From 9d2770100d9aa4cdd0195b374f313d9e4807dcf3 Mon Sep 17 00:00:00 2001
From: Tom Henderson <tomh@tomh.org>
Date: Sat, 6 Sep 2014 09:40:18 -0700
Subject: [PATCH] last TCP option should be END, not NOP

---
 src/internet/model/tcp-header.cc     | 18 +++++++++++++-----
 src/internet/test/tcp-header-test.cc | 19 ++++++++-----------
 2 files changed, 21 insertions(+), 16 deletions(-)

diff --git a/src/internet/model/tcp-header.cc b/src/internet/model/tcp-header.cc
index 096ad5fdf..eb73b5099 100644
--- a/src/internet/model/tcp-header.cc
+++ b/src/internet/model/tcp-header.cc
@@ -21,6 +21,7 @@
 #include <stdint.h>
 #include <iostream>
 #include "tcp-header.h"
+#include "tcp-option.h"
 #include "ns3/buffer.h"
 #include "ns3/address-utils.h"
 #include "ns3/log.h"
@@ -326,12 +327,19 @@ TcpHeader::Serialize (Buffer::Iterator start)  const
       i.Next ((*op)->GetSerializedSize ());
     }
 
-  // padding
+  // padding to word alignment; add NOPs as needed until last byte which is END
   while (optionLen % 4)
-    {
-      ++optionLen;
-      i.WriteU8 (0);
-    }
+  {
+    if ((optionLen % 4) == 3)
+      {
+        i.WriteU8 (TcpOption::END);
+      }
+    else
+      {
+        i.WriteU8 (TcpOption::NOP);
+      }
+    ++optionLen;
+  }
 
   // Make checksum
   if(m_calcChecksum)
diff --git a/src/internet/test/tcp-header-test.cc b/src/internet/test/tcp-header-test.cc
index 263446f26..d87216f5b 100644
--- a/src/internet/test/tcp-header-test.cc
+++ b/src/internet/test/tcp-header-test.cc
@@ -265,21 +265,18 @@ TcpHeaderWithRFC793OptionTestCase::OneOptionAtTime ()
                            buffer.GetSize (), "Header not correctly serialized");
 
     // Inserted only 1 byte NOP, and so implementation should pad; so
-    // the other 3 bytes should be NOP (so 4 byte NOP)
+    // the other 3 bytes should be NOP, NOP, END
     Buffer::Iterator i = buffer.Begin ();
     i.Next (20);
 
     uint8_t value = i.ReadU8 ();
-    NS_TEST_ASSERT_MSG_EQ (value, TcpOption::NOP, "NOP not present");
-    for (uint32_t j = 1; j < 4; ++j)
-      {
-        std::stringstream ss;
-        ss << j;
-
-        value = i.ReadU8 ();
-        NS_TEST_ASSERT_MSG_EQ (value, 0,
-                               "Header not padded with 0 at position " + ss.str ());
-      }
+    NS_TEST_ASSERT_MSG_EQ (value, TcpOption::NOP, "NOP not present at byte 1");
+    value = i.ReadU8 ();
+    NS_TEST_ASSERT_MSG_EQ (value, TcpOption::NOP, "NOP not present at byte 2");
+    value = i.ReadU8 ();
+    NS_TEST_ASSERT_MSG_EQ (value, TcpOption::NOP, "NOP not present at byte 3");
+    value = i.ReadU8 ();
+    NS_TEST_ASSERT_MSG_EQ (value, TcpOption::END, "END not present at byte 4");
   }
 
   {