[release/5.0] Support Async DNS lookup on older Windows from impersonificated conte…

src/libraries/Common/src/Interop/Windows/WinSock/Interop.GetAddrInfoExW.cs

@@ -11,6 +11,8 @@ internal static partial class Interop
 {
     internal static partial class Winsock
     {
+        internal const int WSA_E_CANCELLED = 10111;
+
         internal const string GetAddrInfoExCancelFunctionName = "GetAddrInfoExCancel";
 
         internal const int NS_ALL = 0;

src/libraries/System.Net.NameResolution/src/System/Net/NameResolutionPal.Windows.cs

@@ -166,14 +166,13 @@ public static unsafe string GetHostName()
             SocketError errorCode = (SocketError)Interop.Winsock.GetAddrInfoExW(
                 hostName, null, Interop.Winsock.NS_ALL, IntPtr.Zero, &hints, &context->Result, IntPtr.Zero, &context->Overlapped, s_getAddrInfoExCallback, &context->CancelHandle);
 
-
-            if (errorCode == SocketError.TryAgain)
+            if (errorCode == SocketError.TryAgain || (int)errorCode == Interop.Winsock.WSA_E_CANCELLED)
             {
                 // WSATRY_AGAIN indicates possible problem with reachability according to docs.
                 // However, if servers are really unreachable, we would still get IOPending here
                 // and final result would be posted via overlapped IO.
                 // synchronous failure here may signal issue when GetAddrInfoExW does not work from
-                // impersonated context.
+                // impersonated context. Windows 8 and Server 2012 fail for same reason with different errorCode.
                 GetAddrInfoExContext.FreeContext(context);
                 return null;
             }

src/libraries/System.Security.Principal.Windows/tests/WindowsIdentityImpersonatedTests.netcoreapp.cs

@@ -3,6 +3,8 @@
 
 using System;
 using System.ComponentModel;
+using System.Linq;
+using System.Net;
 using System.Runtime.InteropServices;
 using System.Security.Cryptography;
 using System.Security.Principal;
@@ -57,6 +59,42 @@ void Asserts(WindowsIdentity currentWindowsIdentity)
             Assert.NotEqual(currentWindowsIdentity.Name, WindowsIdentity.GetCurrent().Name);
         }
     }
+
+    [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotWindowsNanoServer))]
+    [OuterLoop]
+    public void RunImpersonated_NameResolution()
+    {
+        WindowsIdentity currentWindowsIdentity = WindowsIdentity.GetCurrent();
+
+        WindowsIdentity.RunImpersonated(_fixture.TestAccount.AccountTokenHandle, () =>
+        {
+            Assert.Equal(_fixture.TestAccount.AccountName, WindowsIdentity.GetCurrent().Name);
+
+            IPAddress[] a1 = Dns.GetHostAddressesAsync("").GetAwaiter().GetResult();
+            IPAddress[] a2 = Dns.GetHostAddresses("");
+
+            Assert.True(a1.Length > 0);
+            Assert.True(a1.SequenceEqual(a2));
+        });
+    }
+
+    [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotWindowsNanoServer))]
+    [OuterLoop]
+    public async Task RunImpersonatedAsync_NameResolution()
+    {
+        WindowsIdentity currentWindowsIdentity = WindowsIdentity.GetCurrent();
+
+        await WindowsIdentity.RunImpersonatedAsync(_fixture.TestAccount.AccountTokenHandle, async () =>
+        {
+            Assert.Equal(_fixture.TestAccount.AccountName, WindowsIdentity.GetCurrent().Name);
+
+            IPAddress[] a1 = await Dns.GetHostAddressesAsync("");
+            IPAddress[] a2 = Dns.GetHostAddresses("");
+
+            Assert.True(a1.Length > 0);
+            Assert.True(a1.SequenceEqual(a2));
+        });
+    }
 }
 
 public class WindowsIdentityFixture : IDisposable