Customizing SignalR's error messages

Question

I use the SignalR 1.0. When exception occurs on the server, the client gets a message like this

{"I":"0","E":"Exception of type 'System.Exception' was thrown.","T":" at METHODNAME in d:\PATH\TO\HUB.cs:line 227\r\n at METHODNAME in d:\PATH\TO\HUB.cs:line 51"}

But I want to make it more user-friendly. How to I can do it? I have read a suggestion to put all server methods into try-catch block. But I think that it is not a true-way.

I traced the Exception and found that the Exception was catched in the Microsoft.AspNet.SignalR.Hubs.HubDispatcher.Incoming method. But it is internal static method which I cannot customize.

In the ideal case I want to get ability to convert an exception to a valid response.

Answer 1

You can use a HubPipelineModule.

For example:

using System;
using System.Threading.Tasks;
using Microsoft.AspNet.SignalR.Hubs;

public class MyHubPipelineModule : HubPipelineModule
{
    protected override Func<IHubIncomingInvokerContext, Task<object>> BuildIncoming(Func<IHubIncomingInvokerContext, Task<object>> invoke)
    {
        return async context =>
        {
            try
            {
                // This is responsible for invoking every server-side Hub method in your SignalR app.
                return await invoke(context); 
            }
            catch (Exception e)
            {
                // If a Hub method throws, have it return the error message instead.
                return e.Message;
            }
        };
    }
}

Then in your Global.asax.cs:

protected void Application_Start()
{
    GlobalHost.HubPipeline.AddModule(new MyHubPipelineModule());
    //...
    RouteTable.Routes.MapHubs();
}