【ASP.NET Core】运行原理(1):创建WebHost

时间:2021-09-14 19:33:23

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

  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

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;
}

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)
{
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

  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