Url rewrite in exception middleware - asp.net-mvc

Question

I'm trying to do some custom exception handling and in there I need to redirect.
They way to go should be like this
app.UseExceptionHandler(appBuilder =>
{
appBuilder.Use(async (ctx, next) =>
{
ctx.Request.Path = "/Error";
await next();
});
});
But nothing happens, just a blank 500 page.
Any ideas except the use of
ctx.Response.Redirect("/Error")

Answer 1

When you use the overload of UseExceptionHandler accepting an Action<IApplicationBuilder>, you need to configure a full pipeline for the sub-builder inside to re-execute the pipeline on the exception branch. In your code, you just set the Request.Path but it is then not handled by any code. You need to add an MVC middleware as the terminal at the end. You can configure it just like you configure your main pipeline (UseMvc, UseEndpoints). In this case the terminal just need to work with the specific request path you set before. Here's the code:
app.UseExceptionHandler(appBuilder => {
appBuilder.Use(async (ctx, next) => {
ctx.Request.Path = "/Error";
await next();
});
//add the terminal to handle the branched request
appBuilder.UseMvc();
});
Now when you run into some unhandled exception, it should work just like app.UseExceptionHandler("/Error").

Answer 2

According to your description, I suggest you could firstly try to understand how the exceptionhanlder works.
According to the source codes, you could find if you want to write the custom middleware ,you should use the second function like this:
public static IApplicationBuilder UseExceptionHandler(this IApplicationBuilder app, Action<IApplicationBuilder> configure)
{
if (app == null)
{
throw new ArgumentNullException(nameof(app));
}
if (configure == null)
{
throw new ArgumentNullException(nameof(configure));
}
var subAppBuilder = app.New();
configure(subAppBuilder);
var exceptionHandlerPipeline = subAppBuilder.Build();
return app.UseExceptionHandler(new ExceptionHandlerOptions
{
ExceptionHandler = exceptionHandlerPipeline
});
}
If you use this function, you could find it will still call the ExceptionHandlerMiddleware with its new exceptionHandlerPipeline. And in the ExceptionHandlerMiddleware , you could find it will call this request delaget.
So if you don't catch the exception and directly set the context path it will not work. So I suggest you could try to use below codes:
app.UseExceptionHandler(appBuilder =>
{
app.Use(async (context, next) =>
{
try
{
await next();
}
catch (Exception ex)
{
ClearHttpContext(context);
var exceptionHandlerFeature = new ExceptionHandlerFeature()
{
Error = ex,
Path = "/Home/Index",
};
context.Request.Path = "/Home/Error";
context.Features.Set<IExceptionHandlerFeature>(exceptionHandlerFeature);
context.Features.Set<IExceptionHandlerPathFeature>(exceptionHandlerFeature);
context.Response.StatusCode = StatusCodes.Status500InternalServerError;
context.Response.OnStarting(ClearCacheHeaders, context.Response);
await next();
}
});
});
ClearCacheHeaders method:
private static Task ClearCacheHeaders(object state)
{
var headers = ((HttpResponse)state).Headers;
headers[HeaderNames.CacheControl] = "no-cache,no-store";
headers[HeaderNames.Pragma] = "no-cache";
headers[HeaderNames.Expires] = "-1";
headers.Remove(HeaderNames.ETag);
return Task.CompletedTask;
}