diff --git a/nsync/src/sync-state.h b/nsync/src/sync-state.h
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+/* -*- Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil -*- */
+/*
+ * Copyright (c) 2012 University of California, Los Angeles
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * This program 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 this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ * Author: Zhenkai Zhu <zhenkai@cs.ucla.edu>
+ *         Chaoyi Bian <bcy@pku.edu.cn>
+ *	   Alexander Afanasyev <alexander.afanasyev@ucla.edu>
+ */
+
+#ifndef SYNC_STATE_H
+#define SYNC_STATE_H
+
+#include "sync-state-leaf-container.h"
+#include <boost/exception/all.hpp>
+#include "boost/tuple/tuple.hpp"
+#include "sync-state.pb.h"
+
+/**
+ * \defgroup sync SYNC protocol
+ *
+ * Implementation of SYNC protocol
+ */
+namespace Sync {
+
+/**
+ * \ingroup sync
+ * @brief this prefix will be used for the dummy node which increases its sequence number whenever
+ * a remove operation happens; this is to prevent the reversion of root digest when we prune 
+ * a branch, i.e. help the root digest to be forward only
+ * No corresponding data msg would be published and no attempt would be made to retrieve the 
+ * data msg
+ */
+const std::string forwarderPrefix = "/d0n0t18ak/t0ps8cr8t";
+
+class State;
+typedef boost::shared_ptr<State> StatePtr;
+typedef boost::shared_ptr<State> StateConstPtr;
+
+/**
+ * \ingroup sync
+ * @brief Container for state leaves and definition of the abstract interface to work with State objects
+ */
+class State
+{
+public:
+  virtual ~State () { };
+  
+  /**
+   * @brief Add or update leaf to the state tree
+   *
+   * @param info name of the leaf
+   * @param seq  sequence number of the leaf
+   */
+  virtual boost::tuple<bool/*inserted*/, bool/*updated*/, SeqNo/*oldSeqNo*/>
+  update (NameInfoConstPtr info, const SeqNo &seq) = 0;
+
+  /**
+   * @brief Remove leaf from the state tree
+   * @param info name of the leaf
+   */
+  virtual bool
+  remove (NameInfoConstPtr info) = 0;
+
+  /**
+   * @brief Get state leaves
+   */
+  const LeafContainer &
+  getLeaves () const 
+  { return m_leaves; }
+  
+protected:
+  LeafContainer m_leaves;
+};
+
+
+/**
+ * @brief Formats a protobuf SyncStateMsg msg
+ * @param oss output SyncStateMsg msg
+ * @param state state
+ * @returns output SyncStateMsg msg
+ */
+SyncStateMsg &
+operator << (SyncStateMsg &ossm, const State &state);
+
+
+/**
+ * @brief Parse a protobuf SyncStateMsg msg
+ * @param iss input SyncStateMsg msg
+ * @param state state
+ * @returns SyncStateMsg msg
+ */
+SyncStateMsg &
+operator >> (SyncStateMsg &issm, State &state);
+
+namespace Error {
+/**
+ * @brief Will be thrown when data cannot be properly decoded to SyncStateMsg
+ */
+struct SyncStateMsgDecodingFailure : virtual boost::exception, virtual std::exception { };
+}
+
+} // Sync
+
+#endif // SYNC_STATE_H