_configureServicesDelegates的承接
在【ASP.NET Core[源码分析篇] - Startup】这篇文章中，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，我们得到了所有需要注册的委托_configureServicesDelegates，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方法BuildCommonServices，这个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里面的方法。
WebHost
当我们的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()
我们先看一下WebHost的Initialize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
- 解析Startup类
- 执行Startup类的ConfigureServices方法注册自定义的服务并返回一个IServiceProvider对象
至此，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()
当我们调用WebHost的扩展方法Run启动应用的时候，本质上是调用了WebHost的StartAsync方法，这个过程创建了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 != )
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[]{ ';' };
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，我们将分步进行剖析。
1. EnsureServer
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HTTP服务器，负责HTTP的监听，接收一组 FeatureCollection 类型的原始请求，并将其包装成 HttpContext 以供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
在上面我们获取了一个Server用来监听请求，那么下一步我们是要构建处理Http请求的管道，IApplicationBuilder 就是用于构建应用程序的请求管道。
我们一般的管道创建是在 Startup 类的 Configure 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 方法之前执行，所有我们看到在BuildApplication方法中，一个大概的步骤是这样的：
- 基于IApplicationBuilderFactory创建IApplicationBuilder对象
- 基于IStartupFilter的管道构建
- 调用IApplicationBuilder对象的Build方法完成完整的管道
public RequestDelegate Build()
{
RequestDelegate requestDelegate = (RequestDelegate) (context =>
{
context.Response.StatusCode = ;
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，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);
}
......
}
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) , 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 为我们开启了一个后台运行服务，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：
- Startup有多少种实例化方式？
- IStartup在哪里被实例化的？
- IServiceCollection何时实例化的？
- IServiceProvider何时实例化的？
- Startup的ConfigureService方法何时被执行？
- IApplicationBuilder何时实例化的？
- Startup的Configure方法何时被执行？
- Http监听管道是何时和如何构建的？