HttpClientStudy/Docs/1.2.使用准则.ipynb

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    "# HttpClient 使用准则\n",
    "System.Net.Http.HttpClient 类用于发送 HTTP 请求以及从 URI 所标识的资源接收 HTTP 响应。 HttpClient 实例是应用于该实例执行的所有请求的设置集合，每个实例使用自身的连接池，该池将其请求与其他请求隔离开来。 \n",
    "\n",
    "从 .NET Core 2.1 开始，SocketsHttpHandler 类提供实现，使行为在所有平台上保持一致。"
   ]
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   "source": [
    "## 准备工作：先执行下面单元，以启动WebApi及设置全局对象、方法及其它"
   ]
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    "//Nuget包\n",
    "\n",
    "//全局引用\n",
    "#r \"./Publish/HttpClientStudy.Core/HttpClientStudy.Core.dll\"\n",
    "\n",
    "//全局对象\n",
    "global using System.IO;\n",
    "global using HttpClientStudy.Core;\n",
    "global using HttpClientStudy.Core.Utilities;\n",
    "\n",
    "string  dllFile = Path.GetFullPath(\"Publish\\\\HttpClientStudy.WebApp\\\\HttpClientStudy.WebApp.dll\",Directory.GetCurrentDirectory());\n",
    "Console.WriteLine($\"指定的文件为：{dllFile}\");\n",
    "//启动WebAPI项目\n",
    "StartupUtility.StartWebApiDll(dllFile);"
   ]
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   "source": [
    "## 1、DNS 行为\n",
    "HttpClient 仅在创建连接时解析 DNS。它不跟踪 DNS 服务器指定的任何生存时间 (TTL)。 \n",
    "\n",
    "如果 DNS 条目定期更改（这可能在某些方案中发生），客户端将不会遵循这些更新。 要解决此问题，可以通过设置 PooledConnectionLifetime 属性来限制连接的生存期，以便在替换连接时重复执行 DNS 查找。"
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   "source": [
    "using System.Net.Http;\n",
    "\n",
    "var handler = new SocketsHttpHandler\n",
    "{\n",
    "    // Recreate every 15 minutes\n",
    "    PooledConnectionLifetime = TimeSpan.FromMinutes(15) \n",
    "};\n",
    "var sharedClient = new HttpClient(handler);"
   ]
  },
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   "metadata": {},
   "source": [
    "上述 HttpClient 配置为重复使用连接 15 分钟。 PooledConnectionLifetime 指定的时间范围过后，系统会关闭连接，然后创建一个新连接。"
   ]
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   "metadata": {},
   "source": [
    "## 2、共用连接(底层自动管理连接池)"
   ]
  },
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   "metadata": {},
   "source": [
    "HttpClient 的连接池链接到其基础 SocketsHttpHandler。 \n",
    "释放 HttpClient 实例时，它会释放池中的所有现有连接。 如果稍后向同一服务器发送请求，则必须重新创建一个新连接。 \n",
    "因此，创建不必要的连接会导致性能损失。 \n",
    "此外，TCP 端口不会在连接关闭后立即释放。 （有关这一点的详细信息，请参阅 RFC 9293 中的 TCP TIME-WAIT。）如果请求速率较高，则可用端口的操作系统限制可能会耗尽。 \n",
    "\n",
    "为了避免端口耗尽问题，建议将 HttpClient 实例重用于尽可能多的 HTTP 请求。"
   ]
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   "source": [
    "### 什么是连接池\n",
    "SocketsHttpHandler为每个唯一端点建立连接池，您的应用程序通过HttpClient向该唯一端点发出出站HTTP请求。在对端点的第一个请求上，当不存在现有连接时，将建立一个新的HTTP连接并将其用于该请求。该请求完成后，连接将保持打开状态并返回到池中。\n",
    "\n",
    "对同一端点的后续请求将尝试从池中找到可用的连接。如果没有可用的连接，并且尚未达到该端点的连接限制，则将建立新的连接。达到连接限制后，请求将保留在队列中，直到连接可以自由发送它们为止。"
   ]
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   "source": [
    "### 如何控制连接池"
   ]
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   "source": [
    "有三个主要设置可用于控制连接池的行为。\n",
    "\n",
    "+ PooledConnectionLifetime，定义连接在池中保持活动状态的时间。此生存期到期后，将不再为将来的请求而合并或发出连接。\n",
    "\n",
    "+ PooledConnectionIdleTimeout，定义闲置连接在未使用时在池中保留的时间。一旦此生存期到期，空闲连接将被清除并从池中删除。\n",
    "\n",
    "+ MaxConnectionsPerServer，定义每个端点将建立的最大出站连接数。每个端点的连接分别池化。例如，如果最大连接数为2，则您的应用程序将请求发送到两个www.github.com和www.google.com，总共可能最多有4个打开的连接。\n",
    "\n",
    "默认情况下，从.NET Core 2.1开始，更高级别的HttpClientHandler将SocketsHttpHandler用作内部处理程序。没有任何自定义配置，将应用连接池的默认设置。\n",
    "\n",
    "该**PooledConnectionLifetime默认是无限的，因此，虽然经常使用的请求，连接可能会无限期地保持打开状态。该PooledConnectionIdleTimeout默认为2分钟，如果在连接池中长时间未使用将被清理。MaxConnectionsPerServer**默认为int.MaxValue，因此连接基本上不受限制。\n",
    "\n",
    "如果希望控制这些值中的任何一个，则可以手动创建SocketsHttpHandler实例，并根据需要进行配置。"
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   "source": [
    "using System.Net.Http;\n",
    "var socketsHandler = new SocketsHttpHandler\n",
    "{\n",
    "\tPooledConnectionLifetime = TimeSpan.FromMinutes(10),\n",
    "\tPooledConnectionIdleTimeout = TimeSpan.FromMinutes(5),\n",
    "\tMaxConnectionsPerServer = 10\n",
    "};\n",
    "\t\n",
    "var client = new HttpClient(socketsHandler);"
   ]
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   "source": [
    "在前面的示例中，对SocketsHttpHandler进行了配置，以使连接将最多在10分钟后停止重新发出并关闭。如果闲置5分钟，则连接将在池的清理过程中被更早地删除。我们还将最大连接数（每个端点）限制为十个。如果我们需要并行发出更多出站请求，则某些请求可能会排队等待，直到10个池中的连接可用为止。\n",
    "要应用处理程序，它将被传递到HttpClient的构造函数中。"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 测试连接寿命"
   ]
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   "source": [
    "using System.Net;\n",
    "using System.Net.Http;\n",
    "\n",
    "//注意：不能使用百度 hao123等站点，可能是大厂服务器的设置问题，会导致查不到效果\n",
    "var ips = await Dns.GetHostAddressesAsync(\"soft.pwidc.cn\");\n",
    "string firstIp = ips.FirstOrDefault().ToString();\n",
    "\t\n",
    "foreach (var ipAddress in ips)\n",
    "{\n",
    "    Console.WriteLine(ipAddress.MapToIPv4().ToString());\n",
    "}\n",
    "\n",
    "//自定义行为\n",
    "var socketsHandler = new SocketsHttpHandler\n",
    "{\n",
    "    //连接池生命周期为10分钟：连接在池中保持活动时间为10分钟\n",
    "    PooledConnectionLifetime = TimeSpan.FromMinutes(10),\n",
    "\n",
    "    //池化链接的空闲超时时间为5分钟: 5分钟内连接不被重用，则被释放后销毁\n",
    "    PooledConnectionIdleTimeout = TimeSpan.FromMinutes(5),\n",
    "    \n",
    "    //每端点的最大连接数设置为10个\n",
    "    MaxConnectionsPerServer = 10\n",
    "};\n",
    "\n",
    "var client = new HttpClient(socketsHandler);\n",
    "\n",
    "for (var i = 0; i < 5; i++)\n",
    "{\n",
    "    _ = await client.GetAsync(\"https://soft.pwidc.cn\");\n",
    "    await Task.Delay(TimeSpan.FromSeconds(2));\n",
    "}\n",
    "\n",
    "Console.WriteLine(\"程序运行大约要10-20秒，请在程序退出后，执行下面命令行查看网络情况\");\n"
   ]
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    "使用自定义设置，依次向同一端点发出5个请求。在每个请求之间，暂停两秒钟。输出从DNS检索到的网站服务器的IPv4地址。我们可以使用此IP地址来查看通过PowerShell中发出的netstat命令对其打开的连接："
   ]
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   "source": [
    "# 如果没有查询到相关网络状态信息，PowerShell不针对出错，但.Net Interactive 会异常：Command failed: SubmitCode: #!set --value @csharp:xxxx\n",
    "#!set --value @csharp:firstIp --name queryIp\n",
    "Write-Host \"请先执行上面的单元，再执行本单元\"\n",
    "Write-Host \"网络状态\"\n",
    "\n",
    "netstat -ano | findstr $queryIp"
   ]
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   "source": [
    "在这种情况下，到远程端点的连接只有1个。在每个请求之后，该连接将返回到池中，因此在发出下一个请求时可以重新使用。\n",
    "如果更改连接的生存期，以使它们在1秒后过期，测试这对行为的影响："
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   "source": [
    "using System.IO;\n",
    "using System.Diagnostics;\n",
    "using System.Net;\n",
    "using System.Net.Http;\n",
    "\n",
    "var ips = await Dns.GetHostAddressesAsync(\"soft.pwidc.cn\");\n",
    "string firstIp = ips.FirstOrDefault().ToString();\n",
    "\t\n",
    "foreach (var ipAddress in ips)\n",
    "{\n",
    "    Console.WriteLine(ipAddress.MapToIPv4().ToString());\n",
    "}\n",
    "\n",
    "//自定义行为\n",
    "var socketsHandler2 = new SocketsHttpHandler\n",
    "{\n",
    "    PooledConnectionLifetime = TimeSpan.FromSeconds(1),\n",
    "    PooledConnectionIdleTimeout = TimeSpan.FromSeconds(1),\n",
    "    MaxConnectionsPerServer = 1\n",
    "};\n",
    "\n",
    "var client2 = new HttpClient(socketsHandler2);\n",
    "\n",
    "for (var i = 0; i < 5; i++)\n",
    "{\n",
    "    if(i>0)\n",
    "    {\n",
    "        await Task.Delay(TimeSpan.FromSeconds(2));\n",
    "    }\n",
    "    _ = await client2.GetAsync(\"http://soft.pwidc.cn\");\n",
    "}\n",
    "\n",
    "Console.WriteLine(\"程序运行大约要10-20，请在程序退出后，执行下面命令行查看网络情况\");\n",
    "\n",
    "//调用命令行，显示查看网络情况\n",
    "string command = $\"netstat -ano | findstr {firstIp}\";\n",
    " \n",
    "// 创建一个新的ProcessStartInfo对象\n",
    "ProcessStartInfo startInfo = new ProcessStartInfo(\"cmd\", $\"/c {command}\")\n",
    "{\n",
    "    RedirectStandardOutput = true, // 重定向标准输出\n",
    "    UseShellExecute = false, // 不使用系统外壳程序启动\n",
    "    CreateNoWindow = true // 不创建新窗口\n",
    "};\n",
    " \n",
    "// 启动进程\n",
    "using (Process process = Process.Start(startInfo))\n",
    "{\n",
    "    // 读取cmd的输出\n",
    "    using (StreamReader reader = process.StandardOutput)\n",
    "    {\n",
    "        string stdoutLine = reader.ReadToEnd();\n",
    "        Console.WriteLine(stdoutLine);\n",
    "    }\n",
    "}"
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   "source": [
    "#!set --value @csharp:firstIp --name queryIp\n",
    "netstat -ano | findstr $queryIp"
   ]
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "在这种情况下，我们可以看到使用了五个连接。其中的前四个在1秒后从池中删除，因此无法在下一个请求中重复使用。结果，每个请求都打开了一个新连接。现在，原始连接处于TIME_WAIT状态，并且操作系统无法将其重新用于新的出站连接。最终连接显示为ESTABLISHED，因为我在它过期之前就抓住了它。"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 测试最大连接数"
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 3、推荐使用方式"
   ]
  }
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