Fix | SqlClient-826 Missed synchronization

src/Microsoft.Data.SqlClient/netcore/src/Common/src/System/Net/InternalException.cs

@@ -2,13 +2,24 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Runtime.Serialization;
+
 namespace System.Net
 {
+    [Serializable]
     internal class InternalException : Exception
     {
-        internal InternalException()
+        public InternalException() : this("InternalException thrown.")
+        {
+        }
+
+        public InternalException(string message) : this(message, null)
+        {
+        }
+
+        public InternalException(string message, Exception innerException) : base(message, innerException)
         {
-            NetEventSource.Fail(this, "InternalException thrown.");
+            NetEventSource.Fail(this, message);
         }
     }
 }

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

@@ -5,7 +5,9 @@
 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
+using System.Diagnostics;
 using System.IO;
+using System.Linq;
 using System.Net;
 using System.Net.Security;
 using System.Net.Sockets;
@@ -322,112 +324,76 @@ 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, string cachedFQDN, ref SQLDNSInfo pendingDNSInfo)
         {
-            IPAddress[] ipAddresses = Dns.GetHostAddresses(serverName);
+            // 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));
 
-            string IPv4String = null;
-            string IPv6String = null;
+            Stopwatch timeTaken = Stopwatch.StartNew();
 
-            Socket[] sockets = new Socket[2];
-            AddressFamily[] preferedIPFamilies = new AddressFamily[] { AddressFamily.InterNetwork, AddressFamily.InterNetworkV6 };
+            foreach (IPAddress ipAddress in ipAddresses)
+            {
+                var socket =
+                    new Socket(ipAddress.AddressFamily, SocketType.Stream, ProtocolType.Tcp) {Blocking = false};
 
-            CancellationTokenSource cts = null;
+                bool thisSocketSelected = false;
 
-            void Cancel()
-            {
-                for (int i = 0; i < sockets.Length; ++i)
-                {
-                    try
-                    {
-                        if (sockets[i] != null && !sockets[i].Connected)
-                        {
-                            sockets[i].Dispose();
-                            sockets[i] = null;
-                        }
-                    }
-                    catch (Exception e)
-                    {
-                        SqlClientEventSource.Log.TrySNITraceEvent(s_className, EventType.ERR, "THIS EXCEPTION IS BEING SWALLOWED: {0}", args0: e?.Message);
-                    }
-                }
-            }
+                // enable keep-alive on socket
+                SetKeepAliveValues(ref socket);
 
-            if (!isInfiniteTimeout)
-            {
-                cts = new CancellationTokenSource(timeout);
-                cts.Token.Register(Cancel);
-            }
+                SqlClientEventSource.Log.TrySNITraceEvent(s_className, EventType.INFO,
+                    "Connecting to IP address {0} and port {1}", ipAddress, port);
 
-            Socket availableSocket = null;
-            try
-            {
-                // We go through the IP list twice.
-                // In the first traversal, we only try to connect with the preferedIPFamilies[0].
-                // In the second traversal, we only try to connect with the preferedIPFamilies[1].
-                for (int i = 0; i < preferedIPFamilies.Length; ++i)
+                try
                 {
-                    foreach (IPAddress ipAddress in ipAddresses)
-                    {
-                        try
-                        {
-                            if (ipAddress != null && ipAddress.AddressFamily == preferedIPFamilies[i])
-                            {
-                                sockets[i] = new Socket(ipAddress.AddressFamily, SocketType.Stream, ProtocolType.Tcp);
+                    socket.Connect(ipAddress, port);
+                    throw new InternalException(
+                        $"Call to {nameof(Socket.Connect)} must throw {nameof(SocketException)} with {SocketError.WouldBlock.ToString()} error code");
+                }
+                catch (SocketException socketException) when (socketException.SocketErrorCode ==
+                                                              SocketError.WouldBlock)
+                {
+                    // https://github.com/dotnet/SqlClient/issues/826#issuecomment-736224118
 
-                                // enable keep-alive on socket
-                                SetKeepAliveValues(ref sockets[i]);
+                    var timeLeft = timeout - timeTaken.Elapsed;
 
-                                SqlClientEventSource.Log.TrySNITraceEvent(s_className, EventType.INFO, "Connecting to IP address {0} and port {1}", args0: ipAddress, args1: port);
-                                sockets[i].Connect(ipAddress, port);
-                                if (sockets[i] != null) // sockets[i] can be null if cancel callback is executed during connect()
-                                {
-                                    if (sockets[i].Connected)
-                                    {
-                                        availableSocket = sockets[i];
-
-                                        if (ipAddress.AddressFamily == AddressFamily.InterNetwork)
-                                        {
-                                            IPv4String = ipAddress.ToString();
-                                        }
-                                        else if (ipAddress.AddressFamily == AddressFamily.InterNetworkV6)
-                                        {
-                                            IPv6String = ipAddress.ToString();
-                                        }
-
-                                        break;
-                                    }
-                                    else
-                                    {
-                                        sockets[i].Dispose();
-                                        sockets[i] = null;
-                                    }
-                                }
-                            }
-                        }
-                        catch (Exception e)
-                        {
-                            SqlClientEventSource.Log.TrySNITraceEvent(s_className, EventType.ERR, "THIS EXCEPTION IS BEING SWALLOWED: {0}", args0: e?.Message);
-                        }
+                    if (timeLeft <= TimeSpan.Zero && !isInfiniteTimeout)
+                        return null;
+                    try
+                    {
+                        int connectionTimeout = isInfiniteTimeout? -1 : checked((int)(timeLeft.TotalMilliseconds * 1000));
+                        Socket.Select(null, new List<Socket> {socket}, null,
+                            connectionTimeout);
                     }
+                    catch (SocketException) { }
 
-                    // If we have already got an valid Socket, we won't do the second traversal.
-                    if (availableSocket != null) 
+                    if (socket.Connected)
                     {
-                        break;
-                    }                    
+                        thisSocketSelected = true;
+                        socket.Blocking = true;
+                        string iPv4String = null;
+                        string iPv6String = null;
+                        string ipAddressString = ipAddress.ToString();
+                        if (socket.AddressFamily == AddressFamily.InterNetwork)
+                            iPv4String = ipAddressString;
+                        else iPv6String = ipAddressString;
+                        pendingDNSInfo = new SQLDNSInfo(cachedFQDN, iPv4String, iPv6String, port.ToString());
+                        return socket;
+                    }
+                }
+                finally
+                {
+                    if (!thisSocketSelected)
+                        socket.Dispose();
                 }
-            }
-            finally
-            {
-                cts?.Dispose();
-            }
-
-            // we only record the ip we can connect with successfully.
-            if (IPv4String != null || IPv6String != null)
-            {
-                pendingDNSInfo = new SQLDNSInfo(cachedFQDN, IPv4String, IPv6String, port.ToString());
             }
 
-            return availableSocket;
+            return null;
         }
 
         private static Task<Socket> ParallelConnectAsync(IPAddress[] serverAddresses, int port)