ppp/spppcomp/vjcompress.c

/*
 * Copyright (c) 2000 by Sun Microsystems, Inc.
 * All rights reserved.
 *
 * Routines to compress and uncompess tcp packets (for transmission
 * over low speed serial lines.
 *
 * 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 (at) helios.ee.lbl.gov), Dec 31, 1989:
 *	- Initial distribution.
 *
 * Modified June 1993 by Paul Mackerras, paulus (at) cs.anu.edu.au,
 * so that the entire packet being decompressed doesn't have
 * to be in contiguous memory (just the compressed header).
 */

/*
 * This version is used under STREAMS in Solaris 2
 *
 * $Id: vjcompress.c,v 1.10 1999/09/15 23:49:06 masputra Exp $
 */

#include <sys/types.h>
#include <sys/param.h>
#include <sys/byteorder.h>	/* for ntohl, etc. */
#include <sys/systm.h>
#include <sys/sysmacros.h>

#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>

#include <net/ppp_defs.h>
#include <net/vjcompress.h>

#pragma ident	"%Z%%M%	%I%	%E% SMI"

#ifndef VJ_NO_STATS
#define	INCR(counter) ++comp->stats.counter
#else
#define	INCR(counter)
#endif

#define	BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (unsigned int)(n))

#undef  BCOPY
#define	BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (unsigned int)(n))

/*
 * I'd like to use offsetof(struct ip,ip_hl) and offsetof(struct
 * tcp,th_off), but these are bitfields.
 */
#define	getip_hl(bp)	(((uchar_t *)bp)[0] & 0x0F)
#define	getth_off(bp)	(((uchar_t *)bp)[12] >> 4)
#define	getip_p(bp)	(((uchar_t *)bp)[offsetof(struct ip, ip_p)])
#define	setip_p(bp, v)	(((uchar_t *)bp)[offsetof(struct ip, ip_p)] = (v))

/*
 * vj_compress_init()
 */
void
vj_compress_init(struct vjcompress *comp, int max_state)
{
	register uint_t		i;
	register struct cstate	*tstate = comp->tstate;

	if (max_state == -1) {
		max_state = MAX_STATES - 1;
	}

	bzero((char *)comp, sizeof (*comp));

	for (i = max_state; i > 0; --i) {
		tstate[i].cs_id = i & 0xff;
		tstate[i].cs_next = &tstate[i - 1];
	}

	tstate[0].cs_next = &tstate[max_state];
	tstate[0].cs_id = 0;

	comp->last_cs = &tstate[0];
	comp->last_recv = 255;
	comp->last_xmit = 255;
	comp->flags = VJF_TOSS;
}

/*
 * ENCODE encodes a number that is known to be non-zero.  ENCODEZ
 * checks for zero (since zero has to be encoded in the long, 3 byte
 * form).
 */
#define	ENCODE(n) {						\
	if ((ushort_t)(n) >= 256) {				\
		*cp++ = 0;					\
		cp[1] = (n) & 0xff;				\
		cp[0] = ((n) >> 8) & 0xff;			\
		cp += 2;					\
	} else {						\
		*cp++ = (n) & 0xff;				\
	}							\
}
#define	ENCODEZ(n) {						\
	if ((ushort_t)(n) >= 256 || (ushort_t)(n) == 0) {	\
		*cp++ = 0;					\
		cp[1] = (n) & 0xff;				\
		cp[0] = ((n) >> 8) & 0xff;			\
		cp += 2;					\
	} else {						\
		*cp++ = (n) & 0xff;				\
	}							\
}

#define	DECODEL(f) {							\
	if (*cp == 0) {							\
		uint32_t tmp = ntohl(f) + ((cp[1] << 8) | cp[2]);	\
		(f) = htonl(tmp);					\
		cp += 3;						\
	} else {							\
		uint32_t tmp = ntohl(f) + (uint32_t)*cp++;		\
		(f) = htonl(tmp);					\
	}								\
}

#define	DECODES(f) {							\
	if (*cp == 0) {							\
		ushort_t tmp = ntohs(f) + ((cp[1] << 8) | cp[2]);	\
		(f) = htons(tmp);					\
		cp += 3;						\
	} else {							\
		ushort_t tmp = ntohs(f) + (uint32_t)*cp++;		\
		(f) = htons(tmp);					\
	}								\
}

#define	DECODEU(f) {							\
	if (*cp == 0) {							\
		(f) = htons((cp[1] << 8) | cp[2]);			\
		cp += 3;						\
	} else {							\
		(f) = htons((uint32_t)*cp++);				\
	}								\
}

uint_t
vj_compress_tcp(register struct ip *ip, uint_t mlen, struct vjcompress *comp,
	int compress_cid, uchar_t **vjhdrp)
{
	register struct cstate	*cs = comp->last_cs->cs_next;
	register uint_t		hlen = getip_hl(ip);
	register struct tcphdr	*oth;
	register struct tcphdr	*th;
	register uint_t		deltaS;
	register uint_t		deltaA;
	register uint_t		changes = 0;
	uchar_t			new_seq[16];
	register uchar_t	*cp = new_seq;
	register uint_t		thlen;

	/*
	 * Bail if this is an IP fragment or if the TCP packet isn't
	 * `compressible' (i.e., ACK isn't set or some other control bit is
	 * set).  (We assume that the caller has already made sure the
	 * packet is IP proto TCP)
	 */
	if ((ip->ip_off & htons(0x3fff)) || mlen < 40) {
		return (TYPE_IP);
	}

	th = (struct tcphdr *)&((int *)ip)[hlen];

	if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) {
		return (TYPE_IP);
	}

	thlen = (hlen + getth_off(th)) << 2;
	if (thlen > mlen) {
		return (TYPE_IP);
	}

	/*
	 * Packet is compressible -- we're going to send either a
	 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet.  Either way we need
	 * to locate (or create) the connection state.  Special case the
	 * most recently used connection since it's most likely to be used
	 * again & we don't have to do any reordering if it's used.
	 */
	INCR(vjs_packets);

	if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
		ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
		*(int *)th != ((int *)&cs->cs_ip)[getip_hl(&cs->cs_ip)]) {

		/*
		 * Wasn't the first -- search for it.
		 *
		 * States are kept in a circularly linked list with
		 * last_cs pointing to the end of the list.  The
		 * list is kept in lru order by moving a state to the
		 * head of the list whenever it is referenced.  Since
		 * the list is short and, empirically, the connection
		 * we want is almost always near the front, we locate
		 * states via linear search.  If we don't find a state
		 * for the datagram, the oldest state is (re-)used.
		 */
		register struct cstate	*lcs;
		register struct cstate	*lastcs = comp->last_cs;

		do {
			lcs = cs; cs = cs->cs_next;

			INCR(vjs_searches);

			if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr &&
				ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr &&
				*(int *)th == ((int *)
					&cs->cs_ip)[getip_hl(&cs->cs_ip)]) {

				goto found;
			}

		} while (cs != lastcs);

		/*
		 * Didn't find it -- re-use oldest cstate.  Send an
		 * uncompressed packet that tells the other side what
		 * connection number we're using for this conversation.
		 * Note that since the state list is circular, the oldest
		 * state points to the newest and we only need to set
		 * last_cs to update the lru linkage.
		 */
		INCR(vjs_misses);

		comp->last_cs = lcs;

		goto uncompressed;

found:
		/*
		 * Found it -- move to the front on the connection list.
		 */
		if (cs == lastcs) {
			comp->last_cs = lcs;
		} else {
			lcs->cs_next = cs->cs_next;
			cs->cs_next = lastcs->cs_next;
			lastcs->cs_next = cs;
		}
	}

	/*
	 * Make sure that only what we expect to change changed. The first
	 * line of the `if' checks the IP protocol version, header length &
	 * type of service.  The 2nd line checks the "Don't fragment" bit.
	 * The 3rd line checks the time-to-live and protocol (the protocol
	 * check is unnecessary but costless).  The 4th line checks the TCP
	 * header length.  The 5th line checks IP options, if any.  The 6th
	 * line checks TCP options, if any.  If any of these things are
	 * different between the previous & current datagram, we send the
	 * current datagram `uncompressed'.
	 */
	oth = (struct tcphdr *)&((int *)&cs->cs_ip)[hlen];

	/* Used to check for IP options. */
	deltaS = hlen;

	if (((ushort_t *)ip)[0] != ((ushort_t *)&cs->cs_ip)[0] ||
		((ushort_t *)ip)[3] != ((ushort_t *)&cs->cs_ip)[3] ||
		((ushort_t *)ip)[4] != ((ushort_t *)&cs->cs_ip)[4] ||
		getth_off(th) != getth_off(oth) ||
		(deltaS > 5 &&
			BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
		(getth_off(th) > 5 &&
			BCMP(th + 1, oth + 1, (getth_off(th) - 5) << 2))) {

		goto uncompressed;
	}

	/*
	 * Figure out which of the changing fields changed.  The
	 * receiver expects changes in the order: urgent, window,
	 * ack, seq (the order minimizes the number of temporaries
	 * needed in this section of code).
	 */
	if (th->th_flags & TH_URG) {

		deltaS = ntohs(th->th_urp);

		ENCODEZ(deltaS);

		changes |= NEW_U;

	} else if (th->th_urp != oth->th_urp) {

		/*
		 * argh! URG not set but urp changed -- a sensible
		 * implementation should never do this but RFC793
		 * doesn't prohibit the change so we have to deal
		 * with it
		 */
		goto uncompressed;
	}

	if ((deltaS = (ushort_t)(ntohs(th->th_win) - ntohs(oth->th_win))) > 0) {
		ENCODE(deltaS);

		changes |= NEW_W;
	}

	if ((deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack)) > 0) {
		if (deltaA > 0xffff) {
			goto uncompressed;
		}

		ENCODE(deltaA);

		changes |= NEW_A;
	}

	if ((deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq)) > 0) {
		if (deltaS > 0xffff) {
			goto uncompressed;
		}

		ENCODE(deltaS);

		changes |= NEW_S;
	}

	switch (changes) {

	case 0:
		/*
		 * Nothing changed. If this packet contains data and the
		 * last one didn't, this is probably a data packet following
		 * an ack (normal on an interactive connection) and we send
		 * it compressed.  Otherwise it's probably a retransmit,
		 * retransmitted ack or window probe.  Send it uncompressed
		 * in case the other side missed the compressed version.
		 */
		if (ip->ip_len != cs->cs_ip.ip_len &&
					ntohs(cs->cs_ip.ip_len) == thlen) {
			break;
		}

		/* (otherwise fall through) */
		/* FALLTHRU */

	case SPECIAL_I:
	case SPECIAL_D:

		/*
		 * actual changes match one of our special case encodings --
		 * send packet uncompressed.
		 */
		goto uncompressed;

	case NEW_S|NEW_A:

		if (deltaS == deltaA &&
				deltaS == ntohs(cs->cs_ip.ip_len) - thlen) {

			/*
			 * special case for echoed terminal traffic
			 */
			changes = SPECIAL_I;
			cp = new_seq;
		}

		break;

	case NEW_S:

		if (deltaS == ntohs(cs->cs_ip.ip_len) - thlen) {

			/*
			 * special case for data xfer
			 */
			changes = SPECIAL_D;
			cp = new_seq;
		}

		break;
	}

	deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
	if (deltaS != 1) {
		ENCODEZ(deltaS);

		changes |= NEW_I;
	}

	if (th->th_flags & TH_PUSH) {
		changes |= TCP_PUSH_BIT;
	}

	/*
	 * Grab the cksum before we overwrite it below.  Then update our
	 * state with this packet's header.
	 */
	deltaA = ntohs(th->th_sum);

	BCOPY(ip, &cs->cs_ip, thlen);

	/*
	 * We want to use the original packet as our compressed packet.
	 * (cp - new_seq) is the number of bytes we need for compressed
	 * sequence numbers.  In addition we need one byte for the change
	 * mask, one for the connection id and two for the tcp checksum.
	 * So, (cp - new_seq) + 4 bytes of header are needed.  thlen is how
	 * many bytes of the original packet to toss so subtract the two to
	 * get the new packet size.
	 */
	deltaS = cp - new_seq;

	cp = (uchar_t *)ip;

	if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
		comp->last_xmit = cs->cs_id;

		thlen -= deltaS + 4;

		*vjhdrp = (cp += thlen);

		*cp++ = changes | NEW_C;
		*cp++ = cs->cs_id;
	} else {
		thlen -= deltaS + 3;

		*vjhdrp = (cp += thlen);

		*cp++ = changes & 0xff;
	}

	*cp++ = (deltaA >> 8) & 0xff;
	*cp++ = deltaA & 0xff;

	BCOPY(new_seq, cp, deltaS);

	INCR(vjs_compressed);

	return (TYPE_COMPRESSED_TCP);

	/*
	 * Update connection state cs & send uncompressed packet (that is,
	 * a regular ip/tcp packet but with the 'conversation id' we hope
	 * to use on future compressed packets in the protocol field).
	 */
uncompressed:

	BCOPY(ip, &cs->cs_ip, thlen);

	ip->ip_p = cs->cs_id;
	comp->last_xmit = cs->cs_id;

	return (TYPE_UNCOMPRESSED_TCP);
}

/*
 * vj_uncompress_err()
 *
 * Called when we may have missed a packet.
 */
void
vj_uncompress_err(struct vjcompress *comp)
{
	comp->flags |= VJF_TOSS;

	INCR(vjs_errorin);
}

/*
 * vj_uncompress_uncomp()
 *
 * "Uncompress" a packet of type TYPE_UNCOMPRESSED_TCP.
 */
int
vj_uncompress_uncomp(uchar_t *buf, int buflen, struct vjcompress *comp)
{
	register uint_t		hlen;
	register struct cstate	*cs;

	hlen = getip_hl(buf) << 2;

	if (getip_p(buf) >= MAX_STATES ||
	    hlen + sizeof (struct tcphdr) > buflen ||
	    (hlen += getth_off(buf+hlen) << 2) > buflen || hlen > MAX_HDR) {

		comp->flags |= VJF_TOSS;

		INCR(vjs_errorin);

		return (0);
	}

	cs = &comp->rstate[comp->last_recv = getip_p(buf)];
	comp->flags &= ~VJF_TOSS;
	setip_p(buf, IPPROTO_TCP);

	BCOPY(buf, &cs->cs_ip, hlen);

	cs->cs_hlen = hlen & 0xff;

	INCR(vjs_uncompressedin);

	return (1);
}

/*
 * vj_uncompress_tcp()
 *
 * Uncompress a packet of type TYPE_COMPRESSED_TCP.
 * The packet starts at buf and is of total length total_len.
 * The first buflen bytes are at buf; this must include the entire
 * compressed TCP/IP header.  This procedure returns the length
 * of the VJ header, with a pointer to the uncompressed IP header
 * in *hdrp and its length in *hlenp.
 */
int
vj_uncompress_tcp(uchar_t *buf, int buflen, int total_len,
	struct vjcompress *comp, uchar_t **hdrp, uint_t *hlenp)
{
	register uchar_t	*cp;
	register uint_t		hlen;
	register uint_t		changes;
	register struct tcphdr	*th;
	register struct cstate	*cs;
	register ushort_t	*bp;
	register uint_t		vjlen;
	register uint32_t	tmp;

	INCR(vjs_compressedin);

	cp = buf;
	changes = *cp++;

	if (changes & NEW_C) {
		/*
		 * Make sure the state index is in range, then grab the state.
		 * If we have a good state index, clear the 'discard' flag.
		 */
		if (*cp >= MAX_STATES) {
			goto bad;
		}

		comp->flags &= ~VJF_TOSS;
		comp->last_recv = *cp++;
	} else {
		/*
		 * this packet has an implicit state index.  If we've
		 * had a line error since the last time we got an
		 * explicit state index, we have to toss the packet
		 */
		if (comp->flags & VJF_TOSS) {
			INCR(vjs_tossed);
			return (-1);
		}
	}

	cs = &comp->rstate[comp->last_recv];
	hlen = getip_hl(&cs->cs_ip) << 2;

	th = (struct tcphdr *)((uint32_t *)&cs->cs_ip+hlen/sizeof (uint32_t));
	th->th_sum = htons((*cp << 8) | cp[1]);

	cp += 2;

	if (changes & TCP_PUSH_BIT) {
		th->th_flags |= TH_PUSH;
	} else {
		th->th_flags &= ~TH_PUSH;
	}

	switch (changes & SPECIALS_MASK) {

	case SPECIAL_I:

		{

		register uint32_t	i;

		i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;

		tmp = ntohl(th->th_ack) + i;
		th->th_ack = htonl(tmp);

		tmp = ntohl(th->th_seq) + i;
		th->th_seq = htonl(tmp);

		}

		break;

	case SPECIAL_D:

		tmp = ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
		th->th_seq = htonl(tmp);

		break;

	default:

		if (changes & NEW_U) {
			th->th_flags |= TH_URG;
			DECODEU(th->th_urp);
		} else {
			th->th_flags &= ~TH_URG;
		}

		if (changes & NEW_W) {
			DECODES(th->th_win);
		}

		if (changes & NEW_A) {
			DECODEL(th->th_ack);
		}

		if (changes & NEW_S) {
			DECODEL(th->th_seq);
		}

		break;
	}

	if (changes & NEW_I) {
		DECODES(cs->cs_ip.ip_id);
	} else {
		cs->cs_ip.ip_id = ntohs(cs->cs_ip.ip_id) + 1;
		cs->cs_ip.ip_id = htons(cs->cs_ip.ip_id);
	}

	/*
	 * At this point, cp points to the first byte of data in the
	 * packet.  Fill in the IP total length and update the IP
	 * header checksum.
	 */
	vjlen = cp - buf;
	buflen -= vjlen;
	if (buflen < 0) {
		/*
		 * we must have dropped some characters (crc should detect
		 * this but the old slip framing won't)
		 */
		goto bad;
	}

	total_len += cs->cs_hlen - vjlen;
	cs->cs_ip.ip_len = htons(total_len);

	/*
	 * recompute the ip header checksum
	 */
	bp = (ushort_t *)&cs->cs_ip;
	cs->cs_ip.ip_sum = 0;

	for (changes = 0; hlen > 0; hlen -= 2) {
		changes += *bp++;
	}

	changes = (changes & 0xffff) + (changes >> 16);
	changes = (changes & 0xffff) + (changes >> 16);
	cs->cs_ip.ip_sum = ~ changes;

	*hdrp = (uchar_t *)&cs->cs_ip;
	*hlenp = cs->cs_hlen;

	return (vjlen);

bad:

	comp->flags |= VJF_TOSS;

	INCR(vjs_errorin);

	return (-1);
}