.NETCore 之 中间件 02

上一篇我们知道可以使用 app.use 注册中间件，但是 这样都写在 Startup 文件可能不是我们想要的。.NET Core 提供了 使用 UseMiddlewareExtensions 扩展中间件。我们看一下需要什么。

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Http.Abstractions;
using Microsoft.Extensions.Internal;

namespace Microsoft.AspNetCore.Builder
{
    /// 

    /// Extension methods for adding typed middleware.
    /// 
    public static class UseMiddlewareExtensions
    {
        internal const string InvokeMethodName = "Invoke";
        internal const string InvokeAsyncMethodName = "InvokeAsync";

        private static readonly MethodInfo GetServiceInfo = typeof(UseMiddlewareExtensions).GetMethod(nameof(GetService), BindingFlags.NonPublic | BindingFlags.Static)!;

        /// 

        /// Adds a middleware type to the application's request pipeline.
        /// 
        /// 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);
        }

        /// 

        /// Adds a middleware type to the application's request pipeline.
        /// 
        /// 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);
                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);
                var instance = ActivatorUtilities.CreateInstance(app.ApplicationServices, middleware, ctorArgs);
                if (parameters.Length == 1)
                {
                    return (RequestDelegate)methodInfo.CreateDelegate(typeof(RequestDelegate), instance);
                }

                var factory = Compile