探究ASP.NET Core Middleware实现方法

 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(); } // 启用该中间件，也就是注册该中间件 app.UserAuthorization();

 public delegate Task RequestDelegate(HttpContext context);

 //-----------------节选自 Microsoft.AspNetCore.Builder.UseMiddlewareExtensions------------------ /// <summary> /// Adds a middleware type to the application's request pipeline. /// </summary> /// The middleware type. /// The  instance. /// The arguments to pass to the middleware type instance's constructor. /// The  instance. public static IApplicationBuilder UseMiddleware(this IApplicationBuilder app, params object[] args) { return app.UseMiddleware(typeof(TMiddleware), args); } /// <summary> /// Adds a middleware type to the application's request pipeline. /// </summary> /// The  instance. /// The middleware type. /// The arguments to pass to the middleware type instance's constructor. /// The  instance. 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(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> _components = new List<Func>(); publicIApplicationBuilder Use(Func middleware) { this._components.Add(middleware); return this; } public RequestDelegate Build() { RequestDelegate app = contex<i style="color:transparent">来源gaodai$ma#com搞$$代**码网</i>t => { context.Response.StatusCode = 404; return Task.CompletedTask; }; foreach (var component in _components.Reverse()) { app = component(app); } return app; }