Timeout using ServiceStack.Client

Question

I have been using service stack via AJAX calls for some time without issue, but have recently created a quick winforms app which utilizes the service stack client (specifically JsonServiceClient).

However - I have hit a problem whereby I consistently get a timeout on a call which works successfully on the the first TWO attempts. It looks like either the service stack client is holding on to some resource, or I am using the client in the wrong way. It only occurs when running against a remote service (works every time on a local machine). Here is my code, and the exception:

        var url = "http://www.TestServer.com/api";
        var taskId = Guid.Parse("30fed418-214b-e411-80c1-22000a5b9fe5");
        var email = "admin@example.com";

        using (var client = new JsonServiceClient(url))
        {
            var result = client.Send(new Authenticate {UserName = "username", Password = "Password01", RememberMe = true});
            client.Put(new AssignTask { AdminTaskId = taskId, Assignee = email });//Call #1 - works fine
            client.Put(new AssignTask { AdminTaskId = taskId, Assignee = email });//Call #2 - works fine

            try
            {
                client.Put(new AssignTask { AdminTaskId = taskId, Assignee = email });//Call #3 - works fine
            }
            catch (WebException ex)
            {
                //Times out every time
               //at System.Net.HttpWebRequest.GetRequestStream(TransportContext& context)
               //at System.Net.HttpWebRequest.GetRequestStream()
               //at ServiceStack.Net40PclExport.GetRequestStream(WebRequest webRequest)
               //at ServiceStack.ServiceClientBase.<>c__DisplayClassa.<SendRequest>b__9(HttpWebRequest client)
               //at ServiceStack.ServiceClientBase.PrepareWebRequest(String httpMethod, String requestUri, Object request, Action`1 sendRequestAction)
               //at ServiceStack.ServiceClientBase.SendRequest(String httpMethod, String requestUri, Object request)
               //at ServiceStack.ServiceClientBase.Send[TResponse](String httpMethod, String relativeOrAbsoluteUrl, Object request)
               //at ServiceStack.ServiceClientBase.Put[TResponse](String relativeOrAbsoluteUrl, Object requestDto)
               //at ServiceStack.ServiceClientBase.Put(Object requestDto)
               //at SSClientIssue.Program.Main(String[] args) in c:\Users\David\Documents\Visual Studio 2013\Projects\SSClientIssue\SSClientIssue\Program.cs:line 27
                throw;
            }

        }

After the timeout, I can close and reload the app (server stays up), and then get same behavior again (two successful calls). IIS logs show that the 3rd call does not make it to the server, so looks like a Client issue.

I have been looking at this for 8 hours and I think my eyes are starting to bleed...If anyone can help I will buy you a beer!

Answer 1

The issue is due to your ServiceClient requests not specifying a known response type.

Response types can either be marked on the Request DTO using the IReturn<T> marker (recommended):

public class GetAllAdminUsernamesRequest : IReturn<List<string>> { ... }

By adding this on the Request DTO, the ServiceClient is able to automatically infer and convert the response, e.g:

List<string> response = client.Get(new GetCurrentAdminUserAdminTasks());

Otherwise an alternative to specifying the Response on the Request DTO, is to specify it on the call-site, e.g:

List<string> response = client.Get<List<string>>(new GetCurrentAdminUserAdminTasks());

If you don't do this the Response is unknown so the ServiceClient will just return the underlying HttpWebResponse so you can inspect the response yourself.

HttpWebResponse tasks = client.Get(new GetCurrentAdminUserAdminTasks());

In order to be able to inspect and read from the HttpWebResponse the response cannot be disposed by the ServiceClient, so it's up to the call-site making the request to properly dispose of it, i.e:

using (HttpWebResponse tasks = client.Get(new GetCurrentAdminUserAdminTasks())) {}
using (HttpWebResponse adminUsers = client.Get(new GetAllAdminUsernames())) {}

try
{
    using (client.Put(new AssignTask { AdminTaskId = taskId, Assignee = user })) {}
    using (client.Put(new AssignTask { AdminTaskId = taskId, Assignee = user })) {}
    using (client.Put(new AssignTask { AdminTaskId = taskId, Assignee = user })) {}
    using (client.Put(new AssignTask { AdminTaskId = taskId, Assignee = user })) {}
}
...

Disposing of your WebResponses responses will resolve your issue.

If you don't do this the underlying WebRequest will throttle open connections and only let a limited number of simultaneous connections through at any one time, possibly as a safe-guard to prevent DDOS attacks. This is what keeps the underlying connections open and WebRequest to block, waiting for them to be released.