Support navigation during prerendering (#10694)

src/Components/Components/ref/Microsoft.AspNetCore.Components.netstandard2.0.cs

@@ -361,6 +361,11 @@ namespace Microsoft.AspNetCore.Components
         public static explicit operator Microsoft.AspNetCore.Components.MarkupString (string value) { throw null; }
         public override string ToString() { throw null; }
     }
+    public partial class NavigationException : System.Exception
+    {
+        public NavigationException(string uri) { }
+        public string Location { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
+    }
     [System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Sequential)]
     public readonly partial struct Parameter
     {

src/Components/Components/src/NavigationException.cs

@@ -0,0 +1,26 @@
+// 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 System;
+
+namespace Microsoft.AspNetCore.Components
+{
+    /// <summary>
+    /// Exception thrown when an <see cref="IUriHelper"/> is not able to navigate to a different url.
+    /// </summary>
+    public class NavigationException : Exception
+    {
+        /// <summary>
+        /// Initializes a new <see cref="NavigationException"/> instance.
+        /// </summary>
+        public NavigationException(string uri)
+        {
+            Location = uri;
+        }
+
+        /// <summary>
+        /// Gets the uri to which navigation was attempted.
+        /// </summary>
+        public string Location { get; }
+    }
+}

src/Components/Server/src/Circuits/CircuitPrerenderer.cs

@@ -5,14 +5,17 @@ using System;
 using System.Linq;
 using System.Runtime.ExceptionServices;
 using System.Threading.Tasks;
+using Microsoft.AspNetCore.Components.Rendering;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Http.Extensions;
+using Microsoft.AspNetCore.Http.Features;
 
 namespace Microsoft.AspNetCore.Components.Server.Circuits
 {
     internal class CircuitPrerenderer : IComponentPrerenderer
     {
         private static object CircuitHostKey = new object();
+        private static object NavigationStatusKey = new object();
 
         private readonly CircuitFactory _circuitFactory;
         private readonly CircuitRegistry _registry;
@@ -26,11 +29,41 @@ namespace Microsoft.AspNetCore.Components.Server.Circuits
         public async Task<ComponentPrerenderResult> PrerenderComponentAsync(ComponentPrerenderingContext prerenderingContext)
         {
             var context = prerenderingContext.Context;
-            var circuitHost = GetOrCreateCircuitHost(context);
+            var navigationStatus = GetOrCreateNavigationStatus(context);
+            if (navigationStatus.Navigated)
+            {
+                // Avoid creating a circuit host if other component earlier in the pipeline already triggered
+                // a navigation request. Instead rendre nothing
+                return new ComponentPrerenderResult(Array.Empty<string>());
+            }
+            var circuitHost = GetOrCreateCircuitHost(context, navigationStatus);
+            ComponentRenderedText renderResult = default;
+            try
+            {
+                renderResult = await circuitHost.PrerenderComponentAsync(
+                    prerenderingContext.ComponentType,
+                    prerenderingContext.Parameters);
+            }
+            catch (NavigationException navigationException)
+            {
+                // Cleanup the state as we won't need it any longer.
+                // Signal callbacks that we don't have to register the circuit.
+                await CleanupCircuitState(context, navigationStatus, circuitHost);
 
-            var renderResult = await circuitHost.PrerenderComponentAsync(
-                prerenderingContext.ComponentType,
-                prerenderingContext.Parameters);
+                // Navigation was attempted during prerendering.
+                if (prerenderingContext.Context.Response.HasStarted)
+                {
+                    // We can't perform a redirect as the server already started sending the response.
+                    // This is considered an application error as the developer should buffer the response until
+                    // all components have rendered.
+                    throw new InvalidOperationException("A navigation command was attempted during prerendering after the server already started sending the response. " +
+                        "Navigation commands can not be issued during server-side prerendering after the response from the server has started. Applications must buffer the" +
+                        "reponse and avoid using features like FlushAsync() before all components on the page have been rendered to prevent failed navigation commands.", navigationException);
+                }
+
+                context.Response.Redirect(navigationException.Location);
+                return new ComponentPrerenderResult(Array.Empty<string>());
+            }
 
             circuitHost.Descriptors.Add(new ComponentDescriptor
             {
@@ -38,9 +71,9 @@ namespace Microsoft.AspNetCore.Components.Server.Circuits
                 Prerendered = true
             });
 
-            var result = new[] {
+            var result = (new[] {
                 $"<!-- M.A.C.Component:{{\"circuitId\":\"{circuitHost.CircuitId}\",\"rendererId\":\"{circuitHost.Renderer.Id}\",\"componentId\":\"{renderResult.ComponentId}\"}} -->",
-            }.Concat(renderResult.Tokens).Concat(
+            }).Concat(renderResult.Tokens).Concat(
                 new[] {
                     $"<!-- M.A.C.Component: {renderResult.ComponentId} -->"
                 });
@@ -48,7 +81,28 @@ namespace Microsoft.AspNetCore.Components.Server.Circuits
             return new ComponentPrerenderResult(result);
         }
 
-        private CircuitHost GetOrCreateCircuitHost(HttpContext context)
+        private CircuitNavigationStatus GetOrCreateNavigationStatus(HttpContext context)
+        {
+            if (context.Items.TryGetValue(NavigationStatusKey, out var existingHost))
+            {
+                return (CircuitNavigationStatus)existingHost;
+            }
+            else
+            {
+                var navigationStatus = new CircuitNavigationStatus();
+                context.Items[NavigationStatusKey] = navigationStatus;
+                return navigationStatus;
+            }
+        }
+
+        private static async Task CleanupCircuitState(HttpContext context, CircuitNavigationStatus navigationStatus, CircuitHost circuitHost)
+        {
+            navigationStatus.Navigated = true;
+            context.Items.Remove(CircuitHostKey);
+            await circuitHost.DisposeAsync();
+        }
+
+        private CircuitHost GetOrCreateCircuitHost(HttpContext context, CircuitNavigationStatus navigationStatus)
         {
             if (context.Items.TryGetValue(CircuitHostKey, out var existingHost))
             {
@@ -66,7 +120,11 @@ namespace Microsoft.AspNetCore.Components.Server.Circuits
                 context.Response.OnCompleted(() =>
                 {
                     result.UnhandledException -= CircuitHost_UnhandledException;
-                    _registry.RegisterDisconnectedCircuit(result);
+                    if (!navigationStatus.Navigated)
+                    {
+                        _registry.RegisterDisconnectedCircuit(result);
+                    }
+
                     return Task.CompletedTask;
                 });
                 context.Items.Add(CircuitHostKey, result);
@@ -105,5 +163,10 @@ namespace Microsoft.AspNetCore.Components.Server.Circuits
 
             return result;
         }
+
+        private class CircuitNavigationStatus
+        {
+            public bool Navigated { get; set; }
+        }
     }
 }

src/Components/Server/src/Circuits/RemoteUriHelper.cs

@@ -90,10 +90,7 @@ namespace Microsoft.AspNetCore.Components.Server.Circuits
 
             if (_jsRuntime == null)
             {
-                throw new InvalidOperationException("Navigation commands can not be issued at this time. This is because the component is being " +
-                    "prerendered and the page has not yet loaded in the browser or because the circuit is currently disconnected. " +
-                    "Components must wrap any navigation calls in conditional logic to ensure those navigation calls are not " +
-                    "attempted during prerendering or while the client is disconnected.");
+                throw new NavigationException(uri);
             }
             _jsRuntime.InvokeAsync<object>(Interop.NavigateTo, uri, forceLoad);
         }

src/Mvc/Mvc.Components.Prerendering/test/HtmlHelperComponentPrerenderingExtensionsTests.cs

@@ -7,9 +7,11 @@ using Microsoft.AspNetCore.Components;
 using Microsoft.AspNetCore.Components.RenderTree;
 using Microsoft.AspNetCore.Html;
 using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http.Features;
 using Microsoft.AspNetCore.Mvc.Rendering;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.JSInterop;
+using Microsoft.Net.Http.Headers;
 using Moq;
 using Xunit;
 
@@ -122,7 +124,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
         }
 
         [Fact]
-        public async Task UriHelperRedirect_ThrowsInvalidOperationException()
+        public async Task UriHelperRedirect_ThrowsInvalidOperationException_WhenResponseHasAlreadyStarted()
         {
             // Arrange
             var ctx = new DefaultHttpContext();
@@ -131,7 +133,9 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
             ctx.Request.PathBase = "/base";
             ctx.Request.Path = "/path";
             ctx.Request.QueryString = new QueryString("?query=value");
-
+            var responseMock = new Mock<IHttpResponseFeature>();
+            responseMock.Setup(r => r.HasStarted).Returns(true);
+            ctx.Features.Set(responseMock.Object);
             var helper = CreateHelper(ctx);
             var writer = new StringWriter();
 
@@ -141,13 +145,62 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
                 RedirectUri = "http://localhost/redirect"
             }));
 
-            Assert.Equal("Navigation commands can not be issued at this time. This is because the component is being " +
-                    "prerendered and the page has not yet loaded in the browser or because the circuit is currently disconnected. " +
-                    "Components must wrap any navigation calls in conditional logic to ensure those navigation calls are not " +
-                    "attempted during prerendering or while the client is disconnected.",
+            Assert.Equal("A navigation command was attempted during prerendering after the server already started sending the response. " +
+                            "Navigation commands can not be issued during server-side prerendering after the response from the server has started. Applications must buffer the" +
+                            "reponse and avoid using features like FlushAsync() before all components on the page have been rendered to prevent failed navigation commands.",
                 exception.Message);
         }
 
+        [Fact]
+        public async Task HtmlHelper_Redirects_WhenComponentNavigates()
+        {
+            // Arrange
+            var ctx = new DefaultHttpContext();
+            ctx.Request.Scheme = "http";
+            ctx.Request.Host = new HostString("localhost");
+            ctx.Request.PathBase = "/base";
+            ctx.Request.Path = "/path";
+            ctx.Request.QueryString = new QueryString("?query=value");
+            var helper = CreateHelper(ctx);
+
+            // Act
+            await helper.RenderComponentAsync<RedirectComponent>(new
+            {
+                RedirectUri = "http://localhost/redirect"
+            });
+
+            // Assert
+            Assert.Equal(302, ctx.Response.StatusCode);
+            Assert.Equal("http://localhost/redirect", ctx.Response.Headers[HeaderNames.Location]);
+        }
+
+        [Fact]
+        public async Task HtmlHelper_AvoidsRendering_WhenNavigationHasHappened()
+        {
+            // Arrange
+            var ctx = new DefaultHttpContext();
+            ctx.Request.Scheme = "http";
+            ctx.Request.Host = new HostString("localhost");
+            ctx.Request.PathBase = "/base";
+            ctx.Request.Path = "/path";
+            ctx.Request.QueryString = new QueryString("?query=value");
+            var helper = CreateHelper(ctx);
+            var stringWriter = new StringWriter();
+
+            await helper.RenderComponentAsync<RedirectComponent>(new
+            {
+                RedirectUri = "http://localhost/redirect"
+            });
+
+            // Act
+            var result = await helper.RenderComponentAsync<GreetingComponent>(new { Name = "George" });
+
+            // Assert
+            Assert.NotNull(result);
+            result.WriteTo(stringWriter, HtmlEncoder.Default);
+            Assert.Equal("", stringWriter.ToString());
+        }
+
         [Fact]
         public async Task CanRender_AsyncComponent()
         {

src/Mvc/Mvc.ViewFeatures/src/Infrastructure/HttpUriHelper.cs

@@ -10,10 +10,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
     {
         protected override void NavigateToCore(string uri, bool forceLoad)
         {
-            // For now throw as we don't have a good way of aborting the request from here.
-            throw new InvalidOperationException("Navigation commands can not be issued during server-side prerendering because the page has not yet loaded in the browser" +
-                    "Components must wrap any navigation commands in conditional logic to ensure those navigation calls are not " +
-                    "attempted during prerendering.");
+            throw new NavigationException(uri);
         }
     }
 }

src/Mvc/Mvc.ViewFeatures/src/RazorComponents/StaticComponentRenderer.cs

@@ -9,6 +9,7 @@ using Microsoft.AspNetCore.Components;
 using Microsoft.AspNetCore.Components.Rendering;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Http.Extensions;
+using Microsoft.AspNetCore.Http.Features;
 using Microsoft.Extensions.DependencyInjection;
 
 namespace Microsoft.AspNetCore.Mvc.ViewFeatures.RazorComponents
@@ -33,9 +34,30 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.RazorComponents
             InitializeUriHelper(httpContext);
             using (var htmlRenderer = new HtmlRenderer(httpContext.RequestServices, _encoder.Encode, dispatcher))
             {
-                var result = await dispatcher.InvokeAsync(() => htmlRenderer.RenderComponentAsync(
-                    componentType,
-                    parameters));
+                ComponentRenderedText result = default;
+                try
+                {
+                    result = await dispatcher.InvokeAsync(() => htmlRenderer.RenderComponentAsync(
+                        componentType,
+                        parameters));
+                }
+                catch (NavigationException navigationException)
+                {
+                    // Navigation was attempted during prerendering.
+                    if (httpContext.Response.HasStarted)
+                    {
+                        // We can't perform a redirect as the server already started sending the response.
+                        // This is considered an application error as the developer should buffer the response until
+                        // all components have rendered.
+                        throw new InvalidOperationException("A navigation command was attempted during prerendering after the server already started sending the response. " +
+                            "Navigation commands can not be issued during server-side prerendering after the response from the server has started. Applications must buffer the" +
+                            "reponse and avoid using features like FlushAsync() before all components on the page have been rendered to prevent failed navigation commands.", navigationException);
+                    }
+
+                    httpContext.Response.Redirect(navigationException.Location);
+                    return Array.Empty<string>();
+                }
+
                 return result.Tokens;
             }
         }

src/Mvc/Mvc.ViewFeatures/test/HtmlHelperComponentExtensionsTests.cs

@@ -9,10 +9,12 @@ using Microsoft.AspNetCore.Components;
 using Microsoft.AspNetCore.Components.RenderTree;
 using Microsoft.AspNetCore.Components.Server;
 using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http.Features;
 using Microsoft.AspNetCore.Mvc.Rendering;
 using Microsoft.AspNetCore.Mvc.ViewFeatures.RazorComponents;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.JSInterop;
+using Microsoft.Net.Http.Headers;
 using Moq;
 using Xunit;
 
@@ -107,7 +109,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Test
         }
 
         [Fact]
-        public async Task UriHelperRedirect_ThrowsInvalidOperationException()
+        public async Task UriHelperRedirect_ThrowsInvalidOperationException_WhenResponseHasAlreadyStarted()
         {
             // Arrange
             var ctx = new DefaultHttpContext();
@@ -116,7 +118,9 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Test
             ctx.Request.PathBase = "/base";
             ctx.Request.Path = "/path";
             ctx.Request.QueryString = new QueryString("?query=value");
-
+            var responseMock = new Mock<IHttpResponseFeature>();
+            responseMock.Setup(r => r.HasStarted).Returns(true);
+            ctx.Features.Set(responseMock.Object);
             var helper = CreateHelper(ctx);
             var writer = new StringWriter();
 
@@ -125,13 +129,36 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Test
             {
                 RedirectUri = "http://localhost/redirect"
             }));
-
-            Assert.Equal("Navigation commands can not be issued during server-side prerendering because the page has not yet loaded in the browser" +
-                    "Components must wrap any navigation commands in conditional logic to ensure those navigation calls are not " +
-                    "attempted during prerendering.",
+            
+            Assert.Equal("A navigation command was attempted during prerendering after the server already started sending the response. " +
+                            "Navigation commands can not be issued during server-side prerendering after the response from the server has started. Applications must buffer the" +
+                            "reponse and avoid using features like FlushAsync() before all components on the page have been rendered to prevent failed navigation commands.",
                 exception.Message);
         }
 
+        [Fact]
+        public async Task HtmlHelper_Redirects_WhenComponentNavigates()
+        {
+            // Arrange
+            var ctx = new DefaultHttpContext();
+            ctx.Request.Scheme = "http";
+            ctx.Request.Host = new HostString("localhost");
+            ctx.Request.PathBase = "/base";
+            ctx.Request.Path = "/path";
+            ctx.Request.QueryString = new QueryString("?query=value");
+            var helper = CreateHelper(ctx);
+
+            // Act
+            await helper.RenderStaticComponentAsync<RedirectComponent>(new
+            {
+                RedirectUri = "http://localhost/redirect"
+            });
+
+            // Assert
+            Assert.Equal(302, ctx.Response.StatusCode);
+            Assert.Equal("http://localhost/redirect", ctx.Response.Headers[HeaderNames.Location]);
+        }
+
         [Fact]
         public async Task CanRender_AsyncComponent()
         {

src/Mvc/test/Mvc.FunctionalTests/ComponentRenderingFunctionalTests.cs

@@ -74,6 +74,37 @@ namespace Microsoft.AspNetCore.Mvc.FunctionalTests
             AssertComponent("\nRouter component\n<p>Routed successfully</p>", "Routing", content);
         }
 
+        [Fact]
+        public async Task Redirects_Navigation_Component()
+        {
+            // Arrange & Act
+            var fixture = Factory.WithWebHostBuilder(builder => builder.ConfigureServices(services => services.AddServerSideBlazor()));
+            fixture.ClientOptions.AllowAutoRedirect = false;
+            var client = CreateClient(fixture);
+
+            var response = await client.GetAsync("http://localhost/components/Navigation");
+
+            // Assert
+            await response.AssertStatusCodeAsync(HttpStatusCode.Redirect);
+            Assert.Equal("/navigation-redirect", response.Headers.Location.ToString());
+        }
+
+        [Fact]
+        public async Task Redirects_Navigation_ComponentInteractive()
+        {
+            // Arrange & Act
+            var fixture = Factory.WithWebHostBuilder(builder => builder.ConfigureServices(services => services.AddServerSideBlazor()));
+            fixture.ClientOptions.AllowAutoRedirect = false;
+            var client = CreateClient(fixture);
+
+            var response = await client.GetAsync("http://localhost/components/Navigation/false");
+
+            // Assert
+            // Assert
+            await response.AssertStatusCodeAsync(HttpStatusCode.Redirect);
+            Assert.Equal("/navigation-redirect", response.Headers.Location.ToString());
+        }
+
         [Fact]
         public async Task Renders_RoutingComponent_UsingRazorComponents_Prerenderer()
         {
@@ -224,7 +255,8 @@ namespace Microsoft.AspNetCore.Mvc.FunctionalTests
         {
         }
 
-        private HttpClient CreateClient(WebApplicationFactory<BasicWebSite.StartupWithoutEndpointRouting> fixture)
+        private HttpClient CreateClient(
+            WebApplicationFactory<BasicWebSite.StartupWithoutEndpointRouting> fixture)
         {
             var loopHandler = new LoopHttpHandler();
 

src/Mvc/test/WebSites/BasicWebSite/Controllers/RazorComponentsController.cs

@@ -70,6 +70,12 @@ namespace BasicWebSite.Controllers
             return Ok(_weatherData);
         }
 
+        [HttpGet("/components/Navigation/{staticPrerender=true}")]
+        public IActionResult Navigation(bool staticPrerender)
+        {
+            return View(staticPrerender);
+        }
+
         private class WeatherRow
         {
             public string DateFormatted { get; internal set; }

src/Mvc/test/WebSites/BasicWebSite/RazorComponents/NavigationComponent.razor

@@ -0,0 +1,9 @@
+@inject IUriHelper Helper
+
+@functions{
+
+    protected override void OnInit()
+    {
+        Helper.NavigateTo("/navigation-redirect");
+    }
+}

src/Mvc/test/WebSites/BasicWebSite/Views/RazorComponents/Navigation.cshtml

@@ -0,0 +1,13 @@
+@using BasicWebSite.RazorComponents;
+@model bool;
+<h1>Navigation components</h1>
+<div id="Navigation">
+    @if (Model)
+    {
+        @(await Html.RenderStaticComponentAsync<NavigationComponent>())
+    }
+    else
+    {
+        @(await Html.RenderComponentAsync<NavigationComponent>())
+    }
+</div>