增加LoopbackDnsHttpHandler，提高GithubMetaProvider从github获取数据的成功率

FastGithub.Scanner/LoopbackDnsHttpHandler.cs

@@ -0,0 +1,68 @@
+using DNS.Client;
+using Microsoft.Extensions.DependencyInjection;
+using System;
+using System.Linq;
+using System.Net;
+using System.Net.Http;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace FastGithub.Scanner
+{
+    /// <summary>
+    /// 由本程序提值的dns的httpHandler
+    /// </summary>
+    [Service(ServiceLifetime.Transient)]
+    sealed class LoopbackDnsHttpHandler : DelegatingHandler
+    {
+        /// <summary>
+        /// 本程序的dns
+        /// </summary>
+        private static readonly DnsClient dnsClient = new(IPAddress.Loopback);
+
+        /// <summary>
+        /// 发送消息
+        /// </summary>
+        /// <param name="request"></param>
+        /// <param name="cancellationToken"></param>
+        /// <returns></returns>
+        protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
+        {
+            var uri = request.RequestUri;
+            if (uri != null && uri.HostNameType == UriHostNameType.Dns)
+            {
+                var address = await LookupAsync(uri.Host);
+                if (address != null)
+                {
+                    var builder = new UriBuilder(uri)
+                    {
+                        Host = address.ToString()
+                    };
+                    request.RequestUri = builder.Uri;
+                    request.Headers.Host = uri.Host;
+                }
+            }
+
+            return await base.SendAsync(request, cancellationToken);
+        }
+
+        /// <summary>
+        /// dns解析ip
+        /// </summary>
+        /// <param name="host"></param>
+        /// <returns></returns>
+        private static async Task<IPAddress?> LookupAsync(string host)
+        {
+            try
+            {
+                using var cancellationTokenSource = new CancellationTokenSource(TimeSpan.FromMilliseconds(500d));
+                var addresses = await dnsClient.Lookup(host, cancellationToken: cancellationTokenSource.Token);
+                return addresses.FirstOrDefault();
+            }
+            catch (Exception)
+            {
+                return default;
+            }
+        }
+    }
+}

FastGithub.Scanner/ScannerServiceCollectionExtensions.cs

@@ -36,7 +36,8 @@ namespace FastGithub
                     Proxy = null,
                     UseProxy = false,
                     AllowAutoRedirect = false
-                });
+                })
+                .AddHttpMessageHandler<LoopbackDnsHttpHandler>();
 
             return services
                 .AddMemoryCache()