.NET 6 Web API中GetHttpClient()调用抛出SocketException问题排查

我在.NET 6开发Web API时，定义了抽象类AdminApiClient继承自ApiClientBase，代码如下：

public abstract class AdminApiClient : ApiClientBase
{
    protected static HttpClient? client;

    public AdminApiClient()
    {
        client = client ?? new HttpClient
        {
            BaseAddress = new Uri("http://localhost:44355/")
        };
    }

    protected override HttpClient GetHttpClient()
    {
        return client;
    }
}

ApiClientBase类代码如下：调用Test方法时，方法内新建的HttpClient发起请求正常，但通过GetHttpClient()获取的复用HttpClient发起请求会抛出异常：

public abstract class ApiClientBase
{
    protected abstract HttpClient GetHttpClient();

    protected async Task<TResult> Test<TResult>()
    {
        var apiName = "api/users/GetTest";

        var httpClient = new HttpClient();

        httpClient.BaseAddress = new Uri("https://localhost:44355/");

        // 运行正常
        var response1 = await httpClient.GetAsync(apiName);

        // 抛出异常
        var response2 = await GetHttpClient().GetAsync(apiName);
    }
}

我困惑的是这段代码能正常运行：

var response1 = await httpClient.GetAsync(apiName);

但这段代码会抛出异常：

var response2 = await GetHttpClient().GetAsync(apiName);

异常信息： #

System.Net.Http.HttpRequestException: 发送请求时出错。
---> System.IO.IOException: 无法从传输连接读取数据: 远程主机强迫关闭了一个现有的连接。
---> System.Net.Sockets.SocketException (10054): 远程主机强迫关闭了一个现有的连接。
--- 内部异常堆栈跟踪结束 ---
在 System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.ThrowException(SocketError error, CancellationToken cancellationToken)
在 System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.System.Threading.Tasks.Sources.IValueTaskSource<System.Int32>.GetResult(Int16 token)
在 System.Net.Http.HttpConnection.InitialFillAsync(Boolean async)
在 System.Net.Http.HttpConnection.SendAsyncCore(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken)
--- 内部异常堆栈跟踪结束 ---
在 System.Net.Http.HttpConnection.SendAsyncCore(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken)
在 System.Net.Http.HttpConnectionPool.SendWithVersionDetectionAndRetryAsync(HttpRequestMessage request, Boolean async, Boolean doRequestAuth, CancellationToken cancellationToken)
在 System.Net.Http.DiagnosticsHandler.SendAsyncCore(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken)
在 System.Net.Http.RedirectHandler.SendAsync(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken)
在 System.Net.Http.HttpClient.g__Core|83_0(HttpRequestMessage request, HttpCompletionOption completionOption, CancellationTokenSource cts, Boolean disposeCts, CancellationTokenSource pendingRequestsCts, CancellationToken originalCancellationToken)
在 Web.Core.ApiClientBase.Test() in C:\Web.Core\ApiClientBase.cs:line 76

原因分析 #

1. BaseAddress协议不匹配：复用的HttpClient使用的是http://localhost:44355/，而测试方法里新建的HttpClient用的是https://localhost:44355/。如果API服务仅监听HTTPS端口，HTTP请求会被直接拒绝，进而导致连接被强制关闭。
2. 静态HttpClient的潜在问题：静态HttpClient实例长期存活，可能出现DNS缓存过期、连接池失效等问题，但本次异常的核心诱因是协议不匹配。

解决方案 #

1. 统一BaseAddress协议：将AdminApiClient中的BaseAddress修改为HTTPS，与测试代码保持一致：

client = client ?? new HttpClient
{
    BaseAddress = new Uri("https://localhost:44355/")
};

2. 使用官方推荐的IHttpClientFactory管理实例：.NET官方推荐通过IHttpClientFactory来管理HttpClient生命周期，既能避免静态实例的各种潜在问题，又能自动维护连接池、处理DNS更新：
   • 在Program.cs中注册服务：

     builder.Services.AddHttpClient<IAdminApiClient, AdminApiClient>(client =>
     {
         client.BaseAddress = new Uri("https://localhost:44355/");
     });
     

   • 修改AdminApiClient通过构造注入获取HttpClient：

     public abstract class AdminApiClient : ApiClientBase
     {
         private readonly HttpClient _client;
     
         public AdminApiClient(HttpClient client)
         {
             _client = client;
         }
     
         protected override HttpClient GetHttpClient()
         {
             return _client;
         }
     }
     

内容的提问来源于stack exchange，提问作者Howard Hee