Add helper to register IHttpContextAccessor (#947)

src/Microsoft.AspNetCore.Http/HttpServiceCollectionExtensions.cs

@@ -0,0 +1,31 @@
+// 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;
+using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.DependencyInjection.Extensions;
+
+namespace Microsoft.Extensions.DependencyInjection
+{
+    /// <summary>
+    /// Extension methods for configuring HttpContext services.
+    /// </summary>
+    public static class HttpServiceCollectionExtensions
+    {
+        /// <summary>
+        /// Adds a default implementation for the <see cref="IHttpContextAccessor"/> service.
+        /// </summary>
+        /// <param name="services">The <see cref="IServiceCollection"/>.</param>
+        /// <returns>The service collection.</returns>
+        public static IServiceCollection AddHttpContextAccessor(this IServiceCollection services)
+        {
+            if (services == null)
+            {
+                throw new ArgumentNullException(nameof(services));
+            }
+
+            services.TryAddSingleton<IHttpContextAccessor, HttpContextAccessor>();
+            return services;
+        }
+    }
+}

test/Microsoft.AspNetCore.Http.Tests/HttpServiceCollectionExtensionsTests.cs

@@ -0,0 +1,33 @@
+// 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;
+using Microsoft.Extensions.DependencyInjection;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Http.Tests
+{
+    public class HttpServiceCollectionExtensionsTests
+    {
+        [Fact]
+        public void AddHttpContextAccessor_AddsWithCorrectLifetime()
+        {
+            // Arrange
+            var services = new ServiceCollection();
+
+            // Act
+            services.AddHttpContextAccessor();
+
+            // Assert
+            var descriptor = services[0];
+            Assert.Equal(ServiceLifetime.Singleton, descriptor.Lifetime);
+            Assert.Equal(typeof(HttpContextAccessor), descriptor.ImplementationType);
+        }
+
+        [Fact]
+        public void AddHttpContextAccessor_ThrowsWithoutServices()
+        {
+            Assert.Throws<ArgumentNullException>("services", () => HttpServiceCollectionExtensions.AddHttpContextAccessor(null));
+        }
+    }
+}

test/Microsoft.AspNetCore.Http.Tests/Microsoft.AspNetCore.Http.Tests.csproj

@@ -9,4 +9,8 @@
     <ProjectReference Include="..\..\src\Microsoft.AspNetCore.Http\Microsoft.AspNetCore.Http.csproj" />
   </ItemGroup>
 
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection" />
+  </ItemGroup>
+
 </Project>