How to cancel NetworkStream.ReadAsync without closing stream

Question

I am trying to use NetworkStream.ReadAsync() to read data but I cannot find how to cancel the ReadAsync() once called. For background, the NetworkStream is provided to me b

Answer 1

I am managing the cancellation by having the Task wait for the cancellation token call between the async call and the await statement like this:

try {

 ....

 Task<int> readTask = input.ReadAsync(buffer, 0, buffer.Length);
 readTask.Wait(myCancellationToken);
 int readBytes= await readTask;

....

}
catch ( OperationCanceledException e )
{
   // handle cancellation
}

Answer 2

You cannot cancel the ReadAsync since the internal call is unmanaged and uses IOCompletion ports.. Your options are as follows.

1. Use Socket.Shutdown(). This will return ReadAsync with a socket error of OperationAborted.
2. Wait for the read to timeout.
3. Check if data is available before reading from the socket.

Answer 3

You can implement an async wrapper around NetworkStream.Read (or ReadAsync), which also receives a cancellationtoken that you can monitor and honor yourself. Something like this:

Task MyCancelableNetworkStreamReadAsync(NetworkStream stream, CancellationToken ct)
{
...
if(this.stream.CanRead)
{
  do 
  {
    //check ct.IsCancellationRequested and act as needed
    bytesRead = await this.stream.ReadAsync(this.buffer, 0, (int)this.buffer.Length);
  }
  while(myNetworkStream.DataAvailable);
}

Please note that I am only trying to illustrate the idea and you might wnt to consider returning Task<TResult>, as well as whether to have the do{}while loop, any additional processing or cleanup, etc. - all according to your needs.

I would also point your attention to the article by Stephen Toub How do I cancel non-cancelable async operations? and the WithCancellation extension he creates there.