Defer reporting API version response headers

Author: Chris Martinez

src/Microsoft.AspNetCore.Mvc.Versioning/ReportApiVersionsAttribute.cs

@@ -1,9 +1,12 @@
 namespace Microsoft.AspNetCore.Mvc
 {
+    using Microsoft.AspNetCore.Http;
     using Microsoft.AspNetCore.Mvc.Abstractions;
     using Microsoft.AspNetCore.Mvc.Filters;
     using Microsoft.AspNetCore.Mvc.Versioning;
     using System;
+    using System.Threading.Tasks;
+    using static System.Threading.Tasks.Task;
 
     /// <content>
     /// Provides additional implementation specific to ASP.NET Core.
@@ -49,8 +52,15 @@ public override void OnActionExecuting( ActionExecutingContext context )
 
             if ( !model.IsApiVersionNeutral )
             {
-                reporter.Report( response.Headers, model );
+                response.OnStarting( ReportApiVersions, (response.Headers, model) );
             }
         }
+
+        Task ReportApiVersions( object state )
+        {
+            var (headers, model) = ((IHeaderDictionary, ApiVersionModel)) state;
+            reporter.Report( headers, model );
+            return CompletedTask;
+        }
     }
 }

test/Microsoft.AspNetCore.Mvc.Versioning.Tests/ReportApiVersionsAttributeTest.cs

@@ -1,68 +1,89 @@
 namespace Microsoft.AspNetCore.Mvc
 {
-    using Abstractions;
-    using AspNetCore.Routing;
-    using Filters;
     using FluentAssertions;
-    using Http;
+    using Microsoft.AspNetCore.Http;
+    using Microsoft.AspNetCore.Mvc.Abstractions;
+    using Microsoft.AspNetCore.Mvc.Filters;
+    using Microsoft.AspNetCore.Mvc.Versioning;
+    using Microsoft.AspNetCore.Routing;
     using Moq;
+    using System;
     using System.Collections.Generic;
     using System.Linq;
-    using Versioning;
+    using System.Threading.Tasks;
     using Xunit;
 
     public class ReportApiVersionsAttributeTest
     {
-        static ActionExecutingContext CreateContext( ApiVersionModel model )
-        {
-            var headers = new HeaderDictionary();
-            var response = new Mock<HttpResponse>();
-            var httpContext = new Mock<HttpContext>();
-            var action = new ActionDescriptor();
-            var actionContext = new ActionContext( httpContext.Object, new RouteData(), action  );
-            var filters = new IFilterMetadata[0];
-            var actionArguments = new Dictionary<string, object>();
-            var controller = default( object );
-
-            response.SetupGet( r => r.Headers ).Returns( headers );
-            httpContext.SetupGet( c => c.Response ).Returns( response.Object );
-            action.SetProperty( model );
-
-            return new ActionExecutingContext( actionContext, filters, actionArguments, controller );
-        }
-
         [Fact]
-        public void on_action_executing_should_add_version_headers()
+        public async Task on_action_executing_should_add_version_headers()
         {
             // arrange
             var supported = new[] { new ApiVersion( 1, 0 ), new ApiVersion( 2, 0 ) };
             var deprecated = new[] { new ApiVersion( 0, 5 ) };
             var model = new ApiVersionModel( supported, deprecated );
-            var context = CreateContext( model );
+            var onStartResponse = new List<(Func<object, Task>, object)>();
+            var context = CreateContext( model, onStartResponse );
             var attribute = new ReportApiVersionsAttribute();
 
             // act
             attribute.OnActionExecuting( context );
 
+            for ( var i = 0; i < onStartResponse.Count; i++ )
+            {
+                var (callback, state) = onStartResponse[i];
+                await callback( state );
+            }
+
             // assert
-            context.HttpContext.Response.Headers["api-supported-versions"].Single().Should().Be( "1.0, 2.0" );
-            context.HttpContext.Response.Headers["api-deprecated-versions"].Single().Should().Be( "0.5" );
+            var headers = context.HttpContext.Response.Headers;
+
+            headers["api-supported-versions"].Single().Should().Be( "1.0, 2.0" );
+            headers["api-deprecated-versions"].Single().Should().Be( "0.5" );
         }
 
         [Fact]
-        public void on_action_executing_should_not_add_headers_for_versionX2Dneutral_controller()
+        public async Task on_action_executing_should_not_add_headers_for_versionX2Dneutral_controller()
         {
             // arrange
-            var context = CreateContext( ApiVersionModel.Neutral );
+            var onStartResponse = new List<(Func<object, Task>, object)>();
+            var context = CreateContext( ApiVersionModel.Neutral, onStartResponse );
             var attribute = new ReportApiVersionsAttribute();
 
             // act
             attribute.OnActionExecuting( context );
 
+            for ( var i = 0; i < onStartResponse.Count; i++ )
+            {
+                var (callback, state) = onStartResponse[i];
+                await callback( state );
+            }
 
             // assert
-            context.HttpContext.Response.Headers.ContainsKey( "api-supported-versions" ).Should().BeFalse();
-            context.HttpContext.Response.Headers.ContainsKey( "api-deprecated-versions" ).Should().BeFalse();
+            var headers = context.HttpContext.Response.Headers;
+
+            headers.ContainsKey( "api-supported-versions" ).Should().BeFalse();
+            headers.ContainsKey( "api-deprecated-versions" ).Should().BeFalse();
+        }
+
+        static ActionExecutingContext CreateContext( ApiVersionModel model, ICollection<(Func<object, Task>, object)> onStartResponse )
+        {
+            var headers = new HeaderDictionary();
+            var response = new Mock<HttpResponse>();
+            var httpContext = new Mock<HttpContext>();
+            var action = new ActionDescriptor();
+            var actionContext = new ActionContext( httpContext.Object, new RouteData(), action );
+            var filters = Array.Empty<IFilterMetadata>();
+            var actionArguments = new Dictionary<string, object>();
+            var controller = default( object );
+
+            response.SetupGet( r => r.Headers ).Returns( headers );
+            response.Setup( r => r.OnStarting( It.IsAny<Func<object, Task>>(), It.IsAny<object>() ) )
+                    .Callback( ( Func<object, Task> callback, object state ) => onStartResponse.Add( (callback, state) ) );
+            httpContext.SetupGet( c => c.Response ).Returns( response.Object );
+            action.SetProperty( model );
+
+            return new ActionExecutingContext( actionContext, filters, actionArguments, controller );
         }
     }
 }