[聚合文章] 【ASP.NET Core】运行原理之启动WebHost

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.Net 2017-12-05 13 阅读
原文链接: http://www.cnblogs.com/neverc/p/7988226.html

问题概要

  1. Hosting中有哪2个ServiceProvider，各自如何创建，以及有哪些ServiceCollection。
  2. 什么时候执行Startup的ConfigureServices 和 Configure方法
  3. 什么时候注册和使用的Server
  4. 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。

  1. 参数args将作为配置项
  2. 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

  1. 生成第二个ServiceProvider _applicationServices(微软的内部字段命名，感觉不太规范);
  2. 初始化Server，读取绑定的地址。
  3. 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

  1. 调用Server.Start，将Initialize方法创建的Application管道传入以供处理消息
  2. 执行HostedServiceExecutor.StartAsync方法
public static void Run(this IWebHost host){    await host.RunAsync(cts.Token, "Application started. Press Ctrl+C to shut down.");}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

  1. hostingServices(WebHostBuilder) 和 _applicationServices(WebHost)。区别是_applicationServices中比hostingServices多处Startup方法注册的服务。
  2. 都是WebHost中执行的。ConfigureServices在_applicationServices生成前，Configure在_applicationServices生成后。
  3. 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

本文链接：http://neverc.cnblogs.com/p/7988226.html

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