optimized the speed of DNS resolution during streaming downloads.

Signed-off-by: OsakaRuma <[email protected]>

src/Starward.Core.ZipStreamDownload/Http/HttpPartialDnsResolve.cs

@@ -0,0 +1,115 @@
+using System.Collections.Concurrent;
+using System.Net;
+using System.Net.Sockets;
+
+namespace Starward.Core.ZipStreamDownload.Http;
+
+/// <summary>
+/// DNS解析、IP地址测试和缓存
+/// <remarks>
+/// 此类的作用是保证多个<see cref="HttpPartialDownloadStreamUri"/>实例共享一个缓存池。
+/// </remarks>
+/// </summary>
+public class HttpPartialDnsResolve
+{
+    /// <summary>
+    /// DNS缓存（主机名与IP地址列表的线程安全字典）
+    /// </summary>
+    private readonly ConcurrentDictionary<string, Lazy<Task<IPAddress[]>>> _hostIpAddresses = new();
+
+    /// <summary>
+    /// 获取可用的IP地址列表（TCP连接测试，异步）
+    /// </summary>
+    /// <param name="host">主机名</param>
+    /// <param name="port">用于测试的TCP端口号</param>
+    /// <returns>一个任务，可用获取可用的IP地址列表</returns>
+    public Task<IPAddress[]> GetIpAddressesAsync(string host, int port)
+    {
+        ArgumentOutOfRangeException.ThrowIfNegativeOrZero(port);
+        ArgumentOutOfRangeException.ThrowIfGreaterThan(port, 0xffff);
+        var iPAddress =
+            _hostIpAddresses.GetOrAdd(host, h => new Lazy<Task<IPAddress[]>>(() => GetIpAddressAsyncCore(h, port)));
+        return iPAddress.Value;
+    }
+
+    /// <summary>
+    /// 获取可用的IP地址列表（TCP连接测试）
+    /// </summary>
+    /// <param name="host">主机名</param>
+    /// <param name="port">用于测试的TCP端口号</param>
+    /// <returns>可用的IP地址列表</returns>
+    public IPAddress[] GetIpAddresses(string host, int port)
+    {
+        ArgumentOutOfRangeException.ThrowIfNegativeOrZero(port);
+        ArgumentOutOfRangeException.ThrowIfGreaterThan(port, 0xffff);
+        var iPAddress =
+            _hostIpAddresses.GetOrAdd(host, h => new Lazy<Task<IPAddress[]>>(() => GetIpAddressAsyncCore(h, port)));
+        return iPAddress.Value.GetAwaiter().GetResult();
+    }
+
+    /// <summary>
+    /// 获取可用的IP地址列表（内部，无缓存）
+    /// </summary>
+    /// <param name="host">主机名</param>
+    /// <param name="port">>用于测试的TCP端口号</param>
+    /// <returns>可用的IP地址列表</returns>
+    private static async Task<IPAddress[]> GetIpAddressAsyncCore(string host, int port)
+    {
+        Exception? lastException = null;
+        List<IPAddress>? addresses = null;
+        try
+        {
+            addresses = ConfuseEnumerable(
+                await Dns.GetHostAddressesAsync(host, AddressFamily.InterNetworkV6)
+                    .ConfigureAwait(false));
+        }
+        catch (SocketException e) when (e.SocketErrorCode == SocketError.NoData)
+        {
+        }
+        if (addresses != null) return (await TestAddressesAsync(addresses).ConfigureAwait(false)).ToArray();
+        try
+        {
+            addresses = ConfuseEnumerable(
+                await Dns.GetHostAddressesAsync(host, AddressFamily.InterNetwork)
+                    .ConfigureAwait(false));
+        }
+        catch (SocketException e) when (e.SocketErrorCode == SocketError.NoData)
+        {
+        }
+        if (addresses != null) return (await TestAddressesAsync(addresses).ConfigureAwait(false)).ToArray();
+        throw lastException ?? new SocketException((int)SocketError.HostNotFound);
+
+        async Task<List<IPAddress>> TestAddressesAsync(List<IPAddress> testAddresses)
+        {
+            var result = new List<IPAddress>();
+            foreach (var address in testAddresses)
+            {
+                try
+                {
+                    using var client = new TcpClient();
+                    var endPoint = new IPEndPoint(address, port);
+                    await client.ConnectAsync(endPoint).ConfigureAwait(false);
+                    result.Add(address);
+                }
+                catch (Exception ex) when (ex is not OperationCanceledException)
+                {
+                    lastException = ex;
+                }
+            }
+            if (result.Count == 0) throw lastException ?? new SocketException((int)SocketError.HostNotFound);
+            return result;
+        }
+    }
+
+    /// <summary>
+    /// 对一个迭代器对象进行随机排序
+    /// </summary>
+    /// <param name="enumerable">一个迭代器的实例</param>
+    /// <typeparam name="T">迭代器的类型</typeparam>
+    /// <returns>一个已经打乱顺序的列表。</returns>
+    private static List<T> ConfuseEnumerable<T>(IEnumerable<T> enumerable)
+    {
+        var random = new Random();
+        return enumerable.OrderBy(_ => random.Next()).ToList();
+    }
+}