.Net Core Web Api实践之中间件的使用（一）

// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseMiddleware();           
            app.UseMvc();
        }

public class RequestMiddleware
    {
        private readonly RequestDelegate _next;
        private readonly IConfig config;

        public RequestMiddleware(RequestDelegate next, IConfig config)
        {
            _next = next;
            this.config = config;
        }

        public Task Invoke(HttpContext context)
        {
            context.Request.EnableRewind(); //支持context.Request.Body重复读取，内部调用了EnableBuffering方法，否则在使用部分方法或属性时会报错误System.NotSupportedException: Specified method is not supported，例如context.Request.Body.Position
            // && context.Request.Path.Value == "/api/Main"
            if (context.Request.ContentLength != null)
            {
                Stream stream = context.Request.Body;
                byte[] buffer = new byte[context.Request.ContentLength.Value];
                stream.Read(buffer, 0, buffer.Length);
                string querystring = Encoding.UTF8.GetString(buffer);

                RequestMiddleParam requestEntity = Newtonsoft.Json.JsonConvert.DeserializeObject(querystring);
                if (requestEntity == null)
                {
                    throw new Exception("无法处理的请求");
                }

                
                string param = Newtonsoft.Json.JsonConvert.SerializeObject(requestMiddleMapParam);        //参数
                //todo 参数校验
                byte[] bs = Encoding.UTF8.GetBytes(param);    //参数转化为utf8码

                //context.Request.Body.Seek(0, SeekOrigin.Begin);
                //context.Request.EnableBuffering();

                var ms = new MemoryStream();
                context.Request.Body = ms;
                context.Request.Body.Write(bs, 0, bs.Length);

                context.Request.Body.Position = 0;   //重置context.Request.Body的Stream指针，否则报A non-empty request body is required.错误
            }

            // Call the next delegate/middleware in the pipeline
            return this._next(context);
        }
    }