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+/*
+ *  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 Fragmentation module documentation file.
+ */
+
+/**
+ * @defgroup fragmentation Data Channel Fragmentation module
+ *
+ * The Data Channel Fragmentation module offers fragmentation of data
+ * channel packets.
+ *
+ * @par State structures
+ * The Data Channel Fragmentation module stores its internal state in a \c
+ * fragment_master structure.  One such structure is present for each VPN
+ * tunnel, and is stored in \c context.c2.fragment of the \c context
+ * associated with that VPN tunnel.
+ *
+ * @par
+ * The \c fragment_master structure contains one \c fragment_list
+ * structure \c fragment_master.incoming.  This is a list of \c fragment
+ * structures, each of which can store the parts of one fragmented packet
+ * while it is being reassembled.  The \c fragment_master structure also
+ * contains one \c buffer called \c fragment_master.outgoing, in which a
+ * data channel large packet to be sent to a remote OpenVPN peer can be
+ * broken up into parts to be sent one by one.
+ *
+ * @par Initialization and cleanup
+ * Every time a new \c fragment_master is needed, it must be allocated and
+ * initialized by the \c fragment_init() function.  Similarly, every time
+ * a \c fragment_master is no longer needed, it must be cleaned up using
+ * the \c fragment_free() function.  These functions take care of the
+ * allocation and freeing of the \c fragment_master structure itself and
+ * all internal memory required for the use of that structure.  Note that
+ * this behavior is different from that displayed by the \link compression
+ * Data Channel Compression module\endlink.
+ *
+ * @par
+ * Because of the one-to-one relationship between \c fragment_master
+ * 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
+ *   fragment_outgoing() \n This function inspects data channel packets as
+ *   they are being made ready to be sent as VPN tunnel packets to a
+ *   remote OpenVPN peer.  If a packet's size is larger than its
+ *   destination VPN tunnel's maximum transmission unit (MTU), then this
+ *   module breaks that packet up into smaller parts, each of which is
+ *   smaller than or equal to the VPN tunnel's MTU.  See \c
+ *   fragment_outgoing() for details.
+ * - For packets which have been received from a remote OpenVPN peer: \c
+ *   fragment_incoming() \n This function inspects data channel packets
+ *   that have been received from a remote OpenVPN peer through a VPN
+ *   tunnel.  It reads the fragmentation header of the packet, and
+ *   depending on its value performs the appropriate action.  See \c
+ *   fragment_incoming() for details.
+ *
+ * @par Settings that control this module's activity
+ * Whether the Data Channel Fragmentation module is active or not depends
+ * on the compile-time \c ENABLE_FRAGMENT preprocessor macro and the
+ * runtime flag \c options.fragment, which gets its value from the
+ * process's configuration sources, such as the configuration file and
+ * commandline %options.
+ */