AddSpaStaticFiles/UseSpaStaticFiles APIs to clean up the React template (or other cases where SPA files are outside wwwroot)

build/dependencies.props

@@ -15,6 +15,7 @@
     <MicrosoftAspNetCoreStaticFilesPackageVersion>2.1.0-preview1-27478</MicrosoftAspNetCoreStaticFilesPackageVersion>
     <MicrosoftAspNetCoreWebSocketsPackageVersion>2.1.0-preview1-27478</MicrosoftAspNetCoreWebSocketsPackageVersion>
     <MicrosoftExtensionsDependencyInjectionPackageVersion>2.1.0-preview1-27478</MicrosoftExtensionsDependencyInjectionPackageVersion>
+    <MicrosoftExtensionsFileProvidersPhysicalPackageVersion>2.1.0-preview1-27478</MicrosoftExtensionsFileProvidersPhysicalPackageVersion>
     <MicrosoftExtensionsLoggingConsolePackageVersion>2.1.0-preview1-27478</MicrosoftExtensionsLoggingConsolePackageVersion>
     <MicrosoftExtensionsLoggingDebugPackageVersion>2.1.0-preview1-27478</MicrosoftExtensionsLoggingDebugPackageVersion>
     <MicrosoftNETCoreApp20PackageVersion>2.0.0</MicrosoftNETCoreApp20PackageVersion>

src/Microsoft.AspNetCore.SpaServices.Extensions/Microsoft.AspNetCore.SpaServices.Extensions.csproj

@@ -12,6 +12,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.AspNetCore.StaticFiles" Version="$(MicrosoftAspNetCoreStaticFilesPackageVersion)" />
     <PackageReference Include="Microsoft.AspNetCore.WebSockets" Version="$(MicrosoftAspNetCoreWebSocketsPackageVersion)" />
+    <PackageReference Include="Microsoft.Extensions.FileProviders.Physical" Version="$(MicrosoftExtensionsFileProvidersPhysicalPackageVersion)" />
   </ItemGroup>
 
 </Project>

src/Microsoft.AspNetCore.SpaServices.Extensions/SpaDefaultPageMiddleware.cs

@@ -3,6 +3,7 @@
 
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Hosting;
+using Microsoft.Extensions.DependencyInjection;
 using System;
 
 namespace Microsoft.AspNetCore.SpaServices
@@ -26,11 +27,12 @@ namespace Microsoft.AspNetCore.SpaServices
                 return next();
             });
 
-            // Serve it as file from wwwroot (by default), or any other configured file provider
-            app.UseStaticFiles(new StaticFileOptions
-            {
-                FileProvider = options.DefaultPageFileProvider
-            });
+            // Serve it as a static file
+            // Developers who need to host more than one SPA with distinct default pages can
+            // override the file provider
+            app.UseSpaStaticFilesInternal(
+                overrideFileProvider: options.DefaultPageFileProvider,
+                allowFallbackOnServingWebRootFiles: true);
 
             // If the default file didn't get served as a static file (usually because it was not
             // present on disk), the SPA is definitely not going to work.

src/Microsoft.AspNetCore.SpaServices.Extensions/StaticFiles/DefaultSpaStaticFileProvider.cs

@@ -0,0 +1,52 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.FileProviders;
+using System;
+using System.IO;
+
+namespace Microsoft.AspNetCore.SpaServices.StaticFiles
+{
+    /// <summary>
+    /// Provides an implementation of <see cref="ISpaStaticFileProvider"/> that supplies
+    /// physical files at a location configured using <see cref="SpaStaticFilesOptions"/>.
+    /// </summary>
+    internal class DefaultSpaStaticFileProvider : ISpaStaticFileProvider
+    {
+        private IFileProvider _fileProvider;
+
+        public DefaultSpaStaticFileProvider(
+            IServiceProvider serviceProvider,
+            SpaStaticFilesOptions options)
+        {
+            if (options == null)
+            {
+                throw new ArgumentNullException(nameof(options));
+            }
+
+            if (string.IsNullOrEmpty(options.RootPath))
+            {
+                throw new ArgumentException($"The {nameof(options.RootPath)} property " +
+                    $"of {nameof(options)} cannot be null or empty.");
+            }
+
+            var env = serviceProvider.GetRequiredService<IHostingEnvironment>();
+            var absoluteRootPath = Path.Combine(
+                env.ContentRootPath,
+                options.RootPath);
+
+            // PhysicalFileProvider will throw if you pass a non-existent path,
+            // but we don't want that scenario to be an error because for SPA
+            // scenarios, it's better if non-existing directory just means we
+            // don't serve any static files.
+            if (Directory.Exists(absoluteRootPath))
+            {
+                _fileProvider = new PhysicalFileProvider(absoluteRootPath);
+            }
+        }
+
+        public IFileProvider FileProvider => _fileProvider;
+    }
+}

src/Microsoft.AspNetCore.SpaServices.Extensions/StaticFiles/ISpaStaticFileProvider.cs

@@ -0,0 +1,20 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.Extensions.FileProviders;
+
+namespace Microsoft.AspNetCore.SpaServices.StaticFiles
+{
+    /// <summary>
+    /// Represents a service that can provide static files to be served for a Single Page
+    /// Application (SPA).
+    /// </summary>
+    public interface ISpaStaticFileProvider
+    {
+        /// <summary>
+        /// Gets the file provider, if available, that supplies the static files for the SPA.
+        /// The value is <c>null</c> if no file provider is available.
+        /// </summary>
+        IFileProvider FileProvider { get; }
+    }
+}

src/Microsoft.AspNetCore.SpaServices.Extensions/StaticFiles/SpaStaticFilesExtensions.cs

@@ -0,0 +1,125 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.SpaServices.StaticFiles;
+using Microsoft.Extensions.FileProviders;
+using Microsoft.Extensions.Options;
+using System;
+
+namespace Microsoft.Extensions.DependencyInjection
+{
+    /// <summary>
+    /// Extension methods for configuring an application to serve static files for a
+    /// Single Page Application (SPA).
+    /// </summary>
+    public static class SpaStaticFilesExtensions
+    {
+        /// <summary>
+        /// Registers an <see cref="ISpaStaticFileProvider"/> service that can provide static
+        /// files to be served for a Single Page Application (SPA).
+        /// </summary>
+        /// <param name="services">The <see cref="IServiceCollection"/>.</param>
+        /// <param name="configuration">If specified, this callback will be invoked to set additional configuration options.</param>
+        public static void AddSpaStaticFiles(
+            this IServiceCollection services,
+            Action<SpaStaticFilesOptions> configuration = null)
+        {
+            services.AddSingleton<ISpaStaticFileProvider>(serviceProvider =>
+            {
+                // Use the options configured in DI (or blank if none was configured)
+                var optionsProvider = serviceProvider.GetService<IOptions<SpaStaticFilesOptions>>();
+                var options = optionsProvider.Value;
+
+                // Allow the developer to perform further configuration
+                configuration?.Invoke(options);
+
+                if (string.IsNullOrEmpty(options.RootPath))
+                {
+                    throw new InvalidOperationException($"No {nameof(SpaStaticFilesOptions.RootPath)} " +
+                        $"was set on the {nameof(SpaStaticFilesOptions)}.");
+                }
+
+                return new DefaultSpaStaticFileProvider(serviceProvider, options);
+            });
+        }
+
+        /// <summary>
+        /// Configures the application to serve static files for a Single Page Application (SPA).
+        /// The files will be located using the registered <see cref="ISpaStaticFileProvider"/> service.
+        /// </summary>
+        /// <param name="applicationBuilder">The <see cref="IApplicationBuilder"/>.</param>
+        public static void UseSpaStaticFiles(this IApplicationBuilder applicationBuilder)
+        {
+            if (applicationBuilder == null)
+            {
+                throw new ArgumentNullException(nameof(applicationBuilder));
+            }
+
+            UseSpaStaticFilesInternal(applicationBuilder,
+                overrideFileProvider: null,
+                allowFallbackOnServingWebRootFiles: false);
+        }
+
+        internal static void UseSpaStaticFilesInternal(
+            this IApplicationBuilder app,
+            IFileProvider overrideFileProvider,
+            bool allowFallbackOnServingWebRootFiles)
+        {
+            var shouldServeStaticFiles = ShouldServeStaticFiles(
+                app,
+                overrideFileProvider,
+                allowFallbackOnServingWebRootFiles,
+                out var fileProviderOrDefault);
+
+            if (shouldServeStaticFiles)
+            {
+                app.UseStaticFiles(new StaticFileOptions
+                {
+                    FileProvider = fileProviderOrDefault
+                });
+            }
+        }
+
+        private static bool ShouldServeStaticFiles(
+            IApplicationBuilder app,
+            IFileProvider overrideFileProvider,
+            bool allowFallbackOnServingWebRootFiles,
+            out IFileProvider fileProviderOrDefault)
+        {
+            if (overrideFileProvider != null)
+            {
+                // If the file provider was explicitly supplied, that takes precedence over any other
+                // configured file provider. This is most useful if the application hosts multiple SPAs
+                // (via multiple calls to UseSpa()), so each needs to serve its own separate static files
+                // instead of using AddSpaStaticFiles/UseSpaStaticFiles.
+                fileProviderOrDefault = overrideFileProvider;
+                return true;
+            }
+
+            var spaStaticFilesService = app.ApplicationServices.GetService<ISpaStaticFileProvider>();
+            if (spaStaticFilesService != null)
+            {
+                // If an ISpaStaticFileProvider was configured but it says no IFileProvider is available
+                // (i.e., it supplies 'null'), this implies we should not serve any static files. This
+                // is typically the case in development when SPA static files are being served from a
+                // SPA development server (e.g., Angular CLI or create-react-app), in which case no
+                // directory of prebuilt files will exist on disk.
+                fileProviderOrDefault = spaStaticFilesService.FileProvider;
+                return fileProviderOrDefault != null;
+            }
+            else if (!allowFallbackOnServingWebRootFiles)
+            {
+                throw new InvalidOperationException($"To use {nameof(UseSpaStaticFiles)}, you must " +
+                    $"first register an {nameof(ISpaStaticFileProvider)} in the service provider, typically " +
+                    $"by calling services.{nameof(AddSpaStaticFiles)}.");
+            }
+            else
+            {
+                // Fall back on serving wwwroot
+                fileProviderOrDefault = null;
+                return true;
+            }
+        }
+    }
+}

src/Microsoft.AspNetCore.SpaServices.Extensions/StaticFiles/SpaStaticFilesOptions.cs

@@ -0,0 +1,23 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Microsoft.AspNetCore.SpaServices.StaticFiles
+{
+    /// <summary>
+    /// Represents options for serving static files for a Single Page Application (SPA).
+    /// </summary>
+    public class SpaStaticFilesOptions
+    {
+        /// <summary>
+        /// Gets or sets the path, relative to the application root, of the directory in which
+        /// the physical files are located.
+        /// 
+        /// If the specified directory does not exist, then the
+        /// <see cref="SpaStaticFilesExtensions.UseSpaStaticFiles(Builder.IApplicationBuilder)"/>
+        /// middleware will not serve any static files.
+        /// </summary>
+        public string RootPath { get; set; }
+    }
+}