Allow Router to bypass OnNavigateAsync guard during 404 re-execution.

Author: ilonatommy

src/Components/Components/src/Routing/RouteTable.cs

@@ -78,6 +78,8 @@ public void Route(RouteContext routeContext)
 
     private static void ProcessParameters(InboundRouteEntry entry, RouteValueDictionary routeValues)
     {
+        routeValues.Remove(Router.AllowRenderDuringPendingNavigationKey);
+
         // Add null values for unused route parameters.
         if (entry.UnusedRouteParameterNames != null)
         {

src/Components/Components/src/Routing/Router.cs

@@ -42,6 +42,8 @@ static readonly IReadOnlyDictionary<string, object> _emptyParametersDictionary
 
     private bool _onNavigateCalled;
 
+    internal const string AllowRenderDuringPendingNavigationKey = "__BlazorAllowRenderDuringPendingNavigation";
+
     [Inject] private NavigationManager NavigationManager { get; set; }
 
     [Inject] private INavigationInterception NavigationInterception { get; set; }
@@ -220,11 +222,14 @@ private void ClearRouteCaches()
 
     internal virtual void Refresh(bool isNavigationIntercepted)
     {
+        var providerRouteData = RoutingStateProvider?.RouteData;
+        var allowRenderDuringPendingNavigation = TryConsumeAllowRenderDuringPendingNavigation(providerRouteData);
+
         // If an `OnNavigateAsync` task is currently in progress, then wait
         // for it to complete before rendering. Note: because _previousOnNavigateTask
         // is initialized to a CompletedTask on initialization, this will still
         // allow first-render to complete successfully.
-        if (_previousOnNavigateTask.Status != TaskStatus.RanToCompletion)
+        if (_previousOnNavigateTask.Status != TaskStatus.RanToCompletion && !allowRenderDuringPendingNavigation)
         {
             if (Navigating != null)
             {
@@ -239,7 +244,7 @@ internal virtual void Refresh(bool isNavigationIntercepted)
         ComponentsActivityHandle activityHandle;
 
         // In order to avoid routing twice we check for RouteData
-        if (RoutingStateProvider?.RouteData is { } endpointRouteData)
+        if (providerRouteData is { } endpointRouteData)
         {
             activityHandle = RecordDiagnostics(endpointRouteData.PageType.FullName, endpointRouteData.Template);
 
@@ -312,6 +317,17 @@ internal virtual void Refresh(bool isNavigationIntercepted)
         _renderHandle.ComponentActivitySource?.StopNavigateActivity(activityHandle, null);
     }
 
+    private static bool TryConsumeAllowRenderDuringPendingNavigation(RouteData? routeData)
+    {
+        if (routeData?.RouteValues.TryGetValue(AllowRenderDuringPendingNavigationKey, out var value) == true && value is true)
+        {
+            (routeData.RouteValues as IDictionary<string, object?>)?.Remove(AllowRenderDuringPendingNavigationKey);
+            return true;
+        }
+
+        return false;
+    }
+
     private ComponentsActivityHandle RecordDiagnostics(string componentType, string template)
     {
         ComponentsActivityHandle activityHandle = default;

src/Components/Endpoints/src/RazorComponentEndpointInvoker.cs

@@ -87,7 +87,8 @@ await _renderer.InitializeStandardComponentServicesAsync(
             context,
             componentType: pageComponent,
             handler: result.HandlerName,
-            form: result.HandlerName != null && context.Request.HasFormContentType ? await context.Request.ReadFormAsync() : null);
+            form: result.HandlerName != null && context.Request.HasFormContentType ? await context.Request.ReadFormAsync() : null,
+            allowRenderingDuringPendingNavigation: isReExecuted);
 
         // Matches MVC's MemoryPoolHttpResponseStreamWriterFactory.DefaultBufferSize
         var defaultBufferSize = 16 * 1024;

src/Components/Endpoints/src/Rendering/EndpointHtmlRenderer.cs

@@ -54,6 +54,8 @@ internal partial class EndpointHtmlRenderer : StaticHtmlRenderer, IComponentPrer
 
     private string _notFoundUrl = string.Empty;
 
+    private const string AllowRenderDuringPendingNavigationKey = "__BlazorAllowRenderDuringPendingNavigation";
+
     public EndpointHtmlRenderer(IServiceProvider serviceProvider, ILoggerFactory loggerFactory)
         : base(serviceProvider, loggerFactory)
     {
@@ -81,12 +83,13 @@ internal async Task InitializeStandardComponentServicesAsync(
         HttpContext httpContext,
         [DynamicallyAccessedMembers(Component)] Type? componentType = null,
         string? handler = null,
-        IFormCollection? form = null)
+        IFormCollection? form = null,
+        bool allowRenderingDuringPendingNavigation = false)
     {
         var navigationManager = httpContext.RequestServices.GetRequiredService<NavigationManager>();
         ((IHostEnvironmentNavigationManager)navigationManager)?.Initialize(
-            GetContextBaseUri(httpContext.Request), 
-            GetFullUri(httpContext.Request), 
+            GetContextBaseUri(httpContext.Request),
+            GetFullUri(httpContext.Request),
             uri => GetErrorHandledTask(OnNavigateTo(uri)));
 
         navigationManager?.OnNotFound += (sender, args) => NotFoundEventArgs = args;
@@ -132,7 +135,13 @@ internal async Task InitializeStandardComponentServicesAsync(
         {
             // Saving RouteData to avoid routing twice in Router component
             var routingStateProvider = httpContext.RequestServices.GetRequiredService<EndpointRoutingStateProvider>();
-            routingStateProvider.RouteData = new RouteData(componentType, httpContext.GetRouteData().Values);
+            var routeValues = new RouteValueDictionary(httpContext.GetRouteData().Values);
+            if (allowRenderingDuringPendingNavigation)
+            {
+                routeValues[AllowRenderDuringPendingNavigationKey] = true;
+            }
+
+            routingStateProvider.RouteData = new RouteData(componentType, routeValues);
             if (httpContext.GetEndpoint() is RouteEndpoint routeEndpoint)
             {
                 routingStateProvider.RouteData.Template = routeEndpoint.RoutePattern.RawText;