We are building an app which will send messages to the browser using SignalR. The user may have multiple browser instances open and we would like each message to be sent to the appropriate browser. Our understanding is that the ClientId ConnectionId would allow us to do this. The issue we're running into is accessing the ClientId ConnectionId, or SessionId, at the appropriate times in the codebase. Here's our scenario:
A MVC Action executes and, as part of that processing, a call to a Biztalk endpoint is made. The Biztalk execution is out of process (from the point of view of the MVC Action) and doesn't return when completed. This is by design. To notify the MVC application that it has completed, Biztalk sends a message to the MVC application's SignalR hub by calling the /myapp/signalr endpoint. The message is received by SignalR and then should be routed to the appropriate browser instance.
Since the message to SignalR is being sent by Biztalk, and not the MVC application, the ClientId of the connection to SignalR is not the one that identifies the browser instance that should receive the message. So what we are attempting to implement is somethign similar to the Return Address pattern by including the ClientId ConnectionId of the browser instance that initiates the Biztalk call in the message to Biztalk. When Biztalk sends its message to SignalR one of the contents is that original ClientId ConnectionId value. When SignalR processes the message from Biztalk it then can use the ClientId ConnectionId included in the message to route that message to the appropriate browser instance. (Yes we know that this won't work if the browser has been closed and re-opened and we're fine with that.)
The problem we face is that when initially sending the message to Biztalk from our MVC Action we cannot access the ClientId ConnectionId as it's only available in the Hub's Context. This is understandable since the MVC Action doesn't know which Hub context to look for.
What we have tried in it's place is to pass the SessionId through the Biztalk message and return it to SignalR. This solves the problem of including the browser instance identifier in the Biztalk message and returning it to SignalR. What it introduces is the fact that when a client connects to the Hub we cannot access the Session (and thus the SessionId) in the Hub's OnConnect method.
David Fowler posted a gist that reportedly shows how to make readonly SessionState accessible in a Hub but it doesn't work. (https://gist.github.com/davidfowl/4692934) As soon as we add this code into our application messages sent to SignalR cause a HTTP 500 error which is caused by SignalR throwing the following exception.
[ArgumentNullException: Value cannot be null.Parameter name: s]
System.IO.StringReader..ctor(String s) +10688601
Microsoft.AspNet.SignalR.Json.JsonNetSerializer.Parse(String json, Type targetType) +77
Microsoft.AspNet.SignalR.Json.JsonSerializerExtensions.Parse(IJsonSerializer serializer, String json) +184
Microsoft.AspNet.SignalR.Hubs.HubRequestParser.Parse(String data) +101
Microsoft.AspNet.SignalR.Hubs.HubDispatcher.OnReceived(IRequest request, String connectionId, String data) +143
Microsoft.AspNet.SignalR.<>c__DisplayClassc.<ProcessRequest>b__7() +96
Microsoft.AspNet.SignalR.<>c__DisplayClass3c.<FromMethod>b__3b() +41
Microsoft.AspNet.SignalR.TaskAsyncHelper.FromMethod(Func`1 func) +67
No matter the mode that we set SessionStateBehavior (as shown by David Fowler's gist) we either get this exception when sending a message to the Hub or SessionState is null when we are in the Hub's OnConnect.
So, after all that pre-amble, what we are asking is how do people update the appropriate client when working with this type of disconnected messaging in SignalR?
