`OwinExtensions.UseBuilder()` should not leave `ApplicationServices` or `RequestServices` `null`

Also correct tests to avoid warnings and to ensure scenarios are actually tested
- tests previously went `async` without waiting for completion

nit: add parameter `null` checks

src/Microsoft.AspNetCore.Owin/OwinExtensions.cs

@@ -12,20 +12,25 @@ using Microsoft.AspNetCore.Owin;
 
 namespace Microsoft.AspNetCore.Builder
 {
+    using AddMiddleware = Action<Func<
+          Func<IDictionary<string, object>, Task>,
+          Func<IDictionary<string, object>, Task>
+        >>;
     using AppFunc = Func<IDictionary<string, object>, Task>;
     using CreateMiddleware = Func<
           Func<IDictionary<string, object>, Task>,
           Func<IDictionary<string, object>, Task>
         >;
-    using AddMiddleware = Action<Func<
-          Func<IDictionary<string, object>, Task>,
-          Func<IDictionary<string, object>, Task>
-        >>;
 
     public static class OwinExtensions
     {
         public static AddMiddleware UseOwin(this IApplicationBuilder builder)
         {
+            if (builder == null)
+            {
+                throw new ArgumentNullException(nameof(builder));
+            }
+
             AddMiddleware add = middleware =>
             {
                 Func<RequestDelegate, RequestDelegate> middleware1 = next1 =>
@@ -61,6 +66,15 @@ namespace Microsoft.AspNetCore.Builder
 
         public static IApplicationBuilder UseOwin(this IApplicationBuilder builder, Action<AddMiddleware> pipeline)
         {
+            if (builder == null)
+            {
+                throw new ArgumentNullException(nameof(builder));
+            }
+            if (pipeline == null)
+            {
+                throw new ArgumentNullException(nameof(pipeline));
+            }
+
             pipeline(builder.UseOwin());
             return builder;
         }
@@ -72,6 +86,18 @@ namespace Microsoft.AspNetCore.Builder
 
         public static IApplicationBuilder UseBuilder(this AddMiddleware app, IServiceProvider serviceProvider)
         {
+            if (app == null)
+            {
+                throw new ArgumentNullException(nameof(app));
+            }
+
+            // Do not set ApplicationBuilder.ApplicationServices to null. May fail later due to missing services but
+            // at least that results in a more useful Exception than a NRE.
+            if (serviceProvider == null)
+            {
+                serviceProvider = new EmptyProvider();
+            }
+
             // Adapt WebSockets by default.
             app(OwinWebSocketAcceptAdapter.AdaptWebSockets);
             var builder = new ApplicationBuilder(serviceProvider: serviceProvider);
@@ -125,9 +151,26 @@ namespace Microsoft.AspNetCore.Builder
 
         public static AddMiddleware UseBuilder(this AddMiddleware app, Action<IApplicationBuilder> pipeline, IServiceProvider serviceProvider)
         {
+            if (app == null)
+            {
+                throw new ArgumentNullException(nameof(app));
+            }
+            if (pipeline == null)
+            {
+                throw new ArgumentNullException(nameof(pipeline));
+            }
+
             var builder = app.UseBuilder(serviceProvider);
             pipeline(builder);
             return app;
         }
+
+        private class EmptyProvider : IServiceProvider
+        {
+            public object GetService(Type serviceType)
+            {
+                return null;
+            }
+        }
     }
 }

test/Microsoft.AspNetCore.Owin.Tests/OwinExtensionTests.cs

@@ -6,27 +6,30 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Builder.Internal;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http.Internal;
 using Microsoft.Extensions.DependencyInjection;
 using Xunit;
 
 namespace Microsoft.AspNetCore.Owin
 {
+    using AddMiddleware = Action<Func<
+          Func<IDictionary<string, object>, Task>,
+          Func<IDictionary<string, object>, Task>
+        >>;
     using AppFunc = Func<IDictionary<string, object>, Task>;
     using CreateMiddleware = Func<
           Func<IDictionary<string, object>, Task>,
           Func<IDictionary<string, object>, Task>
         >;
-    using AddMiddleware = Action<Func<
-          Func<IDictionary<string, object>, Task>,
-          Func<IDictionary<string, object>, Task>
-        >>;
 
     public class OwinExtensionTests
     {
         static AppFunc notFound = env => new Task(() => { env["owin.ResponseStatusCode"] = 404; });
 
         [Fact]
-        public void OwinConfigureServiceProviderAddsServices()
+        public async Task OwinConfigureServiceProviderAddsServices()
         {
             var list = new List<CreateMiddleware>();
             AddMiddleware build = list.Add;
@@ -36,21 +39,61 @@ namespace Microsoft.AspNetCore.Owin
             var builder = build.UseBuilder(applicationBuilder =>
             {
                 serviceProvider = applicationBuilder.ApplicationServices;
-                applicationBuilder.Run(async context =>
+                applicationBuilder.Run(context =>
                 {
                     fakeService = context.RequestServices.GetService<FakeService>();
+                    return Task.FromResult(0);
                 });
-            }, new ServiceCollection().AddSingleton(new FakeService()).BuildServiceProvider());
+            },
+            new ServiceCollection().AddSingleton(new FakeService()).BuildServiceProvider());
 
             list.Reverse();
-            list.Aggregate(notFound, (next, middleware) => middleware(next)).Invoke(new Dictionary<string, object>());
+            await list
+                .Aggregate(notFound, (next, middleware) => middleware(next))
+                .Invoke(new Dictionary<string, object>());
 
-            Assert.NotNull(fakeService);
+            Assert.NotNull(serviceProvider);
             Assert.NotNull(serviceProvider.GetService<FakeService>());
+            Assert.NotNull(fakeService);
         }
 
         [Fact]
-        public void OwinDefaultNoServices()
+        public async Task OwinDefaultNoServices()
+        {
+            var list = new List<CreateMiddleware>();
+            AddMiddleware build = list.Add;
+            IServiceProvider expectedServiceProvider = new ServiceCollection().BuildServiceProvider();
+            IServiceProvider serviceProvider = null;
+            FakeService fakeService = null;
+            bool builderExecuted = false;
+            bool applicationExecuted = false;
+
+            var builder = build.UseBuilder(applicationBuilder =>
+            {
+                builderExecuted = true;
+                serviceProvider = applicationBuilder.ApplicationServices;
+                applicationBuilder.Run(context =>
+                {
+                    applicationExecuted = true;
+                    fakeService = context.RequestServices.GetService<FakeService>();
+                    return Task.FromResult(0);
+                });
+            },
+            expectedServiceProvider);
+
+            list.Reverse();
+            await list
+                .Aggregate(notFound, (next, middleware) => middleware(next))
+                .Invoke(new Dictionary<string, object>());
+
+            Assert.True(builderExecuted);
+            Assert.Equal(expectedServiceProvider, serviceProvider);
+            Assert.True(applicationExecuted);
+            Assert.Null(fakeService);
+        }
+
+        [Fact]
+        public async Task OwinDefaultNullServiceProvider()
         {
             var list = new List<CreateMiddleware>();
             AddMiddleware build = list.Add;
@@ -63,25 +106,60 @@ namespace Microsoft.AspNetCore.Owin
             {
                 builderExecuted = true;
                 serviceProvider = applicationBuilder.ApplicationServices;
-                applicationBuilder.Run(async context =>
+                applicationBuilder.Run(context =>
                 {
                     applicationExecuted = true;
                     fakeService = context.RequestServices.GetService<FakeService>();
+                    return Task.FromResult(0);
                 });
             });
 
             list.Reverse();
-            list.Aggregate(notFound, (next, middleware) => middleware(next)).Invoke(new Dictionary<string, object>());
+            await list
+                .Aggregate(notFound, (next, middleware) => middleware(next))
+                .Invoke(new Dictionary<string, object>());
 
             Assert.True(builderExecuted);
-            Assert.Null(fakeService);
+            Assert.NotNull(serviceProvider);
             Assert.True(applicationExecuted);
-            Assert.Null(serviceProvider);
+            Assert.Null(fakeService);
+        }
+
+        [Fact]
+        public async Task UseOwin()
+        {
+            var serviceProvider = new ServiceCollection().BuildServiceProvider();
+            var builder = new ApplicationBuilder(serviceProvider);
+            IDictionary<string, object> environment = null;
+            var context = new DefaultHttpContext();
+
+            builder.UseOwin(addToPipeline =>
+            {
+                addToPipeline(next =>
+                {
+                    Assert.NotNull(next);
+                    return async env =>
+                    {
+                        environment = env;
+                        await next(env);
+                    };
+                });
+            });
+            await builder.Build().Invoke(context);
+
+            // Dictionary contains context but does not contain "websocket.Accept" or "websocket.AcceptAlt" keys.
+            Assert.NotNull(environment);
+            var value = Assert.Single(
+                    environment,
+                    kvp => string.Equals(typeof(HttpContext).FullName, kvp.Key, StringComparison.Ordinal))
+                .Value;
+            Assert.Equal(context, value);
+            Assert.False(environment.ContainsKey("websocket.Accept"));
+            Assert.False(environment.ContainsKey("websocket.AcceptAlt"));
         }
 
         private class FakeService
         {
-
         }
     }
 }