ASP.NET Core真实管道详解[1]：中间件是个什么东西？

目录
一、一个重要的委托：RequestDelegate
二、描述当前请求的上下文：HttpContext
封装“特性”的容器：FeatureCollection
HttpContext的默认实现：DefaultHttpContext
上下文的创建者：HttpContextFactory
三、管道的注册者和构建者：ApplicationBuilder
ApplicationBuilder的创建者：ApplicationBuilderFactory

 public abstract class HttpContext  {         public abstract HttpRequest     Request { get; }      public abstract HttpResponse    Response { get; }         public abstract AuthenticationManager             Authentication { get; }      public abstract ClaimsPrincipal                   User { get; set; }      public abstract ConnectionInfo                    Connection { get; }       public abstract WebSocketManager                  WebSockets { get; }       public abstract ISession                          Session { get; set; }       public abstract string                            TraceIdentifier { get; set; }      public abstract CancellationToken                 RequestAborted { get; set; }        public abstract IDictionary<object, object>       Items { get; set; }           public abstract IServiceProvider        RequestServices { get; set; }      public abstract IFeatureCollection      Features { get; }  } 

 public abstract class HttpRequest  {      public abstract HttpContext         HttpContext { get; }      public abstract string              Method { get; set; }      public abstract string              Scheme { get; set; }      public abstract bool                IsHttps { get; set; }      public abstract HostString          Host { get; set; }      public abstract PathString          PathBase { get; set; }      public abstract PathString          Path { get; set; }      public abstract QueryString         QueryString { get; set; }      public abstract IQueryCollection    Query { get; set; }      public abstract string              Protocol { get; set; }      public abstract IHeaderDictionary   Headers { get; } >      public abstract IRequestCookieCollection      Cookies { get; set; }      public abstract string                        ContentType { get; set; }      public abstract Stream                        Body { get; set; }      public abstract bool                          HasFormContentType { get; }      public abstract IFormCollection               Form { get; set; }         public abstract Task<IFormCollection> ReadFormAsync(CancellationToken cancellationToken);  } 

 public abstract class HttpResponse  {      public abstract HttpContext           HttpContext { get; }      public abstract int                   StatusCode { get; set; }      public abstract IHeaderDictionary     Headers { get; }      public abstract Stream                Body { get; set; }      public abstract long?                 ContentLength { get; set; }      public abstract IResponseCookies      Cookies { get; }      public abstract bool                  HasStarted { get; }         public abstract void OnStarting(Func<object, Task> callback, object state);      public virtual void OnStarting(Func<Task> callback);      public abstract void OnCompleted(Func<object, Task> callback, object state);      public virtual void RegisterForDispose(IDisposable disposable);      public virtual void OnCompleted(Func<Task> callback);      public virtual void Redirect(string location);      public abstract void Redirect(string location, bool permanent);  } 

 public interface IFeatureCollection : IEnumerable<KeyValuePair<Type, object>>  {      TFeature Get<TFeature>();      void Set<TFeature>(TFeature instance);         bool       IsReadOnly { get; }      object     this[Type key] { get; set; }      int        Revision { get; }  } 

 public class FeatureCollection : IFeatureCollection  {         //其他成员      public FeatureCollection();      public FeatureCollection(IFeatureCollection defaults);  } 

 FeatureCollection defaults = new FeatureCollection();  Debug.Assert(defaults.Revision == 0);     defaults.Set<IFoo>(new Foo());  Debug.Assert(defaults.Revision == 1);     defaults[typeof(IBar)] = new Bar();  Debug.Assert(defaults.Revision == 2);     FeatureCollection features = new FeatureCollection(defaults);  Debug.Assert(features.Revision == 2);  Debug.Assert(features.Get<IFoo>().GetType() == typeof(Foo));     features.Set<IBaz>(new Baz());  Debug.Assert(features.Revision == 3); 

 public class DefaultHttpContext : HttpContext  {      public DefaultHttpContext(IFeatureCollection features);  } 

 public interface IHttpRequestFeature  {      Stream             Body { get; set; }      IHeaderDictionary  Headers { get; set; }      string             Method { get; set; }      string             Path { get; set; }      string             PathBase { get; set; }      string             Protocol { get; set; }      string             QueryString { get; set; }      string             Scheme { get; set; }  }     public interface IHttpResponseFeature  {      Stream             Body { get; set; }      bool               HasStarted { get; }      IHeaderDictionary  Headers { get; set; }      string             ReasonPhrase { get; set; }      int                StatusCode { get; set; }         void OnCompleted(Func<object, Task> callback, object state);      void OnStarting(Func<object, Task> callback, object state);  } 

 public interface IHttpContextFactory  {      HttpContext Create(IFeatureCollection featureCollection);      void Dispose(HttpContext httpContext);  }     public class HttpContextFactory : IHttpContextFactory  {          //省略其他成员      public HttpContext Create(IFeatureCollection featureCollection);      public void Dispose(HttpContext httpContext);  } 

 public interface IApplicationBuilder  {      IServiceProvider             ApplicationServices { get; set; }      IFeatureCollection           ServerFeatures { get; }      IDictionary<string, object>  Properties { get; }         RequestDelegate         Build();      IApplicationBuilder     New();      IApplicationBuilder     Use(Func<RequestDelegate, RequestDelegate> middleware);  } 

 public class ApplicationBuilder : IApplicationBuilder  {      private readonly IList<Func<RequestDelegate, RequestDelegate>> middlewares = new List<Func<RequestDelegate, RequestDelegate>>();         public IDictionary<string, object> Properties { get; }         public IServiceProvider ApplicationServices      {          get { return GetProperty<IServiceProvider>("application.Services"); }          set { SetProperty<IServiceProvider>("application.Services", value); }      }         public IFeatureCollection ServerFeatures      {          get { return GetProperty<IFeatureCollection>("server.Features"); }      }            public ApplicationBuilder(IServiceProvider serviceProvider)      {          this.Properties = new Dictionary<string, object>();          ApplicationServices = serviceProvider;      }         public ApplicationBuilder(IServiceProvider serviceProvider, object server) : this(serviceProvider)      {          SetProperty("server.Features", server);      }         public IApplicationBuilder Use(Func<RequestDelegate, RequestDelegate> middleware)      {          middlewares.Add(middleware);          return this;      }         public IApplicationBuilder New()      {          return new ApplicationBuilder(this);      }         public RequestDelegate Build()      {          RequestDelegate app = context =>          {              context.Response.StatusCode = 404;              return Task.FromResult(0);          };          foreach (var component in middlewares.Reverse())          {              app = component(app);          }          return app;  }         private ApplicationBuilder(ApplicationBuilder builder)      {          this.Properties = builder.Properties;      }                 private T GetProperty<T>(string key)      {          object value;          return Properties.TryGetValue(key, out value) ? (T)value : default(T);      }         private void SetProperty<T>(string key, T value)      {          this.Properties[key] = value;      }  } 

 public interface IApplicationBuilderFactory  {      IApplicationBuilder CreateBuilder(IFeatureCollection serverFeatures);  }     public class ApplicationBuilderFactory : IApplicationBuilderFactory  {      private readonly IServiceProvider _serviceProvider;         public ApplicationBuilderFactory(IServiceProvider serviceProvider)      {          this._serviceProvider = serviceProvider;      }         public IApplicationBuilder CreateBuilder(IFeatureCollection serverFeatures)      {          return new ApplicationBuilder(this._serviceProvider, serverFeatures);      }  }