Troubleshooting SignalR Serialization - json.net

Question

I have the following code:
try {
_hubConnection = new HubConnection(_baseUrl);
_hubConnection.CookieContainer = new CookieContainer();
_hubConnection.CookieContainer.Add(_cookie);
_hubProxy = _hubConnection.CreateHubProxy("appHub");
_hubConnection.Start().Wait();
}
catch (Exception e) {
Elmah.ErrorSignal.FromCurrentContext().Raise(new Exception("Serialization error [hubConnection] - " + e.Message + ", " + e.InnerException.Message + ", " + e.ToString()));
}
Usually, this works. Every once in a while, I get a random serialization error though:
Serialization error [hubConnection] - One or more errors occurred., Unexpected character encountered while parsing value: <. Path '', line 0, position 0., System.AggregateException: One or more errors occurred. ---> Newtonsoft.Json.JsonReaderException: Unexpected character encountered while parsing value: <. Path '', line 0, position 0.
at Newtonsoft.Json.JsonTextReader.ParseValue()
at Newtonsoft.Json.JsonTextReader.Read()
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.ReadForType(JsonReader reader, JsonContract contract, Boolean hasConverter)
at
This Unexpected character encountered while parsing value: < seems very difficult to reproduce, and I don't know how to get detailed information around this. I do have this configured:
var hubConfiguration = new HubConfiguration { EnableDetailedErrors = true };
app.MapSignalR(hubConfiguration);
Does anyone know what might be causing this, or how I might go about troubleshooting?
Full trace:
System.Exception: Messaging Error [hubConnection] at App.Services.NotificationService.SignalObjectToUser(Object data, String username, Boolean isTypingNotification) at App.Services.NotificationService.MessageSentNotification(User toUser, Message message, Int32 conversationId, Boolean isOnline) at App.Services.MessageService.SendMessage(MessageDto message, FStopContext altContext) at App.ApiControllers.MessageController.SendMessage(MessageDto message) at lambda_method(Closure , Object , Object[] ) at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.<>c__DisplayClass10.b__9(Object instance, Object[] methodParameters) at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.Execute(Object instance, Object[] arguments) at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ExecuteAsync(HttpControllerContext controllerContext, IDictionary`2 arguments, CancellationToken cancellationToken)
--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Web.Http.Controllers.ApiControllerActionInvoker.d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Web.Http.Filters.ActionFilterAttribute.d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown --- at System.Web.Http.Filters.ActionFilterAttribute.d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Web.Http.Filters.ActionFilterAttribute.d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Web.Http.Filters.ActionFilterAttribute.d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown --- at System.Web.Http.Filters.ActionFilterAttribute.d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Web.Http.Filters.ActionFilterAttribute.d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Web.Http.Filters.ActionFilterAttribute.d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown --- at System.Web.Http.Filters.ActionFilterAttribute.d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Web.Http.Filters.ActionFilterAttribute.d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Web.Http.Filters.ActionFilterAttribute.d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown --- at System.Web.Http.Filters.ActionFilterAttribute.d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Web.Http.Filters.ActionFilterAttribute.d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Web.Http.Controllers.ActionFilterResult.d__2.MoveNext()
--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Web.Http.Filters.AuthorizationFilterAttribute.d__2.MoveNext()
--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Web.Http.Controllers.ExceptionFilterResult.d__0.MoveNext()

Answer 1

There are a couple of things I would try before digging deeper into the content being transmitted:
Set up the hub connection without a cookie container. This would narrow down whether this is causing the issue.
Rather than using .Wait() on your hub connection, try use an async/await function. I seem to recall having a similar exception when I was using Wait() in the past.
Post back your results.