/*
  *  OpenVPN -- An application to securely tunnel IP networks
  *             over a single TCP/UDP port, with support for SSL/TLS-based
  *             session authentication and key exchange,
  *             packet encryption, packet authentication, and
  *             packet compression.
  *

  *  Copyright (C) 2010-2018 Fox Crypto B.V. <openvpn@fox-it.com>

  *
  *
  *  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.,
  *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

  */
 
 /**
  * @file Data Channel Compression module documentation file.
  */
 
 /**
  * @defgroup compression Data Channel Compression module
  *
  * This module offers compression of data channel packets.
  *
  * @par State structures
  * The Data Channel Compression module stores its internal state in a \c
  * lzo_compress_workspace structure.  This state includes flags which
  * control the module's behavior and preallocated working memory.  One
  * such structure is present for each VPN tunnel, and is stored in the \c
  * context.c2.lzo_compwork of the \c context associated with that VPN
  * tunnel.
  *
  * @par Initialization and cleanup
  * Every time a new \c lzo_compress_workspace is needed, it must be
  * initialized using the \c lzo_compress_init() function.  Similarly,
  * every time a \c lzo_compress_workspace is no longer needed, it must be
  * cleaned up using the \c lzo_compress_uninit() function.  These
  * functions take care of the allocation and freeing of internal working
  * memory, but not of the \c lzo_compress_workspace structures themselves.
  *
  * @par
  * Because of the one-to-one relationship between \c
  * lzo_compress_workspace structures and VPN tunnels, the above-mentioned
  * initialization and cleanup functions are called directly from the \c
  * init_instance() and \c close_instance() functions, which control the
  * initialization and cleanup of VPN tunnel instances and their associated
  * \c context structures.
  *
  * @par Packet processing functions
  * This module receives data channel packets from the \link data_control
  * Data Channel Control module\endlink and processes them according to the
  * settings of the packet's VPN tunnel.  The \link data_control Data
  * Channel Control module\endlink uses the following interface functions:
  * - For packets which will be sent to a remote OpenVPN peer: \c
  *   lzo_compress()
  * - For packets which have been received from a remote OpenVPN peer: \c
  *   lzo_decompress()
  *
  * @par Settings that control this module's activity
  * Whether or not the Data Channel Compression module is active depends on

  * the compile-time \c ENABLE_LZO preprocessor macro and the runtime flags

  * stored in \c lzo_compress_workspace.flags of the associated VPN tunnel.
  * The latter are initialized from \c options.lzo, which gets its value
  * from the process's configuration sources, such as its configuration
  * file or command line %options.
  *
  * @par Adaptive compression
  * The compression module supports adaptive compression.  If this feature
  * is enabled, the compression routines monitor their own performance and
  * turn compression on or off depending on whether it is leading to
  * significantly reduced payload size.
  *
  * @par Compression algorithms
  * This module uses the Lempel-Ziv-Oberhumer (LZO) compression algorithms.
  * These offer lossless compression and are designed for high-performance
  * decompression.  This module uses the external \c lzo library's
  * implementation of the algorithms.
  *
  * @par
  * For more information on the LZO library, see:\n
  * http://www.oberhumer.com/opensource/lzo/
  */