[Blazor] Custom JS initializers (#34798)

* Users can create an ES6 module with `<packageName>.lib.module.js` and declare a beforeStart and afterStarted function to integrate into the blazor start process.
* In WebAssembly beforeStart receives the BlazorWebAssemblyStartOptions object and any publish extension as part of the method arguments.
* In Server beforeStart receives the CircuitStartOptions object and can configure any necessary details.
* In Desktop beforeStart does not receive any argument for the time being.
* afterStarted receives the Blazor object as argument in all cases.
* Callbacks in beforeStart and afterStarted are not invoked in any defined order and are invoked in parallel.

Author: javiercn

src/Components/Authorization/src/AuthorizeRouteView.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Components.Rendering;
@@ -95,6 +96,10 @@ private void RenderAuthorizeRouteViewCore(RenderTreeBuilder builder)
             builder.CloseComponent();
         }
 
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2111:RequiresUnreferencedCode",
+            Justification = "OpenComponent already has the right set of attributes")]
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2110:RequiresUnreferencedCode",
+            Justification = "OpenComponent already has the right set of attributes")]
         private void RenderContentInDefaultLayout(RenderTreeBuilder builder, RenderFragment content)
         {
             builder.OpenComponent<LayoutView>(0);

src/Components/Server/src/Builder/ComponentEndpointConventionBuilder.cs

@@ -12,11 +12,13 @@ public sealed class ComponentEndpointConventionBuilder : IHubEndpointConventionB
     {
         private readonly IEndpointConventionBuilder _hubEndpoint;
         private readonly IEndpointConventionBuilder _disconnectEndpoint;
+        private readonly IEndpointConventionBuilder _jsInitializersEndpoint;
 
-        internal ComponentEndpointConventionBuilder(IEndpointConventionBuilder hubEndpoint, IEndpointConventionBuilder disconnectEndpoint)
+        internal ComponentEndpointConventionBuilder(IEndpointConventionBuilder hubEndpoint, IEndpointConventionBuilder disconnectEndpoint, IEndpointConventionBuilder jsInitializersEndpoint)
         {
             _hubEndpoint = hubEndpoint;
             _disconnectEndpoint = disconnectEndpoint;
+            _jsInitializersEndpoint = jsInitializersEndpoint;
         }
 
         /// <summary>
@@ -27,6 +29,7 @@ public void Add(Action<EndpointBuilder> convention)
         {
             _hubEndpoint.Add(convention);
             _disconnectEndpoint.Add(convention);
+            _jsInitializersEndpoint.Add(convention);
         }
     }
 }

src/Components/Server/src/Builder/ComponentEndpointRouteBuilderExtensions.cs

@@ -3,9 +3,12 @@
 
 using System;
 using Microsoft.AspNetCore.Components.Server;
+using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Http.Connections;
 using Microsoft.AspNetCore.Routing;
 using Microsoft.AspNetCore.SignalR;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
 
 namespace Microsoft.AspNetCore.Builder
 {
@@ -110,7 +113,12 @@ public static ComponentEndpointConventionBuilder MapBlazorHub(
                 endpoints.CreateApplicationBuilder().UseMiddleware<CircuitDisconnectMiddleware>().Build())
                 .WithDisplayName("Blazor disconnect");
 
-            return new ComponentEndpointConventionBuilder(hubEndpoint, disconnectEndpoint);
+            var jsInitializersEndpoint = endpoints.Map(
+                (path.EndsWith('/') ? path : path + "/") + "initializers/",
+                endpoints.CreateApplicationBuilder().UseMiddleware<CircuitJavaScriptInitializationMiddleware>().Build())
+                .WithDisplayName("Blazor initializers");
+
+            return new ComponentEndpointConventionBuilder(hubEndpoint, disconnectEndpoint, jsInitializersEndpoint);
         }
     }
 }

src/Components/Server/src/CircuitJavaScriptInitializationMiddleware.cs

@@ -0,0 +1,26 @@
+// 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.Components.Server;
+using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.Options;
+
+namespace Microsoft.AspNetCore.Builder
+{
+    internal class CircuitJavaScriptInitializationMiddleware
+    {
+        private readonly IList<string> _initializers;
+
+        // We don't need the request delegate for anything, however we need to inject it to satisfy the middleware
+        // contract.
+        public CircuitJavaScriptInitializationMiddleware(IOptions<CircuitOptions> options, RequestDelegate _)
+        {
+            _initializers = options.Value.JavaScriptInitializers;
+        }
+
+        public async Task InvokeAsync(HttpContext context)
+        {
+            await context.Response.WriteAsJsonAsync(_initializers);
+        }
+    }
+}

src/Components/Server/src/CircuitOptions.cs

@@ -1,8 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-using System;
-using Microsoft.AspNetCore.Components.Web;
+using Microsoft.Extensions.Hosting;
 
 namespace Microsoft.AspNetCore.Components.Server
 {
@@ -82,5 +81,7 @@ public sealed class CircuitOptions
         /// Gets options for root components within the circuit.
         /// </summary>
         public CircuitRootComponentOptions RootComponents { get; } = new CircuitRootComponentOptions();
+
+        internal IList<string> JavaScriptInitializers { get; } = new List<string>();
     }
 }

src/Components/Server/src/Circuits/CircuitOptionsJavaScriptInitializersConfiguration.cs

@@ -0,0 +1,33 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Text.Json;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.Extensions.Options;
+
+namespace Microsoft.AspNetCore.Components.Server.Circuits
+{
+    internal class CircuitOptionsJavaScriptInitializersConfiguration : IConfigureOptions<CircuitOptions>
+    {
+        private readonly IWebHostEnvironment _environment;
+
+        public CircuitOptionsJavaScriptInitializersConfiguration(IWebHostEnvironment environment)
+        {
+            _environment = environment;
+        }
+
+        public void Configure(CircuitOptions options)
+        {
+            var file = _environment.WebRootFileProvider.GetFileInfo($"{_environment.ApplicationName}.modules.json");
+            if (file.Exists)
+            {
+                var initializers = JsonSerializer.Deserialize<string[]>(file.CreateReadStream());
+                for (var i = 0; i < initializers.Length; i++)
+                {
+                    var initializer = initializers[i];
+                    options.JavaScriptInitializers.Add(initializer);
+                }
+            }
+        }
+    }
+}

src/Components/Server/src/ComponentHub.cs

@@ -13,6 +13,7 @@
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.SignalR;
 using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
 
 namespace Microsoft.AspNetCore.Components.Server
 {

src/Components/Server/src/DependencyInjection/ComponentServiceCollectionExtensions.cs

@@ -83,6 +83,7 @@ public static IServerSideBlazorBuilder AddServerSideBlazor(this IServiceCollecti
             services.AddScoped<AuthenticationStateProvider, ServerAuthenticationStateProvider>();
 
             services.TryAddEnumerable(ServiceDescriptor.Singleton<IConfigureOptions<CircuitOptions>, CircuitOptionsJSInteropDetailedErrorsConfiguration>());
+            services.TryAddEnumerable(ServiceDescriptor.Singleton<IConfigureOptions<CircuitOptions>, CircuitOptionsJavaScriptInitializersConfiguration>());
 
             if (configure != null)
             {

src/Components/Server/test/ComponentEndpointRouteBuilderExtensionsTest.cs

@@ -2,10 +2,11 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Diagnostics;
-using System.Threading.Tasks;
 using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Hosting;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.FileProviders;
 using Microsoft.Extensions.Hosting;
 using Moq;
 using Xunit;
@@ -54,6 +55,9 @@ public void MapBlazorHub_MostGeneralOverload_MapsUnderlyingHub()
 
         private IApplicationBuilder CreateAppBuilder()
         {
+            var environment = new Mock<IWebHostEnvironment>();
+            environment.SetupGet(e => e.ApplicationName).Returns("app");
+            environment.SetupGet(e => e.WebRootFileProvider).Returns(new NullFileProvider());
             var services = new ServiceCollection();
             services.AddSingleton(Mock.Of<IHostApplicationLifetime>());
             services.AddLogging();
@@ -64,6 +68,7 @@ private IApplicationBuilder CreateAppBuilder()
             services.AddRouting();
             services.AddSignalR();
             services.AddServerSideBlazor();
+            services.AddSingleton(environment.Object);
             services.AddSingleton<IConfiguration>(new ConfigurationBuilder().Build());
 
             var serviceProvider = services.BuildServiceProvider();