.Net 核心 HttpClient 错误?SocketException: 一个现有的连接被远程主机强行关闭 [英] .Net core HttpClient bug? SocketException: An existing connection was forcibly closed by the remote host

问题描述

以下代码在完整的 .Net 框架控制台程序中运行时没有任何错误.但是，在 .Net core 2.1 中运行时出现以下错误.

<前>System.AggregateExceptionHResult=0x80131500Message=发生一个或多个错误.源 = System.Private.CoreLib堆栈跟踪:在 System.Threading.Tasks.Task`1.GetResultCore(Boolean waitCompletionNotification)在 C:source eposConsoleApp1Program.cs:line 38 中的 ConsoleApp1.Program.requestString(String url)在 C:source eposConsoleApp1Program.cs:line 13 中的 ConsoleApp1.Program.Main(String[] args)内部异常 1:HttpRequestException: 无法建立 SSL 连接，请参阅内部异常.内部异常 2:IOException:无法从传输连接读取数据:远程主机强制关闭现有连接.内部异常 3:SocketException: 一个现有的连接被远程主机强行关闭

代码:

class 程序{静态无效主(字符串 [] args){var url = "https://google.com";var (statusCode, html) = requestString(url);Console.WriteLine("%d %s", statusCode, html);}静态 CookieContainer cc = 新 CookieContainer();静态 HttpClientHandler 处理程序 = 新 HttpClientHandler { AllowAutoRedirect = false, CookieContainer = cc };公共静态异步任务<(int statusCode, string content)>requestStringAsync(字符串网址){ServicePointManager.ServerCertificateValidationCallback += (sender, cert, chain, sslPolicyErrors) =>真的;ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls |安全协议类型.Tls11 |SecurityProtocolType.Tls12;//|SecurityProtocolType.Ssl3;使用 (var request = new HttpRequestMessage { RequestUri = new Uri(url), Method = HttpMethod.Get })使用 (var client = new HttpClient(handler)){var response = await client.SendAsync(request);//错误(实际行)//response.EnsureSuccessStatusCode() |>忽略var statusCode = (int)response.StatusCode;var content = await response.Content.ReadAsStringAsync();返回(状态码，内容)；}}public static (int statusCode, string content) requestString(string url){返回 requestStringAsync(url).Result;}}

解决方案

有一个bug 对于 .NET Core 2.1 Preview 提到了这个问题.这可能是原因.但是，我也注意到您的 TLS 设置不正确.您当前正在启用它，但会覆盖已设置的所有其他协议.而不是这样:

ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls |安全协议类型.Tls11 |SecurityProtocolType.Tls12;

你应该使用这个:

ServicePointManager.SecurityProtocol |= SecurityProtocolType.Tls |安全协议类型.Tls11 |SecurityProtocolType.Tls12;//----------------------------------^

我认为这是一个附带问题，但同样值得解决.

更新

上面引用的 GitHub 问题有一个讨论，最终链接到 .NET Core 2.1 SDK 预览版 2.有以下几点要说:

<块引用>

套接字性能和 SocketsHttpHandler

我们对 .NET Core 2.1 中的套接字进行了重大改进.套接字是传出和传入网络通信的基础..NET Core 2.1 中更高级别的网络 API，包括 HttpClient 和 Kestrel，现在基于 .NET 套接字.在早期版本中，这些更高级别的 API 基于本机网络实现.

...

您可以使用以下机制之一来配置进程以使用较旧的 HttpClientHandler:

从代码中，使用 AppContext 类:

AppContext.SetSwitch(System.Net.Http.UseSocketsHttpHandler", false);

AppContext 开关也可以通过配置文件设置.

同样可以通过环境变量 DOTNET_SYSTEM_NET_HTTP_USESOCKETSHTTPHANDLER 实现.要选择退出，请将值设置为 false 或 0.

The following code runs without any error in a full .Net framework console program. However, it got the following error when running in .Net core 2.1.

System.AggregateException
  HResult=0x80131500
  Message=One or more errors occurred.
  Source=System.Private.CoreLib
  StackTrace:
   at System.Threading.Tasks.Task`1.GetResultCore(Boolean waitCompletionNotification)
   at ConsoleApp1.Program.requestString(String url) in C:source
eposConsoleApp1Program.cs:line 38
   at ConsoleApp1.Program.Main(String[] args) in C:source
eposConsoleApp1Program.cs:line 13

Inner Exception 1:
HttpRequestException: The SSL connection could not be established, see inner exception.

Inner Exception 2:
IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host.

Inner Exception 3:
SocketException: An existing connection was forcibly closed by the remote host

Code:

class Program
{
    static void Main(string[] args)
    {
        var url = "https://google.com";
        var (statusCode, html) = requestString(url);
        Console.WriteLine("%d %s", statusCode, html);
    }

    static CookieContainer cc = new CookieContainer();

    static HttpClientHandler handler = new HttpClientHandler { AllowAutoRedirect = false, CookieContainer = cc };

    public static async Task<(int statusCode, string content)> requestStringAsync(string url)
    {
        ServicePointManager.ServerCertificateValidationCallback += (sender, cert, chain, sslPolicyErrors) => true;
        ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;
                                                                     // | SecurityProtocolType.Ssl3;
        using (var request = new HttpRequestMessage { RequestUri = new Uri(url), Method = HttpMethod.Get })
        using (var client = new HttpClient(handler))
        {
            var response = await client.SendAsync(request); // Error (actual line)
            // response.EnsureSuccessStatusCode() |> ignore
            var statusCode = (int)response.StatusCode;
            var content = await response.Content.ReadAsStringAsync();
            return (statusCode, content);
        }
    }

    public static (int statusCode, string content) requestString(string url)
    {
        return requestStringAsync(url).Result;
    }
}

解决方案

There is a bug for .NET Core 2.1 Preview mentioning this issue. That may be the cause. However, I also notice that your setting of TLS is incorrect. You're currently enabling it, but overwriting all other protocols that have been set. Instead of this:

ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;

You should be using this:

ServicePointManager.SecurityProtocol |= SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;
// ----------------------------------^

I think that's a side issue, but worth fixing all the same.

Update

The referenced GitHub issue above has a discussion which eventually links to the official announcement for .NET Core 2.1 SDK Preview 2. It has the following to say:

Sockets Performance and SocketsHttpHandler

We made major improvements to sockets in .NET Core 2.1. Sockets are the basis of both outgoing and incoming networking communication. The higher-level networking APIs in .NET Core 2.1, including HttpClient and Kestrel, are now based on .NET sockets. In earlier versions, these higher-level APIs were based on native networking implementations.

...

You can use one of the following mechanisms to configure a process to use the older HttpClientHandler:

From code, use the AppContext class:

AppContext.SetSwitch("System.Net.Http.UseSocketsHttpHandler", false);

The AppContext switch can also be set by config file.

The same can be achieved via the environment variable DOTNET_SYSTEM_NET_HTTP_USESOCKETSHTTPHANDLER. To opt out, set the value to either false or 0.

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