增加TTL模拟

FastGithub.Dns/DnsServiceCollectionExtensions.cs

@@ -19,6 +19,7 @@ namespace FastGithub
         {
             var assembly = typeof(DnsServiceCollectionExtensions).Assembly;
             return services         
+                .AddMemoryCache()
                 .AddServiceAndOptions(assembly, configuration)
                 .AddHostedService<DnsHostedService>()
                 .AddGithubScanner(configuration);

FastGithub.Dns/FastGithub.Dns.csproj

@@ -7,6 +7,7 @@
 
 	<ItemGroup>
 		<PackageReference Include="DNS" Version="6.1.0" />
+		<PackageReference Include="Microsoft.Extensions.Caching.Memory" Version="5.0.0" />
 	</ItemGroup>
 
 	<ItemGroup>

FastGithub.Dns/GithubRequestResolver.cs

@@ -2,9 +2,12 @@
 using DNS.Protocol;
 using DNS.Protocol.ResourceRecords;
 using FastGithub.Scanner;
+using Microsoft.Extensions.Caching.Memory;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging;
+using System;
 using System.Linq;
+using System.Net;
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -14,13 +17,17 @@ namespace FastGithub.Dns
     sealed class GithubRequestResolver : IRequestResolver
     {
         private readonly IGithubScanService githubScanService;
+        private readonly IMemoryCache memoryCache;
         private readonly ILogger<GithubRequestResolver> logger;
+        private readonly TimeSpan TTL = TimeSpan.FromMinutes(10d);
 
         public GithubRequestResolver(
             IGithubScanService githubScanService,
+            IMemoryCache memoryCache,
             ILogger<GithubRequestResolver> logger)
         {
             this.githubScanService = githubScanService;
+            this.memoryCache = memoryCache;
             this.logger = logger;
         }
 
@@ -32,11 +39,11 @@ namespace FastGithub.Dns
             if (question != null && question.Type == RecordType.A)
             {
                 var domain = question.Name.ToString();
-                var fastAddress = this.githubScanService.FindFastAddress(domain);
+                var address = this.GetGithubAddress(domain, TTL);
 
-                if (fastAddress != null)
+                if (address != null)
                 {
-                    var record = new IPAddressResourceRecord(question.Name, fastAddress);
+                    var record = new IPAddressResourceRecord(question.Name, address);
                     response.AnswerRecords.Add(record);
                     this.logger.LogInformation(record.ToString());
                 }
@@ -44,5 +51,37 @@ namespace FastGithub.Dns
 
             return Task.FromResult<IResponse>(response);
         }
+
+        /// <summary>
+        /// 模拟TTL
+        /// 如果ip可用，则10分钟内返回缓存的ip，防止客户端ip频繁切换
+        /// </summary> 
+        /// <param name="domain"></param>
+        /// <param name="ttl"></param>
+        /// <returns></returns>
+        private IPAddress? GetGithubAddress(string domain, TimeSpan ttl)
+        {
+            if (domain.Contains("github", StringComparison.OrdinalIgnoreCase) == false)
+            {
+                return default;
+            }
+
+            var key = $"ttl:{domain}";
+            if (this.memoryCache.TryGetValue<IPAddress>(key, out var address))
+            {
+                if (this.githubScanService.IsAvailable(domain, address))
+                {
+                    return address;
+                }
+                this.memoryCache.Remove(key);
+            }
+
+            address = this.githubScanService.FindBestAddress(domain);
+            if (address != null)
+            {
+                this.memoryCache.Set(key, address, ttl);
+            }
+            return address;
+        }
     }
 }

FastGithub.Scanner/GithubContextCollection.cs

@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Net;
 
@@ -22,6 +23,17 @@ namespace FastGithub.Scanner
             }
         }
 
+
+        public bool TryGet(string domain, IPAddress address, [MaybeNullWhen(false)] out GithubContext context)
+        {
+            lock (this.syncRoot)
+            {
+                var target = new GithubContext(domain, address);
+                context = this.contextList.Find(item => item.Equals(target));
+                return context != null;
+            }
+        }
+
         public GithubContext[] ToArray()
         {
             lock (this.syncRoot)

FastGithub.Scanner/GithubScanService.cs

@@ -1,7 +1,6 @@
 using FastGithub.Scanner.Middlewares;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging;
-using System;
 using System.Linq;
 using System.Net;
 using System.Threading;
@@ -80,11 +79,15 @@ namespace FastGithub.Scanner
             this.logger.LogInformation("结果扫描结束");
         }
 
-        public IPAddress? FindFastAddress(string domain)
+        public IPAddress? FindBestAddress(string domain)
         {
-            return domain.Contains("github", StringComparison.OrdinalIgnoreCase)
-                ? this.results.FindBestAddress(domain)
-                : default;
+            return this.results.FindBestAddress(domain);
+        }
+
+
+        public bool IsAvailable(string domain, IPAddress address)
+        {
+            return this.results.TryGet(domain, address, out var context) && context.Available;
         }
     }
 }

FastGithub.Scanner/IGithubScanService.cs

@@ -6,8 +6,12 @@ namespace FastGithub.Scanner
 {
     public interface IGithubScanService
     {
-        Task ScanAllAsync(CancellationToken cancellationToken = default);
+        Task ScanAllAsync(CancellationToken cancellationToken);
+
         Task ScanResultAsync();
-        IPAddress? FindFastAddress(string domain);
+
+        bool IsAvailable(string domain, IPAddress address);
+
+        IPAddress? FindBestAddress(string domain);
     }
 }