【ASP.NET Core】运行原理[1]:创建WebHost

本系列将分析ASP.NET Core运行原理

本节将分析WebHost.CreateDefaultBuilder(args).UseStartup<Startup>().Build();代码。

源代码参考.NET Core 2.0.0

问题概要

Hosting中有哪2个ServiceProvider，各自如何创建，以及有哪些ServiceCollection。
什么时候执行Startup的ConfigureServices 和 Configure方法
什么时候注册和使用的Server
手工模拟一个DefaultWebHost环境

WebHost.CreateDefaultBuilder(args)

该方法为WebHost类的静态方法，内部创建1个WebHostBuilder。

参数args将作为配置项
添加了Kestrel、Configuration、Logging、IISIntegration中间件，同时配置ContentRoot和DefaultServiceProvider

public static IWebHostBuilder CreateDefaultBuilder(string[] args)
{
    var builder = new WebHostBuilder()
        .UseKestrel()
        .UseContentRoot(Directory.GetCurrentDirectory())
        .ConfigureAppConfiguration((hostingContext, config) => { var env = hostingContext.HostingEnvironment; config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true) .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: true); if (env.IsDevelopment()) { var appAssembly = Assembly.Load(new AssemblyName(env.ApplicationName)); if (appAssembly != null) { config.AddUserSecrets(appAssembly, optional: true); } } config.AddEnvironmentVariables(); if (args != null) { config.AddCommandLine(args); } }) .ConfigureLogging((hostingContext, logging) => { logging.AddConfiguration(hostingContext.Configuration.GetSection("Logging")); logging.AddConsole(); logging.AddDebug(); }) .UseIISIntegration() .UseDefaultServiceProvider((context, options) => { options.ValidateScopes = context.HostingEnvironment.IsDevelopment(); }); return builder; }

UseKestrel

在UseKestrel()方法中，注册了3个服务到List<Action<WebHostBuilderContext, IServiceCollection>>字段上。(以供后续注册)

public static IWebHostBuilder UseKestrel(this IWebHostBuilder hostBuilder)
{
    return hostBuilder.ConfigureServices((Action<IServiceCollection>) (services => { services.AddSingleton<ITransportFactory, LibuvTransportFactory>(); services.AddTransient<IConfigureOptions<KestrelServerOptions>, KestrelServerOptionsSetup>(); services.AddSingleton<IServer, KestrelServer>(); })); } public IWebHostBuilder ConfigureServices(Action<WebHostBuilderContext, IServiceCollection> configureServices) { this._configureServicesDelegates.Add((_, services) => configureServices(services)); return (IWebHostBuilder) this; }

UseContentRoot

UseContentRoot方法则是添加到IConfiguration字段上,这个字段在构造函数初始化
this._config = (IConfiguration) new ConfigurationBuilder().AddEnvironmentVariables("ASPNETCORE_").Build();

public static IWebHostBuilder UseContentRoot(this IWebHostBuilder hostBuilder, string contentRoot) { if (contentRoot == null) throw new ArgumentNullException(nameof (contentRoot)); return hostBuilder.UseSetting(WebHostDefaults.ContentRootKey, contentRoot); } public IWebHostBuilder UseSetting(string key, string value) { this._config[key] = value; return (IWebHostBuilder) this; }

ConfigureAppConfiguration

ConfigureAppConfiguration方法是添加到List<Action<WebHostBuilderContext, IConfigurationBuilder>>字段上
在外部添加了
AddJsonFile("appsettings.json")、AddJsonFile(string.Format("appsettings.{0}.json", (object) hostingEnvironment.EnvironmentName))
AddEnvironmentVariables()
AddCommandLine(args)

public IWebHostBuilder ConfigureAppConfiguration(Action<WebHostBuilderContext, IConfigurationBuilder> configureDelegate)
{
    this._configureAppConfigurationBuilderDelegates.Add(configureDelegate); return (IWebHostBuilder) this; }

ConfigureLogging

ConfigureLogging注册Log到ServiceCollection上
在外部添加了3个ILoggerProvider
logging.AddConfiguration(hostingContext.Configuration.GetSection("Logging"));
logging.AddConsole();
logging.AddDebug();

public static IWebHostBuilder ConfigureLogging(this IWebHostBuilder hostBuilder, Action<WebHostBuilderContext, ILoggingBuilder> configureLogging)
{
    return hostBuilder.ConfigureServices((context, services) => services.AddLogging(builder => configureLogging(context, builder)); } public IWebHostBuilder ConfigureServices(Action<WebHostBuilderContext, IServiceCollection> configureServices) { this._configureServicesDelegates.Add(configureServices); return (IWebHostBuilder) this; }

UseDefaultServiceProvider

UseDefaultServiceProvider配置和替换服务

var options = new ServiceProviderOptions { ValidateScopes = context.HostingEnvironment.IsDevelopment()}; services.Replace(ServiceDescriptor.Singleton<IServiceProviderFactory<IServiceCollection>>((IServiceProviderFactory<IServiceCollection>) new DefaultServiceProviderFactory(options)));

UseStartup

UseStartup相当于注册了一个IStartup服务。

public static IWebHostBuilder UseStartup(this IWebHostBuilder hostBuilder, Type startupType) { string name = startupType.GetTypeInfo().Assembly.GetName().Name; return hostBuilder.UseSetting(WebHostDefaults.ApplicationKey, name).ConfigureServices((Action<IServiceCollection>) (services => { if (typeof (IStartup).GetTypeInfo().IsAssignableFrom(startupType.GetTypeInfo())) ServiceCollectionServiceExtensions.AddSingleton(services, typeof (IStartup), startupType); else ServiceCollectionServiceExtensions.AddSingleton(services, typeof (IStartup), (Func<IServiceProvider, object>) (sp => { IHostingEnvironment requiredService = sp.GetRequiredService<IHostingEnvironment>(); return (object) new ConventionBasedStartup(StartupLoader.LoadMethods(sp, startupType, requiredService.EnvironmentName)); })); })); }

根据Startup是否继承IStartup，来决定注册的方式。未继承的时候，会使用ConventionBasedStartup来封装自定义的Startup。

Build

Build方法是WebHostBuilder最终的目的，将构造一个WebHost返回。

同时初始化WebHost对象，WebHostBuilder.Build代码：

public IWebHost Build()
{
    var hostingServices = BuildCommonServices(out var hostingStartupErrors); var applicationServices = hostingServices.Clone(); var hostingServiceProvider = hostingServices.BuildServiceProvider(); AddApplicationServices(applicationServices, hostingServiceProvider); var host = new WebHost( applicationServices, hostingServiceProvider, _options, _config, hostingStartupErrors); host.Initialize(); return host; }

在Build方法中，BuildCommonServices最为重要,将构造第一个ServiceCollection。这里我们称为hostingServices。
将包含hostEnv、Config、ApplicationBuilder、Logging、StartupFilter、Startup、Server。参考BuildCommonServices

private IServiceCollection BuildCommonServices(out AggregateException hostingStartupErrors) { if (!this._options.PreventHostingStartup) { foreach (string hostingStartupAssembly in (IEnumerable<string>) this._options.HostingStartupAssemblies) { foreach (HostingStartupAttribute customAttribute in Assembly.Load(new AssemblyName(hostingStartupAssembly)).GetCustomAttributes<HostingStartupAttribute>()) ((IHostingStartup) Activator.CreateInstance(customAttribute.HostingStartupType)).Configure((IWebHostBuilder) this); } } ServiceCollection services = new ServiceCollection(); // hostEnv _hostingEnvironment.Initialize(this._options.ApplicationName, this.ResolveContentRootPath(this._options.ContentRootPath, AppContext.BaseDirectory), this._options); services.AddSingleton<IHostingEnvironment>(this._hostingEnvironment); // config IConfigurationBuilder configurationBuilder = new ConfigurationBuilder().SetBasePath(this._hostingEnvironment.ContentRootPath).AddInMemoryCollection(this._config.AsEnumerable()); foreach (Action<WebHostBuilderContext, IConfigurationBuilder> configurationBuilderDelegate in this._configureAppConfigurationBuilderDelegates) configurationBuilderDelegate(this._context, configurationBuilder); IConfigurationRoot configurationRoot = configurationBuilder.Build(); services.AddSingleton<IConfiguration>((IConfiguration) configurationRoot); services.AddOptions(); // application services.AddTransient<IApplicationBuilderFactory, ApplicationBuilderFactory>(); services.AddTransient<IHttpContextFactory, HttpContextFactory>(); services.AddScoped<IMiddlewareFactory, MiddlewareFactory>(); // log services.AddLogging(); services.AddTransient<IStartupFilter, AutoRequestServicesStartupFilter>(); services.AddTransient<IServiceProviderFactory<IServiceCollection>, DefaultServiceProviderFactory>(); // 配置的StartupType if (!string.IsNullOrEmpty(this._options.StartupAssembly)) { Type startupType = StartupLoader.FindStartupType(this._options.StartupAssembly, this._hostingEnvironment.EnvironmentName); if (typeof (IStartup).GetTypeInfo().IsAssignableFrom(startupType.GetTypeInfo())) ServiceCollectionServiceExtensions.AddSingleton(services, typeof (IStartup), startupType); else ServiceCollectionServiceExtensions.AddSingleton(services, typeof (IStartup), new ConventionBasedStartup(StartupLoader.LoadMethods(startupType))); } // UseStartup、UseKestrel、ConfigureLogging foreach (Action<WebHostBuilderContext, IServiceCollection> servicesDelegate in this._configureServicesDelegates) servicesDelegate(this._context, (IServiceCollection) services); return (IServiceCollection) services; }

当 hostingServices 创建完成后，会马上拷贝一份applicationServices提供给WebHost使用，同时创建第一个ServiceProvider hostingServiceProvider。

host.Initialize()该方法则是初始化WebHost

生成第二个ServiceProvider _applicationServices(微软的内部字段命名，感觉不太规范);
初始化Server，读取绑定的地址。
创建Application管道，生成RequestDelegate。

public void Initialize() { _startup = _hostingServiceProvider.GetService<IStartup>(); _applicationServices = _startup.ConfigureServices(_applicationServiceCollection); EnsureServer(); var builderFactory = _applicationServices.GetRequiredService<IApplicationBuilderFactory>(); var builder = builderFactory.CreateBuilder(Server.Features); builder.ApplicationServices = _applicationServices; var startupFilters = _applicationServices.GetService<IEnumerable<IStartupFilter>>(); Action<IApplicationBuilder> configure = _startup.Configure; foreach (var filter in startupFilters.Reverse()) { configure = filter.Configure(configure); } configure(builder); this._application = builder.Build(); // RequestDelegate }

WebHost.Run

创建完 WebHost 之后，便调用它的 Run 方法，而 Run 方法会去调用 WebHost 的 StartAsync 方法

调用Server.Start，将Initialize方法创建的Application管道传入以供处理消息
执行HostedServiceExecutor.StartAsync方法

public static void Run(this IWebHost host) { host.RunAsync(cts.Token, "Application started. Press Ctrl+C to shut down.").GetAwaiter().GetResult(); } private static async Task RunAsync(this IWebHost host, CancellationToken token, string shutdownMessage) { await host.StartAsync(token); var hostingEnvironment = host.Services.GetService<IHostingEnvironment>(); Console.WriteLine($"Hosting environment: {hostingEnvironment.EnvironmentName}"); Console.WriteLine($"Content root path: {hostingEnvironment.ContentRootPath}"); var serverAddresses = host.ServerFeatures.Get<IServerAddressesFeature>()?.Addresses; if (serverAddresses != null) foreach (var address in serverAddresses) Console.WriteLine($"Now listening on: {address}"); if (!string.IsNullOrEmpty(shutdownMessage)) Console.WriteLine(shutdownMessage); } public virtual async Task StartAsync(CancellationToken cancellationToken = default (CancellationToken)) { Initialize(); _applicationLifetime = _applicationServices.GetRequiredService<IApplicationLifetime>() as ApplicationLifetime; _hostedServiceExecutor = _applicationServices.GetRequiredService<HostedServiceExecutor>(); var httpContextFactory = _applicationServices.GetRequiredService<IHttpContextFactory>(); var hostingApp = new HostingApplication(_application, _logger, diagnosticSource, httpContextFactory); await Server.StartAsync(hostingApp, cancellationToken).ConfigureAwait(false); _applicationLifetime?.NotifyStarted(); await _hostedServiceExecutor.StartAsync(cancellationToken).ConfigureAwait(false); }

问题解答

hostingServices(WebHostBuilder) 和 _applicationServices(WebHost)。区别是_applicationServices中比hostingServices多处Startup方法注册的服务。
都是WebHost中执行的。ConfigureServices在_applicationServices生成前，Configure在_applicationServices生成后。
最初的注册在WebHostBuilder的UseKestrel，使用在WebHost的Run方法

手工模拟一个DefaultWebHost环境

new WebHostBuilder()
    .UseKestrel()                                       // 使用Kestrel服务器
    .UseContentRoot(Directory.GetCurrentDirectory())    // 配置根目录 会在ConfigurationBuilder、 IHostingEnvironment(后续其他中间件) 和 WebHostOptions(WebHost)用到。
    .ConfigureAppConfiguration((context, builder) => builder.AddJsonFile("appsetting.json", true, true)) // 添加配置源 .ConfigureLogging(builder => builder.AddConsole()) // 添加日志适配器 .UseStartup<Startup>() // 选择Startup .Build().Run(); // 生成WebHost 并 启动

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