/*      $NetBSD: slcompress.h,v 1.20 2020/03/05 07:46:36 riastradh Exp $        */
/*      Id: slcompress.h,v 1.4 1994/09/21 06:50:08 paulus Exp   */

/*
* Copyright (c) 1989, 1993
*      The Regents of the University of California.  All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
*    notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
*    notice, this list of conditions and the following disclaimer in the
*    documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
*    may be used to endorse or promote products derived from this software
*    without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
*      @(#)slcompress.h        8.1 (Berkeley) 6/10/93
*/

/*
* Definitions for tcp compression routines.
*
* Van Jacobson ([email protected]), Dec 31, 1989:
*      - Initial distribution.
*/

#ifndef _NET_SLCOMPRESS_H_
#define _NET_SLCOMPRESS_H_

#ifdef _KERNEL_OPT
#include "opt_inet.h"
#endif

#define MAX_STATES 16           /* must be > 2 and < 256 */
#define MAX_HDR MLEN            /* XXX 4bsd-ism: should really be 128 */

/*
* Compressed packet format:
*
* The first octet contains the packet type (top 3 bits), TCP
* 'push' bit, and flags that indicate which of the 4 TCP sequence
* numbers have changed (bottom 5 bits).  The next octet is a
* conversation number that associates a saved IP/TCP header with
* the compressed packet.  The next two octets are the TCP checksum
* from the original datagram.  The next 0 to 15 octets are
* sequence number changes, one change per bit set in the header
* (there may be no changes and there are two special cases where
* the receiver implicitly knows what changed -- see below).
*
* There are 5 numbers which can change (they are always inserted
* in the following order): TCP urgent pointer, window,
* acknowledgement, sequence number and IP ID.  (The urgent pointer
* is different from the others in that its value is sent, not the
* change in value.)  Since typical use of SLIP links is biased
* toward small packets (see comments on MTU/MSS below), changes
* use a variable length coding with one octet for numbers in the
* range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the
* range 256 - 65535 or 0.  (If the change in sequence number or
* ack is more than 65535, an uncompressed packet is sent.)
*/

/*
* Packet types (must not conflict with IP protocol version)
*
* The top nibble of the first octet is the packet type.  There are
* three possible types: IP (not proto TCP or tcp with one of the
* control flags set); uncompressed TCP (a normal IP/TCP packet but
* with the 8-bit protocol field replaced by an 8-bit connection id --
* this type of packet syncs the sender & receiver); and compressed
* TCP (described above).
*
* LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and
* is logically part of the 4-bit "changes" field that follows.  Top
* three bits are actual packet type.  For backward compatibility
* and in the interest of conserving bits, numbers are chosen so the
* IP protocol version number (4) which normally appears in this nibble
* means "IP packet".
*/

/* packet types */
#define TYPE_IP 0x40
#define TYPE_UNCOMPRESSED_TCP 0x70
#define TYPE_COMPRESSED_TCP 0x80
#define TYPE_ERROR 0x00

/* Bits in first octet of compressed packet */
#define NEW_C   0x40    /* flag bits for what changed in a packet */
#define NEW_I   0x20
#define NEW_S   0x08
#define NEW_A   0x04
#define NEW_W   0x02
#define NEW_U   0x01

/* reserved, special-case values of above */
#define SPECIAL_I (NEW_S|NEW_W|NEW_U)           /* echoed interactive traffic */
#define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U)     /* unidirectional data */
#define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U)

#define TCP_PUSH_BIT 0x10


/*
* "state" data for each active tcp conversation on the wire.  This is
* basically a copy of the entire IP/TCP header from the last packet
* we saw from the conversation together with a small identifier
* the transmit & receive ends of the line use to locate saved header.
*/
struct cstate {
       struct cstate *cs_next; /* next most recently used cstate (xmit only) */
       uint16_t cs_hlen;       /* size of hdr (receive only) */
       u_char cs_id;           /* connection # associated with this state */
       u_char cs_filler;
       union {
               char csu_hdr[MAX_HDR];
#ifdef INET
               struct ip csu_ip;       /* ip/tcp hdr from most recent packet */
#endif
       } slcs_u;
};
#define cs_ip slcs_u.csu_ip
#define cs_hdr slcs_u.csu_hdr

/*
* all the state data for one serial line (we need one of these
* per line).
*/
struct slcompress {
       struct cstate *last_cs; /* most recently used tstate */
       u_char last_recv;       /* last rcvd conn. id */
       u_char last_xmit;       /* last sent conn. id */
       uint16_t flags;
#ifndef SL_NO_STATS
       int sls_packets;        /* outbound packets */
       int sls_compressed;     /* outbound compressed packets */
       int sls_searches;       /* searches for connection state */
       int sls_misses;         /* times couldn't find conn. state */
       int sls_uncompressedin; /* inbound uncompressed packets */
       int sls_compressedin;   /* inbound compressed packets */
       int sls_errorin;        /* inbound unknown type packets */
       int sls_tossed;         /* inbound packets tossed because of error */
#endif
       struct cstate tstate[MAX_STATES];       /* xmit connection states */
       struct cstate rstate[MAX_STATES];       /* receive connection states */
};
/* flag values */
#define SLF_TOSS 1              /* tossing rcvd frames because of input err */

void    sl_compress_init(struct slcompress *);
void    sl_compress_setup(struct slcompress *, int);
#ifdef INET
u_int   sl_compress_tcp(struct mbuf *,
           struct ip *, struct slcompress *, int);
#endif
int     sl_uncompress_tcp(u_char **, int, u_int, struct slcompress *);
int     sl_uncompress_tcp_core(u_char *, int, int, u_int,
           struct slcompress *, u_char **, u_int *);

#endif /* !_NET_SLCOMPRESS_H_ */

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