NetworkStream.ReadAsync with a cancellation token never cancels

Question

Here the proof.
Any idea what is wrong in this code ?

    [TestMethod]
    public void TestTest()
    {
        var tcp = new TcpClient() { ReceiveTimeou         


        

Answer 1

Cancellation is cooperative. NetworkStream.ReadAsync must cooperate to be able to be cancelled. It is kind of hard for it to do that because that would potentially leave the stream in an undefined state. What bytes have already been read from the Windows TCP stack and what haven't? IO is not easily cancellable.

Reflector shows that NetworkStream does not override ReadAsync. This means that it will get the default behavior of Stream.ReadAsync which just throws the token away. There is no generic way Stream operations can be cancelled so the BCL Stream class does not even try (it cannot try - there is no way to do this).

You should set a timeout on the Socket.