Merge from main branch:

* address family is choosen by preferences
* ipAdress enumeration returned back to n^2 for readability
* variable renamed to isSocketSelected

Author: Evgeny Gorbovoy

src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SNI/SNITcpHandle.cs

@@ -324,36 +324,43 @@ private Socket TryConnectParallel(string hostName, int port, TimeSpan ts, bool i
         // Only write to the DNS cache when we receive IsSupported flag as true in the Feature Ext Ack from server.
         private static Socket Connect(string serverName, int port, TimeSpan timeout, bool isInfiniteTimeout, SqlConnectionIPAddressPreference ipPreference, string cachedFQDN, ref SQLDNSInfo pendingDNSInfo)
         {
-            // keeping IEnumerable to enumerate entire array only if needed
-            IEnumerable<IPAddress> ipAddresses = Dns.GetHostAddresses(serverName);
-            
-            // First, we try to connect all AddressFamily.InterNetwork
-            // and then all AddressFamily.InterNetworkV6.
-            // Keeping address families inlined in entire method because parameter pendingDNSInfo is bound on them.
-            ipAddresses = ipAddresses
-                .Where (address => address.AddressFamily==AddressFamily.InterNetwork)
-                .Concat(ipAddresses.Where(address => address.AddressFamily==AddressFamily.InterNetworkV6));
+            SqlClientEventSource.Log.TrySNITraceEvent(s_className, EventType.INFO, "IP preference : {0}", Enum.GetName(typeof(SqlConnectionIPAddressPreference), ipPreference));
 
             Stopwatch timeTaken = Stopwatch.StartNew();
 
+            IEnumerable<IPAddress> ipAddresses = Dns.GetHostAddresses(serverName).Where(address =>
+                address.AddressFamily is AddressFamily.InterNetwork or AddressFamily.InterNetworkV6);
+
+            ipAddresses = ipPreference switch
+            {
+                SqlConnectionIPAddressPreference.IPv4First => ipAddresses.OrderByDescending(address =>
+                    address.AddressFamily == AddressFamily.InterNetwork),
+                SqlConnectionIPAddressPreference.IPv6First => ipAddresses.OrderByDescending(address =>
+                    address.AddressFamily == AddressFamily.InterNetworkV6),
+                SqlConnectionIPAddressPreference.UsePlatformDefault => ipAddresses,
+                _ => throw new ArgumentOutOfRangeException(nameof(ipPreference), ipPreference, null)
+            };
+
             foreach (IPAddress ipAddress in ipAddresses)
             {
                 var socket =
-                    new Socket(ipAddress.AddressFamily, SocketType.Stream, ProtocolType.Tcp) {Blocking = false};
+                    new Socket(ipAddress.AddressFamily, SocketType.Stream, ProtocolType.Tcp) { Blocking = false };
 
-                bool thisSocketSelected = false;
+                bool isSocketSelected = false;
 
                 // enable keep-alive on socket
                 SetKeepAliveValues(ref socket);
 
                 SqlClientEventSource.Log.TrySNITraceEvent(s_className, EventType.INFO,
-                    "Connecting to IP address {0} and port {1}", ipAddress, port);
+                    "Connecting to IP address {0} and port {1} using {2} address family.", ipAddress,
+                    port, ipAddress.AddressFamily);
 
                 try
                 {
                     socket.Connect(ipAddress, port);
                     throw new InternalException(
-                        $"Call to {nameof(Socket.Connect)} must throw {nameof(SocketException)} with {SocketError.WouldBlock.ToString()} error code");
+                        $"Call to {nameof(Socket.Connect)} must throw {nameof(SocketException)} " +
+                        $"with {SocketError.WouldBlock.ToString()} error code");
                 }
                 catch (SocketException socketException) when (socketException.SocketErrorCode ==
                                                               SocketError.WouldBlock)
@@ -374,7 +381,7 @@ private static Socket Connect(string serverName, int port, TimeSpan timeout, boo
 
                     if (socket.Connected)
                     {
-                        thisSocketSelected = true;
+                        isSocketSelected = true;
                         socket.Blocking = true;
                         string iPv4String = null;
                         string iPv6String = null;
@@ -388,7 +395,7 @@ private static Socket Connect(string serverName, int port, TimeSpan timeout, boo
                 }
                 finally
                 {
-                    if (!thisSocketSelected)
+                    if (!isSocketSelected)
                         socket.Dispose();
                 }
             }