pppcompress.c

unix and linux net driver

/*-
 * Copyright (c) 1989 The 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.
 *
 *	@(#)slcompress.c	7.7 (Berkeley) 5/7/91
 */

/*
 * Routines to compress and uncompess tcp packets (for transmission
 * over low speed serial lines.
 *
 * Van Jacobson ([e-mail]), Dec 31, 1989:
 *    - Initial distribution.
 *
 *	$Id: pppcompress.c,v 1.2 1996/05/24 07:04:14 paulus Exp $
 */
  
#include <sys/types.h>
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/mbuf.h>
#include <sys/socket.h>
#include <sys/socketvar.h>

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

#include <net/pppcompress.h>

#ifndef SL_NO_STATS
#define INCR(counter) ++comp->counter;
#else
#define INCR(counter)
#endif

#define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n))
#define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n))
#ifndef KERNEL
#define ovbcopy bcopy
#endif

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

	if ((unsigned) max_state > MAX_STATES - 1)
		max_state = MAX_STATES - 1;
	bzero((char *)comp, sizeof(*comp));
	for (i = max_state; i > 0; --i) {
		tstate[i].cs_id = i;
		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 = SLF_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 ((u_short)(n) >= 256) { \
		*cp++ = 0; \
		cp[1] = (n); \
		cp[0] = (n) >> 8; \
		cp += 2; \
	} else { \
		*cp++ = (n); \
	} \
}
#define ENCODEZ(n) { \
	if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \
		*cp++ = 0; \
		cp[1] = (n); \
		cp[0] = (n) >> 8; \
		cp += 2; \
	} else { \
		*cp++ = (n); \
	} \
}

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

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

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

u_int
vj_compress_tcp(m, ip, comp, compress_cid)
	struct mbuf *m;
	register struct ip *ip;
	struct vjcompress *comp;
	int compress_cid;
{
	register struct cstate *cs = comp->last_cs->cs_next;
	register u_int hlen = ip->ip_hl;
	register struct tcphdr *oth;
	register struct tcphdr *th;
	register u_int deltaS, deltaA;
	register u_int changes = 0;
	u_char new_seq[16];
	register u_char *cp = new_seq;

	/*
	 * 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)) || m->m_len < 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);
	/*
	 * 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(sls_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)[cs->cs_ip.ip_hl]) {
		/*
		 * 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(sls_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)[cs->cs_ip.ip_hl])
				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(sls_misses)
		comp->last_cs = lcs;
		hlen += th->th_off;
		hlen <<= 2;
		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];
	deltaS = hlen;
	hlen += th->th_off;
	hlen <<= 2;

	if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0] ||
	    ((u_short *)ip)[3] != ((u_short *)&cs->cs_ip)[3] ||
	    ((u_short *)ip)[4] != ((u_short *)&cs->cs_ip)[4] ||
	    th->th_off != oth->th_off ||
	    (deltaS > 5 &&
	     BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
	    (th->th_off > 5 &&
	     BCMP(th + 1, oth + 1, (th->th_off - 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 = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win))) {
		ENCODE(deltaS);
		changes |= NEW_W;
	}

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

	if (deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq)) {
		if (deltaS > 0xffff)
			goto uncompressed;
		ENCODE(deltaS);
		changes |= NEW_S;