sys/net/slcompress.h

   1 /*
   2  * Definitions for tcp compression routines.
   3  */
   4 /*-
   5  * SPDX-License-Identifier: BSD-3-Clause
   6  *
   7  * Copyright (c) 1989, 1993
   8  *      The Regents of the University of California.  All rights reserved.
   9  *
  10  * Redistribution and use in source and binary forms, with or without
  11  * modification, are permitted provided that the following conditions
  12  * are met:
  13  * 1. Redistributions of source code must retain the above copyright
  14  *    notice, this list of conditions and the following disclaimer.
  15  * 2. Redistributions in binary form must reproduce the above copyright
  16  *    notice, this list of conditions and the following disclaimer in the
  17  *    documentation and/or other materials provided with the distribution.
  18  * 3. Neither the name of the University nor the names of its contributors
  19  *    may be used to endorse or promote products derived from this software
  20  *    without specific prior written permission.
  21  *
  22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  *
  34  *      Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
  35  *      - Initial distribution.
  36  */
  37
  38 #ifndef _NET_SLCOMPRESS_H_
  39 #define _NET_SLCOMPRESS_H_
  40
  41 #define MAX_STATES 16           /* must be > 2 and < 256 */
  42 #define MAX_HDR 128
  43
  44 /*
  45  * Compressed packet format:
  46  *
  47  * The first octet contains the packet type (top 3 bits), TCP
  48  * 'push' bit, and flags that indicate which of the 4 TCP sequence
  49  * numbers have changed (bottom 5 bits).  The next octet is a
  50  * conversation number that associates a saved IP/TCP header with
  51  * the compressed packet.  The next two octets are the TCP checksum
  52  * from the original datagram.  The next 0 to 15 octets are
  53  * sequence number changes, one change per bit set in the header
  54  * (there may be no changes and there are two special cases where
  55  * the receiver implicitly knows what changed -- see below).
  56  *
  57  * There are 5 numbers which can change (they are always inserted
  58  * in the following order): TCP urgent pointer, window,
  59  * acknowledgement, sequence number and IP ID.  (The urgent pointer
  60  * is different from the others in that its value is sent, not the
  61  * change in value.)  Since typical use of SLIP links is biased
  62  * toward small packets (see comments on MTU/MSS below), changes
  63  * use a variable length coding with one octet for numbers in the
  64  * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the
  65  * range 256 - 65535 or 0.  (If the change in sequence number or
  66  * ack is more than 65535, an uncompressed packet is sent.)
  67  */
  68
  69 /*
  70  * Packet types (must not conflict with IP protocol version)
  71  *
  72  * The top nibble of the first octet is the packet type.  There are
  73  * three possible types: IP (not proto TCP or tcp with one of the
  74  * control flags set); uncompressed TCP (a normal IP/TCP packet but
  75  * with the 8-bit protocol field replaced by an 8-bit connection id --
  76  * this type of packet syncs the sender & receiver); and compressed
  77  * TCP (described above).
  78  *
  79  * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and
  80  * is logically part of the 4-bit "changes" field that follows.  Top
  81  * three bits are actual packet type.  For backward compatibility
  82  * and in the interest of conserving bits, numbers are chosen so the
  83  * IP protocol version number (4) which normally appears in this nibble
  84  * means "IP packet".
  85  */
  86
  87 /* packet types */
  88 #define TYPE_IP 0x40
  89 #define TYPE_UNCOMPRESSED_TCP 0x70
  90 #define TYPE_COMPRESSED_TCP 0x80
  91 #define TYPE_ERROR 0x00
  92
  93 /* Bits in first octet of compressed packet */
  94 #define NEW_C   0x40    /* flag bits for what changed in a packet */
  95 #define NEW_I   0x20
  96 #define NEW_S   0x08
  97 #define NEW_A   0x04
  98 #define NEW_W   0x02
  99 #define NEW_U   0x01
 100
 101 /* reserved, special-case values of above */
 102 #define SPECIAL_I (NEW_S|NEW_W|NEW_U)           /* echoed interactive traffic */
 103 #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U)     /* unidirectional data */
 104 #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U)
 105
 106 #define TCP_PUSH_BIT 0x10
 107
 108 /*
 109  * "state" data for each active tcp conversation on the wire.  This is
 110  * basically a copy of the entire IP/TCP header from the last packet
 111  * we saw from the conversation together with a small identifier
 112  * the transmit & receive ends of the line use to locate saved header.
 113  */
 114 struct cstate {
 115         struct cstate *cs_next; /* next most recently used cstate (xmit only) */
 116         u_int16_t cs_hlen;      /* size of hdr (receive only) */
 117         u_char cs_id;           /* connection # associated with this state */
 118         u_char cs_filler;
 119         union {
 120                 char csu_hdr[MAX_HDR];
 121                 struct ip csu_ip;       /* ip/tcp hdr from most recent packet */
 122         } slcs_u;
 123 };
 124 #define cs_ip slcs_u.csu_ip
 125 #define cs_hdr slcs_u.csu_hdr
 126
 127 /*
 128  * all the state data for one serial line (we need one of these
 129  * per line).
 130  */
 131 struct slcompress {
 132         struct cstate *last_cs; /* most recently used tstate */
 133         u_char last_recv;       /* last rcvd conn. id */
 134         u_char last_xmit;       /* last sent conn. id */
 135         u_int16_t flags;
 136 #ifndef SL_NO_STATS
 137         int sls_packets;        /* outbound packets */
 138         int sls_compressed;     /* outbound compressed packets */
 139         int sls_searches;       /* searches for connection state */
 140         int sls_misses;         /* times couldn't find conn. state */
 141         int sls_uncompressedin; /* inbound uncompressed packets */
 142         int sls_compressedin;   /* inbound compressed packets */
 143         int sls_errorin;        /* inbound unknown type packets */
 144         int sls_tossed;         /* inbound packets tossed because of error */
 145 #endif
 146         struct cstate tstate[MAX_STATES];       /* xmit connection states */
 147         struct cstate rstate[MAX_STATES];       /* receive connection states */
 148 };
 149 /* flag values */
 150 #define SLF_TOSS 1              /* tossing rcvd frames because of input err */
 151
 152 void     sl_compress_init(struct slcompress *, int);
 153 u_int    sl_compress_tcp(struct mbuf *, struct ip *, struct slcompress *, int);
 154 int      sl_uncompress_tcp(u_char **, int, u_int, struct slcompress *);
 155 int      sl_uncompress_tcp_core(u_char *, int, int, u_int,
 156             struct slcompress *, u_char **, u_int *);
 157
 158 #endif /* !_NET_SLCOMPRESS_H_ */