Threaded Proxy?

Hi,
Thanks for reading this!
For the people who never read any of my posts I am trying to write a proxy server in c#.
I am trying to "keep it simple" and stay away from asynchronous requests, but is not possible to totally avoid threading and I think I am encountering some multi threading problems.

The idea is to have a listener socket, binded to a certain prefix. Whatever requests I get there, I append them the correct credentials and send them straight to the (atuthenticated) server on the other side; then I grabb the bytes of the response and show them in the browser. For this I am using the HttpListenerContext class.

Code:

---

        public void Start()
        {
            try
            {
                m_listener.Start();
                while (true)
                {
                    try
                    {
                        HttpListenerContext request = m_listener.GetContext();
                        ThreadPool.QueueUserWorkItem(ProcessRequest, request);
                    }
                    catch (Exception e)
                    {
                        System.Diagnostics.Debug.WriteLine(e.ToString());
                    }
                }
            }
            catch (Exception e)
            {
                System.Diagnostics.Debug.WriteLine(e.ToString());
            }
            System.Diagnostics.Debug.WriteLine("Listening socket on port " + m_port);
        }

---

The function ProcessRequest does the actual job that I wanted. (note that it does it in an asynchronous way!)

Code:

---

            private void ProcessRequest(object listenerContext)
        {
            try
            {
                var context = (HttpListenerContext)listenerContext;

                try
                {
                                        // READ ADDRESS HERE...
                    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(address);

                    Stream instream = context.Request.InputStream;
                    Stream outstream = response.GetResponseStream();
                                       
                                        //TRANSFER DATA FROM REQUEST STREAM TO RESPONSE STREAM                                                                               
                    // Close streams
                    instream.Close();
                    outstream.Close();
                    context.Response.OutputStream.Close();
                }
                catch (Exception ex)
                {

                }
            }
            catch
            {
                Restart();
            }
        }

---

Normally, everything goes ok; however, whenever I have a client that does a lot of requests very quickly (almost parallely) there is a problem in line writing the output stream (with the bytes that I just grabbed from the server) and an error is thrown:

An operation was attempted on a nonexistent network connection

This is misterious; is the network connection referring to the incoming stream (the server that I am comunicating with)? if its there is no apparent problem, because I checked and the connection is still on... or is this connection referring to the output stream? if it is, there is also no apparent problem cause I checked it with the functon CanWrite and it returns true, so it is looks in good health;
If anybody has any "light" to to bring into this question I would really appreciate it, cause I googled it to exhaustion and did not come to any conclusions :pirate: :v:

Anyway, moving on: I caught the error and figure out that I need to somehow close the streams that are opened; I did not find a clean easy way to do it (cause I cannot access the streams anymore), so the "brute-force" approach was to close the actual listener and start it again (so that I can again listen for connections);

Code:

---

        private void Restart()
        {
            Stop();
            Start();
        }

---

Most of the times, this is ok, but sometimes, when I enter the Start() function, there is a problem with this line:

Code:

---

HttpListenerContext request = m_listener.GetContext();

---

and an exception is thrown:

The I/O operation has been aborted because of either a thread exit or an application request


and then I am in a bit of a mess.
Apart from trying to solve this particular errors that cause my application to fail requests once in a while, I am looking at the bigger picture and wondering if the issues I am encountering are from not approaching properly the situation; am I having simultaneous access to the code and no handling properly the multithreading (I actually tried a lock() of the critical section without any improvement...) ? do I need multithreading here? or is it something else?
As I said, any help here would be much appreciated! Thanks in advance :^:

So I think the summary of the situation concerning multithreading in C# is (correct me if I'm wrong):
- use asynchronous requests and let the system handle the multithreading; (1)
- use threadPool and let the system handle the multitreading (distribute tasks among worker threads); (2)
- implement "real" multi threading, handling synchronization, locks, etc; (3)

I wanted to keep it as simple as possible, without having to write a lot of "thread" of code (unless absolutely necessary), so I tried to stick to option (2), which as Luc Pattyn mentioned, has some limitations but I think I can "live" with them (that is, the app fails sometimes, I can catch the errors and carry on without major implications for the user).

One thing that I amended in my code, was removing the "restart" of the listener on the event of an exception; there is no need to stop and start the listener on error, and in fact, when I had a lot of threads running, the "restart" of the listener itself was a cause of problems...

The I/O operation has been aborted because of either a thread exit or an application request

So, after refactoring my "ProcessRequest" callback, it now looks like this: no restart of the listener and separate handling of different types of exceptions; one important thing is to close the Context.Response after an error, so that it sends a response to the client;

Code:

---

      private void ProcessRequest(object listenerContext)
        {
            try
            {
                byte[] buffer;
                var context = (HttpListenerContext)listenerContext;

                try
                {
                    //Make necessary replacements in the host name
                    Uri aUri = context.Request.Url;
                    string url = aUri.AbsolutePath + aUri.Query;

                    System.Uri uri = m_service.GetUri();
                    string address = uri.Scheme + "://" + uri.Host + ":" + uri.Port + url;

                    // Build Request
                    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(address);
                                       
                                        //DO STUFF
                                       
                    // Close streams
                    instream.Close();
                    outstream.Close();
                    context.Response.OutputStream.Close();
                }

                catch (System.ArgumentException ex)
                {
                    context.Response.StatusCode = int.Parse(ex.Message);
                    context.Response.StatusDescription = GetStatusDescription(context.Response.StatusCode);

                    byte[] buff = System.Text.Encoding.UTF8.GetBytes("<HTML><BODY><b>Proxy Failure:</b> (" +
                        context.Response.StatusCode + ") " + context.Response.StatusDescription + "</HTML></BODY>");

                    context.Response.ContentLength64 = buff.Length;
                    context.Response.OutputStream.Write(buff, 0, buff.Length);
                }
                catch (System.Net.HttpListenerException ex) { }
                catch (System.Net.WebException ex)
                {
                    int status = (int)((HttpWebResponse)ex.Response).StatusCode;

                    context.Response.StatusCode = status;
                    context.Response.StatusDescription = GetStatusDescription(status);

                    context.Response.Close();
                }
                catch (Exception ex) { }//Default
            }
            catch (Exception ex)
            {
                System.Diagnostics.Debug.WriteLine(ex.Message);
                // It should not come here! Are we having troubles closing the stream?
            }
        }

---

It's not the best solution, has it fails to deliver some jobs (not properly handling the multithreading), but its kind of working and is simple.
cheers,
Jo