动手写一个简版 asp.net core

Intro

之前看到过蒋金楠老师的一篇 200 行代码带你了解 asp.net core 框架，最近参考蒋老师和 Edison 的文章和代码，结合自己对 asp.net core 的理解 ，最近自己写了一个 MiniAspNetCore ，写篇文章总结一下。

HttpContext

HttpContext 可能是最为常用的一个类了， HttpContext 是请求上下文，包含了所有的请求信息以及响应信息，以及一些自定义的用于在不同中间件中传输数据的信息

来看一下 HttpContext 的定义:

public class HttpContext
{public IServiceProvider RequestServices { get; set; }public HttpRequest Request { get; set; }public HttpResponse Response { get; set; }public IFeatureCollection Features { get; set; }public HttpContext(IFeatureCollection featureCollection){Features = featureCollection;Request = new HttpRequest(featureCollection);Response = new HttpResponse(featureCollection);}
}

HttpRequest 即为请求信息对象，包含了所有请求相关的信息，

HttpResponse 为响应信息对象，包含了请求对应的响应信息

RequestServices 为 asp.net core 里的 RequestServices，代表当前请求的服务提供者，可以使用它来获取具体的服务实例

Features 为 asp.net core 里引入的对象，可以用来在不同中间件中传递信息和用来解耦合

，下面我们就来看下 HttpRequest 和 HttpResponse 是怎么实现的

HttpRequest:

public class HttpRequest
{private readonly IRequestFeature _requestFeature;public HttpRequest(IFeatureCollection featureCollection){_requestFeature = featureCollection.Get<IRequestFeature>();}public Uri Url => _requestFeature.Url;public NameValueCollection Headers => _requestFeature.Headers;public string Method => _requestFeature.Method;public string Host => _requestFeature.Url.Host;public Stream Body => _requestFeature.Body;
}

HttpResponse:

public class HttpResponse
{private readonly IResponseFeature _responseFeature;public HttpResponse(IFeatureCollection featureCollection){_responseFeature = featureCollection.Get<IResponseFeature>();}public bool ResponseStarted => _responseFeature.Body.Length > 0;public int StatusCode{get => _responseFeature.StatusCode;set => _responseFeature.StatusCode = value;}public async Task WriteAsync(byte[] responseBytes){if (_responseFeature.StatusCode <= 0){_responseFeature.StatusCode = 200;}if (responseBytes != null && responseBytes.Length > 0){await _responseFeature.Body.WriteAsync(responseBytes);}}
}

Features

上面我们提供我们可以使用 Features 在不同中间件中传递信息和解耦合

由上面 HttpRequest/ HttpResponse 的代码我们可以看出来， HttpRequest 和 HttpResponse 其实就是在 IRequestFeature 和 IResponseFeature 的基础上封装了一层，真正的核心其实是 IRequestFeature/ IResponseFeature ，而这里使用接口就很好的实现了解耦，可以根据不同的 WebServer 使用不同的 RequestFeature/ ResponseFeature，来看下 IRequestFeature/ IResponseFeature 的实现

public interface IRequestFeature
{Uri Url { get; }string Method { get; }NameValueCollection Headers { get; }Stream Body { get; }
}
public interface IResponseFeature
{public int StatusCode { get; set; }NameValueCollection Headers { get; set; }public Stream Body { get; }
}

这里的实现和 asp.net core 的实际的实现方式应该不同，asp.net core 里 Headers 同一个 Header 允许有多个值，asp.net core 里是 StringValues 来实现的，这里简单处理了，使用了一个 NameValueCollection 对象

上面提到的 Features 是一个 IFeatureCollection 对象，相当于是一系列的 Feature 对象组成的，来看下 FeatureCollection 的定义：

public interface IFeatureCollection : IDictionary<Type, object> { }
public class FeatureCollection : Dictionary<Type, object>, IFeatureCollection
{
}

这里 IFeatureCollection 直接实现 IDictionary<Type,object> ，通过一个字典 Feature 类型为 Key，Feature 对象为 Value 的字典来保存

为了方便使用，可以定义两个扩展方法来方便的Get/Set

public static class FeatureExtensions
{public static IFeatureCollection Set<TFeature>(this IFeatureCollection featureCollection, TFeature feature){featureCollection[typeof(TFeature)] = feature;return featureCollection;}public static TFeature Get<TFeature>(this IFeatureCollection featureCollection){var featureType = typeof(TFeature);return featureCollection.ContainsKey(featureType) ? (TFeature)featureCollection[featureType] : default(TFeature);}
}

Web服务器

上面我们已经提到了 Web 服务器通过 IRequestFeature/ IResponseFeature 来实现不同 web 服务器和应用程序的解耦，web 服务器只需要提供自己的 RequestFeature/ ResponseFeature 即可

为了抽象不同的 Web 服务器，我们需要定义一个 IServer 的抽象接口，定义如下：

public interface IServer
{Task StartAsync(Func<HttpContext, Task> requestHandler, CancellationToken cancellationToken = default);
}

IServer 定义了一个 StartAsync 方法，用来启动 Web服务器，

StartAsync 方法有两个参数，一个是 requestHandler，是一个用来处理请求的委托，另一个是取消令牌用来停止 web 服务器

示例使用了 HttpListener 来实现了一个简单 Web 服务器， HttpListenerServer 定义如下：

public class HttpListenerServer : IServer
{private readonly HttpListener _listener;private readonly IServiceProvider _serviceProvider;public HttpListenerServer(IServiceProvider serviceProvider, IConfiguration configuration){_listener = new HttpListener();var urls = configuration.GetAppSetting("ASPNETCORE_URLS")?.Split(';');if (urls != null && urls.Length > 0){foreach (var url in urls.Where(u => u.IsNotNullOrEmpty()).Select(u => u.Trim()).Distinct()){// Prefixes must end in a forward slash ("/")// https://stackoverflow.com/questions/26157475/use-of-httplistener_listener.Prefixes.Add(url.EndsWith("/") ? url : $"{url}/");}}else{_listener.Prefixes.Add("http://localhost:5100/");}_serviceProvider = serviceProvider;}public async Task StartAsync(Func<HttpContext, Task> requestHandler, CancellationToken cancellationToken = default){_listener.Start();if (_listener.IsListening){Console.WriteLine("the server is listening on ");Console.WriteLine(_listener.Prefixes.StringJoin(","));}while (!cancellationToken.IsCancellationRequested){var listenerContext = await _listener.GetContextAsync();var featureCollection = new FeatureCollection();featureCollection.Set(listenerContext.GetRequestFeature());featureCollection.Set(listenerContext.GetResponseFeature());using (var scope = _serviceProvider.CreateScope()){var httpContext = new HttpContext(featureCollection){RequestServices = scope.ServiceProvider,};await requestHandler(httpContext);}listenerContext.Response.Close();}_listener.Stop();}
}

HttpListenerServer 实现的 RequestFeature/ ResponseFeatue

public class HttpListenerRequestFeature : IRequestFeature
{private readonly HttpListenerRequest _request;public HttpListenerRequestFeature(HttpListenerContext listenerContext){_request = listenerContext.Request;}public Uri Url => _request.Url;public string Method => _request.HttpMethod;public NameValueCollection Headers => _request.Headers;public Stream Body => _request.InputStream;
}
public class HttpListenerResponseFeature : IResponseFeature
{private readonly HttpListenerResponse _response;public HttpListenerResponseFeature(HttpListenerContext httpListenerContext){_response = httpListenerContext.Response;}public int StatusCode { get => _response.StatusCode; set => _response.StatusCode = value; }public NameValueCollection Headers{get => _response.Headers;set{_response.Headers = new WebHeaderCollection();foreach (var key in value.AllKeys)_response.Headers.Add(key, value[key]);}}public Stream Body => _response.OutputStream;
}

为了方便使用，为 HttpListenerContext 定义了两个扩展方法，就是上面 HttpListenerServer 中的 GetRequestFeature/ GetResponseFeature：

public static class HttpListenerContextExtensions
{public static IRequestFeature GetRequestFeature(this HttpListenerContext context){return new HttpListenerRequestFeature(context);}public static IResponseFeature GetResponseFeature(this HttpListenerContext context){return new HttpListenerResponseFeature(context);}
}

RequestDelegate

在上面的 IServer 定义里有一个 requestHandler 的 对象，在 asp.net core 里是一个名称为 RequestDelegate 的对象，而用来构建这个委托的在 asp.net core 里是 IApplicationBuilder，这些在蒋老师和 Edison 的文章和代码里都可以看到，这里我们只是简单介绍下，我在 MiniAspNetCore 的示例中没有使用这些对象，而是使用了自己抽象的 PipelineBuilder 和原始委托实现的

asp.net core 里 RequestDelegate 定义：

public delegate Task RequestDelegate(HttpContext context);

其实和我们上面定义用的 Func<HttpContext,Task> 是等价的

IApplicationBuilder 定义：

/// <summary>
/// Defines a class that provides the mechanisms to configure an application's request pipeline.
/// </summary>
public interface IApplicationBuilder
{/// <summary>/// Gets or sets the <see cref="T:System.IServiceProvider" /> that provides access to the application's service container./// </summary>IServiceProvider ApplicationServices { get; set; }/// <summary>/// Gets the set of HTTP features the application's server provides./// </summary>IFeatureCollection ServerFeatures { get; }/// <summary>/// Gets a key/value collection that can be used to share data between middleware./// </summary>IDictionary<string, object> Properties { get; }/// <summary>/// Adds a middleware delegate to the application's request pipeline./// </summary>/// <param name="middleware">The middleware delegate.</param>/// <returns>The <see cref="T:Microsoft.AspNetCore.Builder.IApplicationBuilder" />.</returns>IApplicationBuilder Use(Func<RequestDelegate, RequestDelegate> middleware);/// <summary>/// Creates a new <see cref="T:Microsoft.AspNetCore.Builder.IApplicationBuilder" /> that shares the <see cref="P:Microsoft.AspNetCore.Builder.IApplicationBuilder.Properties" /> of this/// <see cref="T:Microsoft.AspNetCore.Builder.IApplicationBuilder" />./// </summary>/// <returns>The new <see cref="T:Microsoft.AspNetCore.Builder.IApplicationBuilder" />.</returns>IApplicationBuilder New();/// <summary>/// Builds the delegate used by this application to process HTTP requests./// </summary>/// <returns>The request handling delegate.</returns>RequestDelegate Build();
}

我们这里没有定义 IApplicationBuilder，使用了简化抽象的 IAsyncPipelineBuilder，定义如下：

public interface IAsyncPipelineBuilder<TContext>
{IAsyncPipelineBuilder<TContext> Use(Func<Func<TContext, Task>, Func<TContext, Task>> middleware);Func<TContext, Task> Build();IAsyncPipelineBuilder<TContext> New();
}

对于 asp.net core 的中间件来说 ，上面的 TContext 就是 HttpContext，替换之后也就是下面这样的：

public interface IAsyncPipelineBuilder<HttpContext>
{IAsyncPipelineBuilder<HttpContext> Use(Func<Func<HttpContext, Task>, Func<HttpContext, Task>> middleware);Func<HttpContext, Task> Build();IAsyncPipelineBuilder<HttpContext> New();
}

是不是和 IApplicationBuilder 很像，如果不像可以进一步把 Func<HttpContext,Task> 使用 RequestDelegate 替换

public interface IAsyncPipelineBuilder<HttpContext>
{IAsyncPipelineBuilder<HttpContext> Use(Func<RequestDelegate, RequestDelegate> middleware);RequestDelegate Build();IAsyncPipelineBuilder<HttpContext> New();
}

最后再将接口名称替换一下：

public interface IApplicationBuilder1
{IApplicationBuilder1 Use(Func<RequestDelegate, RequestDelegate> middleware);RequestDelegate Build();IApplicationBuilder1 New();
}

至此，就完全可以看出来了，这 IAsyncPipelineBuilder<HttpContext> 就是一个简版的 IApplicationBuilder

IAsyncPipelineBuilder 和 IApplicationBuilder 的作用是将注册的多个中间件构建成一个请求处理的委托

中间件处理流程：

更多关于 PipelineBuilder 构建中间件的信息可以查看 让 .NET 轻松构建中间件模式代码 了解更多

WebHost

通过除了 Web 服务器之外，还有一个 Web Host 的概念，可以简单的这样理解，一个 Web 服务器上可以有多个 Web Host，就像 IIS/nginx (Web Server) 可以 host 多个站点

可以说 WebHost 离我们的应用更近，所以我们还需要 IHost 来托管应用

public interface IHost
{Task RunAsync(CancellationToken cancellationToken = default);
}

WebHost 定义：

public class WebHost : IHost
{private readonly Func<HttpContext, Task> _requestDelegate;private readonly IServer _server;public WebHost(IServiceProvider serviceProvider, Func<HttpContext, Task> requestDelegate){_requestDelegate = requestDelegate;_server = serviceProvider.GetRequiredService<IServer>();}public async Task RunAsync(CancellationToken cancellationToken = default){await _server.StartAsync(_requestDelegate, cancellationToken).ConfigureAwait(false);}
}

为了方便的构建 Host对象，引入了 HostBuilder 来方便的构建一个 Host，定义如下：

public interface IHostBuilder
{IHostBuilder ConfigureConfiguration(Action<IConfigurationBuilder> configAction);IHostBuilder ConfigureServices(Action<IConfiguration, IServiceCollection> configureAction);IHostBuilder Initialize(Action<IConfiguration, IServiceProvider> initAction);IHostBuilder ConfigureApplication(Action<IConfiguration, IAsyncPipelineBuilder<HttpContext>> configureAction);IHost Build();
}

WebHostBuilder：

public class WebHostBuilder : IHostBuilder
{private readonly IConfigurationBuilder _configurationBuilder = new ConfigurationBuilder();private readonly IServiceCollection _serviceCollection = new ServiceCollection();private Action<IConfiguration, IServiceProvider> _initAction = null;private readonly IAsyncPipelineBuilder<HttpContext> _requestPipeline = PipelineBuilder.CreateAsync<HttpContext>(context =>{context.Response.StatusCode = 404;return Task.CompletedTask;});public IHostBuilder ConfigureConfiguration(Action<IConfigurationBuilder> configAction){configAction?.Invoke(_configurationBuilder);return this;}public IHostBuilder ConfigureServices(Action<IConfiguration, IServiceCollection> configureAction){if (null != configureAction){var configuration = _configurationBuilder.Build();configureAction.Invoke(configuration, _serviceCollection);}return this;}public IHostBuilder ConfigureApplication(Action<IConfiguration, IAsyncPipelineBuilder<HttpContext>> configureAction){if (null != configureAction){var configuration = _configurationBuilder.Build();configureAction.Invoke(configuration, _requestPipeline);}return this;}public IHostBuilder Initialize(Action<IConfiguration, IServiceProvider> initAction){if (null != initAction){_initAction = initAction;}return this;}public IHost Build(){var configuration = _configurationBuilder.Build();_serviceCollection.AddSingleton<IConfiguration>(configuration);var serviceProvider = _serviceCollection.BuildServiceProvider();_initAction?.Invoke(configuration, serviceProvider);return new WebHost(serviceProvider, _requestPipeline.Build());}public static WebHostBuilder CreateDefault(string[] args){var webHostBuilder = new WebHostBuilder();webHostBuilder.ConfigureConfiguration(builder => builder.AddJsonFile("appsettings.json", true, true)).UseHttpListenerServer();return webHostBuilder;}
}

这里的示例我在 IHostBuilder 里增加了一个 Initialize 的方法来做一些初始化的操作，我觉得有些数据初始化配置初始化等操作应该在这里操作，而不应该在 Startup 的 Configure 方法里处理，这样 Configure 方法可以更纯粹一些，只配置 asp.net core 的请求管道，这纯属个人意见，没有对错之分

这里 Host 的实现和 asp.net core 的实现不同，有需要的可以深究源码，在 asp.net core 2.x 的版本里是有一个 IWebHost 的，在 asp.net core 3.x 以及 .net 5 里是没有 IWebHost 的取而代之的是通用主机 IHost， 通过实现了一个 IHostedService 来实现 WebHost 的

Run

运行示例代码：

public class Program
{private static readonly CancellationTokenSource Cts = new CancellationTokenSource();public static async Task Main(string[] args){Console.CancelKeyPress += OnExit;var host = WebHostBuilder.CreateDefault(args).ConfigureServices((configuration, services) =>{}).ConfigureApplication((configuration, app) =>{app.When(context => context.Request.Url.PathAndQuery.StartsWith("/favicon.ico"), pipeline => { });app.When(context => context.Request.Url.PathAndQuery.Contains("test"),p => { p.Run(context => context.Response.WriteAsync("test")); });app.Use(async (context, next) =>{await context.Response.WriteLineAsync($"middleware1, requestPath:{context.Request.Url.AbsolutePath}");await next();}).Use(async (context, next) =>{await context.Response.WriteLineAsync($"middleware2, requestPath:{context.Request.Url.AbsolutePath}");await next();}).Use(async (context, next) =>{await context.Response.WriteLineAsync($"middleware3, requestPath:{context.Request.Url.AbsolutePath}");await next();});app.Run(context => context.Response.WriteAsync("Hello Mini Asp.Net Core"));}).Initialize((configuration, services) =>{}).Build();await host.RunAsync(Cts.Token);}private static void OnExit(object sender, EventArgs e){Console.WriteLine("exiting ...");Cts.Cancel();}
}

在示例项目目录下执行 dotnet run，并访问 http://localhost:5100/:

仔细观察浏览器 console 或 network 的话，会发现还有一个请求，浏览器会默认请求 /favicon.ico 获取网站的图标

因为我们针对这个请求没有任何中间件的处理，所以直接返回了 404

在访问 /test，可以看到和刚才的输出完全不同，因为这个请求走了另外一个分支，相当于 asp.net core 里 Map/ MapWhen 的效果，另外 Run 代表里中间件的中断，不会执行后续的中间件

More

上面的实现只是我在尝试写一个简版的 asp.net core 框架时的实现，和 asp.net core 的实现并不完全一样，如果需要请参考源码，上面的实现仅供参考，上面实现的源码可以在 Github 上获取 https://github.com/WeihanLi/SamplesInPractice/tree/master/MiniAspNetCore

asp.net core 源码：https://github.com/dotnet/aspnetcore

Reference

• https://www.cnblogs.com/artech/p/inside-asp-net-core-framework.html

• https://www.cnblogs.com/artech/p/mini-asp-net-core-3x.html

• https://www.cnblogs.com/edisonchou/p/aspnet_core_mini_implemention_introduction.html

• 让 .NET 轻松构建中间件模式代码

• 让 .NET 轻松构建中间件模式代码（二）

• https://github.com/WeihanLi/SamplesInPractice/tree/master/MiniAspNetCore