public interface IServer : IDisposable { IFeatureCollection Features { get; } // 堆代码 duidaima.com Task StartAsync<TContext>( IHttpApplication<TContext> application, CancellationToken cancellationToken) where TContext : notnull; Task StopAsync(CancellationToken cancellationToken); }虽然不同服务器类型的定义方式千差万别,但是背后的模式基本上与下面这个以伪代码定义的服务器类型一致。如下这个Server利用IListener对象来监听和接收请求,该对象是利用构造函数中注入的IListenerFactory工厂根据指定的监听地址创建出来的。StartAsync<TContext>方法从Features特性集合中提取出IServerAddressesFeature特性,并针对它提供的每个监听地址创建一个IListener对象。该方法为每个IListener对象开启一个“接收和处理请求”的循环,循环中的每次迭代都会调用IListener对象的AcceptAsync方法来接收请求,我们利用RequestContext对象来表示请求上下文。
public class Server : IServer { private readonly IListenerFactory _listenerFactory; private readonly List<IListener> _listeners = new(); public IFeatureCollection Features { get; } = new FeatureCollection(); public Server(IListenerFactory listenerFactory) => _listenerFactory = listenerFactory; public async Task StartAsync<TContext>( IHttpApplication<TContext> application, CancellationToken cancellationToken) where TContext : notnull { var addressFeature = Features .Get<IServerAddressesFeature>()!; foreach (var address in addressFeature.Addresses) { var listener = await _listenerFactory .BindAsync(address); _listeners.Add(listener); _ = StartAcceptLoopAsync(listener); } async Task StartAcceptLoopAsync(IListener listener) { while (true) { var requestContext = await listener.AcceptAsync(); _ = ProcessRequestAsync(requestContext); } } async Task ProcessRequestAsync(RequestContext requestContext) { var feature = new RequestContextFeature(requestContext); var contextFeatures = new FeatureCollection(); contextFeatures.Set<IHttpRequestFeature>(feature); contextFeatures.Set<IHttpResponseFeature>(feature); contextFeatures.Set<IHttpResponseBodyFeature>(feature); var context = application.CreateContext(contextFeatures); Exception? exception = null; try { await application.ProcessRequestAsync(context); } catch (Exception ex) { exception = ex; } finally { application.DisposeContext(context, exception); } } } public Task StopAsync(CancellationToken cancellationToken) => Task.WhenAll(_listeners.Select( listener => listener.StopAsync())); public void Dispose() => _listeners.ForEach( listener => listener.Dispose()); } public interface IListenerFactory { Task<IListener> BindAsync(string listenAddress); } public interface IListener : IDisposable { Task<RequestContext> AcceptAsync(); Task StopAsync(); } public class RequestContext { ... } public class RequestContextFeature : IHttpRequestFeature, IHttpResponseFeature, IHttpResponseBodyFeature { public RequestContextFeature(RequestContext requestContext); ... }
StartAsync<TContext>方法接下来利用此RequestContext上下文将RequestContextFeature特性创建出来。RequestContextFeature特性类型同时实现了IHttpRequestFeature, IHttpResponseFeature和 IHttpResponseBodyFeature这三个核心接口,我们特性针对这三个接口将特性对象添加到创建的FeatureCollection集合中。
特性集合随后作为参数调用IHttpApplication<TContext>的CreateContext方法将TContext上下文创建出来,后者将进一步作为参数调用另一个ProcessRequestAsync方法将请求分发给中间件管道进行处理。待处理结束,IHttpApplication<TContext>对象的DisposeContext方法被调用,创建的TContext上下文承载的资源得以释放。
public class HttpRequestFeature : IHttpRequestFeature { public string Protocol { get; set; } public string Scheme { get; set; } public string Method { get; set; } public string PathBase { get; set; } public string Path { get; set; } public string QueryString { get; set; } public string RawTarget { get; set; } public IHeaderDictionary Headers { get; set; } public Stream Body { get; set; } } public class HttpResponseFeature : IHttpResponseFeature { public int StatusCode { get; set; } public string? ReasonPhrase { get; set; } public IHeaderDictionary Headers { get; set; } public Stream Body { get; set; } public virtual bool HasStarted => false; public HttpResponseFeature() { StatusCode = 200; Headers = new HeaderDictionary(); Body = Stream.Null; } public virtual void OnStarting( Func<object, Task> callback, object state) { } public virtual void OnCompleted( Func<object, Task> callback, object state) { } }如果我们使用HttpRequestFeature来描述请求,意味着HttpListener在接受到请求之后需要将请求信息从HttpListenerContext上下文转移到该特性上。如果使用HttpResponseFeature来描述响应,待中间件管道在完成针对请求的处理后,我们还需要将该特性承载的响应数据应用到HttpListenerContext上下文上。
public class StreamBodyFeature : IHttpResponseBodyFeature { public Stream Stream { get; } public PipeWriter Writer { get; } public StreamBodyFeature(Stream stream) { Stream = stream; Writer = PipeWriter.Create(Stream); } public Task CompleteAsync() => Task.CompletedTask; public void DisableBuffering() { } public Task SendFileAsync( string path, long offset, long? count, CancellationToken cancellationToken = default) => throw new NotImplementedException(); public Task StartAsync( CancellationToken cancellationToken = default) => Task.CompletedTask; }四、HttpListenerServer
public class HttpListenerServer : IServer { // 堆代码 duidaima.com private readonly HttpListener _listener = new(); public IFeatureCollection Features { get; } = new FeatureCollection(); public HttpListenerServer() => Features.Set<IServerAddressesFeature>( new ServerAddressesFeature()); public Task StartAsync<TContext>( IHttpApplication<TContext> application, CancellationToken cancellationToken) where TContext : notnull { var pathbases = new HashSet<string>( StringComparer.OrdinalIgnoreCase); var addressesFeature = Features .Get<IServerAddressesFeature>()!; foreach (string address in addressesFeature.Addresses) { _listener.Prefixes.Add(address.TrimEnd('/') + "/"); pathbases.Add(new Uri(address) .AbsolutePath.TrimEnd('/')); } _listener.Start(); while (true) { var listenerContext = _listener.GetContext(); _ = ProcessRequestAsync(listenerContext); } async Task ProcessRequestAsync( HttpListenerContext listenerContext) { FeatureCollection features = new(); var requestFeature = CreateRequestFeature( pathbases, listenerContext); var responseFeature = new HttpResponseFeature(); var body = new MemoryStream(); var bodyFeature = new StreamBodyFeature(body); features.Set<IHttpRequestFeature>(requestFeature); features.Set<IHttpResponseFeature>(responseFeature); features.Set<IHttpResponseBodyFeature>(bodyFeature); var context = application.CreateContext(features); Exception? exception = null; try { await application.ProcessRequestAsync(context); var response = listenerContext.Response; response.StatusCode = responseFeature.StatusCode; if (responseFeature.ReasonPhrase is not null) { response.StatusDescription = responseFeature.ReasonPhrase; } foreach (var kv in responseFeature.Headers) { response.AddHeader(kv.Key, kv.Value); } body.Position = 0; await body.CopyToAsync( listenerContext.Response.OutputStream); } catch (Exception ex) { exception = ex; } finally { body.Dispose(); application.DisposeContext(context, exception); listenerContext.Response.Close(); } } } public void Dispose() => _listener.Stop(); private static HttpRequestFeature CreateRequestFeature( HashSet<string> pathbases, HttpListenerContext listenerContext) { var request = listenerContext.Request; var url = request.Url!; var absolutePath = url.AbsolutePath; var protocolVersion = request.ProtocolVersion; var requestHeaders = new HeaderDictionary(); foreach (string key in request.Headers) { requestHeaders.Add( key, request.Headers.GetValues(key)); } var requestFeature = new HttpRequestFeature { Body = request.InputStream, Headers = requestHeaders, Method = request.HttpMethod, QueryString = url.Query, Scheme = url.Scheme, Protocol = $"{url.Scheme.ToUpper()}/{protocolVersion.Major}.{protocolVersion.Minor}" }; var pathBase = pathbases.First( it => absolutePath.StartsWith( it, StringComparison.OrdinalIgnoreCase)); requestFeature.Path = absolutePath[pathBase.Length..]; requestFeature.PathBase = pathBase; return requestFeature; } public Task StopAsync( CancellationToken cancellationToken) { _listener.Stop(); return Task.CompletedTask; } }
在调用Start方法将HttpListener启动后,StartAsync<TContext>方法开始“请求接收处理”循环。接收到的请求上下文被封装成HttpListenerContext上下文,其承载的请求信息利用CreateRequestFeature方法转移到创建的HttpRequestFeature特性上。
StartAsync<TContext>方法创建的“空”HttpResponseFeature对象来描述响应,另一个描述响应主体的StreamBodyFeature特性则根据创建的MemoryStream对象构建而成,意味着中间件管道写入的响应主体的内容将暂存到这个内存流中。我们将这三个特性注册到创建的FeatureCollection集合上,并将后者作为参数调用了IHttpApplication<TContext>对象的CreateContext方法将TContext上下文创建出来。此上下文进一步作为参数调用了IHttpApplication<TContext>对象的ProcessRequestAsync方法,中间件管道得以接管请求。
using App; using Microsoft.AspNetCore.Hosting.Server; using Microsoft.Extensions.DependencyInjection.Extensions; var builder = WebApplication.CreateBuilder(args); builder.Services.Replace( ServiceDescriptor.Singleton<IServer, HttpListenerServer>()); var app = builder.Build(); app.Run(context => context.Response.WriteAsync("Hello World!")); app.Run("http://localhost:5000/foobar/");
我们采用上面的演示程序来检测HttpListenerServer能否正常工作。我们为HttpListenerServer类型创建了一个ServiceDescriptor对象将现有的服务器的服务注册替换掉。在调用WebApplication对象的Run方法时显式指定了具有PathBase(“/foobar”)的监听地址“http://localhost:5000/foobar/”,如图1所示的浏览器以此地址访问应用,会得到我们希望的结果。
图1