Throw an exception if layouts have circular references.

Fixes #3100

src/Microsoft.AspNet.Mvc.Razor/Properties/Resources.Designer.cs

@@ -446,6 +446,22 @@ namespace Microsoft.AspNet.Mvc.Razor
             return string.Format(CultureInfo.CurrentCulture, GetString("CouldNotResolveApplicationRelativeUrl_TagHelper"), p0, p1, p2, p3, p4, p5);
         }
 
+        /// <summary>
+        /// A circular layout reference was detected when rendering '{0}'. The layout page '{1}' has already been rendered.
+        /// </summary>
+        internal static string LayoutHasCircularReference
+        {
+            get { return GetString("LayoutHasCircularReference"); }
+        }
+
+        /// <summary>
+        /// A circular layout reference was detected when rendering '{0}'. The layout page '{1}' has already been rendered.
+        /// </summary>
+        internal static string FormatLayoutHasCircularReference(object p0, object p1)
+        {
+            return string.Format(CultureInfo.CurrentCulture, GetString("LayoutHasCircularReference"), p0, p1);
+        }
+
         private static string GetString(string name, params string[] formatterNames)
         {
             var value = _resourceManager.GetString(name);

src/Microsoft.AspNet.Mvc.Razor/RazorView.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
+using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Http.Features;
 using Microsoft.AspNet.Mvc.Rendering;
@@ -35,7 +36,8 @@ namespace Microsoft.AspNet.Mvc.Razor
         /// <param name="htmlEncoder">The HTML encoder.</param>
         /// <param name="isPartial">Determines if the view is to be executed as a partial.</param>
         /// pages</param>
-        public RazorView(IRazorViewEngine viewEngine,
+        public RazorView(
+            IRazorViewEngine viewEngine,
                          IRazorPageActivator pageActivator,
                          IViewStartProvider viewStartProvider,
                          IRazorPage razorPage,
@@ -170,7 +172,8 @@ namespace Microsoft.AspNet.Mvc.Razor
             RazorPage.Layout = layout;
         }
 
-        private async Task RenderLayoutAsync(ViewContext context,
+        private async Task RenderLayoutAsync(
+            ViewContext context,
                                              IBufferedTextWriter bodyWriter)
         {
             // A layout page can specify another layout page. We'll need to continue
@@ -192,6 +195,15 @@ namespace Microsoft.AspNet.Mvc.Razor
 
                 var layoutPage = GetLayoutPage(context, previousPage.Layout);
 
+                if (renderedLayouts.Count > 0 &&
+                    renderedLayouts.Any(l => string.Equals(l.Path, layoutPage.Path, StringComparison.Ordinal)))
+                {
+                    // If the layout has been previously rendered as part of this view, we're potentially in a layout
+                    // rendering cycle.
+                    throw new InvalidOperationException(
+                        Resources.FormatLayoutHasCircularReference(previousPage.Path, layoutPage.Path));
+                }
+
                 // Notify the previous page that any writes that are performed on it are part of sections being written
                 // in the layout.
                 previousPage.IsLayoutBeingRendered = true;

src/Microsoft.AspNet.Mvc.Razor/Resources.resx

@@ -200,4 +200,7 @@
 
 @{3} "{4}, {5}"</value>
   </data>
+  <data name="LayoutHasCircularReference" xml:space="preserve">
+    <value>A circular layout reference was detected when rendering '{0}'. The layout page '{1}' has already been rendered.</value>
+  </data>
 </root>

test/Microsoft.AspNet.Mvc.Razor.Test/RazorViewTest.cs

@@ -8,7 +8,6 @@ using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Http.Features;
 using Microsoft.AspNet.Http.Internal;
-using Microsoft.AspNet.Mvc.Actions;
 using Microsoft.AspNet.Mvc.ModelBinding;
 using Microsoft.AspNet.PageExecutionInstrumentation;
 using Microsoft.Framework.WebEncoders.Testing;
@@ -568,11 +567,13 @@ namespace Microsoft.AspNet.Mvc.Razor
                     await v.RenderSectionAsync("sectionA");
                 });
             });
+            nestedLayout.Path = "NestedLayout";
             var baseLayout = new TestableRazorPage(v =>
             {
                 v.HtmlEncoder = htmlEncoder;
                 v.RenderSection("sectionB");
             });
+            baseLayout.Path = "Layout";
 
             var viewEngine = new Mock<IRazorViewEngine>();
             viewEngine.Setup(p => p.FindPage(It.IsAny<ActionContext>(), "NestedLayout"))
@@ -784,6 +785,8 @@ namespace Microsoft.AspNet.Mvc.Razor
                 v.RenderBodyPublic();
                 v.Layout = "~/Shared/Layout2.cshtml";
             });
+            layout1.Path = "~/Shared/Layout1.cshtml";
+
             var layout2 = new TestableRazorPage(v =>
             {
                 v.HtmlEncoder = htmlEncoder;
@@ -791,6 +794,8 @@ namespace Microsoft.AspNet.Mvc.Razor
                 v.Write(v.RenderSection("bar"));
                 v.RenderBodyPublic();
             });
+            layout2.Path = "~/Shared/Layout2.cshtml";
+
             var viewEngine = new Mock<IRazorViewEngine>();
             viewEngine.Setup(p => p.FindPage(It.IsAny<ActionContext>(), "~/Shared/Layout1.cshtml"))
                        .Returns(new RazorPageResult("~/Shared/Layout1.cshtml", layout1));
@@ -812,6 +817,87 @@ namespace Microsoft.AspNet.Mvc.Razor
             Assert.Equal(expected, viewContext.Writer.ToString());
         }
 
+        [Fact]
+        public async Task RenderAsync_Throws_IfLayoutPageReferencesSelf()
+        {
+            // Arrange
+            var expectedMessage = "A circular layout reference was detected when rendering " +
+                "'Shared/Layout.cshtml'. The layout page 'Shared/Layout.cshtml' has already been rendered.";
+            var page = new TestableRazorPage(v =>
+            {
+                v.Layout = "_Layout";
+            });
+            var layout = new TestableRazorPage(v =>
+            {
+                v.Layout = "_Layout";
+                v.RenderBodyPublic();
+            });
+            layout.Path = "Shared/Layout.cshtml";
+
+            var viewEngine = new Mock<IRazorViewEngine>();
+            viewEngine.Setup(p => p.FindPage(It.IsAny<ActionContext>(), "_Layout"))
+                       .Returns(new RazorPageResult("_Layout", layout));
+
+            var view = new RazorView(viewEngine.Object,
+                                     Mock.Of<IRazorPageActivator>(),
+                                     CreateViewStartProvider(),
+                                     page,
+                                     new CommonTestEncoder(),
+                                     isPartial: false);
+            var viewContext = CreateViewContext(view);
+
+            // Act and Assert
+            var exception = await Assert.ThrowsAsync<InvalidOperationException>(() => view.RenderAsync(viewContext));
+
+            // Assert
+            Assert.Equal(expectedMessage, exception.Message);
+        }
+
+        [Fact]
+        public async Task RenderAsync_Throws_IfNestedLayoutPagesResultInCyclicReferences()
+        {
+            // Arrange
+            var expectedMessage = "A circular layout reference was detected when rendering " +
+                "'/Shared/Layout2.cshtml'. The layout page 'Shared/_Layout.cshtml' has already been rendered.";
+            var page = new TestableRazorPage(v =>
+            {
+                v.Layout = "_Layout";
+            });
+            var layout1 = new TestableRazorPage(v =>
+            {
+                v.Layout = "_Layout2";
+                v.RenderBodyPublic();
+            });
+            layout1.Path = "Shared/_Layout.cshtml";
+
+            var layout2 = new TestableRazorPage(v =>
+            {
+                v.Layout = "_Layout";
+                v.RenderBodyPublic();
+            });
+            layout2.Path = "/Shared/Layout2.cshtml";
+
+            var viewEngine = new Mock<IRazorViewEngine>();
+            viewEngine.Setup(p => p.FindPage(It.IsAny<ActionContext>(), "_Layout"))
+                       .Returns(new RazorPageResult("_Layout", layout1));
+            viewEngine.Setup(p => p.FindPage(It.IsAny<ActionContext>(), "_Layout2"))
+                       .Returns(new RazorPageResult("_Layout2", layout2));
+
+            var view = new RazorView(viewEngine.Object,
+                                     Mock.Of<IRazorPageActivator>(),
+                                     CreateViewStartProvider(),
+                                     page,
+                                     new CommonTestEncoder(),
+                                     isPartial: false);
+            var viewContext = CreateViewContext(view);
+
+            // Act and Assert
+            var exception = await Assert.ThrowsAsync<InvalidOperationException>(() => view.RenderAsync(viewContext));
+
+            // Assert
+            Assert.Equal(expectedMessage, exception.Message);
+        }
+
         [Fact]
         public async Task RenderAsync_ExecutesNestedLayoutsWithNestedSections()
         {
@@ -848,6 +934,8 @@ namespace Microsoft.AspNet.Mvc.Razor
                     await writer.WriteLineAsync(htmlEncoder.HtmlEncode(v.RenderSection("foo").ToString()));
                 });
             });
+            nestedLayout.Path = "~/Shared/Layout2.cshtml";
+
             var baseLayout = new TestableRazorPage(v =>
             {
                 v.HtmlEncoder = htmlEncoder;
@@ -855,6 +943,8 @@ namespace Microsoft.AspNet.Mvc.Razor
                 v.RenderBodyPublic();
                 v.Write(v.RenderSection("foo"));
             });
+            baseLayout.Path = "~/Shared/Layout1.cshtml";
+
             var viewEngine = new Mock<IRazorViewEngine>();
             viewEngine.Setup(p => p.FindPage(It.IsAny<ActionContext>(), "~/Shared/Layout1.cshtml"))
                        .Returns(new RazorPageResult("~/Shared/Layout1.cshtml", nestedLayout));