SSR streaming not started with custom router.

dotnet · ilonatommy · Jul 17, 2025 · Jul 9, 2025 · Jul 11, 2025 · Jul 11, 2025
commit f0784284cfb64d2e7022b57c6412965973cdf781
@@ -61,7 +61,7 @@ public event EventHandler<NotFoundEventArgs> OnNotFound
     // The URI. Always represented an absolute URI.
     private string? _uri;
     private bool _isInitialized;
-    internal string NotFoundPageRoute { get; set; } = string.Empty;
+    private readonly NotFoundEventArgs _notFoundEventArgs = new();
 
     /// <summary>
     /// Gets or sets the current base URI. The <see cref="BaseUri" /> is always represented as an absolute URI in string form with trailing slash.
@@ -211,7 +211,7 @@ private void NotFoundCore()
         }
         else
         {
-            _notFound.Invoke(this, new NotFoundEventArgs(NotFoundPageRoute));
+            _notFound.Invoke(this, _notFoundEventArgs);
         }
     }
 

@@ -8,8 +8,9 @@ Microsoft.AspNetCore.Components.NavigationManager.OnNotFound -> System.EventHand
 Microsoft.AspNetCore.Components.NavigationManager.NotFound() -> void
 Microsoft.AspNetCore.Components.Routing.IHostEnvironmentNavigationManager.Initialize(string! baseUri, string! uri, System.Func<string!, System.Threading.Tasks.Task!>! onNavigateTo) -> void
 Microsoft.AspNetCore.Components.Routing.NotFoundEventArgs
-Microsoft.AspNetCore.Components.Routing.NotFoundEventArgs.NotFoundEventArgs(string! url) -> void
-Microsoft.AspNetCore.Components.Routing.NotFoundEventArgs.Path.get -> string!
+Microsoft.AspNetCore.Components.Routing.NotFoundEventArgs.NotFoundEventArgs() -> void
+Microsoft.AspNetCore.Components.Routing.NotFoundEventArgs.Path.get -> string?
+Microsoft.AspNetCore.Components.Routing.NotFoundEventArgs.Path.set -> void
 Microsoft.AspNetCore.Components.Infrastructure.ComponentStatePersistenceManager.ComponentStatePersistenceManager(Microsoft.Extensions.Logging.ILogger<Microsoft.AspNetCore.Components.Infrastructure.ComponentStatePersistenceManager!>! logger, System.IServiceProvider! serviceProvider) -> void
 Microsoft.AspNetCore.Components.Infrastructure.ComponentStatePersistenceManager.SetPlatformRenderMode(Microsoft.AspNetCore.Components.IComponentRenderMode! renderMode) -> void
 Microsoft.AspNetCore.Components.Infrastructure.RegisterPersistentComponentStateServiceCollectionExtensions

@@ -9,16 +9,7 @@ namespace Microsoft.AspNetCore.Components.Routing;
 public sealed class NotFoundEventArgs : EventArgs
 {
     /// <summary>
-    /// Gets the path of NotFoundPage.
+    /// Gets the path of NotFoundPage. If the path is set, it indicates that the router has handled the rendering of the NotFound contents.
     /// </summary>
-    public string Path { get; }
-
-    /// <summary>
-    /// Initializes a new instance of <see cref="NotFoundEventArgs" />.
-    /// </summary>
-    public NotFoundEventArgs(string url)
-    {
-        Path = url;
-    }
-
+    public string? Path { get; set; }
 }
@@ -29,6 +29,7 @@ static readonly IReadOnlyDictionary<string, object> _emptyParametersDictionary
     string _locationAbsolute;
     bool _navigationInterceptionEnabled;
     ILogger<Router> _logger;
+    string _notFoundPageRoute;
 
     private string _updateScrollPositionForHashLastLocation;
     private bool _updateScrollPositionForHash;
@@ -159,7 +160,7 @@ public async Task SetParametersAsync(ParameterView parameters)
             var routeAttribute = (RouteAttribute)routeAttributes[0];
             if (routeAttribute.Template != null)
             {
-                NavigationManager.NotFoundPageRoute = routeAttribute.Template;
+                _notFoundPageRoute = routeAttribute.Template;
             }
         }
 
@@ -381,12 +382,14 @@ private void OnLocationChanged(object sender, LocationChangedEventArgs args)
         }
     }
 
-    private void OnNotFound(object sender, EventArgs args)
+    private void OnNotFound(object sender, NotFoundEventArgs args)
     {
         if (_renderHandle.IsInitialized)
         {
             Log.DisplayingNotFound(_logger);
             RenderNotFound();
+            // setting the path signals to the endpoint renderer that router handled rendering
+            args.Path = _notFoundPageRoute ?? "not-found-handled-by-router";
         }
     }
 

@@ -168,6 +168,17 @@ await _renderer.InitializeStandardComponentServicesAsync(
             componentStateHtmlContent.WriteTo(bufferWriter, HtmlEncoder.Default);
         }
 
+        if (context.Response.StatusCode == StatusCodes.Status404NotFound &&
+            !isReExecuted &&
+            string.IsNullOrEmpty(_renderer.NotFoundEventArgs?.Path))
+        {
+            // Router did not handle the NotFound event, otherwise this would not be empty.
+            // Don't flush the response if we have an unhandled 404 rendering
+            // This will allow the StatusCodePages middleware to re-execute the request
+            context.Response.ContentType = null;
+            return;
+        }
+
         // Invoke FlushAsync to ensure any buffered content is asynchronously written to the underlying
         // response asynchronously. In the absence of this line, the buffer gets synchronously written to the
         // response as part of the Dispose which has a perf impact.

@@ -109,7 +109,7 @@ internal async Task SetNotFoundResponseAsync(string baseUri, NotFoundEventArgs a
 
     private string GetNotFoundUrl(string baseUri, NotFoundEventArgs args)
     {
-        string path = args.Path;
+        string? path = args.Path;
         if (string.IsNullOrEmpty(path))
         {
             var pathFormat = _httpContext.Items[nameof(StatusCodePagesOptions)] as string;

@@ -63,6 +63,7 @@ public EndpointHtmlRenderer(IServiceProvider serviceProvider, ILoggerFactory log
     }
 
     internal HttpContext? HttpContext => _httpContext;
+    internal NotFoundEventArgs? NotFoundEventArgs { get; set; }
 
     internal void SetHttpContext(HttpContext httpContext)
     {
@@ -87,6 +88,7 @@ internal async Task InitializeStandardComponentServicesAsync(
 
         navigationManager?.OnNotFound += (sender, args) =>
         {
+            NotFoundEventArgs = args;
             _ = GetErrorHandledTask(SetNotFoundResponseAsync(navigationManager.BaseUri, args));
         };
 

@@ -944,7 +944,7 @@ public async Task Renderer_WhenNoNotFoundPathProvided_Throws()
         httpContext.Items[nameof(StatusCodePagesOptions)] = null; // simulate missing re-execution route
 
         var exception = await Assert.ThrowsAsync<InvalidOperationException>(async () =>
-            await renderer.SetNotFoundResponseAsync(httpContext, new NotFoundEventArgs(""))
+            await renderer.SetNotFoundResponseAsync(httpContext, new NotFoundEventArgs())
         );
         string expectedError = "The NotFoundPage route must be specified or re-execution middleware has to be set to render NotFoundPage when the response has started.";
 

@@ -117,6 +117,16 @@ public void BrowserNavigationToNotExistingPathReExecutesTo404(bool streaming)
     private void AssertReExecutionPageRendered() =>
         Browser.Equal("Welcome On Page Re-executed After Not Found Event", () => Browser.Exists(By.Id("test-info")).Text);
 
+    private void AssertBrowserDefaultNotFoundViewRendered()
+    {
+        var mainMessage = Browser.FindElement(By.Id("main-message"));
+
+        Browser.True(
+            () => mainMessage.FindElement(By.CssSelector("p")).Text
+            .Contains("No webpage was found for the web address:", StringComparison.OrdinalIgnoreCase)
+        );
+    }
+
     private void AssertNotFoundPageRendered()
     {
         Browser.Equal("Welcome On Custom Not Found Page", () => Browser.FindElement(By.Id("test-info")).Text);
@@ -152,6 +162,30 @@ public void NotFoundSetOnInitialization_ResponseNotStarted_SSR(bool hasReExecuti
         AssertUrlNotChanged(testUrl);
     }
 
+    [Theory]
+    [InlineData(true)]
+    [InlineData(false)]
+    // our custom router does not support NotFoundPage nor NotFound fragment to simulate most probable custom router behavior
+    public void NotFoundSetOnInitialization_ResponseNotStarted_CustomRouter_SSR(bool hasReExecutionMiddleware)
+    {
+        string reexecution = hasReExecutionMiddleware ? "/reexecution" : "";
+        string testUrl = $"{ServerPathBase}{reexecution}/set-not-found-ssr?useCustomRouter=true";
+        Navigate(testUrl);
+
+        if (hasReExecutionMiddleware)
+        {
+            AssertReExecutionPageRendered();
+        }
+        else
+        {
+            // Apps that don't support re-execution and don't have blazor's router,
+            // cannot render custom NotFound contents.
+            // The browser will display default 404 page.
+            AssertBrowserDefaultNotFoundViewRendered();
+        }
+        AssertUrlNotChanged(testUrl);
+    }
+
     [Theory]
     [InlineData(true, true)]
     [InlineData(true, false)]

@@ -1,12 +1,17 @@
 @using Components.TestServer.RazorComponents.Pages.Forms
 @using Components.WasmMinimal.Pages.NotFound
 @using TestContentPackage.NotFound
+@using Components.TestServer.RazorComponents
 
 @code {
     [Parameter]
     [SupplyParameterFromQuery(Name = "useCustomNotFoundPage")]
     public string? UseCustomNotFoundPage { get; set; }
 
+    [Parameter]
+    [SupplyParameterFromQuery(Name = "useCustomRouter")]
+    public string? UseCustomRouter { get; set; }
+
     private Type? NotFoundPageType { get; set; }
 
     protected override void OnParametersSet()
@@ -30,13 +35,25 @@
     <HeadOutlet />
 </head>
 <body>
-    <Router AppAssembly="@typeof(App).Assembly" AdditionalAssemblies="new[] { typeof(TestContentPackage.NotFound.NotFoundPage).Assembly }" NotFoundPage="NotFoundPageType">
-        <Found Context="routeData">
-            <RouteView RouteData="@routeData" />
-            <FocusOnNavigate RouteData="@routeData" Selector="[data-focus-on-navigate]" />
-        </Found>
-        <NotFound><p id="not-found-fragment">There's nothing here</p></NotFound>
-    </Router>
+    @if(string.Equals(UseCustomRouter, "true", StringComparison.OrdinalIgnoreCase))
+    {
+        <CustomRouter AppAssembly="@typeof(App).Assembly">
+            <Found Context="routeData">
+                <RouteView RouteData="@routeData" />
+                <FocusOnNavigate RouteData="@routeData" Selector="[data-focus-on-navigate]" />
+            </Found>
+        </CustomRouter>
+    }
+    else
+    {
+        <Router AppAssembly="@typeof(App).Assembly" AdditionalAssemblies="new[] { typeof(TestContentPackage.NotFound.NotFoundPage).Assembly }" NotFoundPage="NotFoundPageType">
+            <Found Context="routeData">
+                <RouteView RouteData="@routeData" />
+                <FocusOnNavigate RouteData="@routeData" Selector="[data-focus-on-navigate]" />
+            </Found>
+            <NotFound><p id="not-found-fragment">There's nothing here</p></NotFound>
+        </Router>
+    }
     <script>
         // This script must come before blazor.web.js to test that
         // the framework does the right thing when an element is already focused.