ASP.NET Core[原始碼分析篇] - WebHost
阿新 • • 發佈：2019-08-20
_configureServicesDelegates的承接
在【ASP.NET Core[原始碼分析篇] - Startup】這篇文章中，我們得知了目前為止（UseStartup），所有的動作都是在_configureServicesDelegates裡面添加了註冊的委託，那麼系統是什麼時候執行這些委託完成註冊的呢？
真正的註冊
通過之前的一系列眼花繚亂的操作，我們得到了所有需要註冊的委託_configureServicesDelegates，我們看一下WebHostBuilder.Build如何實現真正的註冊。
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));
}
}這裡面有個最重要的方法BuildCommonServices，這個方法實現了委託的真正的執行。
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;
}從上面的程式碼我們可以看到，首先建立了一個真正的ServiceCollection例項，然後基於這個例項添加了一些額外的重要的註冊（ApplicationBuilderFactory，HttpContextFactory，DefaultServiceProviderFactory等），然後把這個ServiceCollection例項作為引數傳遞到_configureServicesDelegates列表的各個委託中並執行，這樣的話所有在Startup需要註冊的例項都已經註冊在services這個ServiceCollection例項中。
需要注意的是，到此為止程式並沒有執行Startup裡面的方法。
WebHost
當我們的BuildCommonServices完成後，返回一個ServiceCollection例項，並且基於這個ServiceCollection例項生成了一個ServiceProvider物件，然後做為生成WebHost物件的引數傳遞到WebHost中。
WebHost webHost = new WebHost(serviceCollection2, providerFromFactory, this._options, this._config, hostingStartupErrors); webHost.Initialize();
WebHost.Initialize()
我們先看一下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"));
}
從上面的程式碼流程可以看出
- 解析Startup類
- 執行Startup類的ConfigureServices方法註冊自定義的服務並返回一個IServiceProvider物件
直至，我們的Startup類中的ConfigureServices已經執行過，並且WebHost已經具有了IServiceProvider物件
WebHost.Run()
當我們呼叫WebHost的擴充套件方法Run啟動應用的時候，本質上是呼叫了WebHost的StartAsync方法，這個過程建立了我們應用程式最為重要的用於監聽、接收、處理和響應HTTP請求的管道。
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);
}
這塊主要是Server的建立，管道的建立和監聽Http請求的Server啟動，我們將分步進行剖析。
1. EnsureServer
我們先看一下這個Server是什麼
public interface IServer : IDisposable
{
IFeatureCollection Features { get; }
Task StartAsync<TContext>(IHttpApplication<TContext> application, CancellationToken cancellationToken);
Task StopAsync(CancellationToken cancellationToken);
}
IServer的例項其實是在開始Program裡面的CreateDefaultBuilder中，已經指定了KestrelServer作為預設的Server例項。
public static IWebHostBuilder UseKestrel(this IWebHostBuilder hostBuilder)
{
hostBuilder.UseLibuv();
return hostBuilder.ConfigureServices(services =>
{
services.AddTransient<IConfigureOptions<KestrelServerOptions>, KestrelServerOptionsSetup>();
services.AddSingleton<IServer, KestrelServer>();
});
}
那麼這個Server是做什麼用的呢？Server 是一個HTTP伺服器，負責HTTP的監聽，接收一組 FeatureCollection 型別的原始請求，並將其包裝成 HttpContext 以供我們的應用程式完成響應的處理。那它負責監聽哪裡？從程式碼可以看到Addresses 是通過在 launchSettings.json 或者是ServerUrlsKey（UseUrls）中來查詢的。
2. BuildApplication
在上面我們獲取了一個Server用來監聽請求，那麼下一步我們是要構建處理Http請求的管道，IApplicationBuilder 就是用於構建應用程式的請求管道。
我們一般的管道建立是在 Startup 類的 Configure 方法中對 IApplicationBuilder 進行配置，嗯其實在這裡還有一個 IStartupFilter 也可以用來配置 IApplicationBuilder，並且在 Startup 類的Configure 方法之前執行，所有我們看到在BuildApplication方法中，一個大概的步驟是這樣的：
- 基於IApplicationBuilderFactory建立IApplicationBuilder物件
- 基於IStartupFilter的管道構建
- 呼叫IApplicationBuilder物件的Build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
在這裡，Server的啟動是需要一個IHttpApplication型別的引數的，來負責 HttpContext 的建立，我們看一下這個引數
public interface IHttpApplication<TContext>
{
TContext CreateContext(IFeatureCollection contextFeatures);
Task ProcessRequestAsync(TContext context);
void DisposeContext(TContext context, Exception exception);
}
它的預設實現類是它的預設實現是 HostingApplication 類
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);
}
......
}
我們來看一下Server的Http監聽繫結
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);
}
}
至此為止，Server已經繫結一個監聽埠，註冊了HTTP連線事件，剩下的就是開啟監聽了。
4. HostedService
HostedService 為我們開啟了一個後臺執行服務，它會在隨著程式啟動而啟動。
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);
}
}
總結
這兩篇文章從Startup開始到最後的Http管道建立和HttpServer的啟動監聽，涉及到了很多關鍵點，從程式碼流程來看，只要抓住幾個關鍵點即可理解整體的一個流程。大家可以帶著以下這些問題去跟著文章走：
- Startup有多少種例項化方式？
- IStartup在哪裡被例項化的？
- IServiceCollection何時例項化的？
- IServiceProvider何時例項化的？
- Startup的ConfigureService方法何時被執行？
- IApplicationBuilder何時例項化的？
- Startup的Configure方法何時被執行？
- Http監聽管道是何時和如何構建的？