101 lines
3.7 KiB
C
101 lines
3.7 KiB
C
/**
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* @file fragmentproto.h
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* @author Ambroz Bizjak <ambrop7@gmail.com>
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*
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* @section LICENSE
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the author nor the
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* names of its contributors may be used to endorse or promote products
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* derived from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
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* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* @section DESCRIPTION
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*
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* Definitions for FragmentProto, a protocol that allows sending of arbitrarily sized packets over
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* a link with a fixed MTU.
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*
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* All multi-byte integers in structs are little-endian, unless stated otherwise.
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*
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* A FragmentProto packet consists of a number of chunks.
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* Each chunk consists of:
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* - the chunk header (struct {@link fragmentproto_chunk_header})
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* - the chunk payload, i.e. part of the frame specified in the header
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*/
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#ifndef BADVPN_PROTOCOL_FRAGMENTPROTO_H
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#define BADVPN_PROTOCOL_FRAGMENTPROTO_H
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#include <stdint.h>
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#include <misc/balign.h>
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#include <misc/packed.h>
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typedef uint16_t fragmentproto_frameid;
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/**
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* FragmentProto chunk header.
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*/
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B_START_PACKED
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struct fragmentproto_chunk_header {
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/**
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* Identifier of the frame this chunk belongs to.
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* Frames should be given ascending identifiers as they are encoded
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* into chunks (except when the ID wraps to zero).
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*/
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fragmentproto_frameid frame_id;
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/**
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* Position in the frame where this chunk starts.
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*/
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uint16_t chunk_start;
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/**
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* Length of the chunk's payload.
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*/
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uint16_t chunk_len;
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/**
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* Whether this is the last chunk of the frame, i.e.
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* the total length of the frame is chunk_start + chunk_len.
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*/
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uint8_t is_last;
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} B_PACKED;
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B_END_PACKED
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/**
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* Calculates how many chunks are needed at most for encoding one frame of the
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* given maximum size with FragmentProto onto a carrier with a given MTU.
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* This includes the case when the first chunk of a frame is not the first chunk
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* in a FragmentProto packet.
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*
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* @param carrier_mtu MTU of the carrier, i.e. maximum length of FragmentProto packets. Must be >sizeof(struct fragmentproto_chunk_header).
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* @param frame_mtu maximum frame size. Must be >=0.
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* @return maximum number of chunks needed. Will be >0.
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*/
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static int fragmentproto_max_chunks_for_frame (int carrier_mtu, int frame_mtu)
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{
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ASSERT(carrier_mtu > sizeof(struct fragmentproto_chunk_header))
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ASSERT(frame_mtu >= 0)
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return (bdivide_up(frame_mtu, (carrier_mtu - sizeof(struct fragmentproto_chunk_header))) + 1);
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}
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#endif
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