SpaApplicationBuilderExtensions.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using Microsoft.AspNetCore.SpaServices;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Options;

namespace Microsoft.AspNetCore.Builder;

/// <summary>
/// Provides extension methods used for configuring an application to
/// host a client-side Single Page Application (SPA).
/// </summary>
public static class SpaApplicationBuilderExtensions
{
    /// <summary>
    /// Handles all requests from this point in the middleware chain by returning
    /// the default page for the Single Page Application (SPA).
    ///
    /// This middleware should be placed late in the chain, so that other middleware
    /// for serving static files, MVC actions, etc., takes precedence.
    /// </summary>
    /// <param name="app">The <see cref="IApplicationBuilder"/>.</param>
    /// <param name="configuration">
    /// This callback will be invoked so that additional middleware can be registered within
    /// the context of this SPA.
    /// </param>
    public static void UseSpa(this IApplicationBuilder app, Action<ISpaBuilder> configuration)
    {
        ArgumentNullException.ThrowIfNull(configuration);

        // Use the options configured in DI (or blank if none was configured). We have to clone it
        // otherwise if you have multiple UseSpa calls, their configurations would interfere with one another.
        var optionsProvider = app.ApplicationServices.GetService<IOptions<SpaOptions>>()!;
        var options = new SpaOptions(optionsProvider.Value);

        var spaBuilder = new DefaultSpaBuilder(app, options);
        configuration.Invoke(spaBuilder);
        SpaDefaultPageMiddleware.Attach(spaBuilder);
    }
}