SMBServer: TCP KeepAlive is now used to detect dead clients

SMBLibrary/Server/SMBServer.cs

@@ -112,6 +112,8 @@ namespace SMBLibrary.Server
                 return;
             }
 
+            // Windows will set the TCP keepalive timeout to 120 seconds for an SMB connection
+            SocketUtils.SetKeepAlive(clientSocket, TimeSpan.FromMinutes(2));
             ConnectionState state = new ConnectionState(Log);
             // Disable the Nagle Algorithm for this tcp socket:
             clientSocket.NoDelay = true;

SMBLibrary/Utilities/SocketUtils.cs

@@ -8,6 +8,25 @@ namespace Utilities
 {
     public class SocketUtils
     {
+        public static void SetKeepAlive(Socket socket, TimeSpan timeout)
+        {
+            // The default settings when a TCP socket is initialized sets the keep-alive timeout to 2 hours and the keep-alive interval to 1 second.
+            SetKeepAlive(socket, true, timeout, TimeSpan.FromSeconds(1));
+        }
+
+        /// <param name="timeout">the timeout, in milliseconds, with no activity until the first keep-alive packet is sent</param>
+        /// <param name="interval">the interval, in milliseconds, between when successive keep-alive packets are sent if no acknowledgement is received</param>
+        public static void SetKeepAlive(Socket socket, bool enable, TimeSpan timeout, TimeSpan interval)
+        {
+            socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.KeepAlive, true);
+            // https://msdn.microsoft.com/en-us/library/dd877220.aspx
+            byte[] tcp_keepalive = new byte[12];
+            LittleEndianWriter.WriteUInt32(tcp_keepalive, 0, Convert.ToUInt32(enable));
+            LittleEndianWriter.WriteUInt32(tcp_keepalive, 4, (uint)timeout.TotalMilliseconds);
+            LittleEndianWriter.WriteUInt32(tcp_keepalive, 8, (uint)interval.TotalMilliseconds);
+            socket.IOControl(IOControlCode.KeepAliveValues, tcp_keepalive, null);
+        }
+
         /// <summary>
         /// Socket will be forcefully closed, all pending data will be ignored, and socket will be deallocated.
         /// </summary>