如何修复C#中PostAsync请求未生效的代理配置问题？

基于.NET Framework 4.6.1开发WPF的.dll组件，服务通过HTTP请求访问Azure Function服务器。已实现修改用户设置及配置代理的界面，但请求并未应用配置好的代理设置。

静态类ConnexionService代码 #

public static class ConnexionService
{
    private static HttpClient httpClient;
    private static HttpClientHandler clientHandler = new HttpClientHandler();

    public static void SetupProxy()
    {
        try
        {
            if (Properties.Settings.Default.ProxyUsage)
            {
                // 代理服务器地址和端口
                Uri proxyAddress = new Uri($"http://{Properties.Settings.Default.ProxyAdress}:{Properties.Settings.Default.ProxyPort}");

                // 创建代理对象
                WebProxy proxy = new WebProxy(Address: proxyAddress, BypassOnLocal: false)
                {
                    UseDefaultCredentials = false,
                    Credentials = new NetworkCredential(
                       userName: Properties.Settings.Default.ProxyUser,
                       password: Properties.Settings.Default.ProxyPassword)
                };
                
                // 创建HttpClientHandler并配置代理
                clientHandler = new HttpClientHandler()
                {
                    UseProxy = true,
                    Proxy = proxy
                };
                httpClient = new HttpClient(handler: clientHandler, disposeHandler: true);
            }
            else {
                httpClient = new HttpClient();
            }
        }
        catch(Exception e)
        {
            Console.WriteLine(e.ToString());
        }
    }

    public static HttpClient getHttpClient()
    {
        SetupProxy();
        return httpClient;
    }
}

AuthenticationService中的使用代码 #

public class AuthenticationService 
{
    private readonly string Path = $"{Properties.Settings.Default.URL_API_DEV}/authentication";

    public async Task<Profile> LogIn(Profile profile)
    {
        var encryption = new Encryption();

        HttpContent content = new StringContent(encryption.Encrypt(JsonConvert.SerializeObject(profile)), Encoding.UTF8, "text/plain");
        try
        {
            using (var client = ConnexionService.getHttpClient())
            {
                var endpoint = new Uri($"{Path.Trim()}/login");

                var send = await client.PostAsync(endpoint, content);

                if (!send.IsSuccessStatusCode)
                {
                    Console.WriteLine($"错误 : {send.StatusCode}");
                    return new Profile();
                }

                var encryptedResult = await send.Content.ReadAsStringAsync();
                var decryptedResult = encryption.Decrypt(encryptedResult);
                var response = JsonConvert.DeserializeObject<Profile>(decryptedResult);
                return response;
            }
        }
        catch (HttpRequestException e)
        {
            Console.WriteLine($"错误 : {e.Message}");
            return new Profile();
        }
    }
}

核心问题 #

1. 错误使用using销毁静态HttpClient：AuthenticationService中用using (var client = ConnexionService.getHttpClient())会自动销毁静态的httpClient实例，导致后续请求时实例已失效，代理配置无法生效，还会引发套接字资源耗尽问题。
2. 重复创建HttpClient：getHttpClient()每次调用都会执行SetupProxy()重新创建HttpClient，违背了HttpClient设计为复用的原则，也会导致代理配置无法稳定生效。

修复步骤 #

1. 移除using语句：静态HttpClient为长期复用设计，无需每次请求销毁，直接复用即可：

   // 替换原using块代码
   var client = ConnexionService.getHttpClient();
   var endpoint = new Uri($"{Path.Trim()}/login");
   var send = await client.PostAsync(endpoint, content);
   // 后续逻辑保持不变
   

2. 优化ConnexionService逻辑：仅在代理配置变化时更新HttpClient实例，避免重复创建：

   public static class ConnexionService
   {
       private static HttpClient httpClient;
       private static HttpClientHandler clientHandler;
       // 记录当前代理配置，判断是否需要更新
       private static bool _currentProxyUsage;
       private static string _currentProxyAddress;
       private static int _currentProxyPort;
       private static string _currentProxyUser;
   
       public static void SetupProxy()
       {
           try
           {
               var settings = Properties.Settings.Default;
               // 配置无变化则直接返回
               if (httpClient != null 
                   && _currentProxyUsage == settings.ProxyUsage
                   && _currentProxyAddress == settings.ProxyAdress
                   && _currentProxyPort == settings.ProxyPort
                   && _currentProxyUser == settings.ProxyUser)
               {
                   return;
               }
   
               // 销毁旧实例
               httpClient?.Dispose();
               clientHandler?.Dispose();
   
               if (settings.ProxyUsage)
               {
                   Uri proxyAddress = new Uri($"http://{settings.ProxyAdress}:{settings.ProxyPort}");
                   WebProxy proxy = new WebProxy(proxyAddress, BypassOnLocal: false)
                   {
                       UseDefaultCredentials = false,
                       Credentials = new NetworkCredential(settings.ProxyUser, settings.ProxyPassword)
                   };
                   
                   clientHandler = new HttpClientHandler()
                   {
                       UseProxy = true,
                       Proxy = proxy
                   };
                   httpClient = new HttpClient(clientHandler, disposeHandler: true);
                   // 更新配置记录
                   _currentProxyUsage = true;
                   _currentProxyAddress = settings.ProxyAdress;
                   _currentProxyPort = settings.ProxyPort;
                   _currentProxyUser = settings.ProxyUser;
               }
               else 
               {
                   httpClient = new HttpClient();
                   // 更新配置记录
                   _currentProxyUsage = false;
                   _currentProxyAddress = null;
                   _currentProxyPort = 0;
                   _currentProxyUser = null;
               }
           }
           catch(Exception e)
           {
               Console.WriteLine(e.ToString());
           }
       }
   
       public static HttpClient getHttpClient()
       {
           SetupProxy();
           return httpClient;
       }
   }
   

3. 监听配置变化：用户修改代理设置后，主动调用ConnexionService.SetupProxy()触发实例更新，确保新配置立即生效。

内容的提问来源于stack exchange，提问作者Pablo Arrieumerlou