Question

I am connecting to a 3rd party server. I know right now they allow 8 connections from the same remote user. However i dont know if they will raise or lower the connection limit. So i want my app to dynamically find out. How can i do this?

I’m using C#, MSVS 2008

I started a bounty for anyone who can give me working C#. If no one does then i’ll give it to the best answer.

I find this very difficult to do and had a few failed attempts 🙁

Answer 1

I will take this bounty good sir. Not exactly sure why you want to do this and why someone allows 8 connections.

Defined in 1999 (RFC 2616) “clients
that use persistent connections should
limit the number of simultaneous
connections that they maintain to a
given server. A single-user client
SHOULD NOT maintain more than 2
connections with any server or proxy.
A proxy SHOULD use up to 2*N
connections to another server or
proxy, where N is the number of
simultaneously active users. These
guidelines are intended to improve
HTTP response times and avoid
congestion.” Since developers are
using AJAX or AJAX-like requests to
update a Web page the http limits are
discussed more and more.

Like the RFC says, I was only able to get 2 open connections to web servers.

But here’s the code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Threading;

namespace ConnectionTest
{
    public class RequestCounter
    {
        public int Counter = 0;
        public void Increment()
        {
            Interlocked.Increment(ref Counter);
        }
    }

    public class RequestThread
    {
        public AutoResetEvent AsyncWaitHandle { get; private set; }
        public RequestCounter RequestCounter;
        public String Url;
        public HttpWebRequest Request;
        public HttpWebResponse Response;

        public RequestThread(AutoResetEvent r, String u, RequestCounter rc)
        {
            Url = u;
            AsyncWaitHandle = r;
            RequestCounter = rc;
        }

        public void Close()
        {
            if (Response != null)
                Response.Close();

            if (Request != null)
                Request.Abort();
        }
    }

    public class ConnectionTest
    {
        static void Main()
        {
            string url = "http://www.google.com/";
            int max = GetMaxConnections(25, url);
            Console.WriteLine(String.Format("{0} Max Connections to {1}",max,url));
            Console.ReadLine();
        }

        private static int GetMaxConnections(int maxThreads, string url)
        {
            RequestCounter requestCounter = new RequestCounter();

            List<RequestThread> threadState = new List<RequestThread>();
            for (int i = 0; i < maxThreads; i++)
                threadState.Add(new RequestThread(new AutoResetEvent(false), url, requestCounter));

            List<Thread> threads = new List<Thread>();
            foreach (RequestThread state in threadState)
            {
                Thread t = new Thread(StartRequest);
                t.Start(state);
                threads.Add(t);
            }

            WaitHandle[] handles = (from state in threadState select state.AsyncWaitHandle).ToArray();
            WaitHandle.WaitAll(handles, 5000); // waits seconds

            foreach (Thread t in threads)
                t.Abort();

            foreach(RequestThread rs in threadState)
                rs.Close();

            return requestCounter.Counter;
        }

        public static void StartRequest(object rt)
        {
            RequestThread state = (RequestThread) rt;
            try
            {
                state.Request = (HttpWebRequest)WebRequest.Create(state.Url);
                state.Request.ReadWriteTimeout = 4000; //Waits 4 seconds

                state.Response = (HttpWebResponse)state.Request.GetResponse();
                if (state.Response.StatusDescription.Equals("OK", StringComparison.InvariantCultureIgnoreCase))
                    state.RequestCounter.Increment();

                //Do not close, or you will free a connection. Close Later
                //response.Close(); 
            }
            catch (WebException e)
            {
                //Console.WriteLine("Message:{0}", e.Message);
                state.Close();
            }
            catch (ThreadAbortException e)
            {
                //Console.WriteLine("Thread Aborted");
                state.Close();
            }
            catch(Exception e)
            {
                //Console.WriteLine("Real Exception");    
                state.Close();
            }
            finally
            {
                state.AsyncWaitHandle.Set();
            }
        }
    }
}