学习ASP.NET Core, 怎能不了解请求处理管道[3]: 自定义一个服务器感受一下管道是如何监听、接收和响应请求的

我们在《服务器在管道中的“龙头”地位》中对ASP.NET Core默认提供的具有跨平台能力的KestrelServer进行了介绍,为了让读者朋友们对管道中的服务器具有更加深刻的认识,接下来我们采用实例演示的形式创建一个自定义的服务器。这个自定义的服务器直接利用HttpListener来完成针对请求的监听、接收和响应,我们将其命名为HttpListenerServer。在正式介绍HttpListenerServer的设计和实现之前,我们先来显示一下如何将它应用到 一个具体的Web应用中。我们依然采用最简单的Hello World应用来演示针对HttpListenerServer的应用,所以我们在Startup类的Configure方法中编写如下的程序直接响应一个“Hello World”字符串。[本文已经同步到《ASP.NET Core框架揭秘》之中]

   1: public class Startup
   2: {
   3:     public void Configure(IApplicationBuilder app)
   4:     {
   5:         app.Run(async context => await context.Response.WriteAsync("Hello World!"));
   6:     }
   7: }

在作为程序入口的Main方法中,我们直接创建一个WebHostBuilder对象并调用扩展方法UseHttpListener完成针对自定义HttpListenerServer的注册。我们接下来调用UseStartup方法注册上面定义的这个启动类型,然后调用Build方法创建一个WebHost对象,最后调用Run方法运行这个作为宿主的WebHost。

   1: public class Program
   2: {
   3:     public static void Main()
   4:     {
   5:         new WebHostBuilder()
   6:             .UseHttpListener()
   7:             .UseStartup<Startup>()
   8:             .Build()
   9:             .Run();
  10:     }
  11: }
  12:  
  13: public static class WebHostBuilderExtensions
  14: {
  15:     public static IWebHostBuilder UseHttpListener(this IWebHostBuilder builder)
  16:     {
  17:         builder.ConfigureServices(services => services.AddSingleton<IServer, HttpListenerServer>());
  18:         return builder;
  19:     }
  20: }

我们自定义的扩展方法UseHttpListener的逻辑很简单,它只是调用WebHostBuilder的ConfigureServices方法将我们自定义的HttpListenerServer类型以单例模式注册到指定的ServiceCollection上而已。我们直接运行这个程序并利用浏览器访问默认的监听地址(http://localhost:5000),服务端响应的“Hello World”字符串会按照如下图所示的形式显示在浏览器上。

image

接下来我们来介绍一下HttpListenerServer的大体涉及。除了HttpListenerServer这个实现了IServer的自定义Server类型之外,我们只定义了一个名为HttpListenerServerFeature的特性类型,图7所示的UML基本上体现了HttpListenerServer的总体设计。

6

如果我们利用HttpListener来监听请求,它会为接收到的每次请求创建一个属于自己的上下文,具体来说这是一个类型为HttpListenerContext对象。我们可以利用这个HttpListenerContext对象获取所有与请求相关的信息,针对请求的任何响应也都是利用它完成的。上面这个HttpListenerServerFeature实际上就是对这个作为原始上下文的HttpListenerContext对象的封装,或者说它是管道使用的DefaultHttpContext与这个原始上下文之间沟通的中介。

如下所示的代码片段展示了HttpListenerServerFeature类型的完整定义。简单起见,我们并没有实现上面提到过的所有特性接口,而只是选择性地实现了IHttpRequestFeature和IHttpResponseFeature这两个最为核心的特性接口。它的构造函数除了具有一个类型为HttpListenerContext的参数之外,还具有一个字符串的参数pathBase用来指定请求URL的基地址(对应IHttpRequestFeature的PathBase属性),我们利用它来计算请求URL的相对地址(对应IHttpRequestFeature的Path属性)。IHttpRequestFeature和IHttpResponseFeature中定义的属性都可以直接利用HttpListenerContext对应的成员来实现,这方面并没有什么特别之处。

   1: public class HttpListenerServerFeature : IHttpRequestFeature, IHttpResponseFeature
   2: {
   3:     private readonly HttpListenerContext     httpListenerContext;
   4:     private string                           queryString;
   5:     private IHeaderDictionary                requestHeaders;
   6:     private IHeaderDictionary                responseHeaders;
   7:     private string                           protocol;
   8:     private readonly string                  pathBase;
   9:  
  10:     public HttpListenerServerFeature(HttpListenerContext httpListenerContext, string pathBase)
  11:     {
  12:         this.httpListenerContext     = httpListenerContext;
  13:         this.pathBase                 = pathBase;
  14:     }
  15:  
  16:     #region IHttpRequestFeature
  17:  
  18:     Stream IHttpRequestFeature.Body
  19:     {
  20:         get { return httpListenerContext.Request.InputStream; }
  21:         set { throw new NotImplementedException(); }
  22:     }
  23:  
  24:     IHeaderDictionary IHttpRequestFeature.Headers
  25:     {
  26:         get { return requestHeaders ?? (requestHeaders = GetHttpHeaders(httpListenerContext.Request.Headers)); }
  27:         set { throw new NotImplementedException(); }
  28:     }
  29:  
  30:     string IHttpRequestFeature.Method
  31:     {
  32:         get { return httpListenerContext.Request.HttpMethod; }
  33:         set { throw new NotImplementedException(); }
  34:     }
  35:  
  36:     string IHttpRequestFeature.Path
  37:     {
  38:         get { return httpListenerContext.Request.RawUrl.Substring(pathBase.Length);}
  39:         set { throw new NotImplementedException(); }
  40:     }
  41:  
  42:     string IHttpRequestFeature.PathBase
  43:     {
  44:         get { return pathBase; }
  45:         set { throw new NotImplementedException(); }
  46:     }
  47:  
  48:     string IHttpRequestFeature.Protocol
  49:     {
  50:         get{ return protocol ?? (protocol = this.GetProtocol());}
  51:         set { throw new NotImplementedException(); }
  52:     }
  53:  
  54:     string IHttpRequestFeature.QueryString
  55:     {
  56:         Get { return queryString ?? (queryString = this.ResolveQueryString());}
  57:         set { throw new NotImplementedException(); }
  58:     }
  59:  
  60:     string IHttpRequestFeature.Scheme
  61:     {
  62:         get { return httpListenerContext.Request.IsWebSocketRequest ? "https" : "http"; }
  63:         set { throw new NotImplementedException(); }
  64:     }
  65:     #endregion
  66:  
  67:     #region IHttpResponseFeature
  68:     Stream IHttpResponseFeature.Body
  69:     {
  70:         get { return httpListenerContext.Response.OutputStream; }
  71:         set { throw new NotImplementedException(); }
  72:     }
  73:  
  74:     string IHttpResponseFeature.ReasonPhrase
  75:     {
  76:         get { return httpListenerContext.Response.StatusDescription; }
  77:         set { httpListenerContext.Response.StatusDescription = value; }
  78:     }
  79:  
  80:     bool IHttpResponseFeature.HasStarted
  81:     {
  82:         get { return httpListenerContext.Response.SendChunked; }
  83:     }
  84:  
  85:     IHeaderDictionary IHttpResponseFeature.Headers
  86:     {
  87:         get { return responseHeaders ?? (responseHeaders = GetHttpHeaders(httpListenerContext.Response.Headers)); }
  88:         set { throw new NotImplementedException(); }
  89:     }
  90:     int IHttpResponseFeature.StatusCode
  91:     {
  92:         get { return httpListenerContext.Response.StatusCode; }
  93:         set { httpListenerContext.Response.StatusCode = value; }
  94:     }
  95:  
  96:     void IHttpResponseFeature.OnCompleted(Func<object, Task> callback, object state)
  97:     {
  98:         throw new NotImplementedException();
  99:     }
 100:  
 101:     void IHttpResponseFeature.OnStarting(Func<object, Task> callback, object state)
 102:     {
 103:         throw new NotImplementedException();
 104:     }
 105:     #endregion
 106:  
 107:     private string ResolveQueryString()
 108:     {
 109:         string queryString = "";
 110:         var collection = httpListenerContext.Request.QueryString;
 111:         for (int i = 0; i < collection.Count; i++)
 112:         {
 113:             queryString += $"{collection.GetKey(i)}={collection.Get(i)}&";
 114:         }
 115:         return queryString.TrimEnd('&');
 116:     }
 117:  
 118:     private IHeaderDictionary GetHttpHeaders(NameValueCollection headers)
 119:     {
 120:         HeaderDictionary dictionary = new HeaderDictionary();
 121:         foreach (string name in headers.Keys)
 122:         {
 123:             dictionary[name] = new StringValues(headers.GetValues(name));
 124:         }
 125:         return dictionary;
 126:     }
 127:  
 128:     private string GetProtocol()
 129:     {
 130:         HttpListenerRequest request = httpListenerContext.Request;
 131:         Version version = request.ProtocolVersion;
 132:         return string.Format("{0}/{1}.{2}", request.IsWebSocketRequest ? "HTTPS" : "HTTP", version.Major, version.Minor);
 133:     }
 134: }

接下来我们来看看HttpListenerServer的定义。如下面的代码片段所示,用来监听请求的HttpListener在构造函数中被创建,与此同时,我们会创建一个用于获取监听地址的ServerAddressesFeature对象并将其添加到属于自己的特性列表中。当HttpListenerServer随着Start方法的调用而被启动后,它将这个ServerAddressesFeature对象提取出来,然后利用它得到所有的地址并添加到HttpListener的Prefixes属性表示的监听地址列表中。接下来,HttpListener的Start方法被调用,并在一个无限循环中开启请求的监听与接收。

   1: public class HttpListenerServer : IServer
   2: {
   3:     private readonly HttpListener listener;
   4:  
   5:     public IFeatureCollection Features { get; } = new FeatureCollection();
   6:     
   7:     public HttpListenerServer()
   8:     {
   9:         listener = new HttpListener();
  10:         this.Features.Set<IServerAddressesFeature>(new ServerAddressesFeature());
  11:     }
  12:  
  13:     public void Dispose()
  14:     {
  15:         listener.Stop();
  16:      }
  17:  
  18:     public void Start<TContext>(IHttpApplication<TContext> application)
  19:     {
  20:         foreach (string address in this.Features.Get<IServerAddressesFeature>().Addresses)
  21:         {
  22:             listener.Prefixes.Add(address.TrimEnd('/') + "/");
  23:         }
  24:  
  25:         listener.Start();
  26:         while (true)
  27:         {
  28:             HttpListenerContext httpListenerContext = listener.GetContext();
  29:  
  30:             string listenUrl = this.Features.Get<IServerAddressesFeature>().Addresses
  31:              .First(address => httpListenerContext.Request.Url.IsBaseOf(new Uri(address)));
  32:             string pathBase = new Uri(listenUrl).LocalPath.TrimEnd('/') ;
  33:             HttpListenerServerFeature feature = new HttpListenerServerFeature(httpListenerContext, pathBase);
  34:  
  35:             FeatureCollection features = new FeatureCollection();
  36:             features.Set<IHttpRequestFeature>(feature);
  37:             features.Set<IHttpResponseFeature>(feature);
  38:             TContext context = application.CreateContext(features);
  39:  
  40:             application.ProcessRequestAsync(context).ContinueWith(task =>
  41:             {
  42:                 httpListenerContext.Response.Close();
  43:                 application.DisposeContext(context, task.Exception);
  44:             });
  45:         }
  46:     }
  47: }

HttpListener的GetContext方法以同步的方式监听请求,并利用接收到的请求创建返回的HttpListenerContext对象。我们利用它解析出当前请求的基地址,并进一步创建出描述当前原始上下文的HttpListenerServerFeature。接下来我们将这个对象分别采用特性接口IHttpRequestFeature和IHttpResponseFeature添加到创建的FeatureCollection对象中。然后我们将这个FeatureCollection作为参数调用HttpApplication的CreateContext创建出上下文对象,并将其作为参数调用HttpApplication的ProcessContext方法让注册的中间件来逐个地对请求进行处理。

posted @ 2016-11-16 08:02 Artech 阅读(...) 评论(...) 编辑 收藏