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/*

 * Definitions for tcp compression routines.

 *

 * $Id: vjcompress.h,v 1.1.1.1 2004-11-12 23:09:52 phoenix Exp $

 *

 * Copyright (c) 1989 Regents of the University of California.

 * All rights reserved.

 *

 * Redistribution and use in source and binary forms are permitted

 * provided that the above copyright notice and this paragraph are

 * duplicated in all such forms and that any documentation,

 * advertising materials, and other materials related to such

 * distribution and use acknowledge that the software was developed

 * by the University of California, Berkeley.  The name of the

 * University may not be used to endorse or promote products derived

 * from this software without specific prior written permission.

 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR

 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED

 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.

 *

 *      Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:

 *      - Initial distribution.

 */

#ifndef _VJCOMPRESS_H_

#define _VJCOMPRESS_H_

#define MAX_STATES 16           /* must be > 2 and < 256 */

#define MAX_HDR    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,

 * acknowlegement, 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 state (xmit only) */

    u_short 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];

        struct ip csu_ip;       /* ip/tcp hdr from most recent packet */

    } vjcs_u;

};

#define cs_ip vjcs_u.csu_ip

#define cs_hdr vjcs_u.csu_hdr

/*

 * all the state data for one serial line (we need one of these per line).

 */

struct vjcompress {

    struct cstate *last_cs;     /* most recently used tstate */

    u_char last_recv;           /* last rcvd conn. id */

    u_char last_xmit;           /* last sent conn. id */

    u_short flags;

#ifndef VJ_NO_STATS

    struct vjstat stats;

#endif

    struct cstate tstate[MAX_STATES];   /* xmit connection states */

    struct cstate rstate[MAX_STATES];   /* receive connection states */

};

/* flag values */

#define VJF_TOSS 1              /* tossing rcvd frames because of input err */

extern void  vj_compress_init __P((struct vjcompress *comp, int max_state));

extern u_int vj_compress_tcp __P((struct ip *ip, u_int mlen,

                                struct vjcompress *comp, int compress_cid_flag,

                                u_char **vjhdrp));

extern void  vj_uncompress_err __P((struct vjcompress *comp));

extern int   vj_uncompress_uncomp __P((u_char *buf, int buflen,

                                struct vjcompress *comp));

extern int   vj_uncompress_tcp __P((u_char *buf, int buflen, int total_len,

                                struct vjcompress *comp, u_char **hdrp,

                                u_int *hlenp));

#endif /* _VJCOMPRESS_H_ */