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diff --git a/src/swap.hpp b/src/swap.hpp
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+/*
+    Copyright (c) 2007-2010 iMatix Corporation
+
+    This file is part of 0MQ.
+
+    0MQ is free software; you can redistribute it and/or modify it under
+    the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation; either version 3 of the License, or
+    (at your option) any later version.
+
+    0MQ 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 Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef __ZMQ_SWAP_HPP_INCLUDED__
+#define __ZMQ_SWAP_HPP_INCLUDED__
+
+#include "../include/zmq.h"
+
+#include <string>
+#include "stdint.hpp"
+
+namespace zmq
+{
+
+    //  This class implements a message swap. Messages are retrieved from
+    //  the swap in the same order as they entered it.
+
+    class swap_t
+    {
+    public:
+
+        enum { default_block_size = 8192 };
+
+        //  Creates the swap.
+        swap_t (int64_t filesize_);
+
+        ~swap_t ();
+
+        int init ();
+
+        //  Stores the message into the swap. The function
+        //  returns false if the swap is full; true otherwise.
+        bool store (zmq_msg_t *msg_);
+
+        //  Fetches the oldest message from the swap. It is an error
+        //  to call this function when the swap is empty.
+        void fetch (zmq_msg_t *msg_);
+
+        void commit ();
+
+        void rollback ();
+
+        //  Returns true if the swap is empty; false otherwise.
+        bool empty ();
+
+        //  Returns true if and only if the swap is full.
+        bool full ();
+
+    private:
+
+        //  Copies data from a memory buffer to the backing file.
+        //  Wraps around when reaching maximum file size.
+        void copy_from_file (void *buffer_, size_t count_);
+
+        //  Copies data from the backing file to the memory buffer.
+        //  Wraps around when reaching end-of-file.
+        void copy_to_file (const void *buffer_, size_t count_);
+
+        //  Returns the buffer space available.
+        int64_t buffer_space ();
+
+        void fill_buf (char *buf, int64_t pos);
+
+        void save_write_buf ();
+
+        //  File descriptor to the backing file.
+        int fd;
+
+        //  Name of the backing file.
+        std::string filename;
+
+        //  Maximum size of the backing file.
+        int64_t filesize;
+
+        //  File offset associated with the fd file descriptor.
+        int64_t file_pos;
+
+        //  File offset the next message will be stored at.
+        int64_t write_pos;
+
+        //  File offset the next message will be read from.
+        int64_t read_pos;
+
+        int64_t commit_pos;
+
+        size_t block_size;
+
+        char *buf1;
+        char *buf2;
+        char *read_buf;
+        char *write_buf;
+
+        int64_t write_buf_start_addr;
+    };
+
+}
+
+#endif