【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

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

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