realize any exceptions from writing to the stream.
await Task.WhenAll(writeTask, flushTask).ConfigureAwait(false);
for (int i = 0; i < ProtocolMagicNumber.Length; i++)
{
if (recvBuffer[i] != ProtocolMagicNumber[i])
{
string message = "Protocol handshake mismatch.";
if (options.TraceSource.Switch.ShouldTrace(TraceEventType.Critical))
{
options.TraceSource.TraceEvent(TraceEventType.Critical, (int)TraceEventId.HandshakeFailed, message);
}
throw new MultiplexingProtocolException(message);
}
}
bool?isOdd = null;
for (int i = 0; i < randomSendBuffer.Length; i++)
{
byte sent = randomSendBuffer[i];
byte recv = recvBuffer[ProtocolMagicNumber.Length + i];
if (sent > recv)
{
isOdd = true;
break;
}
else if (sent < recv)
{
isOdd = false;
break;
}
}
if (!isOdd.HasValue)
{
string message = "Unable to determine even/odd party.";
if (options.TraceSource.Switch.ShouldTrace(TraceEventType.Critical))
{
options.TraceSource.TraceEvent(TraceEventType.Critical, (int)TraceEventId.HandshakeFailed, message);
}
throw new MultiplexingProtocolException(message);
}
if (options.TraceSource.Switch.ShouldTrace(TraceEventType.Information))
{
options.TraceSource.TraceEvent(TraceEventType.Information, (int)TraceEventId.HandshakeSuccessful, "Multiplexing protocol established successfully.");
}
return(new MultiplexingStream(stream, isOdd.Value, options));
}
