ASP.net core MVC catch all route serve static file

I had to make some additions to @DavidG answer. Here is what I ended up with

Startup.cs

app.UseStaticFiles();

app.UseMvc(routes =>
{
   routes.MapRoute("default", "{controller}/{action}");

   routes.MapRoute("Spa", "{*url}", defaults: new { controller = "Home", action = "Spa" });
});

HomeController.cs

public class HomeController : Controller
{
  public IActionResult Spa()
  {
      return File("~/index.html", "text/html");
  }
}

ASP.NET Core catch all routes for Web API and MVC are configured differently

With Web API (if you're using prefix "api" for all server-side controllers eg. Route("api/[controller"]):

app.Use(async (context, next) => 
{ 
    await next(); 
    var path = context.Request.Path.Value;

    if (!path.StartsWith("/api") && !Path.HasExtension(path)) 
    { 
        context.Request.Path = "/index.html"; 
        await next(); 
    } 
});            

app.UseStaticFiles();
app.UseDefaultFiles();

app.UseMvc();

With MVC (dotnet add package Microsoft.AspNetCore.SpaServices -Version x.y.z):

app.UseStaticFiles();
app.UseDefaultFiles();

app.UseMvc(routes => 
{ 
    routes.MapRoute( 
        name: "default", 
        template: "{controller=Home}/{action=Index}"); 

    routes.MapSpaFallbackRoute("spa", new { controller = "Home", action = "Index" }); 
});  

In case you don't want manually specify which routes are for api:

app.UseDefaultFiles();
app.UseStaticFiles();

app.UseMvc() // suggestion: you can move all the SPA requests to for example /app/<endpoints_for_the_Spa> and let the mvc return 404 in case <endpoints_for_the_Spa> is not recognized by the backend. This way SPA will not receive index.html

// at this point the request did not hit the api nor any of the files

// return index instead of 404 and let the SPA to take care of displaying the "not found" message
app.Use(async (context, next) => {
    context.Request.Path = "/index.html";
    await next();
});
app.UseStaticFiles(); // this will return index.html

What I'm using that works well is Microsoft.AspNetCore.Builder.SpaRouteExtensions.MapSpaFallbackRoute:

app.UseMvc(routes =>
{
    // Default route for SPA components, excluding paths which appear to be static files (have an extension)
    routes.MapSpaFallbackRoute(
        "spaFallback",
        new { controller = "Home", action = "Index" });
});

HomeController.Index has the equivalent of your index.html. You can probably route to a static page also.

A bit off topic, but if you also have an API in the same project under an api folder you can set a default 404 response for any API routes that don't match:

routes.MapRoute(
    "apiDefault",
    "api/{*url}",
    new { controller = "Home", action = "ApiNotFound" });

You would end up with the following behavior:

• /controller => No extension, so serve SPA default page from HomeController.Index and let SPA handle routing
• /file.txt => Extension detected, serve static file
• /api/controller => proper API response (use attribute routing or set up another map for the API controllers)
• /api/non-existent-route => 404 NotFound() returned from HomeController.ApiNotFound

In many cases you'll want an API in a separate project, but this is a viable alternative.

In order to serve index.html from wwwroot folder the following directives should be added (.Net Core 2).

This allows to serve static files:

app.UseStaticFiles();

This allows to get default files, e.g. index.html:

app.UseDefaultFiles();

In ASP.NET Core 3.1, I've used the following:

Startup.cs

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    app.UseRouting();

    app.UseCors();

    app.UseEndpoints(endpoints =>
    {
        endpoints.MapControllers();
    });

    app.UseDefaultFiles();
    app.UseStaticFiles();
}

MyController.cs

[HttpGet("{anything}")]
public IActionResult GetSPA()
{
    return File("~/index.html", "text/html");
}

In .NET Core 6, add app.MapFallbackToFile("index.html"); in your Program.cs file.

Here is example code from the ASP.NET Core with React project template:

app.MapControllerRoute(
    name: "default",
    pattern: "{controller}/{action=Index}/{id?}");

app.MapFallbackToFile("index.html");  

app.Run();