Asynchronous HttpListener receives each request twice

Question

I implemented an asynchronous HTTP listener in C #.

I followed the tutorial provided here by Microsoft

and found another tutorial, which I stupidly did not bookmark and now can not find again. Bearing in mind that I have code that I would not have written myself, but the explanations provided made sense, so I followed this up.

Now I am faced with two problems:

Firstly, I have to restart the listener after each request with Listener.Stop (), and then call the StartListening method again, and secondly, when I do this, I get each request twice. The request makes net sent twice, but I get it twice. However, it does not get twice when I pause the Thread that I am listening for about 2 seconds.

I apologize if I am very vague in my explanations, but I also understand my problem, I have no idea what causes it. Since the callback method is where most things happen, I will just post it, please tell me if you need any more code. Any help would be greatly appreciated since I was really stuck on this.

public void ListenAsynchronously()
    {

        if (listener.Prefixes.Count == 0) foreach (string s in prefixes) listener.Prefixes.Add(s);

        try
        {
            listener.Start();
        }
        catch (Exception e)
        {
            Logging.logException(e); 
        }

        System.Threading.ThreadPool.QueueUserWorkItem(new System.Threading.WaitCallback(Listen));
    }


    private void Listen(object state)
    {
        while (listener.IsListening)
        {
            listener.BeginGetContext(new AsyncCallback(ListenerCallback), listener);
            listenForNextRequest.WaitOne();
        }
    }
     private void ListenerCallback(IAsyncResult ar)
    {

        HttpListener httplistener = ar.AsyncState as System.Net.HttpListener;
        System.Net.HttpListenerContext context = null;

        int requestNumber = System.Threading.Interlocked.Increment(ref requestCounter);

        if (httplistener == null) return;

        try
        {
            context = httplistener.EndGetContext(ar);
        }
        catch(Exception ex)
        {
            return;
        }
        finally
        {
            listenForNextRequest.Set();
        }

        if (context == null) return;


        System.Net.HttpListenerRequest request = context.Request;

        if (request.HasEntityBody)
        {
            using (System.IO.StreamReader sr = new System.IO.StreamReader(request.InputStream, request.ContentEncoding))
            {
                string requestData = sr.ReadToEnd();

                //Stuff I do with the request happens here

            }
        }


        try
        {
            using (System.Net.HttpListenerResponse response = context.Response)
            {
                //response stuff happens here

                }

                byte[] buffer = System.Text.Encoding.UTF8.GetBytes(responseString);
                response.ContentLength64 = buffer.LongLength;
                response.OutputStream.Write(buffer, 0, buffer.Length);
                response.Close();


                StopListening();
                //If I dont set the thread to sleep here, I receive the double requests
                System.Threading.Thread.Sleep(2500);

                ListenAsynchronously(); 


            }
        }
        catch (Exception e)
        {
        }

    }

Answer 1

, StopListening() ListenAsynchronously() ListenerCallback(). Listen() . , HttpListener. ListenAsynchronously ,

public class HttpListenerCallbackState
{
    private readonly HttpListener _listener;
    private readonly AutoResetEvent _listenForNextRequest;

    public HttpListenerCallbackState(HttpListener listener)
    {
        if (listener == null) throw new ArgumentNullException("listener");
        _listener = listener;
        _listenForNextRequest = new AutoResetEvent(false);
    }

    public HttpListener Listener { get { return _listener; } }
    public AutoResetEvent ListenForNextRequest { get { return _listenForNextRequest; } }
}

public class HttpRequestHandler
{
    private int requestCounter = 0;
    private ManualResetEvent stopEvent = new ManualResetEvent(false);

    public void ListenAsynchronously(IEnumerable<string> prefixes)
    {
        HttpListener listener = new HttpListener();

        foreach (string s in prefixes)
        {
            listener.Prefixes.Add(s);
        }

        listener.Start();
        HttpListenerCallbackState state = new HttpListenerCallbackState(listener);
        ThreadPool.QueueUserWorkItem(Listen, state);
    }

    public void StopListening()
    {
        stopEvent.Set();
    }


    private void Listen(object state)
    {
        HttpListenerCallbackState callbackState = (HttpListenerCallbackState)state;

        while (callbackState.Listener.IsListening)
        {
            callbackState.Listener.BeginGetContext(new AsyncCallback(ListenerCallback), callbackState);
            int n = WaitHandle.WaitAny(new WaitHandle[] { callbackState.ListenForNextRequest, stopEvent});

            if (n == 1)
            {
                // stopEvent was signalled 
                callbackState.Listener.Stop();
                break;
            }
        }
    }

    private void ListenerCallback(IAsyncResult ar)
    {
        HttpListenerCallbackState callbackState = (HttpListenerCallbackState)ar.AsyncState;
        HttpListenerContext context = null;

        int requestNumber = Interlocked.Increment(ref requestCounter);

        try
        {
            context = callbackState.Listener.EndGetContext(ar);
        }
        catch (Exception ex)
        {
            return;
        }
        finally
        {
            callbackState.ListenForNextRequest.Set();
        }

        if (context == null) return;


        HttpListenerRequest request = context.Request;

        if (request.HasEntityBody)
        {
            using (System.IO.StreamReader sr = new System.IO.StreamReader(request.InputStream, request.ContentEncoding))
            {
                string requestData = sr.ReadToEnd();

                //Stuff I do with the request happens here  
            }
        }


        try
        {
            using (HttpListenerResponse response = context.Response)
            {
                //response stuff happens here  
                string responseString = "Ok";

                byte[] buffer = Encoding.UTF8.GetBytes(responseString);
                response.ContentLength64 = buffer.LongLength;
                response.OutputStream.Write(buffer, 0, buffer.Length);
                response.Close();
            }
        }
        catch (Exception e)
        {
        }
    }
}