Andrew Gray Andrew Gray - 2 months ago 23
C# Question

Application_Error in global.asax not catching errors in WebAPI

For a project I am working on, one of the things we're implementing is something that we have code for in some of my teams older ASP.NET and MVC projects - an

Application_Error
exception catcher that dispatches an email to the development team with the exception experience and most relevant details.

Here's how it looks:

Global.asax:

protected void Application_Error(object sender, EventArgs e)
{
Exception ex = Server.GetLastError();
string path = "N/A";
if (sender is HttpApplication)
path = ((HttpApplication) sender).Request.Url.PathAndQuery;

string args = string.Format("<b>Path:</b> {0}", path);

// Custom code that generates an HTML-formatted exception dump
string message = Email.GenerateExceptionMessage(ex, args);

// Custom code that sends an email to the dev team.
Email.SendUnexpectedErrorMessage("Some App", message);
}


One "minor" problem, though - when I intentionally have a part of the code throw an exception in order to test this mechanism...

public static void GetMuffinsByTopping(string topping)
{
throw new Exception("Test Exception!", new Exception("Test Inner Exception!!!"));

// Actual repository code is unreachable while this test code is there
}


The front-end JavaScript is immediately intercepting an HTTP 500 request, but the global.asax.cs code noted above is not being reached (I set a breakpoint on the first executing line of the method.)

Question: In what way can I get the "old"
Application_Error
handler to dispatch error emails, so that our team's developers can more easily debug our application?

Answer

Abstract out your error handling logic from Application_Error into its own function. Create a Web API exception filter.

using System.Web.Http.Filters;

public class NotImplExceptionFilterAttribute : ExceptionFilterAttribute 
{
    public override void OnException(HttpActionExecutedContext context)
    {
        ErrorLogService.LogError(context.Exception);
    }
}

protected void Application_Error(object sender, EventArgs e)
{
    Exception ex = Server.GetLastError();
    ErrorLogService.LogError(ex);
} 

public static class ErrorLogService
{
    public static void LogError(Exception ex)
    {
        //Email developers, call fire department, log to database etc.
    }
}
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