1/*-
2 * Definitions for tcp compression routines.
3 *
4 * SPDX-License-Identifier: BSD-3-Clause
5 *
6 * Copyright (c) 1989, 1993
7 *	The Regents of the University of California.  All rights reserved.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 * 1. Redistributions of source code must retain the above copyright
13 *    notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 *    notice, this list of conditions and the following disclaimer in the
16 *    documentation and/or other materials provided with the distribution.
17 * 3. Neither the name of the University nor the names of its contributors
18 *    may be used to endorse or promote products derived from this software
19 *    without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 *
33 *	Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
34 *	- Initial distribution.
35 *
36 * $FreeBSD$
37 */
38
39#define MIN_VJ_STATES 3
40#define MAX_VJ_STATES 255
41#define DEF_VJ_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 * acknowlegement, 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 */
114struct cstate {
115  struct cstate *cs_next;	/* next most recently used cstate (xmit only) */
116  u_short 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
125#define cs_ip slcs_u.csu_ip
126#define cs_hdr slcs_u.csu_hdr
127
128/*
129 * all the state data for one serial line (we need one of these
130 * per line).
131 */
132struct slcompress {
133  struct cstate *last_cs;	/* most recently used tstate */
134  u_char last_recv;		/* last rcvd conn. id */
135  u_char last_xmit;		/* last sent conn. id */
136  u_short flags;
137  struct cstate tstate[MAX_VJ_STATES];	/* xmit connection states */
138  struct cstate rstate[MAX_VJ_STATES];	/* receive connection states */
139};
140
141struct slstat {
142  int sls_packets;		/* outbound packets */
143  int sls_compressed;		/* outbound compressed packets */
144  int sls_searches;		/* searches for connection state */
145  int sls_misses;		/* times couldn't find conn. state */
146  int sls_uncompressedin;	/* inbound uncompressed packets */
147  int sls_compressedin;		/* inbound compressed packets */
148  int sls_errorin;		/* inbound unknown type packets */
149  int sls_tossed;		/* inbound packets tossed because of error */
150};
151
152/* flag values */
153#define SLF_TOSS 1		/* tossing rcvd frames because of input err */
154
155struct mbuf;
156struct cmdargs;
157
158extern void sl_compress_init(struct slcompress *, int);
159extern u_char sl_compress_tcp(struct mbuf *, struct ip *, struct slcompress *,
160                              struct slstat *, int);
161extern int sl_uncompress_tcp(u_char **, int, u_int, struct slcompress *,
162                             struct slstat *, int);
163extern int sl_Show(struct cmdargs const *);
164