SignalR returns error - Unexpected end when deserializing object

Question

I have simple project, where I'm using signalR, When page loads, signalR scripts are loaded succefully, however right after that, call to

http://localhost:24634/signalr/signalr/connect?transport=foreverFrame&connectionId=dca2db9c-b16a-4b96-96dc-9a6b187b6d9e&connectionData=[{"name":"notifier"}]&tid=5&frameId=1

returns 500 Internal Server Error, I checked this request in fiddler, error message says

Unexpected end when deserializing object.

Here's my Hub Definitin

[HubName("notifier")]
    public class PublishingNotifier: Hub
    {   
        [HubMethodName("send")]
        public void SendMessage(string message)
        {
            Clients.getNotification(message);
        }
    }

and here's my client code

$(function () {

            var publishingNotifier = $.connection.notifier;

            publishingNotifier.getNotification = function (message) {
                // do something
            };

            $('input[type=submit][id*=cmsB_ChangeStatusToPublishedTop]').on('click', function (e) {
                // do something else
            });

            $.connection.hub.start();
        });

Any ideas what can be cause of this error ?

EDIT Here is Stack Trace information

[JsonSerializationException: Unexpected end when deserializing object. Line 1, position 2.]
Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CheckedRead(JsonReader reader) +75
Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, Object existingValue) +48
Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, Object existingValue) +86
Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateList(IWrappedCollection wrappedList, JsonReader reader, String reference, JsonArrayContract contract) +635
Newtonsoft.Json.Serialization.<>c_DisplayClass1.<CreateAndPopulateList>b_0(IList l, Boolean isTemporaryListReference) +124
Newtonsoft.Json.Utilities.CollectionUtils.CreateAndPopulateList(Type listType, Action2 populateList) +546
Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateAndPopulateList(JsonReader reader, String reference, JsonArrayContract contract) +101
Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateList(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, Object existingValue, String reference) +62
Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, Object existingValue) +113
Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueNonProperty(JsonReader reader, Type objectType, JsonContract contract, JsonConverter converter) +118
Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType) +125
Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType) +311
Newtonsoft.Json.JsonConvert.DeserializeObject(String value, Type type, JsonSerializerSettings settings) +107
Newtonsoft.Json.JsonConvert.DeserializeObject(String value, JsonSerializerSettings settings) +66
SignalR.JsonNetSerializer.Parse(String json) +57
SignalR.Hubs.HubDispatcher.CreateConnection(String connectionId, IEnumerable1 groups, IRequest request) +140
SignalR.PersistentConnection.ProcessRequestAsync(HostContext context) +227 SignalR.Hubs.HubDispatcher.ProcessRequestAsync(HostContext context) +120
SignalR.Hosting.AspNet.AspNetHandler.ProcessRequestAsync(HttpContextBase context) +463
SignalR.Hosting.AspNet.HttpTaskAsyncHandler.System.Web.IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, Object extraData) +68
System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +301 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +155

EDIT2:

One more note - from the page that runs without any errors, requested url looks like this

localhost:24634/signalr/signalr/connect?transport=foreverFrame&connectionId=98e6d5b3-b164-4013-92c2-418aa6254f9e&connectionData=%5B%7B%22name%22%3A%22notifier%22%7D%5D&tid=7&frameId=1

and the failing request url looks like this

localhost:24634/signalr/signalr/connect?transport=foreverFrame&connectionId=9b398750-99d6-4188-88b5-b41ad9eb82d5&connectionData=[{"name":"notifier"}]&tid=1&frameId=1

As you may notice, the ways connectionData query string parameter is defined in urls are different, in particular, for the first url, connectionData has been url encoded the query string value, and the second query string parameter has been html encoded. I've looked into request headers, failing request Content-Type is text/html, and the second request's Content-Type: application/json.

EDIT 3:

I've found where connectionData get's parsed, in jquery.signalR-0.5.3.js file, here's code that actually encodes connectionData value

if (connection.data) {
  qs += "&connectionData=" + window.escape(connection.data);
}

as you can see, window.escape() is responsible for encoding connectionData, but, if I debug this code, I can see that window.escape(connection.data) indeed html encodes connection.data instead of url encoding. But this is happening only on one page, on anothers, it works as expected.

Answer 1

To sum up, the problem turned out to be that window.escape was overridden by a third party JS library. This caused window.escape to behave differently than "normal" causing SignalR to fail as a side-effect.

So basically - when these "weird" issues occur - check if you have included libraries that "interfere" and make sure to use proper namespacing ( e.g. using the module pattern ) to avoid this issue.

Answer 2

BUG

I do not know if this could help, but I had the error "unexpected end when deserializing object message c #", when I was trying to deserialize my json. It happened to me sometimes, sometimes not. I do not know what it depends on.

My json was like that:

https://api.myjson.com/bins/l83m8

Debugging the Xamarin App on visual studio 2019 gives me the following:

var content = await _client.GetStringAsync(Connection.URL);
invitaciones = JsonConvert.DeserializeObject<RootObject>(content);

The variable "content" sometimes gives me https://textsaver.flap.tv/lists/2lss and sometimes gives me https://textsaver.flap.tv/lists/2lsu.

If you look very carefully, you are gonna release that both are different, only because, the first one is missing a } just in the end.

If you deserialize both with https://www.unserialize.me/ tool, and then validate the result on https://jsonformatter.curiousconcept.com/ (default options), you are gonna see that the first one isn't valid, and the second is valid.

Solution:

Add a validation: if the string content (json) don't ends with }, put a } on the end.I know it's pretty silly, but solves my problem.

 var content = await _client.GetStringAsync(Connection.URL);
 if (!content.EndsWith("}"))
     content = content + "}";
 invitaciones = JsonConvert.DeserializeObject<RootObject>(content);

Packages: Newtonsoft.Json 12.0.2, Xamarin.Forms 3.6.0.344457 .