Question

I’ve been working with signalR for a little while now and this is the first instance of a problem I have a come across.

I have a client at domain “x” connected to my hub server on domain “y”. all is well… however when i try to invoke the client side method using a Client.Group(groupID).someMethod the client connected from outside of the hub domain isn’t getting a response? however if i use Client.All.someMethod everything works fine (The client gets a response).

Am I missing something when it comes to the groups and cross domain support?

Also, i had a little trouble getting the connection to the server hub from the outside domain, In the examples on github it wasn’t clear if the reference in the head should be:

<script src="http://localhost:61215/signalr/hubs" type="text/javascript"></script>

or

<script src="/signalr/hubs" type="text/javascript"></script>

the latter didn’t work…

Thanks in advance

Answer 1

Your issue with groups is likely do to the fact that groups aren’t automatically rejoined when a client reconnects. This isn’t an issue when running on the same domain because your clients are likely using the forever-frame or server-sent-events transport which won’t reconnect unless there is some issue with the underlying connection.

However, cross-origin access to SignalR requires either the WebSocket or long-polling transport. The latter is likely being used in your case considering the issue you are having with groups. (NOTE: Your SignalR server needs to be running .NET 4.5 on Windows 8 or 2012 to support WebSockets). The long-polling transport has to reconnect to the SignalR server every time it receives messages.

To fix this issue with the following:

namespace MySignalRApplication
{
    public class Global : System.Web.HttpApplication
    {
        protected void Application_Start(object sender, EventArgs e)
        {
            GlobalHost.HubPipeline.EnableAutoRejoiningGroups();
        }
    }    
}

By calling GlobalHost.HubPipeline.EnableAutoRejoiningGroups() you are allowing clients to rejoin groups when they reconnect. However, SignalR as of RC2 doesn’t verify the reconnecting clients were previously in the groups they are trying to rejoin. Of course, a well-behaving client will only try to rejoin groups it was previously in, but enabling automatic group rejoining on RC2 allows attackers to add themselves to any group. This is not an issue for many applications, but that’s why group rejoining isn’t enabled by default.

In the RTM version of SignalR, automatic group rejoining will be enabled by default. The list of groups the client tries to rejoin with will also be signed by the server making it much more secure.

As for your second question:

When ever you load JavaScript hosted on a domain that is different from the HTML being served, the script src must contain the absolute URL.

<script src="/signalr/hubs" type="text/javascript"></script>

The above contains a relative URL which is why it doesn’t work.