動手寫一個簡版 asp.net core
Intro
之前看到過蔣金楠老師的一篇 200 行代碼帶你了解 asp.net core 框架，最近參考蔣老師和 Edison 的文章和代碼，結合自己對 asp.net core 的理解 ，最近自己寫了一個 MiniAspNetCore ，寫篇文章總結一下。
HttpContext
HttpContext 可能是最為常用的一個類了，HttpContext 是請求上下文，包含了所有的請求信息以及響應信息，以及一些自定義的用於在不同中間件中傳輸數據的信息
來看一下 HttpContext 的定義:
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 即為請求信息對象，包含了所有請求相關的信息，
HttpResponse 為響應信息對象，包含了請求對應的響應信息
RequestServices 為 asp.net core 里的RequestServices，代表當前請求的服務提供者，可以使用它來獲取具體的服務實例
Features 為 asp.net core 里引入的對象，可以用來在不同中間件中傳遞信息和用來解耦合
，下面我們就來看下 HttpRequest 和 HttpResponse 是怎么實現的
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
上面我們提到我們可以使用 Features 在不同中間件中傳遞信息和解耦合
由上面 HttpRequest/HttpResponse 的代碼我們可以看出來，HttpRequest 和 HttpResponse 其實就是在 IRequestFeature 和 IResponseFeature 的基礎上封裝了一層，真正的核心其實是 IRequestFeature/IResponseFeature ，而這里使用接口就很好的實現了解耦，可以根據不同的 WebServer 使用不同的 RequestFeature/ResponseFeature，來看下 IRequestFeature/IResponseFeature 的實現
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; }
}
這里的實現和 asp.net core 的實際的實現方式應該不同，asp.net core 里 Headers 同一個 Header 允許有多個值，asp.net core 里是 StringValues 來實現的，這里簡單處理了，使用了一個
NameValueCollection對象
上面提到的 Features 是一個 IFeatureCollection 對象，相當於是一系列的 Feature 對象組成的，來看下 FeatureCollection 的定義：
public interface IFeatureCollection : IDictionary<Type, object> { }
public class FeatureCollection : Dictionary<Type, object>, IFeatureCollection
{
}
這里 IFeatureCollection 直接實現 IDictionary<Type, object> ，通過一個字典 Feature 類型為 Key，Feature 對象為 Value 的字典來保存
為了方便使用，可以定義兩個擴展方法來方便的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服務器
上面我們已經提到了 Web 服務器通過 IRequestFeature/IResponseFeature 來實現不同 web 服務器和應用程序的解耦，web 服務器只需要提供自己的 RequestFeature/ResponseFeature 即可
為了抽象不同的 Web 服務器，我們需要定義一個 IServer 的抽象接口，定義如下：
public interface IServer
{
Task StartAsync(Func<HttpContext, Task> requestHandler, CancellationToken cancellationToken = default);
}
IServer 定義了一個 StartAsync 方法，用來啟動 Web服務器，
StartAsync 方法有兩個參數，一個是 requestHandler，是一個用來處理請求的委托，另一個是取消令牌用來停止 web 服務器
示例使用了 HttpListener 來實現了一個簡單 Web 服務器，HttpListenerServer 定義如下：
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 實現的 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;
}
為了方便使用，為 HttpListenerContext 定義了兩個擴展方法，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 定義里有一個 requestHandler 的 對象，在 asp.net core 里是一個名稱為 RequestDelegate 的對象，而用來構建這個委托的在 asp.net core 里是 IApplicationBuilder，這些在蔣老師和 Edison 的文章和代碼里都可以看到，這里我們只是簡單介紹下，我在 MiniAspNetCore 的示例中沒有使用這些對象，而是使用了自己抽象的 PipelineBuilder 和原始委托實現的
asp.net core 里 RequestDelegate 定義：
public delegate Task RequestDelegate(HttpContext context);
其實和我們上面定義用的 Func<HttpContext, Task> 是等價的
IApplicationBuilder 定義：
/// <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();
}
我們這里沒有定義 IApplicationBuilder，使用了簡化抽象的 IAsyncPipelineBuilder，定義如下：
public interface IAsyncPipelineBuilder<TContext>
{
IAsyncPipelineBuilder<TContext> Use(Func<Func<TContext, Task>, Func<TContext, Task>> middleware);
Func<TContext, Task> Build();
IAsyncPipelineBuilder<TContext> New();
}
對於 asp.net core 的中間件來說 ，上面的 TContext 就是 HttpContext，替換之后也就是下面這樣的：
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，如果不像可以進一步把 Func<HttpContext, Task> 使用 RequestDelegate 替換
public interface IAsyncPipelineBuilder<HttpContext>
{
IAsyncPipelineBuilder<HttpContext> Use(Func<RequestDelegate, RequestDelegate> middleware);
RequestDelegate Build();
IAsyncPipelineBuilder<HttpContext> New();
}
最后再將接口名稱替換一下：
public interface IApplicationBuilder1
{
IApplicationBuilder1 Use(Func<RequestDelegate, RequestDelegate> middleware);
RequestDelegate Build();
IApplicationBuilder1 New();
}
至此，就完全可以看出來了，這 IAsyncPipelineBuilder<HttpContext> 就是一個簡版的 IApplicationBuilder
IAsyncPipelineBuilder 和 IApplicationBuilder 的作用是將注冊的多個中間件構建成一個請求處理的委托
中間件處理流程：
更多關於 PipelineBuilder 構建中間件的信息可以查看 讓 .NET 輕松構建中間件模式代碼 了解更多
WebHost
通過除了 Web 服務器之外，還有一個 Web Host 的概念，可以簡單的這樣理解，一個 Web 服務器上可以有多個 Web Host，就像 IIS/nginx (Web Server) 可以 host 多個站點
可以說 WebHost 離我們的應用更近，所以我們還需要 IHost 來托管應用
public interface IHost
{
Task RunAsync(CancellationToken cancellationToken = default);
}
WebHost 定義：
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);
}
}
為了方便的構建 Host對象，引入了 HostBuilder 來方便的構建一個 Host，定義如下：
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;
}
}
這里的示例我在
IHostBuilder里增加了一個Initialize的方法來做一些初始化的操作，我覺得有些數據初始化配置初始化等操作應該在這里操作，而不應該在Startup的Configure方法里處理，這樣Configure方法可以更純粹一些，只配置 asp.net core 的請求管道，這純屬個人意見，沒有對錯之分這里 Host 的實現和 asp.net core 的實現不同，有需要的可以深究源碼，在 asp.net core 2.x 的版本里是有一個
IWebHost的，在 asp.net core 3.x 以及 .net 5 里是沒有IWebHost的取而代之的是通用主機IHost， 通過實現了一個IHostedService來實現WebHost的
Run
運行示例代碼：
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();
}
}
在示例項目目錄下執行 dotnet run，並訪問 http://localhost:5100/:
仔細觀察瀏覽器 console 或 network 的話，會發現還有一個請求，瀏覽器會默認請求 /favicon.ico 獲取網站的圖標
因為我們針對這個請求沒有任何中間件的處理，所以直接返回了 404
在訪問 /test，可以看到和剛才的輸出完全不同，因為這個請求走了另外一個分支，相當於 asp.net core 里 Map/MapWhen 的效果，另外 Run 代表里中間件的中斷，不會執行后續的中間件
More
上面的實現只是我在嘗試寫一個簡版的 asp.net core 框架時的實現，和 asp.net core 的實現並不完全一樣，如果需要請參考源碼，上面的實現僅供參考，上面實現的源碼可以在 Github 上獲取 https://github.com/WeihanLi/SamplesInPractice/tree/master/MiniAspNetCore
asp.net core 源碼：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
- https://www.cnblogs.com/weihanli/p/12700006.html
- https://www.cnblogs.com/weihanli/p/12709603.html
- https://github.com/WeihanLi/SamplesInPractice/tree/master/MiniAspNetCore