From 241e06c38d240a2fc88762b1b63755193103ef3f Mon Sep 17 00:00:00 2001
From: Tal Aloni <tal.aloni.il@gmail.com>
Date: Sat, 4 Mar 2017 12:59:22 +0200
Subject: [PATCH] SMBServer: TCP KeepAlive is now used to detect dead clients

---
 SMBLibrary/Server/SMBServer.cs      |  2 ++
 SMBLibrary/Utilities/SocketUtils.cs | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/SMBLibrary/Server/SMBServer.cs b/SMBLibrary/Server/SMBServer.cs
index 525aa41..56b152b 100644
--- a/SMBLibrary/Server/SMBServer.cs
+++ b/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;
diff --git a/SMBLibrary/Utilities/SocketUtils.cs b/SMBLibrary/Utilities/SocketUtils.cs
index 3231c21..60ab8b1 100644
--- a/SMBLibrary/Utilities/SocketUtils.cs
+++ b/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>