model: PacketHeader<T> and interface with NS-3

This commit creates a compatible interface to convert ndn-cxx Interest
and Data structures into NS-3's Ptr<Packet> and back.

Refs: #2048, #2230
diff --git a/model/ndn-header.hpp b/model/ndn-header.hpp
new file mode 100644
index 0000000..86395d2
--- /dev/null
+++ b/model/ndn-header.hpp
@@ -0,0 +1,65 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2011-2014  Regents of the University of California.
+ *
+ * This file is part of ndnSIM. See AUTHORS for complete list of ndnSIM authors and
+ * contributors.
+ *
+ * ndnSIM is free software: you can redistribute it and/or modify it under the terms
+ * of the GNU General Public License as published by the Free Software Foundation,
+ * either version 3 of the License, or (at your option) any later version.
+ *
+ * ndnSIM is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
+ * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+ * PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * ndnSIM, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
+ **/
+
+#ifndef NDNSIM_NDN_HEADER_HPP
+#define NDNSIM_NDN_HEADER_HPP
+
+#include "ns3/header.h"
+
+#include "ndn-common.hpp"
+
+namespace ns3 {
+namespace ndn {
+
+template<class Pkt>
+class PacketHeader : public Header {
+public:
+  static ns3::TypeId
+  GetTypeId();
+
+  virtual TypeId
+  GetInstanceTypeId(void) const;
+
+  PacketHeader();
+
+  PacketHeader(const Pkt& packet);
+
+  virtual uint32_t
+  GetSerializedSize(void) const;
+
+  virtual void
+  Serialize(ns3::Buffer::Iterator start) const;
+
+  virtual uint32_t
+  Deserialize(ns3::Buffer::Iterator start);
+
+  virtual void
+  Print(std::ostream& os) const;
+
+  shared_ptr<const Pkt>
+  getPacket();
+
+private:
+  shared_ptr<const Pkt> m_packet;
+};
+
+} // namespace ndn
+} // namespace ns3
+
+#endif // NDNSIM_NDN_HEADER_HPP