Purpose of MapSpaFallbackRoute

What is the purpose of the following code which is automatically loaded to the Startup class with this project:

routes.MapSpaFallbackRoute(
    name: "spa-fallback",
    defaults: new { controller = "Home", action = "Index" });

This results in a 200 being thrown when a non-existent API endpoint is hit instead of a 404.

It's for when you want to handle the 404 within your front-end application (and as noted below, let all Routes go through so your front-end can handle them)

@MarkPieszak

@MarkPieszak My use case - which I assume is very common - is to want to handle bad angular routes in the front-end (by either sending to a "404" routes or just loading a "home" route), but throw 404s on bad API calls (that is, requests whose URL follows a certain pattern eg. "/api").

Can you give me a recommendation?

You want to use a mapWhen looking for something that starts with /api, use this below and you'll be all set:

           // this part you already have
           app.UseMvc(routes =>
            {
                routes.MapRoute(
                    name: "default",
                    template: "{controller=Home}/{action=Index}/{id?}");
            });

            // here you can see we make sure it doesn't start with /api, if it does, it'll 404 within .NET if it can't be found
            app.MapWhen(x => !x.Request.Path.Value.StartsWith("/api"), builder =>
            {
                builder.UseMvc(routes =>
                {
                    routes.MapSpaFallbackRoute(
                        name: "spa-fallback",
                        defaults: new { controller = "Home", action = "Index" });
                });
            });

Hope that helps!

@MarkPieszak

Thanks @MarkPieszak for the answer. If this becomes a common request, we could add a further excludePrefix option onto MapSpaFallbackRoute so you can set it to api.

Also:

It's for when you want to handle the 404 within your front-end application.

That's not the whole story. It's mostly just so that all URLs that might be handled by your front-end application cause the front-end application to be returned. For example, a request for the URL /counter (in the default template) should cause the front-end application to be loaded, which will then display a suitable UI. If you didn't have MapSpaFallbackRoute then the server would just return a 404 for /counter since there's no matching MVC controller.

@MarkPieszak

@MarkPieszak Perfect. Your solution works as desired.

Fantastic responsiveness as usual.

If you didn't have MapSpaFallbackRoute then the server would just return a 404 for /counter since there's no matching MVC controller.

So umm yeah, this is REALLY an important point that I hope does not get lost :)

Meaning. I can send someone a url like this:

http://helloworlddata.azurewebsites.net/counter

..and it works even though there is really no /counter page. It exists only as an Angular route :)

@SteveSandersonMS

That's not the whole story. It's mostly just so that all URLs that might be handled by your front-end application cause the front-end application to be returned. For example, a request for the URL /counter (in the default template) should cause the front-end application to be loaded, which will then display a suitable UI. If you didn't have MapSpaFallbackRoute then the server would just return a 404 for /counter since there's no matching MVC controller.

Yes apologies I should of mentioned that! @SteveSandersonMS

@MarkPieszak

For anyone who wants to use ASP.NET Razor Pages that came out with .NET Core 2.0 I never could get map fallback route to work so I pivoted and went a different direction which implements @MarkPieszak 's solution of only routing all requests to the SPA when the route doesn't start with API.

public void ConfigureServices(IServiceCollection services) =>
  services
    .AddMvc()
    .AddRazorPagesOptions(options =>
    {
      options.Conventions.AddPageRoute("/Index", "{*url:regex(^(?!api).*$)}");
    });

@buvinghausen

@buvinghausen That works well. Just be aware that every request that doesn't match a static file will get routed to your SPA - even requests with file extensions. MapSpaFallbackRoute does not match requests that look like filenames - that is, have an extension at the end.

Edit: I just realize you do account for periods in the request - but I'll leave my comment here just in case it helps others. Thanks!

Edit2: Just opened an issue with https://github.com/aspnet/JavaScriptServices with a suggestion: #1354

 app.UseMvc(routes =>
                {
                    routes.MapSpaFallbackRoute(
                    name: "spa-fallback-admin",
                    defaults: new { area="Admin", controller = "Home", action = "Index" });
                });

is this the correct way to using controller from some areas?

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Purpose of MapSpaFallbackRoute #973

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MarkPieszak commented on May 24, 2017

im1dermike commented on May 24, 2017

MarkPieszak commented on May 24, 2017

SteveSandersonMS commented on May 24, 2017

SteveSandersonMS commented on May 24, 2017

im1dermike commented on May 24, 2017

ADefWebserver commented on May 24, 2017

MarkPieszak commented on May 24, 2017

buvinghausen commented on Sep 9, 2017

pholly commented on Oct 25, 2017

ripasfilqadar commented on Apr 5, 2018

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