C# GetResponse not coming back

Question

I have an strange problem. My .NET DataController send a response to an Java server (REST). All works fine, but when I send a response very often, suddenly the GetResponse method not coming back just hangs. I don't know what's the problem is.

Here is my code

ServicePointManager.DefaultConnectionLimit = 20;

public string HttpGet(string url, string requestAccept)
{
  if(string.IsNullOrEmpty(url))
    throw new Exception("HttpGet: no REST service URL provided");
  if(string.IsNullOrEmpty(requestAccept))
    requestAccept = defaultRequestAccept;

  if(!url.Equals("pc/alive"))
  {
    if(string.IsNullOrEmpty(SessionId))
    {
      if(string.IsNullOrEmpty(Authorization()))
        throw new WebException("HttpGet: no login");
    }
  }

  int tries = RestAccessData.MaxReconnect;
  string result = string.Empty;

  do
  {
    try
    {
      var request = NewWebRequest(url, "GET", false, true, requestAccept);

      using(var response = request.GetResponse() as HttpWebResponse)
      {
        UpdateSessionId(response);

        HttpStatusCode statusCode = response.StatusCode;
        LOG.Debug("...StatusCode: {0} ({1})", (int) response.StatusCode, response.StatusDescription);

        if((int) response.StatusCode < 500)
          lastContactWithServer = DateTime.Now.Ticks;

        switch(statusCode)
        {
        // Informational 1xx
        case HttpStatusCode.Continue: // 100
        case HttpStatusCode.SwitchingProtocols: // 101

          throw new HttpResponseException(response);

        // Successful 2xx
        case HttpStatusCode.OK: // 200

          result = ReadContent(response);
          response.Close();

          return (result);

        case HttpStatusCode.NoContent: // 204 The server has fulfilled the request but does not need to return an entity-body, and might want to return updated metainformation.

          response.Close();
          return (string.Empty);

        case HttpStatusCode.Created: // 201
        case HttpStatusCode.NonAuthoritativeInformation: // 203

          result = ReadContent(response);
          throw new HttpResponseException(response, result);

        case HttpStatusCode.Accepted: // 202 The request has been accepted for processing, but the processing has not been completed.
        case HttpStatusCode.ResetContent: // 205 The server has fulfilled the request and the user agent SHOULD reset the document view which caused the request to be sent.
        case HttpStatusCode.PartialContent: // 206 The server has fulfilled the partial GET request for the resource.

          throw new HttpResponseException(response);

        case HttpStatusCode.Unauthorized:

          throw new HttpResponseException(response);

        default:

          throw new HttpResponseException(response);
        }
      }
    }
    catch(WebException ex)
    {
      HandleWebException(ex);
    }
    catch(HttpResponseException ex)
    {
      throw ex;
    }
    catch(SystemException ex)
    {
      LOG.Error(ex, "caused a(n) {0}", ex.GetType().Name);
    }
    catch(Exception ex)
    {
      LOG.Warn(ex, "HttpGet: An error occured while trying to contact the server. Reason: {0}", ex.Message);
      throw new UserException("An error occured while trying to contact the server.", ex);
    }
  }
  while(0 < tries--);

  return (string.Empty);
}

private HttpWebRequest NewWebRequest(string urlAsString, string requestType, bool withContentType, bool applicationJson, string requestAccept)
{
  urlAsString = string.Format("{0}{1}", RestAccessData.GetUrl(), EncodeUrl(urlAsString));
  Uri url;

  if(!Uri.TryCreate(urlAsString, UriKind.Absolute, out url))
    throw new NotSupportedException("url is not compatible");

  LOG.Info("RESTUrl {0}", urlAsString);

  try
  {
    var request = HttpWebRequest.Create(url) as HttpWebRequest;

    if(!string.IsNullOrEmpty(SessionId))
    {
      CookieContainer cookies = new CookieContainer();
      Cookie cookie = new Cookie
      {
        Name = "JSESSIONID",
        Value = SessionId,
        Domain = url.Host
      };

      cookies.Add(cookie);
      request.CookieContainer = cookies;
    }

    request.Timeout = RestAccessData.Timeout;
    request.Method = requestType;
    request.AllowAutoRedirect = true;
    request.AllowWriteStreamBuffering = true;
    request.KeepAlive = false;
    request.ContentLength = 0;
    request.Headers["Accept-Charset"] = "utf-8";
    request.Accept = requestAccept;
    request.UserAgent = LvsClient;

    if(withContentType)
      request.ContentType = applicationJson ? defaultApplicationJson : defaultApplicationWwwForm;

    if(!string.IsNullOrEmpty(credential.UserName) && !string.IsNullOrEmpty(credential.Password))
      request.Headers["Authorization"] = string.Format("Basic {0}", Convert.ToBase64String(Encoding.UTF8.GetBytes(string.Format("{0}:{1}", credential.UserName, credential.Password))));

    return (request);
  }
  catch(Exception ex)
  {
    throw new UserException(TH.Translate("NewWebRequest caused an error"), ex);
  }
}

Any ideas where the problem is?

Answer 1

This line is making me uncomfortable:

using(var response = request.GetResponse() as HttpWebResponse)

If the response is not an HttpWebResponse then it will never be disposed - the as operator will give you `null.

Answer 2

I found a solution. Very useful is this MSDN article about Understanding MaxServicePointIdleTime and DefaultConnectionLimit. After I play with MaxServicePointIdleTime property and read this comment

change the connection limit at any time

I found a good balance between connection alive and connection close. My client works fine after playing with MaxServicePointIdleTime and DefaultConnectionLimit.