ASP.NET Core Middleware的实现方法详解

using System.Threading.Tasks;using Alyio.AspNetCore.ApiMessages;using Gridsum.WebDissector.Common;using Microsoft.AspNetCore.Http; namespace Gridsum.WebDissector{ sealed class AuthorizationMiddleware { private readonly RequestDelegate _next; // 下一个中间件执行委托的引用  public AuthorizationMiddleware(RequestDelegate next) { _next = next; }  public Task Invoke(HttpContext context) // 贯穿始终的HttpContext对象 { if (context.Request.Path.Value.StartsWith("/api/")) { return _next(context); } if (context.User.Identity.IsAuthenticated && context.User().DisallowBrowseWebsite) { throw new ForbiddenMessage("You are not allow to browse the website."); } return _next(context); } }}  public static IApplicationBuilder UserAuthorization(this IApplicationBuilder app) { return app.UseMiddleware<AuthorizationMiddleware>(); } // 启用该中间件，也就是注册该中间件 app.UserAuthorization();

//-----------------节选自 Microsoft.AspNetCore.Builder.UseMiddlewareExtensions------------------ /// <summary> /// Adds a middleware type to the application's request pipeline. /// </summary> /// <typeparam name="TMiddleware">The middleware type.</typeparam> /// <param name="app">The <see cref="IApplicationBuilder"/> instance.</param> /// <param name="args">The arguments to pass to the middleware type instance's constructor.</param> /// <returns>The <see cref="IApplicationBuilder"/> instance.</returns> public static IApplicationBuilder UseMiddleware<TMiddleware>(this IApplicationBuilder app, params object[] args) { return app.UseMiddleware(typeof(TMiddleware), args); } /// <summary> /// Adds a middleware type to the application's request pipeline. /// </summary> /// <param name="app">The <see cref="IApplicationBuilder"/> instance.</param> /// <param name="middleware">The middleware type.</param> /// <param name="args">The arguments to pass to the middleware type instance's constructor.</param> /// <returns>The <see cref="IApplicationBuilder"/> instance.</returns> public static IApplicationBuilder UseMiddleware(this IApplicationBuilder app, Type middleware, params object[] args) { if (typeof(IMiddleware).GetTypeInfo().IsAssignableFrom(middleware.GetTypeInfo())) { // IMiddleware doesn't support passing args directly since it's // activated from the container if (args.Length > 0) { throw new NotSupportedException(Resources.FormatException_UseMiddlewareExplicitArgumentsNotSupported(typeof(IMiddleware))); }  return UseMiddlewareInterface(app, middleware); }  var applicationServices = app.ApplicationServices; return app.Use(next => { var methods = middleware.GetMethods(BindingFlags.Instance | BindingFlags.Public); // 执行委托名称被限制为Invoke/InvokeAsync var invokeMethods = methods.Where(m => string.Equals(m.Name, InvokeMethodName, StringComparison.Ordinal) || string.Equals(m.Name, InvokeAsyncMethodName, StringComparison.Ordinal) ).ToArray();  if (invokeMethods.Length > 1) { throw new InvalidOperationException(Resources.FormatException_UseMiddleMutlipleInvokes(InvokeMethodName, InvokeAsyncMethodName)); }  if (invokeMethods.Length == 0) { throw new InvalidOperationException(Resources.FormatException_UseMiddlewareNoInvokeMethod(InvokeMethodName, InvokeAsyncMethodName, middleware)); }  var methodInfo = invokeMethods[0]; if (!typeof(Task).IsAssignableFrom(methodInfo.ReturnType)) { throw new InvalidOperationException(Resources.FormatException_UseMiddlewareNonTaskReturnType(InvokeMethodName, InvokeAsyncMethodName, nameof(Task))); }  var parameters = methodInfo.GetParameters(); if (parameters.Length == 0 || parameters[0].ParameterType != typeof(HttpContext)) { throw new InvalidOperationException(Resources.FormatException_UseMiddlewareNoParameters(InvokeMethodName, InvokeAsyncMethodName, nameof(HttpContext))); }  var ctorArgs = new object[args.Length + 1]; ctorArgs[0] = next; Array.Copy(args, 0, ctorArgs, 1, args.Length); // 通过反射形成中间件实例的时候，构造函数第一个参数被指定为 下一个中间件的执行委托 var instance = ActivatorUtilities.CreateInstance(app.ApplicationServices, middleware, ctorArgs); if (parameters.Length == 1) { return (RequestDelegate)methodInfo.CreateDelegate(typeof(RequestDelegate), instance); } // 当前执行委托除了可指定HttpContext参数以外， 还可以注入更多的依赖参数  var factory = Compile<object>(methodInfo, parameters);  return context =>   { var serviceProvider = context.RequestServices ?? applicationServices; if (serviceProvider == null) { throw new InvalidOperationException(Resources.FormatException_UseMiddlewareIServiceProviderNotAvailable(nameof(IServiceProvider))); }  return factory(instance, context, serviceProvider); }; }); } //-------------------节选自 Microsoft.AspNetCore.Builder.Internal.ApplicationBuilder-------------------private readonly IList<Func<RequestDelegate, RequestDelegate>> _components = new List<Func<RequestDelegate, RequestDelegate>>(); publicIApplicationBuilder Use(Func<RequestDelegate,RequestDelegate>middleware){ this._components.Add(middleware); return this;}  public RequestDelegate Build() { RequestDelegate app = context => { context.Response.StatusCode = 404; return Task.CompletedTask; };  foreach (var component in _components.Reverse()) { app = component(app); }  return app; }