/*	slcompress.h	7.4	90/06/28	*/
/*
 * Definitions for tcp compression routines.
 *
 * Copyright (c) 1989 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. 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.
 *
 *	Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
 *	- Initial distribution.
 */

# ifndef _slcompress_h
# define _slcompress_h

# include "global.h"

# include "inet4/ip.h"


# define MAX_STATES	16	/* must be > 2 and < 256 */
# define MAX_HDR	128	/* 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,
 * 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 cstate (xmit only) */
	ushort		cs_hlen;	/* size of hdr (receive only) */
	uchar		cs_id;		/* connection # associated with this state */
	uchar		cs_filler;
	union {
		char 	csu_hdr[MAX_HDR];
		struct ip_dgram csu_ip;	/* ip/tcp hdr from most recent packet */
	} 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 */
	uchar		last_recv;	/* last rcvd conn. id */
	uchar		last_xmit;	/* last sent conn. id */
	ushort		flags;
# ifndef SL_NO_STATS
	long		sls_packets;	/* outbound packets */
	long		sls_compressed;	/* outbound compressed packets */
	long		sls_searches;	/* searches for connection state */
	long		sls_misses;	/* times couldn't find conn. state */
	long		sls_uncompressedin; /* inbound uncompressed packets */
	long		sls_compressedin; /* inbound compressed packets */
	long		sls_errorin;	/* inbound unknown type packets */
	long		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			slc_getstats (struct slcompress *, long *);
struct slcompress *	slc_init (void);
void			slc_free (struct slcompress *);
long			slc_uncompress (BUF *, uchar type, struct slcompress *);
uchar			slc_compress (BUF *, struct slcompress *, long compress_cid_flag);

INLINE uchar
slc_type (BUF *b)
{
	uchar c = *b->dstart & 0xf0;
	
	if (c == IP_VERSION << 4)
		return TYPE_IP;
	if (c & 0x80)
		return TYPE_COMPRESSED_TCP;
	if (c == TYPE_UNCOMPRESSED_TCP)
		return TYPE_UNCOMPRESSED_TCP;
	
	return TYPE_ERROR;
}


# endif /* _slcompress_h */
