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https://github.com/OpenVPN/openvpn.git
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74bbc71b75
Signed-off-by: Alon Bar-Lev <alon.barlev@gmail.com> Acked-by: Adriaan de Jong <dejong@fox-it.com> Acked-by: David Sommerseth <davids@redhat.com> Signed-off-by: David Sommerseth <davids@redhat.com>
93 lines
4.1 KiB
C
93 lines
4.1 KiB
C
/*
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* OpenVPN -- An application to securely tunnel IP networks
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* over a single TCP/UDP port, with support for SSL/TLS-based
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* session authentication and key exchange,
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* packet encryption, packet authentication, and
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* packet compression.
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*
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* Copyright (C) 2010 Fox Crypto B.V. <openvpn@fox-it.com>
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*
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2
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* as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program (see the file COPYING included with this
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* distribution); if not, write to the Free Software Foundation, Inc.,
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* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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/**
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* @file Data Channel Compression module documentation file.
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*/
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/**
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* @defgroup compression Data Channel Compression module
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*
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* This module offers compression of data channel packets.
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*
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* @par State structures
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* The Data Channel Compression module stores its internal state in a \c
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* lzo_compress_workspace structure. This state includes flags which
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* control the module's behavior and preallocated working memory. One
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* such structure is present for each VPN tunnel, and is stored in the \c
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* context.c2.lzo_compwork of the \c context associated with that VPN
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* tunnel.
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*
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* @par Initialization and cleanup
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* Every time a new \c lzo_compress_workspace is needed, it must be
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* initialized using the \c lzo_compress_init() function. Similarly,
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* every time a \c lzo_compress_workspace is no longer needed, it must be
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* cleaned up using the \c lzo_compress_uninit() function. These
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* functions take care of the allocation and freeing of internal working
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* memory, but not of the \c lzo_compress_workspace structures themselves.
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*
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* @par
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* Because of the one-to-one relationship between \c
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* lzo_compress_workspace structures and VPN tunnels, the above-mentioned
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* initialization and cleanup functions are called directly from the \c
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* init_instance() and \c close_instance() functions, which control the
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* initialization and cleanup of VPN tunnel instances and their associated
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* \c context structures.
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*
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* @par Packet processing functions
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* This module receives data channel packets from the \link data_control
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* Data Channel Control module\endlink and processes them according to the
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* settings of the packet's VPN tunnel. The \link data_control Data
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* Channel Control module\endlink uses the following interface functions:
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* - For packets which will be sent to a remote OpenVPN peer: \c
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* lzo_compress()
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* - For packets which have been received from a remote OpenVPN peer: \c
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* lzo_decompress()
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*
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* @par Settings that control this module's activity
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* Whether or not the Data Channel Compression module is active depends on
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* the compile-time \c ENABLE_LZO preprocessor macro and the runtime flags
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* stored in \c lzo_compress_workspace.flags of the associated VPN tunnel.
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* The latter are initialized from \c options.lzo, which gets its value
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* from the process's configuration sources, such as its configuration
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* file or command line %options.
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*
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* @par Adaptive compression
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* The compression module supports adaptive compression. If this feature
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* is enabled, the compression routines monitor their own performance and
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* turn compression on or off depending on whether it is leading to
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* significantly reduced payload size.
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*
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* @par Compression algorithms
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* This module uses the Lempel-Ziv-Oberhumer (LZO) compression algorithms.
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* These offer lossless compression and are designed for high-performance
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* decompression. This module uses the external \c lzo library's
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* implementation of the algorithms.
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*
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* @par
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* For more information on the LZO library, see:\n
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* http://www.oberhumer.com/opensource/lzo/
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*/
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