Decode ASP.NET WEB API exception to user frendly message

I am using EXT.NET to communicate with ASP.NET WinForms WEB API server.
From time to time my WEB API server throw some exceptions.
How I can parse these messages so users can read message.

Here is how I make call to web server

Code:

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<ext:Button ID="adoDugme" runat="server" Text="klikniMe" Icon="CarStart">
    <DirectEvents>
        <Click
             
              Url="~/desktopmodules/parkingKartice/api/op/SaveModel"
              Success =" alert(Ext.encode(result));"
                Failure="alert(Ext.decode(result).ExceptionMessage)"   
                Type="Load"
                Method="POST"
               
                Json="true" >
            <ExtraParams>
                <ext:Parameter Name="values" Value="Ext.encode(#{grid}.getRowsValues({dirtyRowsOnly : true}))" Mode="Raw"></ext:Parameter>
            </ExtraParams>
            </Click>
    </DirectEvents>

</ext:Button>

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Here is what I get when I fall into exception

Attachment 9581

If i simply comment Failure handler , I get Ext.Net error window but message is again unreadebile

Hi @Admir,

So, what do you see in an alert box?

Code:

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Failure="alert(Ext.decode(result).ExceptionMessage)"

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When I call

Code:

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alert(Ext.decode(result).ExceptionMessage)

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Chrome's console report exception like this

Code:

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Uncaught Ext.JSON.decode(): You're trying to decode an invalid JSON String: [object Object]
Ext.Error.Ext.extend.statics.raise
Ext.JSON.me.decode
Ext.net.directRequest.userFailure (index):46
o.failure
Ext.apply.callback
Ext.define.onComplete
Ext.define.onStateChange
(anonymous function)

---

Here is How Response looks like

Code:

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{"Message":"An error has occurred.","ExceptionMessage":"Nema ovdje nikoga","ExceptionType":"System.Exception","StackTrace":"  at Christoc.Modules.parkingKartice.opController.SaveModel(HttpRequestMessage request) in c:\\dnn\\DesktopModules\\parkingKartice\\opController.cs:line 67\r\n  at lambda_method(Closure , Object , Object[] )\r\n  at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.<>c__DisplayClass13.<GetExecutor>b__c(Object instance, Object[] methodParameters)\r\n  at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.Execute(Object instance, Object[] arguments)\r\n  at System.Threading.Tasks.TaskHelpers.RunSynchronously[TResult](Func`1 func, CancellationToken cancellationToken)"}

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When I passte that to json2csharp.com

I get decoded class

Code:

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public class RootObject
{
    public string Message { get; set; }
    public string ExceptionMessage { get; set; }
    public string ExceptionType { get; set; }
    public string StackTrace { get; set; }
}

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I think to decode it by Ext.decode(), all double quotes have to be escaped by "\" symbol.