Add application startup check that dispatcher is added to request pipeline (#614)

src/Microsoft.AspNetCore.Routing/Builder/DispatcherApplicationBuilderExtensions.cs

@@ -10,10 +10,14 @@ namespace Microsoft.AspNetCore.Builder
 {
     public static class DispatcherApplicationBuilderExtensions
     {
+        private const string DispatcherRegisteredKey = "__DispatcherMiddlewareRegistered";
+
         public static IApplicationBuilder UseDispatcher(this IApplicationBuilder builder)
         {
             VerifyDispatcherIsRegistered(builder);
 
+            builder.Properties[DispatcherRegisteredKey] = true;
+
             return builder.UseMiddleware<DispatcherMiddleware>();
         }
 
@@ -21,6 +25,14 @@ namespace Microsoft.AspNetCore.Builder
         {
             VerifyDispatcherIsRegistered(builder);
 
+            if (!builder.Properties.TryGetValue(DispatcherRegisteredKey, out _))
+            {
+                var message = $"{nameof(DispatcherMiddleware)} must be added to the request execution pipeline before {nameof(EndpointMiddleware)}. " +
+                    $"Please add {nameof(DispatcherMiddleware)} by calling '{nameof(IApplicationBuilder)}.{nameof(UseDispatcher)}' inside the call to 'Configure(...)' in the application startup code.";
+
+                throw new InvalidOperationException(message);
+            }
+
             return builder.UseMiddleware<EndpointMiddleware>();
         }
 

src/Microsoft.AspNetCore.Routing/EndpointMiddleware.cs

@@ -34,7 +34,10 @@ namespace Microsoft.AspNetCore.Routing
             var feature = httpContext.Features.Get<IEndpointFeature>();
             if (feature == null)
             {
-                throw new InvalidOperationException("Unable to execute an endpoint because the dispatcher was not run. Ensure dispatcher middleware is registered.");
+                var message = $"Unable to execute an endpoint because the {nameof(DispatcherMiddleware)} was not run for this request. " +
+                    $"Ensure {nameof(DispatcherMiddleware)} is added to the request execution pipeline before {nameof(EndpointMiddleware)} in application startup code.";
+
+                throw new InvalidOperationException(message);
             }
 
             if (feature.Invoker != null)

test/Microsoft.AspNetCore.Routing.Tests/DispatcherApplicationBuilderExtensionsTest.cs

@@ -12,7 +12,7 @@ using Xunit;
 
 namespace Microsoft.AspNetCore.Builder
 {
-    public class DispatcherApplicationBuilderExtensions
+    public class DispatcherApplicationBuilderExtensionsTest
     {
         [Fact]
         public void UseDispatcher_ServicesNotRegistered_Throws()
@@ -69,7 +69,26 @@ namespace Microsoft.AspNetCore.Builder
         }
 
         [Fact]
-        public async Task UseEndpoint_ServicesRegistered_SetsFeature()
+        public void UseEndpoint_ServicesRegisteredAndNoDispatcherRegistered_Throws()
+        {
+            // Arrange
+            var services = CreateServices();
+
+            var app = new ApplicationBuilder(services);
+
+            // Act
+            var ex = Assert.Throws<InvalidOperationException>(() => app.UseEndpoint());
+
+            // Assert
+            Assert.Equal(
+                "DispatcherMiddleware must be added to the request execution pipeline before EndpointMiddleware. " +
+                "Please add DispatcherMiddleware by calling 'IApplicationBuilder.UseDispatcher' " +
+                "inside the call to 'Configure(...)' in the application startup code.",
+                ex.Message);
+        }
+
+        [Fact]
+        public async Task UseEndpoint_ServicesRegisteredAndDispatcherRegistered_SetsFeature()
         {
             // Arrange
             var services = CreateServices();

test/Microsoft.AspNetCore.Routing.Tests/EndpointMiddlewareTest.cs

@@ -34,7 +34,10 @@ namespace Microsoft.AspNetCore.Routing
             // Assert
             var ex = await Assert.ThrowsAsync<InvalidOperationException>(async () => await invokeTask);
 
-            Assert.Equal("Unable to execute an endpoint because the dispatcher was not run. Ensure dispatcher middleware is registered.", ex.Message);
+            Assert.Equal(
+                "Unable to execute an endpoint because the DispatcherMiddleware was not run for this request. " +
+                "Ensure DispatcherMiddleware is added to the request execution pipeline before EndpointMiddleware in application startup code.",
+                ex.Message);
         }
 
         private class ServiceProvider : IServiceProvider