Support hot reload for Blazor component endpoints

src/Components/Endpoints/src/Builder/RazorComponentEndpointDataSource.cs

@@ -24,22 +24,27 @@ internal class RazorComponentEndpointDataSource<[DynamicallyAccessedMembers(Comp
     private readonly IApplicationBuilder _applicationBuilder;
     private readonly RenderModeEndpointProvider[] _renderModeEndpointProviders;
     private readonly RazorComponentEndpointFactory _factory;
-
+    private readonly HotReloadService? _hotReloadService;
     private List<Endpoint>? _endpoints;
-    // TODO: Implement endpoint data source updates https://github.com/dotnet/aspnetcore/issues/47026
-    private readonly CancellationTokenSource _cancellationTokenSource;
-    private readonly IChangeToken _changeToken;
+    private CancellationTokenSource _cancellationTokenSource;
+    private IChangeToken _changeToken;
+
+    // Internal for testing.
+    internal ComponentApplicationBuilder Builder => _builder;
+    internal List<Action<EndpointBuilder>> Conventions => _conventions;
 
     public RazorComponentEndpointDataSource(
         ComponentApplicationBuilder builder,
         IEnumerable<RenderModeEndpointProvider> renderModeEndpointProviders,
         IApplicationBuilder applicationBuilder,
-        RazorComponentEndpointFactory factory)
+        RazorComponentEndpointFactory factory,
+        HotReloadService? hotReloadService = null)
     {
         _builder = builder;
         _applicationBuilder = applicationBuilder;
         _renderModeEndpointProviders = renderModeEndpointProviders.ToArray();
         _factory = factory;
+        _hotReloadService = hotReloadService;
         DefaultBuilder = new RazorComponentsEndpointConventionBuilder(
             _lock,
             builder,
@@ -62,7 +67,7 @@ public override IReadOnlyList<Endpoint> Endpoints
             // The order is as follows:
             // * MapRazorComponents gets called and the data source gets created.
             // * The RazorComponentEndpointConventionBuilder is returned and the user gets a chance to call on it to add conventions.
-            // * The first request arrives and the DfaMatcherBuilder acesses the data sources to get the endpoints.
+            // * The first request arrives and the DfaMatcherBuilder accesses the data sources to get the endpoints.
             // * The endpoints get created and the conventions get applied.
             Initialize();
             Debug.Assert(_changeToken != null);
@@ -89,47 +94,61 @@ private void Initialize()
 
     private void UpdateEndpoints()
     {
-        var endpoints = new List<Endpoint>();
-        var context = _builder.Build();
-
-        foreach (var definition in context.Pages)
+        lock (_lock)
         {
-            _factory.AddEndpoints(endpoints, typeof(TRootComponent), definition, _conventions, _finallyConventions);
-        }
+            var endpoints = new List<Endpoint>();
+            var context = _builder.Build();
 
-        ICollection<IComponentRenderMode> renderModes = Options.ConfiguredRenderModes;
+            foreach (var definition in context.Pages)
+            {
+                _factory.AddEndpoints(endpoints, typeof(TRootComponent), definition, _conventions, _finallyConventions);
+            }
 
-        foreach (var renderMode in renderModes)
-        {
-            var found = false;
-            foreach (var provider in _renderModeEndpointProviders)
+            ICollection<IComponentRenderMode> renderModes = Options.ConfiguredRenderModes;
+
+            foreach (var renderMode in renderModes)
             {
-                if (provider.Supports(renderMode))
+                var found = false;
+                foreach (var provider in _renderModeEndpointProviders)
+                {
+                    if (provider.Supports(renderMode))
+                    {
+                        found = true;
+                        RenderModeEndpointProvider.AddEndpoints(
+                            endpoints,
+                            typeof(TRootComponent),
+                            provider.GetEndpointBuilders(renderMode, _applicationBuilder.New()),
+                            renderMode,
+                            _conventions,
+                            _finallyConventions);
+                    }
+                }
+
+                if (!found)
                 {
-                    found = true;
-                    RenderModeEndpointProvider.AddEndpoints(
-                        endpoints,
-                        typeof(TRootComponent),
-                        provider.GetEndpointBuilders(renderMode, _applicationBuilder.New()),
-                        renderMode,
-                        _conventions,
-                        _finallyConventions);
+                    throw new InvalidOperationException($"Unable to find a provider for the render mode: {renderMode.GetType().FullName}. This generally " +
+                        $"means that a call to 'AddWebAssemblyComponents' or 'AddServerComponents' is missing. " +
+                        $"Alternatively call 'AddWebAssemblyRenderMode', 'AddServerRenderMode' might be missing if you have set UseDeclaredRenderModes = false.");
                 }
             }
 
-            if (!found)
+            var oldCancellationTokenSource = _cancellationTokenSource;
+            _endpoints = endpoints;
+            _cancellationTokenSource = new CancellationTokenSource();
+            _changeToken = new CancellationChangeToken(_cancellationTokenSource.Token);
+            oldCancellationTokenSource?.Cancel();
+            if (_hotReloadService is { MetadataUpdateSupported : true })
             {
-                throw new InvalidOperationException($"Unable to find a provider for the render mode: {renderMode.GetType().FullName}. This generally " +
-                    $"means that a call to 'AddWebAssemblyComponents' or 'AddServerComponents' is missing. " +
-                    $"Alternatively call 'AddWebAssemblyRenderMode', 'AddServerRenderMode' might be missing if you have set UseDeclaredRenderModes = false.");
+                ChangeToken.OnChange(_hotReloadService.GetChangeToken, UpdateEndpoints);
             }
         }
-
-        _endpoints = endpoints;
     }
+
     public override IChangeToken GetChangeToken()
     {
-        // TODO: Handle updates if necessary (for hot reload).
+        Initialize();
+        Debug.Assert(_changeToken != null);
+        Debug.Assert(_endpoints != null);
         return _changeToken;
     }
 }

src/Components/Endpoints/src/Builder/RazorComponentEndpointDataSourceFactory.cs

@@ -14,20 +14,23 @@ internal class RazorComponentEndpointDataSourceFactory
 {
     private readonly RazorComponentEndpointFactory _factory;
     private readonly IEnumerable<RenderModeEndpointProvider> _providers;
+    private readonly HotReloadService? _hotReloadService;
 
     public RazorComponentEndpointDataSourceFactory(
         RazorComponentEndpointFactory factory,
-        IEnumerable<RenderModeEndpointProvider> providers)
+        IEnumerable<RenderModeEndpointProvider> providers,
+        HotReloadService? hotReloadService = null)
     {
         _factory = factory;
         _providers = providers;
+        _hotReloadService = hotReloadService;
     }
 
     public RazorComponentEndpointDataSource<TRootComponent> CreateDataSource<[DynamicallyAccessedMembers(Component)] TRootComponent>(IEndpointRouteBuilder endpoints)
     {
         var builder = ComponentApplicationBuilder.GetBuilder<TRootComponent>() ??
             DefaultRazorComponentApplication<TRootComponent>.Instance.GetBuilder();
 
-        return new RazorComponentEndpointDataSource<TRootComponent>(builder, _providers, endpoints.CreateApplicationBuilder(), _factory);
+        return new RazorComponentEndpointDataSource<TRootComponent>(builder, _providers, endpoints.CreateApplicationBuilder(), _factory, _hotReloadService);
     }
 }

src/Components/Endpoints/src/DependencyInjection/HotReloadService.cs

@@ -0,0 +1,42 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Reflection.Metadata;
+using Microsoft.Extensions.Primitives;
+
+[assembly: MetadataUpdateHandler(typeof(Microsoft.AspNetCore.Components.Endpoints.HotReloadService))]
+
+namespace Microsoft.AspNetCore.Components.Endpoints;
+
+internal sealed class HotReloadService : IDisposable
+{
+    public HotReloadService()
+    {
+        UpdateApplicationEvent += NotifyUpdateApplication;
+        MetadataUpdateSupported = MetadataUpdater.IsSupported;
+    }
+
+    private CancellationTokenSource _tokenSource = new();
+    private static event Action<Type[]?>? UpdateApplicationEvent;
+
+    public bool MetadataUpdateSupported { get; internal set; }
+
+    public IChangeToken GetChangeToken() => new CancellationChangeToken(_tokenSource.Token);
+
+    public static void UpdateApplication(Type[]? changedTypes)
+    {
+        UpdateApplicationEvent?.Invoke(changedTypes);
+    }
+
+    private void NotifyUpdateApplication(Type[]? changedTypes)
+    {
+        var current = Interlocked.Exchange(ref _tokenSource, new CancellationTokenSource());
+        current.Cancel();
+    }
+
+    public void Dispose()
+    {
+        UpdateApplicationEvent -= NotifyUpdateApplication;
+        _tokenSource.Dispose();
+    }
+}

src/Components/Endpoints/src/DependencyInjection/RazorComponentsServiceCollectionExtensions.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Diagnostics.CodeAnalysis;
+using System.Reflection.Metadata;
 using Microsoft.AspNetCore.Components;
 using Microsoft.AspNetCore.Components.Endpoints;
 using Microsoft.AspNetCore.Components.Endpoints.DependencyInjection;
@@ -45,6 +46,10 @@ public static IRazorComponentsBuilder AddRazorComponents(this IServiceCollection
         // Endpoints
         services.TryAddSingleton<RazorComponentEndpointDataSourceFactory>();
         services.TryAddSingleton<RazorComponentEndpointFactory>();
+        if (MetadataUpdater.IsSupported)
+        {
+            services.TryAddSingleton<HotReloadService>();
+        }
         services.TryAddScoped<IRazorComponentEndpointInvoker, RazorComponentEndpointInvoker>();
 
         // Common services required for components server side rendering