global.asax 中的 Application_Error 未捕获 WebAPI 中的错误

Question

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 1

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

//register your filter with Web API pipeline
//this belongs in the Application_Start event in Global Application Handler class (global.asax)
//or some other location that runs on startup
GlobalConfiguration.Configuration.Filters.Add(new LogExceptionFilterAttribute());

//Create filter
public class LogExceptionFilterAttribute : ExceptionFilterAttribute 
{
    public override void OnException(HttpActionExecutedContext context)
    {
        ErrorLogService.LogError(context.Exception);
    }
}

//in global.asax or global.asax.cs
protected void Application_Error(object sender, EventArgs e)
{
    Exception ex = Server.GetLastError();
    ErrorLogService.LogError(ex);
} 

//common service to be used for logging errors
public static class ErrorLogService
{
    public static void LogError(Exception ex)
    {
        //Email developers, call fire department, log to database etc.
    }
}

Errors from Web API do not trigger the Application_Error event. But we can create an exception filter and register it to handle the errors. Also see Global Error Handling in ASP.NET Web API 2 .

Answer 2

In my case, i prefer not use Web.config. Then i created code above in Global.asax file:

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

        //Not Found (When user digit unexisting url)
        if(ex is HttpException && ((HttpException)ex).GetHttpCode() == 404)
        {
            HttpContextWrapper contextWrapper = new HttpContextWrapper(this.Context);

            RouteData routeData = new RouteData();
            routeData.Values.Add("controller", "Error");
            routeData.Values.Add("action", "NotFound");

            IController controller = new ErrorController();
            RequestContext requestContext = new RequestContext(contextWrapper, routeData);
            controller.Execute(requestContext);
            Response.End();
        }
        else //Unhandled Errors from aplication
        {
            ErrorLogService.LogError(ex);
            HttpContextWrapper contextWrapper = new HttpContextWrapper(this.Context);

            RouteData routeData = new RouteData();
            routeData.Values.Add("controller", "Error");
            routeData.Values.Add("action", "Index");

            IController controller = new ErrorController();
            RequestContext requestContext = new RequestContext(contextWrapper, routeData);
            controller.Execute(requestContext);
            Response.End();
        }
    }

And thtat is my ErrorController.cs

public class ErrorController : Controller
{
    // GET: Error
    public ViewResult Index()
    {
        Response.StatusCode = 500;
        Exception ex = Server.GetLastError();
        return View("~/Views/Shared/SAAS/Error.cshtml", ex);
    }

    public ViewResult NotFound()
    {
        Response.StatusCode = 404;
        return View("~/Views/Shared/SAAS/NotFound.cshtml");
    }
}

And that is my ErrorLogService.cs copyed from @mason class

//common service to be used for logging errors
public static class ErrorLogService
{
    public static void LogError(Exception ex)
    {
        //Do what you want here, save log in database, send email to police station
    }
}