From e5e60ddb9fb95a8132b785e596cc62f84fb8dbc3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E9=99=88=E5=9B=BD=E4=BC=9F?= <366193849@qq.com>
Date: Mon, 30 Aug 2021 09:16:37 +0800
Subject: [PATCH] =?UTF-8?q?=E6=8F=90=E9=AB=98=E5=9F=9F=E5=90=8D=E8=A7=A3?=
 =?UTF-8?q?=E6=9E=90=E6=88=90=E5=8A=9F=E7=8E=87?=
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---
 FastGithub.DomainResolve/DomainResolver.cs | 61 ++++++++++------------
 1 file changed, 27 insertions(+), 34 deletions(-)

diff --git a/FastGithub.DomainResolve/DomainResolver.cs b/FastGithub.DomainResolve/DomainResolver.cs
index 0357b47..0be2b36 100644
--- a/FastGithub.DomainResolve/DomainResolver.cs
+++ b/FastGithub.DomainResolve/DomainResolver.cs
@@ -27,10 +27,9 @@ namespace FastGithub.DomainResolve
         private readonly DnscryptProxy dnscryptProxy;
         private readonly ILogger<DomainResolver> logger;
 
-        private readonly TimeSpan lookupTimeout = TimeSpan.FromSeconds(5d);
         private readonly TimeSpan connectTimeout = TimeSpan.FromSeconds(5d);
-        private readonly TimeSpan dnscryptExpiration = TimeSpan.FromMinutes(5d);
-        private readonly TimeSpan fallbackExpiration = TimeSpan.FromMinutes(1d);
+        private readonly TimeSpan dnscryptExpiration = TimeSpan.FromMinutes(10d);
+        private readonly TimeSpan fallbackExpiration = TimeSpan.FromMinutes(2d);
         private readonly TimeSpan loopbackExpiration = TimeSpan.FromSeconds(5d);
         private readonly ConcurrentDictionary<DnsEndPoint, SemaphoreSlim> semaphoreSlims = new();
 
@@ -81,7 +80,16 @@ namespace FastGithub.DomainResolve
             try
             {
                 await semaphore.WaitAsync();
-                return await this.ResolveNoCacheAsync(domain, cancellationToken);
+
+                for (var i = 0; i < 2; i++)
+                {
+                    var address = await this.ResolveCoreAsync(domain, cancellationToken);
+                    if (address != null)
+                    {
+                        return address;
+                    }
+                }
+                throw new FastGithubException($"当前解析不到{domain.Host}可用的ip，请刷新重试");
             }
             finally
             {
@@ -91,12 +99,11 @@ namespace FastGithub.DomainResolve
 
         /// <summary>
         /// 解析域名
-        /// 不使用缓存
         /// </summary>
         /// <param name="domain"></param>
         /// <param name="cancellationToken"></param>
         /// <returns></returns>
-        private async Task<IPAddress> ResolveNoCacheAsync(DnsEndPoint domain, CancellationToken cancellationToken)
+        private async Task<IPAddress?> ResolveCoreAsync(DnsEndPoint domain, CancellationToken cancellationToken)
         {
             if (this.domainResolveCache.TryGetValue<IPAddress>(domain, out var address))
             {
@@ -112,12 +119,12 @@ namespace FastGithub.DomainResolve
             if (address == null)
             {
                 expiration = this.fallbackExpiration;
-                address = await this.FallbackLookupAsync(domain, cancellationToken);
+                address = await this.LookupByFallbackAsync(domain, cancellationToken);
             }
 
             if (address == null)
             {
-                throw new FastGithubException($"当前解析不到{domain.Host}可用的ip，请刷新重试");
+                return default;
             }
 
             // 往往是被污染的dns
@@ -137,7 +144,7 @@ namespace FastGithub.DomainResolve
         /// <param name="domain"></param>
         /// <param name="cancellationToken"></param>
         /// <returns></returns>
-        private async Task<IPAddress?> FallbackLookupAsync(DnsEndPoint domain, CancellationToken cancellationToken)
+        private async Task<IPAddress?> LookupByFallbackAsync(DnsEndPoint domain, CancellationToken cancellationToken)
         {
             foreach (var dns in this.fastGithubConfig.FallbackDns)
             {
@@ -151,7 +158,7 @@ namespace FastGithub.DomainResolve
         }
 
         /// <summary>
-        /// 查找ip
+        /// 查找最快的可用ip
         /// </summary>
         /// <param name="dns"></param>
         /// <param name="domain"></param>
@@ -159,34 +166,20 @@ namespace FastGithub.DomainResolve
         /// <returns></returns>
         private async Task<IPAddress?> LookupAsync(IPEndPoint dns, DnsEndPoint domain, CancellationToken cancellationToken)
         {
-            const int MAX_TRY_COUNT = 2;
-            for (var i = 0; i < MAX_TRY_COUNT; i++)
+            try
             {
-                try
-                {
-                    var dnsClient = new DnsClient(dns);
-                    using var timeoutTokenSource = new CancellationTokenSource(this.lookupTimeout);
-                    using var linkedTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken, timeoutTokenSource.Token);
-                    var addresses = await dnsClient.Lookup(domain.Host, RecordType.A, linkedTokenSource.Token);
-                    addresses = addresses.Where(address => this.disableIPAddressCache.TryGetValue(address, out _) == false).ToList();
-                    return await this.FindFastValueAsync(addresses, domain.Port, cancellationToken);
-                }
-                catch (OperationCanceledException)
-                {
-                    continue;
-                }
-                catch (Exception ex)
-                {
-                    this.logger.LogWarning($"dns({dns})无法解析{domain.Host}：{ex.Message}");
-                    return default;
-                }
+                var dnsClient = new DnsClient(dns);
+                var addresses = await dnsClient.Lookup(domain.Host, RecordType.A, cancellationToken);
+                addresses = addresses.Where(address => this.disableIPAddressCache.TryGetValue(address, out _) == false).ToList();
+                return await this.FindFastValueAsync(addresses, domain.Port, cancellationToken);
+            }
+            catch (Exception ex)
+            {
+                this.logger.LogWarning($"dns({dns})无法解析{domain.Host}：{ex.Message}");
+                return default;
             }
-
-            this.logger.LogWarning($"dns({dns})无法解析{domain.Host}");
-            return default;
         }
 
-
         /// <summary>
         /// 获取最快的ip
         /// </summary>