ASP.NET Core[源码分析篇] - WebHost

 _configureServicesDelegates的承接

  在【ASP.NET Core[源码分析篇] - Startup】这篇文章中,TT快三TT快三我 们 得知了目前为止(UseStartup),所有的动作都是在_configureServicesDelegates里面添加了注册的委托,那么系统是什么时候执行这些委托完成注册的呢?

  真正的注册 

  通过之前的一系列眼花缭乱的操作,TT快三TT快三我 们 得到了所有需要注册的委托_configureServicesDelegates,TT快三TT快三我 们 看一下WebHostBuilder.Build如何实现真正的注册。

  WebHostBuilder.Build()

  public IWebHost Build()
    {
      if (this._webHostBuilt)
        throw new InvalidOperationException(Resources.WebHostBuilder_SingleInstance);
      this._webHostBuilt = true;
      AggregateException hostingStartupErrors;
      IServiceCollection serviceCollection1 = this.BuildCommonServices(out hostingStartupErrors);
      IServiceCollection serviceCollection2 = serviceCollection1.Clone();
      IServiceProvider providerFromFactory = GetProviderFromFactory(serviceCollection1);
      .....

    WebHost webHost = new WebHost(serviceCollection2, providerFromFactory, this._options, this._config, hostingStartupErrors);
      try
      {
        webHost.Initialize();
        return (IWebHost) webHost;
      }
      catch
      {
        webHost.Dispose();
        throw;
      }

    IServiceProvider GetProviderFromFactory(IServiceCollection collection)
      {
        ServiceProvider serviceProvider = collection.BuildServiceProvider();
        IServiceProviderFactory<IServiceCollection> service = ((IServiceProvider) serviceProvider).GetService<IServiceProviderFactory<IServiceCollection>>();
        if (service == null)
          return (IServiceProvider) serviceProvider;
        using (serviceProvider)
          return service.CreateServiceProvider(service.CreateBuilder(collection));
      }
    }

  这里面有个最重要的TT快三方法 BuildCommonServices,这个TT快三方法 实现了委托的真正的执行。

private IServiceCollection BuildCommonServices(
      out AggregateException hostingStartupErrors)
    {
        .....
     ServiceCollection services = new ServiceCollection();
services.AddTransient
<IApplicationBuilderFactory, ApplicationBuilderFactory>(); services.AddTransient<IHttpContextFactory, HttpContextFactory>(); services.AddScoped<IMiddlewareFactory, MiddlewareFactory>(); services.AddOptions(); services.AddLogging(); services.AddTransient<IStartupFilter, AutoRequestServicesStartupFilter>(); services.AddTransient<IServiceProviderFactory<IServiceCollection>, DefaultServiceProviderFactory>();     ..... foreach (Action<WebHostBuilderContext, IServiceCollection> servicesDelegate in this._configureServicesDelegates) servicesDelegate(this._context, (IServiceCollection) services); return (IServiceCollection) services; }

  从上面的代码TT快三TT快三我 们 可以看到,首先创建了一个真正的ServiceCollection实例,然后基于这个实例添加了一些额外的重要的注册(ApplicationBuilderFactory,HttpContextFactory,DefaultServiceProviderFactory等),然后把这个ServiceCollection实例作为参数传递到_configureServicesDelegates列表的各个委托中并执行,这样的话所有在Startup需要注册的实例都已经注册在services这个ServiceCollection实例中。

  需要注意的是,到此为止程序并没有执行Startup里面的TT快三方法 。

  WebHost

   当TT快三TT快三我 们 的BuildCommonServices完成后,返回一个ServiceCollection实例,并且基于这个ServiceCollection实例生成了一个ServiceProvider对象,然后做为生成WebHost对象的参数传递到WebHost中。

WebHost webHost = new WebHost(serviceCollection2, providerFromFactory, this._options, this._config, hostingStartupErrors);

webHost.Initialize();  

  WebHost.Initialize()

  TT快三TT快三我 们 先看一下WebHost的InitializeTT快三方法

  public void Initialize()
    {
      try
      {
        this.EnsureApplicationServices();
      }
      catch (Exception ex)
      {
        if (this._applicationServices == null)
          this._applicationServices = (IServiceProvider) this._applicationServiceCollection.BuildServiceProvider();
        if (!this._options.CaptureStartupErrors)
          throw;
        else
          this._applicationServicesException = ExceptionDispatchInfo.Capture(ex);
      }
    }

  private void EnsureApplicationServices()
    {
      if (this._applicationServices != null)
        return;
      this.EnsureStartup();
      this._applicationServices = this._startup.ConfigureServices(this._applicationServiceCollection);
    }

    private void EnsureStartup()
    {
      if (this._startup != null)
        return;
      this._startup = this._hostingServiceProvider.GetService<IStartup>();
      if (this._startup == null)
        throw new InvalidOperationException(string.Format("No startup configured. Please specify startup via WebHostBuilder.UseStartup, WebHostBuilder.Configure, injecting {0} or specifying the startup assembly via {1} in the web host configuration.", (object) "IStartup", (object) "StartupAssemblyKey"));
    }

  从上面的代码流程可以看出

  1. 解析Startup类
  2. 执行Startup类的ConfigureServicesTT快三方法 注册自定义的TT快三服务 并返回一个IServiceProvider对象

  至此,TT快三TT快三我 们 的Startup类中的ConfigureServices已经执行过,并且WebHost已经具有了IServiceProvider对象  

  WebHost.Run()

  当TT快三TT快三我 们 调用WebHost的扩展TT快三方法 Run启动应用的时候,本质上是调用了WebHost的StartAsyncTT快三方法 ,这个过程创建了TT快三TT快三我 们 应用程序最为重要的用于监听、接收、处理和响应HTTP请求的管道。 

  public virtual async Task StartAsync(CancellationToken cancellationToken = default (CancellationToken))
    {
      HostingEventSource.Log.HostStart();
      this._logger = this._applicationServices.GetRequiredService<ILogger<WebHost>>();
      this._logger.Starting();
      RequestDelegate application = this.BuildApplication();
      this._applicationLifetime = this._applicationServices.GetRequiredService<Microsoft.AspNetCore.Hosting.IApplicationLifetime>() as ApplicationLifetime;
      this._hostedServiceExecutor = this._applicationServices.GetRequiredService<HostedServiceExecutor>();
      DiagnosticListener requiredService1 = this._applicationServices.GetRequiredService<DiagnosticListener>();
      IHttpContextFactory requiredService2 = this._applicationServices.GetRequiredService<IHttpContextFactory>();
      ILogger<WebHost> logger = this._logger;
      DiagnosticListener diagnosticSource = requiredService1;
      IHttpContextFactory httpContextFactory = requiredService2;
      await this.Server.StartAsync<HostingApplication.Context>((IHttpApplication<HostingApplication.Context>) new HostingApplication(application, (ILogger) logger, diagnosticSource, httpContextFactory), cancellationToken).ConfigureAwait(false);
      this._applicationLifetime?.NotifyStarted();
      await this._hostedServiceExecutor.StartAsync(cancellationToken).ConfigureAwait(false);
     .....
    }

  private RequestDelegate BuildApplication()
    {
        this._applicationServicesException?.Throw();
        this.EnsureServer();
        IApplicationBuilder builder = this._applicationServices.GetRequiredService<IApplicationBuilderFactory>().CreateBuilder(this.Server.Features);
        builder.ApplicationServices = this._applicationServices;
        IEnumerable<IStartupFilter> service = this._applicationServices.GetService<IEnumerable<IStartupFilter>>();
        Action<IApplicationBuilder> next = new Action<IApplicationBuilder>(this._startup.Configure);
        foreach (IStartupFilter startupFilter in service.Reverse<IStartupFilter>())
          next = startupFilter.Configure(next);
        next(builder);
        return builder.Build();
      }

  private void EnsureServer()
    {
      if (this.Server != null)
        return;
      this.Server = this._applicationServices.GetRequiredService<IServer>();
      IServerAddressesFeature addressesFeature = this.Server.Features?.Get<IServerAddressesFeature>();
      ICollection<string> addresses = addressesFeature?.Addresses;
      if (addresses == null || addresses.IsReadOnly || addresses.Count != 0)
        return;
      string str1 = this._config[WebHostDefaults.ServerUrlsKey] ?? this._config[WebHost.DeprecatedServerUrlsKey];
      if (string.IsNullOrEmpty(str1))
        return;
      addressesFeature.PreferHostingUrls = WebHostUtilities.ParseBool(this._config, WebHostDefaults.PreferHostingUrlsKey);
      string str2 = str1;
      char[] separator = new char[1]{ ';' };
      foreach (string str3 in str2.Split(separator, StringSplitOptions.RemoveEmptyEntries))
        addresses.Add(str3);
    }

  这块主要是Server的创建,管道的创建和监听Http请求的Server启动,TT快三TT快三我 们 将分步进行剖析。

  1. EnsureServer

   TT快三TT快三我 们 先看一下这个Server是什么

public interface IServer : IDisposable
{
    IFeatureCollection Features { get; }

    Task StartAsync<TContext>(IHttpApplication<TContext> application, CancellationToken cancellationToken);

    Task StopAsync(CancellationToken cancellationToken);
}

  IServer的实例其实是在开始Program里面的CreateDefaultBuilder中,已经指定了KestrelServer作为默认的Server实例。  

public static IWebHostBuilder UseKestrel(this IWebHostBuilder hostBuilder)
{
    hostBuilder.UseLibuv();

    return hostBuilder.ConfigureServices(services =>
    {
        services.AddTransient<IConfigureOptions<KestrelServerOptions>, KestrelServerOptionsSetup>();
        services.AddSingleton<IServer, KestrelServer>();
    });
}

   那么这个Server是做什么用的呢?Server 是一个HTTPTT快三服务 器,负责HTTP的监听,接收一组 FeatureCollection 类型的原始请求,并将其TT快三包装 成 HttpContext 以供TT快三TT快三我 们 的应用程序完成响应的处理。那它负责监听哪里?从代码可以看到Addresses 是通过在UseUrls里面指定的参数(WebHostDefaults.ServerUrlsKey) 或者是DeprecatedServerUrlsKey(配置文件里面的server.urls)中来查找的。

  2. BuildApplication

  在上面TT快三TT快三我 们 获取了一个Server用来监听请求,那么下一步TT快三TT快三我 们 是要构建处理Http请求的管道,IApplicationBuilder 就是用于构建应用程序的请求管道。

  TT快三TT快三我 们 一般的管道创建是在 Startup 类的 Configure TT快三方法 中对 IApplicationBuilder 进行配置,嗯其实在这里还有一个 IStartupFilter 也可以用来配置 IApplicationBuilder,并且在 Startup 类的Configure TT快三方法 之前执行,所有TT快三TT快三我 们 看到在BuildApplicationTT快三方法 中,一个大概的步骤是这样的:

  1. 基于IApplicationBuilderFactory创建IApplicationBuilder对象
  2. 基于IStartupFilter的管道构建
  3. 调用IApplicationBuilder对象的BuildTT快三方法 完成完整的管道
public RequestDelegate Build()
    {
      RequestDelegate requestDelegate = (RequestDelegate) (context =>
      {
        context.Response.StatusCode = 404;
        return Task.CompletedTask;
      });
      foreach (Func<RequestDelegate, RequestDelegate> func in this._components.Reverse<Func<RequestDelegate, RequestDelegate>>())
        requestDelegate = func(requestDelegate);
      return requestDelegate;
    }

  3. Server.StartAsync

  在这里,Server的启动是需要一个IHttpApplication类型的参数的,来负责 HttpContext 的创建,TT快三TT快三我 们 看一下这个参数

public interface IHttpApplication<TContext>
{
    TContext CreateContext(IFeatureCollection contextFeatures);

    Task ProcessRequestAsync(TContext context);

    void DisposeContext(TContext context, Exception exception);
}

  它的默认实现类是它的默认实现是 HostingApplication 类

public class HostingApplication : IHttpApplication<HostingApplication.Context>
  {
    private readonly RequestDelegate _application;
    private readonly IHttpContextFactory _httpContextFactory;public Task ProcessRequestAsync(HostingApplication.Context context)
    {
      return this._application(context.HttpContext);
    }
  ...... }

  TT快三TT快三我 们 来看一下Server的Http监听绑定

public async Task StartAsync<TContext>(
      IHttpApplication<TContext> application,
      CancellationToken cancellationToken)
    {
      try
      {
        if (!BitConverter.IsLittleEndian)
          throw new PlatformNotSupportedException(CoreStrings.BigEndianNotSupported);
        this.ValidateOptions();
        if (this._hasStarted)
          throw new InvalidOperationException(CoreStrings.ServerAlreadyStarted);
        this._hasStarted = true;
        this._heartbeat.Start();
        await AddressBinder.BindAsync(this._serverAddresses, this.Options, (ILogger) this.Trace, new Func<ListenOptions, Task>(OnBind)).ConfigureAwait(false);
      }
      catch (Exception ex)
      {
        this.Trace.LogCritical((EventId) 0, ex, "Unable to start Kestrel.");
        this.Dispose();
        throw;
      }

      async Task OnBind(ListenOptions endpoint)
      {
        endpoint.UseHttpServer<TContext>((IList<IConnectionAdapter>) endpoint.ConnectionAdapters, this.ServiceContext, application, endpoint.Protocols);
        ConnectionDelegate connectionDelegate = endpoint.Build();
        if (this.Options.Limits.MaxConcurrentConnections.HasValue)
          connectionDelegate = new ConnectionDelegate(new ConnectionLimitMiddleware(connectionDelegate, this.Options.Limits.MaxConcurrentConnections.Value, this.Trace).OnConnectionAsync);
        ConnectionDispatcher connectionDispatcher = new ConnectionDispatcher(this.ServiceContext, connectionDelegate);
        ITransport transport = this._transportFactory.Create((IEndPointInformation) endpoint, (IConnectionDispatcher) connectionDispatcher);
        this._transports.Add(transport);
        await transport.BindAsync().ConfigureAwait(false);
      }
    }

  至此为止,Server已经绑定一个监听端口,注册了HTTP连接事件,剩下的就是开启监听了。  

  4. HostedService

  HostedService 为TT快三TT快三我 们 开启了一个后台运行TT快三服务 ,它会在随着程序启动而启动。  

public class HostedServiceExecutor
  {
    private readonly IEnumerable<IHostedService> _services;public async Task StartAsync(CancellationToken token)
    {
    
await this.ExecuteAsync((Func<IHostedService, Task>) (service => service.StartAsync(token))); } public async Task StopAsync(CancellationToken token) {
    await this.ExecuteAsync((Func<IHostedService, Task>) (service => service.StopAsync(token))); } private async Task ExecuteAsync(Func<IHostedService, Task> callback) { List<Exception> exceptions = (List<Exception>) null; foreach (IHostedService service in this._services) { try { await callback(service); } catch (Exception ex) { if (exceptions == null) exceptions = new List<Exception>(); exceptions.Add(ex); } } if (exceptions != null) throw new AggregateException((IEnumerable<Exception>) exceptions); } }

  总结

  这两篇文章从Startup开始到最后的Http管道创建和HttpServer的启动监听,涉及到了很多关键点,从代码流程来看,只要抓住几个关键点即可理解整体的一个流程。大家可以带着以下这些问题去跟着文章走:

  1. Startup有多少种实例化方式?
  2. IStartup在哪里被实例化的?
  3. IServiceCollection何时实例化的?
  4. IServiceProvider何时实例化的?
  5. Startup的ConfigureServiceTT快三方法 何时被执行?
  6. IApplicationBuilder何时实例化的?
  7. Startup的ConfigureTT快三方法 何时被执行?
  8. Http监听管道是何时和如何构建的?
posted @ 2019-08-20 09:25 lex-wu 阅读(...) 评论(...) 编辑 收藏