更新

HttpClientStudy.Core/PipelineClient.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.InteropServices;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace HttpClientStudy.Core
+{
+    /// <summary>
+    /// 管道方式 HttpClient客户端
+    /// </summary>
+    public class PipelineClient
+    {
+        public List<DelegatingHandler> HttpMessageHandlers { get; set; }
+
+        public PipelineClient() 
+        {
+            HttpMessageHandlers = new List<DelegatingHandler>()
+            { 
+                new CustomHeadersHandler(),
+                new LoggingHandler(),
+            };
+
+        }
+
+        public PipelineClient(List<DelegatingHandler> httpMessageHandlers) 
+        { 
+            HttpMessageHandlers = httpMessageHandlers;
+            if (httpMessageHandlers == null || httpMessageHandlers?.Count == 0)
+            {
+                HttpMessageHandlers = new List<DelegatingHandler>();
+            }
+        }
+
+        public void AddDelegatingHandler(DelegatingHandler handler)
+        { 
+            this.HttpMessageHandlers.Add(handler);
+        }
+
+        public HttpClient CreateHttpClient()
+        {
+            //创建处理器链
+
+            //最终处理器：最后一个请求处理程序，默认是SocketsHttpHandler.
+            HttpMessageHandler currentPipeLine = new SocketsHttpHandler()
+            { 
+                //自定义配置
+                PooledConnectionLifetime = TimeSpan.FromSeconds(120),
+            }; 
+            //pipeline = new CustomHeadersHandler() { InnerHandler = pipeline};
+            //pipeline = new LoggingHandler () { InnerHandler = pipeline};
+
+            //倒序组装：完成后执行顺序与注册顺序一致
+            HttpMessageHandlers.Reverse();
+            for (int i = 0; i < HttpMessageHandlers.Count; i++)
+            {
+                HttpMessageHandlers[i].InnerHandler = currentPipeLine;
+                currentPipeLine = HttpMessageHandlers[i];
+            }
+
+            // 利用管道创建HttpClient
+            var httpClient = new HttpClient(currentPipeLine);
+
+            return httpClient;
+        }
+    }
+
+    /// <summary>
+    /// 默认处理器1 - 添加自定义请求头
+    /// </summary>
+    public class CustomHeadersHandler : DelegatingHandler
+    {
+        protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
+        {
+            // 在请求中添加自定义头部
+            request.Headers.Add("X-Custom-Header", "CustomValue");
+
+            // 调用管道中的下一个处理器
+            return await base.SendAsync(request, cancellationToken);
+
+            //响应信息(可不处理)
+        }
+    }
+
+    /// <summary>
+    /// 默认处理器1 - 简单的日志记录
+    /// </summary>
+    public class LoggingHandler : DelegatingHandler
+    {
+        protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
+        {
+            // 记录请求信息
+            Console.WriteLine($"Request: {request.Method} {request.RequestUri}");
+
+            // 调用管道中的下一个处理器，并获取响应
+            var response = await base.SendAsync(request, cancellationToken);
+
+            // 记录响应信息
+            Console.WriteLine($"Response: {response.StatusCode}");
+
+            return response;
+        }
+    }
+
+}

HttpClientStudy.UnitTest/DelegatingHandlerTest.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Net.Http;
+using System.Text;
+using System.Threading.Tasks;
+
+using Microsoft.Extensions.Logging;
+
+namespace HttpClientStudy.UnitTest
+{
+    public class DelegatingHandlerTest
+    {
+        private readonly ITestOutputHelper _logger;
+        public DelegatingHandlerTest(ITestOutputHelper outputHelper) 
+        {
+            _logger = outputHelper;
+        }
+
+        [Fact]
+        public async Task Test()
+        { 
+            //构建管道
+            var handler = new HandlerA() 
+            { 
+                //相当于下一个中间件(管道)
+                InnerHandler = new HandlerB() 
+            };
+
+            HttpClient httpClient = new HttpClient(handler);
+
+            var sd = await httpClient.GetAsync("http://127.0.0.1");
+            var contentText = await sd.Content.ReadAsStringAsync();
+
+            _logger.WriteLine(contentText);
+        }
+    }
+
+    public class HandlerB : DelegatingHandler
+    {
+        protected override async Task<HttpResponseMessage> SendAsync( HttpRequestMessage request, CancellationToken cancellationToken)
+        {
+            InnerHandler = new SocketsHttpHandler() { };
+
+            //请求前业务
+
+            var response = await base.SendAsync(request, cancellationToken);
+
+            //响应后业务
+
+            return response;
+        }
+    }
+
+    public class HandlerA : DelegatingHandler
+    {
+        protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
+        {
+            //请求前业务
+
+            var response = await base.SendAsync(request, cancellationToken);
+
+            //响应后业务
+
+            return response;
+        }
+    }
+}

HttpClientStudy.UnitTest/HttpClientQuestTest.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+using System.Net.Http.Json;
+using System.Net;
+using Newtonsoft.Json;
+using Microsoft.AspNetCore.Mvc;
+using System.Text.Json;
+using System.Security.Authentication.ExtendedProtection;
+using Newtonsoft.Json.Linq;
+using System.Text.Json.Serialization.Metadata;
+
+namespace HttpClientStudy.UnitTest
+{
+    /// <summary>
+    /// HttpClient 常见问题测试
+    /// </summary>
+    public class HttpClientQuestTest
+    {
+        private readonly ITestOutputHelper _logger;
+
+        public HttpClientQuestTest(ITestOutputHelper outputHelper) 
+        {
+            _logger = outputHelper;
+        }
+
+        /// <summary>
+        /// 多HttpClient实例问题
+        /// 1、HttpClient虽然继承了 IDisposable 接口，但它是可以被共享的，且线程安全。Using使用并不能立即释放
+        /// 2、网络特性：虽然HttpClient客户端断开，但Web服务并不知道，连接依然存在，状态为 “ TIME_WAIT”(继续等待看是否还有延迟的包会传输过来。)
+        ///    Windows默认为 240s
+        /// 引发常见问题：
+        /// 1、HttpClient 多实例并存，有很大资源消耗；
+        /// 2、在高并发的情况下，连接来不及释放， socket 被耗尽: 程序异常
+        /// 3、连带着会出现“各种套接字问题” 
+        /// 
+        /// 查看问题：
+        /// 程序并发或多次请求后，通过 netstate 查看下 TCP 连接情况：有很多 TIME_WAIT 状态连接；很可能程序异常；
+        /// 
+        /// 解决：
+        /// 1、复用HttpClient
+        /// 2、HttpClientFactory
+        /// 3、解决DNS问题可以给HttpClient传参：SocketsHttpHandler
+        /// </summary>
+        /// <returns></returns>
+        [Fact]
+        public async Task Multi_ClientObject_Test()
+        {
+            for (int i = 0; i < 1000; i++)
+            {
+                HttpClient httpClient = new HttpClient();
+
+                var responseMessage = await httpClient.GetAsync("https://www.baidu.com");
+
+                responseMessage.EnsureSuccessStatusCode();
+            }
+        }
+
+        [Fact]
+        public async Task Multi_ClientObject2_Test()
+        {
+            HttpClient httpClient = new HttpClient()
+            {
+                BaseAddress = new Uri("https://www.baidu.com")
+            };
+            for (int i = 0; i < 10000; i++)
+            {
+                var responseMessage = await httpClient.GetAsync("");
+
+                responseMessage.EnsureSuccessStatusCode();
+            }
+        }
+    }
+}   

HttpClientStudy.UnitTest/PipelineClientTest.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace HttpClientStudy.UnitTest
+{
+    public class PipelineClientTest
+    {
+        public PipelineClientTest() { }
+
+        [Fact]
+        public async Task Test()
+        { 
+            HttpClient client = new PipelineClient().CreateHttpClient();
+
+            var r = await client.GetAsync("https://www.baidu.com");
+            r.EnsureSuccessStatusCode();
+
+
+        }
+    }
+}