从虚拟机调用本地API报各种 SSL 连接不上的错误，这给本地调试造成了极大的不便，在被这个问题困扰了多日以后，终于在GitHub上找到答案
基于这个 帖子 ，有一个回复
他写了一个帮助类，专门用来调试本地的API，并给出了这个调用类的用法，此帮助类如下
using System.Net.Security;public class DevHttpsConnectionHelper
{public DevHttpsConnectionHelper(int sslPort){SslPort = sslPort;DevServerRootUrl = FormattableString.Invariant($"https://{DevServerName}:{SslPort}");LazyHttpClient = new Lazy<HttpClient>(() => new HttpClient(GetPlatformMessageHandler()));}public int SslPort { get; }public string DevServerName =>
#if WINDOWS"localhost";
#elif ANDROID"10.0.2.2";
#elsethrow new PlatformNotSupportedException("Only Windows and Android currently supported.");
#endifpublic string DevServerRootUrl { get; }private Lazy<HttpClient> LazyHttpClient;public HttpClient HttpClient => LazyHttpClient.Value;public HttpMessageHandler? GetPlatformMessageHandler(){
#if WINDOWSreturn null;
#elif ANDROIDvar handler = new CustomAndroidMessageHandler();handler.ServerCertificateCustomValidationCallback = (message, cert, chain, errors) =>{if (cert != null && cert.Issuer.Equals("CN=localhost"))return true;return errors == SslPolicyErrors.None;};return handler;#elsethrow new PlatformNotSupportedException("Only Windows and Android currently supported.");
#endif}#if ANDROIDinternal sealed class CustomAndroidMessageHandler : Xamarin.Android.Net.AndroidMessageHandler{protected override Javax.Net.Ssl.IHostnameVerifier GetSSLHostnameVerifier(Javax.Net.Ssl.HttpsURLConnection connection)=> new CustomHostnameVerifier();private sealed class CustomHostnameVerifier : Java.Lang.Object, Javax.Net.Ssl.IHostnameVerifier{public bool Verify(string? hostname, Javax.Net.Ssl.ISSLSession? session){returnJavax.Net.Ssl.HttpsURLConnection.DefaultHostnameVerifier.Verify(hostname, session)|| hostname == "10.0.2.2" && session.PeerPrincipal?.Name == "CN=localhost";}}}
#endif
}在安卓机里面是没有 localhost 的，也没有 127.0.0.1 代表本机的取而代之的是 10.0.2.2 。在 HTTPS 里面，证书是被强制使用的，本地 Web API 会有一个默认证书，他里面带一个 “CN=localhost” 所以上面的类针对这个进行了过滤，并且 Android 的底层用的不是默认的 .net 的 HttpClient ，使用了 GetPlatformMessageHandler 进行了重写，这个可是Java 的包。
我的本地调用使用
var devSslHelper = new DevHttpsConnectionHelper(sslPort: 5001);_blazorHubConnection = new HubConnectionBuilder()
#if ANDROID.WithUrl(devSslHelper.DevServerRootUrl + "/hubs/devicehub", configureHttpConnection: o =>{o.HttpMessageHandlerFactory = m => devSslHelper.GetPlatformMessageHandler();})
#else.WithUrl(devSslHelper.DevServerRootUrl + "/hubs/devicehub")
#endif.Build();这个时候就不报 SSL 的连接错误了，可以方便的正常调试
