Remove IServerLoader and add the IServerFactory to the DI container

- This change removes the indirection and between the IServerLoader and
the IServerFactory. We now add the IServerFactory directly to the DI
container and resolve it from there.
- Moved logic that resolves IServerFactory from an assembly to a static
helper

src/Microsoft.AspNetCore.Hosting.Abstractions/IWebHostBuilder.cs

@@ -26,13 +26,6 @@ namespace Microsoft.AspNetCore.Hosting
         /// <returns>The <see cref="IWebHostBuilder"/>.</returns>
         IWebHostBuilder UseLoggerFactory(ILoggerFactory loggerFactory);
 
-        /// <summary>
-        /// Specify the <see cref="IServerFactory"/> to be used by the web host.
-        /// </summary>
-        /// <param name="factory">The <see cref="IServerFactory"/> to be used.</param>
-        /// <returns>The <see cref="IWebHostBuilder"/>.</returns>
-        IWebHostBuilder UseServer(IServerFactory factory);
-
         /// <summary>
         /// Specify the startup type to be used by the web host. 
         /// </summary>

src/Microsoft.AspNetCore.Hosting/Internal/ServerLoader.cs

@@ -0,0 +1,31 @@
+using System;
+using System.Linq;
+using System.Reflection;
+using Microsoft.AspNetCore.Hosting.Server;
+
+namespace Microsoft.AspNetCore.Hosting.Internal
+{
+    internal static class ServerLoader
+    {
+        internal static Type ResolveServerFactoryType(string assemblyName)
+        {
+            var assembly = Assembly.Load(new AssemblyName(assemblyName));
+            if (assembly == null)
+            {
+                throw new InvalidOperationException(string.Format("The assembly {0} failed to load.", assemblyName));
+            }
+
+            var serverTypeInfo = assembly.DefinedTypes.Where(
+                t => t.ImplementedInterfaces.FirstOrDefault(interf => interf.Equals(typeof(IServerFactory))) != null)
+                .FirstOrDefault();
+
+            if (serverTypeInfo == null)
+            {
+                throw new InvalidOperationException($"No server type found that implements IServerFactory in assembly: {assemblyName}.");
+            }
+
+            return serverTypeInfo.AsType();
+        }
+
+    }
+}

src/Microsoft.AspNetCore.Hosting/Internal/WebHost.cs

@@ -31,14 +31,16 @@ namespace Microsoft.AspNetCore.Hosting.Internal
         private RequestDelegate _application;
         private ILogger<WebHost> _logger;
 
+        // Used for testing only
+        internal WebHostOptions Options => _options;
+
         // Only one of these should be set
         internal string StartupAssemblyName { get; set; }
         internal StartupMethods Startup { get; set; }
         internal Type StartupType { get; set; }
 
-        // Only one of these should be set
+        private IServerFactory ServerFactory { get; set; }
-        internal IServerFactory ServerFactory { get; set; }
+
-        internal string ServerFactoryLocation { get; set; }
         private IServer Server { get; set; }
 
         public WebHost(
@@ -207,18 +209,9 @@ namespace Microsoft.AspNetCore.Hosting.Internal
         {
             if (Server == null)
             {
-                if (ServerFactory == null)
+                ServerFactory = _applicationServices.GetRequiredService<IServerFactory>();
-                {
-                    // Blow up if we don't have a server set at this point
-                    if (ServerFactoryLocation == null)
-                    {
-                        throw new InvalidOperationException("IHostingBuilder.UseServer() is required for " + nameof(Start) + "()");
-                    }
-
-                    ServerFactory = _applicationServices.GetRequiredService<IServerLoader>().LoadServerFactory(ServerFactoryLocation);
-                }
-
                 Server = ServerFactory.CreateServer(_config);
+
                 var addresses = Server.Features?.Get<IServerAddressesFeature>()?.Addresses;
                 if (addresses != null && !addresses.IsReadOnly && addresses.Count == 0)
                 {

src/Microsoft.AspNetCore.Hosting/Internal/WebHostOptions.cs

@@ -23,7 +23,7 @@ namespace Microsoft.AspNetCore.Hosting.Internal
             DetailedErrors = ParseBool(configuration, WebHostDefaults.DetailedErrorsKey);
             CaptureStartupErrors = ParseBool(configuration, WebHostDefaults.CaptureStartupErrorsKey);
             Environment = configuration[WebHostDefaults.EnvironmentKey];
-            ServerFactoryLocation = configuration[WebHostDefaults.ServerKey];
+            ServerFactoryAssembly = configuration[WebHostDefaults.ServerKey];
             WebRoot = configuration[WebHostDefaults.WebRootKey];
             ContentRootPath = configuration[WebHostDefaults.ContentRootKey];
         }
@@ -36,7 +36,7 @@ namespace Microsoft.AspNetCore.Hosting.Internal
 
         public string Environment { get; set; }
 
-        public string ServerFactoryLocation { get; set; }
+        public string ServerFactoryAssembly { get; set; }
 
         public string WebRoot { get; set; }
 

src/Microsoft.AspNetCore.Hosting/Server/IServerLoader.cs

@@ -1,10 +0,0 @@
-// 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.
-
-namespace Microsoft.AspNetCore.Hosting.Server
-{
-    public interface IServerLoader
-    {
-        IServerFactory LoadServerFactory(string assemblyName);
-    }
-}

src/Microsoft.AspNetCore.Hosting/Server/ServerLoader.cs

@@ -1,50 +0,0 @@
-// 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 System.Linq;
-using System.Reflection;
-using Microsoft.Extensions.DependencyInjection;
-
-namespace Microsoft.AspNetCore.Hosting.Server
-{
-    public class ServerLoader : IServerLoader
-    {
-        private readonly IServiceProvider _services;
-
-        public ServerLoader(IServiceProvider services)
-        {
-            _services = services;
-        }
-
-        public IServerFactory LoadServerFactory(string assemblyName)
-        {
-            if (assemblyName == null)
-            {
-                throw new ArgumentNullException(nameof(assemblyName));
-            }
-
-            if (string.IsNullOrEmpty(assemblyName))
-            {
-                throw new ArgumentException(string.Empty, nameof(assemblyName));
-            }
-
-            var assembly = Assembly.Load(new AssemblyName(assemblyName));
-            if (assembly == null)
-            {
-                throw new Exception(string.Format("The assembly {0} failed to load.", assemblyName));
-            }
-
-            var serverTypeInfo = assembly.DefinedTypes.Where(
-                t => t.ImplementedInterfaces.FirstOrDefault(interf => interf.Equals(typeof(IServerFactory))) != null)
-                .FirstOrDefault();
-
-            if (serverTypeInfo == null)
-            {
-                throw new InvalidOperationException($"No server type found that implements IServerFactory in assembly: {assemblyName}.");
-            }
-
-            return (IServerFactory)ActivatorUtilities.GetServiceOrCreateInstance(_services, serverTypeInfo.AsType());
-        }
-    }
-}

src/Microsoft.AspNetCore.Hosting/WebHostBuilder.cs

@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
+using System.Linq;
 using System.Reflection;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Hosting.Builder;
@@ -38,9 +39,6 @@ namespace Microsoft.AspNetCore.Hosting
         private StartupMethods _startup;
         private Type _startupType;
 
-        // Only one of these should be set
-        private IServerFactory _serverFactory;
-
         /// <summary>
         /// Initializes a new instance of the <see cref="WebHostBuilder"/> class.
         /// </summary>
@@ -89,22 +87,6 @@ namespace Microsoft.AspNetCore.Hosting
             return this;
         }
 
-        /// <summary>
-        /// Specify the <see cref="IServerFactory"/> to be used by the web host.
-        /// </summary>
-        /// <param name="factory">The <see cref="IServerFactory"/> to be used.</param>
-        /// <returns>The <see cref="IWebHostBuilder"/>.</returns>
-        public IWebHostBuilder UseServer(IServerFactory factory)
-        {
-            if (factory == null)
-            {
-                throw new ArgumentNullException(nameof(factory));
-            }
-
-            _serverFactory = factory;
-            return this;
-        }
-
         /// <summary>
         /// Specify the startup type to be used by the web host.
         /// </summary>
@@ -189,10 +171,6 @@ namespace Microsoft.AspNetCore.Hosting
 
             var host = new WebHost(hostingServices, startupLoader, _options, _config);
 
-            // Only one of these should be set, but they are used in priority
-            host.ServerFactory = _serverFactory;
-            host.ServerFactoryLocation = _options.ServerFactoryLocation;
-
             // Only one of these should be set, but they are used in priority
             host.Startup = _startup;
             host.StartupType = _startupType;
@@ -227,8 +205,6 @@ namespace Microsoft.AspNetCore.Hosting
             services.AddLogging();
 
             services.AddTransient<IStartupLoader, StartupLoader>();
-
-            services.AddTransient<IServerLoader, ServerLoader>();
             services.AddTransient<IApplicationBuilderFactory, ApplicationBuilderFactory>();
             services.AddTransient<IHttpContextFactory, HttpContextFactory>();
             services.AddOptions();
@@ -248,6 +224,13 @@ namespace Microsoft.AspNetCore.Hosting
             services.AddSingleton(defaultPlatformServices.Application);
             services.AddSingleton(defaultPlatformServices.Runtime);
 
+            if (!string.IsNullOrEmpty(_options.ServerFactoryAssembly))
+            {
+                // Add the server factory
+                var serverFactoryType = ServerLoader.ResolveServerFactoryType(_options.ServerFactoryAssembly);
+                services.AddSingleton(typeof(IServerFactory), serverFactoryType);
+            }
+
             foreach (var configureServices in _configureServicesDelegates)
             {
                 configureServices(services);

src/Microsoft.AspNetCore.Hosting/WebHostBuilderExtensions.cs

@@ -2,9 +2,12 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Linq;
+using System.Reflection;
 using Microsoft.AspNetCore.Hosting.Internal;
 using Microsoft.AspNetCore.Hosting.Server;
 using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
 
 namespace Microsoft.AspNetCore.Hosting
 {
@@ -104,6 +107,27 @@ namespace Microsoft.AspNetCore.Hosting
             return hostBuilder.UseSetting(WebHostDefaults.ServerKey, assemblyName);
         }
 
+        /// <summary>
+        /// Specify the <see cref="IServerFactory"/> to be used by the web host.
+        /// </summary>
+        /// <param name="hostBuilder">The <see cref="IWebHostBuilder"/> to configure.</param>
+        /// <param name="factory">The <see cref="IServerFactory"/> to be used.</param>
+        /// <returns>The <see cref="IWebHostBuilder"/>.</returns>
+        public static IWebHostBuilder UseServer(this IWebHostBuilder hostBuilder, IServerFactory factory)
+        {
+            if (factory == null)
+            {
+                throw new ArgumentNullException(nameof(factory));
+            }
+
+            return hostBuilder.ConfigureServices(services =>
+            {
+                // It would be nicer if this was transient but we need to pass in the
+                // factory instance directly
+                services.AddSingleton(factory);
+            });
+        }
+
         /// <summary>
         /// Specify the server to be used by the web host.
         /// </summary>
@@ -117,6 +141,8 @@ namespace Microsoft.AspNetCore.Hosting
                 throw new ArgumentNullException(nameof(server));
             }
 
+            // It would be nicer if this was transient but we need to pass in the
+            // server instance directly
             return hostBuilder.UseServer(new ServerFactory(server));
         }
 

test/Microsoft.AspNetCore.Hosting.Tests/WebHostBuilderTests.cs

@@ -242,14 +242,14 @@ namespace Microsoft.AspNetCore.Hosting
         public void CodeBasedSettingsCodeBasedOverride()
         {
             var hostBuilder = new WebHostBuilder()
-                .UseSetting(WebHostDefaults.ServerKey, "ServerA")
+                .UseSetting(WebHostDefaults.EnvironmentKey, "EnvA")
-                .UseSetting(WebHostDefaults.ServerKey, "ServerB")
+                .UseSetting(WebHostDefaults.EnvironmentKey, "EnvB")
                 .UseServer(new TestServer())
                 .UseStartup<StartupNoServices>();
 
             var host = (WebHost)hostBuilder.Build();
 
-            Assert.Equal("ServerB", host.ServerFactoryLocation);
+            Assert.Equal("EnvB", host.Options.Environment);
         }
 
         [Fact]
@@ -257,7 +257,7 @@ namespace Microsoft.AspNetCore.Hosting
         {
             var settings = new Dictionary<string, string>
             {
-                { WebHostDefaults.ServerKey, "ServerB" }
+                { WebHostDefaults.EnvironmentKey, "EnvB" }
             };
 
             var config = new ConfigurationBuilder()
@@ -265,14 +265,14 @@ namespace Microsoft.AspNetCore.Hosting
                 .Build();
 
             var hostBuilder = new WebHostBuilder()
-                .UseSetting(WebHostDefaults.ServerKey, "ServerA")
+                .UseSetting(WebHostDefaults.EnvironmentKey, "EnvA")
                 .UseConfiguration(config)
                 .UseServer(new TestServer())
                 .UseStartup<StartupNoServices>();
 
             var host = (WebHost)hostBuilder.Build();
 
-            Assert.Equal("ServerB", host.ServerFactoryLocation);
+            Assert.Equal("EnvB", host.Options.Environment);
         }
 
         [Fact]
@@ -280,7 +280,7 @@ namespace Microsoft.AspNetCore.Hosting
         {
             var settings = new Dictionary<string, string>
             {
-                { WebHostDefaults.ServerKey, "ServerA" }
+                { WebHostDefaults.EnvironmentKey, "EnvA" }
             };
 
             var config = new ConfigurationBuilder()
@@ -289,13 +289,13 @@ namespace Microsoft.AspNetCore.Hosting
 
             var hostBuilder = new WebHostBuilder()
                 .UseConfiguration(config)
-                .UseSetting(WebHostDefaults.ServerKey, "ServerB")
+                .UseSetting(WebHostDefaults.EnvironmentKey, "EnvB")
                 .UseServer(new TestServer())
                 .UseStartup<StartupNoServices>();
 
             var host = (WebHost)hostBuilder.Build();
 
-            Assert.Equal("ServerB", host.ServerFactoryLocation);
+            Assert.Equal("EnvB", host.Options.Environment);
         }
 
         [Fact]
@@ -303,7 +303,7 @@ namespace Microsoft.AspNetCore.Hosting
         {
             var settings = new Dictionary<string, string>
             {
-                { WebHostDefaults.ServerKey, "ServerA" }
+                { WebHostDefaults.EnvironmentKey, "EnvA" }
             };
 
             var config = new ConfigurationBuilder()
@@ -312,7 +312,7 @@ namespace Microsoft.AspNetCore.Hosting
 
             var overrideSettings = new Dictionary<string, string>
             {
-                { WebHostDefaults.ServerKey, "ServerB" }
+                { WebHostDefaults.EnvironmentKey, "EnvB" }
             };
 
             var overrideConfig = new ConfigurationBuilder()
@@ -327,7 +327,7 @@ namespace Microsoft.AspNetCore.Hosting
 
             var host = (WebHost)hostBuilder.Build();
 
-            Assert.Equal("ServerB", host.ServerFactoryLocation);
+            Assert.Equal("EnvB", host.Options.Environment);
         }
 
         [Fact]

test/Microsoft.AspNetCore.Hosting.Tests/WebHostConfigurationsTests.cs

@@ -34,7 +34,7 @@ namespace Microsoft.AspNetCore.Hosting.Tests
             var config = new WebHostOptions(new ConfigurationBuilder().AddInMemoryCollection(parameters).Build());
 
             Assert.Equal("wwwroot", config.WebRoot);
-            Assert.Equal("Microsoft.AspNetCore.Server.Kestrel", config.ServerFactoryLocation);
+            Assert.Equal("Microsoft.AspNetCore.Server.Kestrel", config.ServerFactoryAssembly);
             Assert.Equal("MyProjectReference", config.Application);
             Assert.Equal("Development", config.Environment);
             Assert.True(config.CaptureStartupErrors);

test/Microsoft.AspNetCore.Hosting.Tests/WebHostTests.cs

@@ -24,7 +24,7 @@ using Xunit;
 
 namespace Microsoft.AspNetCore.Hosting
 {
-    public class WebHostTests : IServerFactory, IServer
+    public class WebHostTests : IServerFactory
     {
         private readonly IList<StartInstance> _startInstances = new List<StartInstance>();
         private IFeatureCollection _featuresSupportedByThisHost = NewFeatureCollection();
@@ -66,7 +66,7 @@ namespace Microsoft.AspNetCore.Hosting
         public void WebHostThrowsWithNoServer()
         {
             var ex = Assert.Throws<InvalidOperationException>(() => CreateBuilder().Build().Start());
-            Assert.True(ex.Message.Contains("UseServer()"));
+            Assert.Equal("No service for type 'Microsoft.AspNetCore.Hosting.Server.IServerFactory' has been registered.", ex.Message);
         }
 
         [Fact]
@@ -108,7 +108,7 @@ namespace Microsoft.AspNetCore.Hosting
         }
 
         [Fact]
-        public void CanDefaultAddresseIfNotConfigured()
+        public void CanDefaultAddressesIfNotConfigured()
         {
             var vals = new Dictionary<string, string>
             {
@@ -128,7 +128,7 @@ namespace Microsoft.AspNetCore.Hosting
         public void WebHostCanBeStarted()
         {
             var host = CreateBuilder()
-                .UseServer((IServerFactory)this)
+                .UseServer(this)
                 .UseStartup("Microsoft.AspNetCore.Hosting.Tests")
                 .Start();
 
@@ -145,7 +145,7 @@ namespace Microsoft.AspNetCore.Hosting
         public void WebHostShutsDownWhenTokenTriggers()
         {
             var host = CreateBuilder()
-                .UseServer((IServerFactory)this)
+                .UseServer(this)
                 .UseStartup("Microsoft.AspNetCore.Hosting.Tests")
                 .Build();
 
@@ -173,7 +173,7 @@ namespace Microsoft.AspNetCore.Hosting
         public void WebHostDisposesServiceProvider()
         {
             var host = CreateBuilder()
-                .UseServer((IServerFactory)this)
+                .UseServer(this)
                 .ConfigureServices(s =>
                 {
                     s.AddTransient<IFakeService, FakeService>();
@@ -200,7 +200,7 @@ namespace Microsoft.AspNetCore.Hosting
         public void WebHostNotifiesApplicationStarted()
         {
             var host = CreateBuilder()
-                .UseServer((IServerFactory)this)
+                .UseServer(this)
                 .Build();
             var applicationLifetime = host.Services.GetService<IApplicationLifetime>();
 
@@ -216,7 +216,7 @@ namespace Microsoft.AspNetCore.Hosting
         public void WebHostInjectsHostingEnvironment()
         {
             var host = CreateBuilder()
-                .UseServer((IServerFactory)this)
+                .UseServer(this)
                 .UseStartup("Microsoft.AspNetCore.Hosting.Tests")
                 .UseEnvironment("WithHostingEnvironment")
                 .Build();
@@ -237,7 +237,7 @@ namespace Microsoft.AspNetCore.Hosting
                 {
                     services.AddTransient<IStartupLoader, TestLoader>();
                 })
-                .UseServer((IServerFactory)this)
+                .UseServer(this)
                 .UseStartup("Microsoft.AspNetCore.Hosting.Tests");
 
             Assert.Throws<NotImplementedException>(() => builder.Build());
@@ -246,7 +246,7 @@ namespace Microsoft.AspNetCore.Hosting
         [Fact]
         public void CanCreateApplicationServicesWithAddedServices()
         {
-            var host = CreateBuilder().UseServer((IServerFactory)this).ConfigureServices(services => services.AddOptions()).Build();
+            var host = CreateBuilder().UseServer(this).ConfigureServices(services => services.AddOptions()).Build();
             Assert.NotNull(host.Services.GetRequiredService<IOptions<object>>());
         }
 
@@ -256,7 +256,7 @@ namespace Microsoft.AspNetCore.Hosting
             // Verify ordering
             var configureOrder = 0;
             var host = CreateBuilder()
-                .UseServer((IServerFactory)this)
+                .UseServer(this)
                 .ConfigureServices(services =>
                 {
                     services.AddTransient<IStartupFilter>(serviceProvider => new TestFilter(
@@ -300,7 +300,7 @@ namespace Microsoft.AspNetCore.Hosting
         [Fact]
         public void EnvDefaultsToProductionIfNoConfig()
         {
-            var host = CreateBuilder().UseServer((IServerFactory)this).Build();
+            var host = CreateBuilder().UseServer(this).Build();
             var env = host.Services.GetService<IHostingEnvironment>();
             Assert.Equal(EnvironmentName.Production, env.EnvironmentName);
         }
@@ -317,7 +317,7 @@ namespace Microsoft.AspNetCore.Hosting
                 .AddInMemoryCollection(vals);
             var config = builder.Build();
 
-            var host = CreateBuilder(config).UseServer((IServerFactory)this).Build();
+            var host = CreateBuilder(config).UseServer(this).Build();
             var env = host.Services.GetService<IHostingEnvironment>();
             Assert.Equal("Staging", env.EnvironmentName);
         }
@@ -334,7 +334,7 @@ namespace Microsoft.AspNetCore.Hosting
                 .AddInMemoryCollection(vals);
             var config = builder.Build();
 
-            var host = CreateBuilder(config).UseServer((IServerFactory)this).Build();
+            var host = CreateBuilder(config).UseServer(this).Build();
             var env = host.Services.GetService<IHostingEnvironment>();
             Assert.Equal(Path.GetFullPath("testroot"), env.WebRootPath);
             Assert.True(env.WebRootFileProvider.GetFileInfo("TextFile.txt").Exists);
@@ -343,7 +343,7 @@ namespace Microsoft.AspNetCore.Hosting
         [Fact]
         public void IsEnvironment_Extension_Is_Case_Insensitive()
         {
-            var host = CreateBuilder().UseServer((IServerFactory)this).Build();
+            var host = CreateBuilder().UseServer(this).Build();
             using (host)
             {
                 host.Start();
@@ -401,7 +401,7 @@ namespace Microsoft.AspNetCore.Hosting
         public void WebHost_InvokesConfigureMethodsOnlyOnce()
         {
             var host = CreateBuilder()
-                .UseServer((IServerFactory)this)
+                .UseServer(this)
                 .UseStartup<CountStartup>()
                 .Build();
             using (host)
@@ -434,7 +434,7 @@ namespace Microsoft.AspNetCore.Hosting
         public void WebHost_ThrowsForBadConfigureServiceSignature()
         {
             var builder = CreateBuilder()
-                .UseServer((IServerFactory)this)
+                .UseServer(this)
                 .UseStartup<BadConfigureServicesStartup>();
 
             var ex = Assert.Throws<InvalidOperationException>(() => builder.Build());
@@ -450,7 +450,7 @@ namespace Microsoft.AspNetCore.Hosting
         private IWebHost CreateHost(RequestDelegate requestDelegate)
         {
             var builder = CreateBuilder()
-                .UseServer((IServerFactory)this)
+                .UseServer(this)
                 .Configure(
                     appBuilder =>
                     {
@@ -497,7 +497,7 @@ namespace Microsoft.AspNetCore.Hosting
         {
             _instanceFeaturesSupportedByThisHost = new FeatureCollection();
             _instanceFeaturesSupportedByThisHost.Set<IServerAddressesFeature>(new ServerAddressesFeature());
-            return this;
+            return new FakeServer(this);
         }
 
         private class StartInstance : IDisposable
@@ -671,5 +671,24 @@ namespace Microsoft.AspNetCore.Hosting
         {
             public string TraceIdentifier { get; set; }
         }
+
+        private class FakeServer : IServer
+        {
+            private readonly WebHostTests _webHostTests;
+
+            public FakeServer(WebHostTests webHostTests)
+            {
+                _webHostTests = webHostTests;
+            }
+
+            public IFeatureCollection Features => _webHostTests.Features;
+
+            public void Dispose() => _webHostTests.Dispose();
+
+            public void Start<TContext>(IHttpApplication<TContext> application)
+            {
+                _webHostTests.Start<TContext>(application);
+            }
+        }
     }
 }