Using Web API inside a ASP.NET 5 MVC 6 Application

Question

I have an ASP.NET 5 MVC 6 application containing custom error pages. If I now want to add an API controller under the /api path, I have seen the following pattern using the Map method:

public class Startup
{
    public void Configure(IApplicationBuilder application)
    {
        application.Map("/api", ConfigureApi);

        application.UseStatusCodePagesWithReExecute("/error/{0}");

        application.UseMvc();
    }

    private void ConfigureApi(IApplicationBuilder application)
    {
        app.Run(async (context) =>
        {
            await context.Response.WriteAsync("Hello World from API!");
        });
    }
}

The above code creates a brand new separate application under the /api path. This is great, as you don't want custom error pages for your Web API but do want them for your MVC application.

Am I right in thinking that in the ConfigureApi, I should be adding MVC again so I can use controllers? Also, how do I configure the services, options and filters specifically for this sub-application? Is there a way to have a ConfigureServices(IServiceCollection services) for this sub-application?

private void ConfigureApi(IApplicationBuilder app)
{
    application.UseMvc();
}

Answer 1

Here's how you could do with a little extension method enabling "conditional middleware execution":

public class Startup {
    public void Configure(IApplicationBuilder app) {
        app.UseWhen(context => !context.Request.Path.StartsWithSegments(new PathString("/api")), branch => {
            // Register the status code middleware, but only for non-API calls.
            branch.UseStatusCodePagesWithReExecute("/error/{0}");
        });

        app.UseMvc();
   }
}


public static class AppBuilderExtensions {
    public static IApplicationBuilder UseWhen(this IApplicationBuilder app,
        Func<HttpContext, bool> condition, Action<IApplicationBuilder> configuration) {
        if (app == null) {
            throw new ArgumentNullException(nameof(app));
        }

        if (condition == null) {
            throw new ArgumentNullException(nameof(condition));
        }

        if (configuration == null) {
            throw new ArgumentNullException(nameof(configuration));
        }

        var builder = app.New();
        configuration(builder);

        return app.Use(next => {
            builder.Run(next);

            var branch = builder.Build();

            return context => {
                if (condition(context)) {
                    return branch(context);
                }

                return next(context);
            };
        });
    }
}