[unix-history] / usr / src / sys.386bsd / net / slcompress.c

/*-
 * 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 (van@helios.ee.lbl.gov), Dec 31, 1989:
 *	- Initial distribution.
 *
 * static char rcsid[] =
 * "$Header: slcompress.c,v 1.19 89/12/31 08:52:59 van Exp $";
 */

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

#include "slcompress.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
sl_compress_init(comp)
	struct slcompress *comp;
{
	register u_int i;
	register struct cstate *tstate = comp->tstate;

	bzero((char *)comp, sizeof(*comp));
	for (i = MAX_STATES - 1; i > 0; --i) {
		tstate[i].cs_id = i;
		tstate[i].cs_next = &tstate[i - 1];
	}
	tstate[0].cs_next = &tstate[MAX_STATES - 1];
	tstate[0].cs_id = 0;
	comp->last_cs = &tstate[0];
	comp->last_recv = 255;
	comp->last_xmit = 255;
}


/* 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_char
sl_compress_tcp(m, ip, comp, compress_cid)
	struct mbuf *m;
	register struct ip *ip;
	struct slcompress *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;
	}

	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) == hlen)
			break;

		/* (fall through) */

	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) - hlen) {
			/* special case for echoed terminal traffic */
			changes = SPECIAL_I;
			cp = new_seq;
		}
		break;

	case NEW_S:
		if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
			/* 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, hlen);

	/*
	 * 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.  hlen 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 = (u_char *)ip;
	if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
		comp->last_xmit = cs->cs_id;
		hlen -= deltaS + 4;
		cp += hlen;
		*cp++ = changes | NEW_C;
		*cp++ = cs->cs_id;
	} else {
		hlen -= deltaS + 3;
		cp += hlen;
		*cp++ = changes;
	}
	m->m_len -= hlen;
	m->m_data += hlen;
	*cp++ = deltaA >> 8;
	*cp++ = deltaA;
	BCOPY(new_seq, cp, deltaS);
	INCR(sls_compressed)
	return (TYPE_COMPRESSED_TCP);

	/*
	 * Update connection state cs & send uncompressed packet ('uncompressed'
	 * means 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, hlen);
	ip->ip_p = cs->cs_id;
	comp->last_xmit = cs->cs_id;
	return (TYPE_UNCOMPRESSED_TCP);
}


int
sl_uncompress_tcp(bufp, len, type, comp)
	u_char **bufp;
	int len;
	u_int type;
	struct slcompress *comp;
{
	register u_char *cp;
	register u_int hlen, changes;
	register struct tcphdr *th;
	register struct cstate *cs;
	register struct ip *ip;

	switch (type) {

	case TYPE_UNCOMPRESSED_TCP:
		ip = (struct ip *) *bufp;
		if (ip->ip_p >= MAX_STATES)
			goto bad;
		cs = &comp->rstate[comp->last_recv = ip->ip_p];
		comp->flags &=~ SLF_TOSS;
		ip->ip_p = IPPROTO_TCP;
		hlen = ip->ip_hl;
		hlen += ((struct tcphdr *)&((int *)ip)[hlen])->th_off;
		hlen <<= 2;
		BCOPY(ip, &cs->cs_ip, hlen);
		cs->cs_ip.ip_sum = 0;
		cs->cs_hlen = hlen;
		INCR(sls_uncompressedin)
		return (len);

	default:
		goto bad;

	case TYPE_COMPRESSED_TCP:
		break;
	}
	/* We've got a compressed packet. */
	INCR(sls_compressedin)
	cp = *bufp;
	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 &=~ SLF_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 & SLF_TOSS) {
			INCR(sls_tossed)
			return (0);
		}
	}
	cs = &comp->rstate[comp->last_recv];
	hlen = cs->cs_ip.ip_hl << 2;
	th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
	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 u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
		th->th_ack = htonl(ntohl(th->th_ack) + i);
		th->th_seq = htonl(ntohl(th->th_seq) + i);
		}
		break;

	case SPECIAL_D:
		th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
				   - cs->cs_hlen);
		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 = htons(ntohs(cs->cs_ip.ip_id) + 1);

	/*
	 * At this point, cp points to the first byte of data in the
	 * packet.  If we're not aligned on a 4-byte boundary, copy the
	 * data down so the ip & tcp headers will be aligned.  Then back up
	 * cp by the tcp/ip header length to make room for the reconstructed
	 * header (we assume the packet we were handed has enough space to
	 * prepend 128 bytes of header).  Adjust the length to account for
	 * the new header & fill in the IP total length.
	 */
	len -= (cp - *bufp);
	if (len < 0)
		/* we must have dropped some characters (crc should detect
		 * this but the old slip framing won't) */
		goto bad;

	if ((int)cp & 3) {
		if (len > 0)
			(void) ovbcopy(cp, (caddr_t)((int)cp &~ 3), len);
		cp = (u_char *)((int)cp &~ 3);
	}
	cp -= cs->cs_hlen;
	len += cs->cs_hlen;
	cs->cs_ip.ip_len = htons(len);
	BCOPY(&cs->cs_ip, cp, cs->cs_hlen);
	*bufp = cp;

	/* recompute the ip header checksum */
	{
		register u_short *bp = (u_short *)cp;
		for (changes = 0; hlen > 0; hlen -= 2)
			changes += *bp++;
		changes = (changes & 0xffff) + (changes >> 16);
		changes = (changes & 0xffff) + (changes >> 16);
		((struct ip *)cp)->ip_sum = ~ changes;
	}
	return (len);
bad:
	comp->flags |= SLF_TOSS;
	INCR(sls_errorin)
	return (0);
}
Commit	Line	Data
05df3b37 WJ	1	/*-
	2	* Copyright (c) 1989 The Regents of the University of California.
	3	* All rights reserved.
	4	*
	5	* Redistribution and use in source and binary forms, with or without
	6	* modification, are permitted provided that the following conditions
	7	* are met:
	8	* 1. Redistributions of source code must retain the above copyright
	9	* notice, this list of conditions and the following disclaimer.
	10	* 2. Redistributions in binary form must reproduce the above copyright
	11	* notice, this list of conditions and the following disclaimer in the
	12	* documentation and/or other materials provided with the distribution.
	13	* 3. All advertising materials mentioning features or use of this software
	14	* must display the following acknowledgement:
	15	* This product includes software developed by the University of
	16	* California, Berkeley and its contributors.
	17	* 4. 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	* @(#)slcompress.c 7.7 (Berkeley) 5/7/91
	34	*/
	35
	36	/*
	37	* Routines to compress and uncompess tcp packets (for transmission
	38	* over low speed serial lines.
	39	*
	40	* Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
	41	* - Initial distribution.
	42	*
	43	* static char rcsid[] =
	44	* "$Header: slcompress.c,v 1.19 89/12/31 08:52:59 van Exp $";
	45	*/
	46
	47	#include <sys/param.h>
	48	#include <sys/mbuf.h>
	49	#include <netinet/in.h>
	50	#include <netinet/in_systm.h>
	51	#include <netinet/ip.h>
	52	#include <netinet/tcp.h>
	53
	54	#include "slcompress.h"
	55
	56	#ifndef SL_NO_STATS
	57	#define INCR(counter) ++comp->counter;
	58	#else
	59	#define INCR(counter)
	60	#endif
	61
	62	#define BCMP(p1, p2, n) bcmp((char )(p1), (char )(p2), (int)(n))
	63	#define BCOPY(p1, p2, n) bcopy((char )(p1), (char )(p2), (int)(n))
	64	#ifndef KERNEL
65	#define ovbcopy bcopy
66	#endif
67
68
69	void
70	sl_compress_init(comp)
71	struct slcompress *comp;
72	{
73	register u_int i;
74	register struct cstate *tstate = comp->tstate;
75
76	bzero((char )comp, sizeof(comp));
77	for (i = MAX_STATES - 1; i > 0; --i) {
78	tstate[i].cs_id = i;
79	tstate[i].cs_next = &tstate[i - 1];
80	}
81	tstate[0].cs_next = &tstate[MAX_STATES - 1];
82	tstate[0].cs_id = 0;
83	comp->last_cs = &tstate[0];
84	comp->last_recv = 255;
85	comp->last_xmit = 255;
86	}
87
88
89	/* ENCODE encodes a number that is known to be non-zero. ENCODEZ
90	* checks for zero (since zero has to be encoded in the long, 3 byte
91	* form).
92	*/
93	#define ENCODE(n) { \
94	if ((u_short)(n) >= 256) { \
95	*cp++ = 0; \
96	cp[1] = (n); \
97	cp[0] = (n) >> 8; \
98	cp += 2; \
99	} else { \
100	*cp++ = (n); \
101	} \
102	}
103	#define ENCODEZ(n) { \
104	if ((u_short)(n) >= 256 \|\| (u_short)(n) == 0) { \
105	*cp++ = 0; \
106	cp[1] = (n); \
107	cp[0] = (n) >> 8; \
108	cp += 2; \
109	} else { \
110	*cp++ = (n); \
111	} \
112	}
113
114	#define DECODEL(f) { \
115	if (*cp == 0) {\
116	(f) = htonl(ntohl(f) + ((cp[1] << 8) \| cp[2])); \
117	cp += 3; \
118	} else { \
119	(f) = htonl(ntohl(f) + (u_long)*cp++); \
120	} \
121	}
122
123	#define DECODES(f) { \
124	if (*cp == 0) {\
125	(f) = htons(ntohs(f) + ((cp[1] << 8) \| cp[2])); \
126	cp += 3; \
127	} else { \
128	(f) = htons(ntohs(f) + (u_long)*cp++); \
129	} \
130	}
131
132	#define DECODEU(f) { \
133	if (*cp == 0) {\
134	(f) = htons((cp[1] << 8) \| cp[2]); \
135	cp += 3; \
136	} else { \
137	(f) = htons((u_long)*cp++); \
138	} \
139	}
140
141
142	u_char
143	sl_compress_tcp(m, ip, comp, compress_cid)
144	struct mbuf *m;
145	register struct ip *ip;
146	struct slcompress *comp;
147	int compress_cid;
148	{
149	register struct cstate *cs = comp->last_cs->cs_next;
150	register u_int hlen = ip->ip_hl;
151	register struct tcphdr *oth;
152	register struct tcphdr *th;
153	register u_int deltaS, deltaA;
154	register u_int changes = 0;
155	u_char new_seq[16];
156	register u_char *cp = new_seq;
157
158	/*
159	* Bail if this is an IP fragment or if the TCP packet isn't
160	* `compressible' (i.e., ACK isn't set or some other control bit is
161	* set). (We assume that the caller has already made sure the
162	* packet is IP proto TCP).
163	*/
164	if ((ip->ip_off & htons(0x3fff)) \|\| m->m_len < 40)
165	return (TYPE_IP);
166
167	th = (struct tcphdr )&((int )ip)[hlen];
168	if ((th->th_flags & (TH_SYN\|TH_FIN\|TH_RST\|TH_ACK)) != TH_ACK)
169	return (TYPE_IP);
170	/*
171	* Packet is compressible -- we're going to send either a
172	* COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
173	* to locate (or create) the connection state. Special case the
174	* most recently used connection since it's most likely to be used
175	* again & we don't have to do any reordering if it's used.
176	*/
177	INCR(sls_packets)
178	if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr \|\|
179	ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr \|\|
180	(int )th != ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
181	/*
182	* Wasn't the first -- search for it.
183	*
184	* States are kept in a circularly linked list with
185	* last_cs pointing to the end of the list. The
186	* list is kept in lru order by moving a state to the
187	* head of the list whenever it is referenced. Since
188	* the list is short and, empirically, the connection
189	* we want is almost always near the front, we locate
190	* states via linear search. If we don't find a state
191	* for the datagram, the oldest state is (re-)used.
192	*/
193	register struct cstate *lcs;
194	register struct cstate *lastcs = comp->last_cs;
195
196	do {
197	lcs = cs; cs = cs->cs_next;
198	INCR(sls_searches)
199	if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
200	&& ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
201	&& (int )th == ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl])
202	goto found;
203	} while (cs != lastcs);
204
205	/*
206	* Didn't find it -- re-use oldest cstate. Send an
207	* uncompressed packet that tells the other side what
208	* connection number we're using for this conversation.
209	* Note that since the state list is circular, the oldest
210	* state points to the newest and we only need to set
211	* last_cs to update the lru linkage.
212	*/
213	INCR(sls_misses)
214	comp->last_cs = lcs;
215	hlen += th->th_off;
216	hlen <<= 2;
217	goto uncompressed;
218
219	found:
220	/*
221	* Found it -- move to the front on the connection list.
222	*/
223	if (cs == lastcs)
224	comp->last_cs = lcs;
225	else {
226	lcs->cs_next = cs->cs_next;
227	cs->cs_next = lastcs->cs_next;
228	lastcs->cs_next = cs;
229	}
230	}
231
232	/*
233	* Make sure that only what we expect to change changed. The first
234	* line of the `if' checks the IP protocol version, header length &
235	* type of service. The 2nd line checks the "Don't fragment" bit.
236	* The 3rd line checks the time-to-live and protocol (the protocol
237	* check is unnecessary but costless). The 4th line checks the TCP
238	* header length. The 5th line checks IP options, if any. The 6th
239	* line checks TCP options, if any. If any of these things are
240	* different between the previous & current datagram, we send the
241	* current datagram `uncompressed'.
242	*/
243	oth = (struct tcphdr )&((int )&cs->cs_ip)[hlen];
244	deltaS = hlen;
245	hlen += th->th_off;
246	hlen <<= 2;
247
248	if (((u_short )ip)[0] != ((u_short )&cs->cs_ip)[0] \|\|
249	((u_short )ip)[3] != ((u_short )&cs->cs_ip)[3] \|\|
250	((u_short )ip)[4] != ((u_short )&cs->cs_ip)[4] \|\|
251	th->th_off != oth->th_off \|\|
252	(deltaS > 5 &&
253	BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) \|\|
254	(th->th_off > 5 &&
255	BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
256	goto uncompressed;
257
258	/*
259	* Figure out which of the changing fields changed. The
260	* receiver expects changes in the order: urgent, window,
261	* ack, seq (the order minimizes the number of temporaries
262	* needed in this section of code).
263	*/
264	if (th->th_flags & TH_URG) {
265	deltaS = ntohs(th->th_urp);
266	ENCODEZ(deltaS);
267	changes \|= NEW_U;
268	} else if (th->th_urp != oth->th_urp)
269	/* argh! URG not set but urp changed -- a sensible
270	* implementation should never do this but RFC793
271	* doesn't prohibit the change so we have to deal
272	* with it. */
273	goto uncompressed;
274
275	if (deltaS = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win))) {
276	ENCODE(deltaS);
277	changes \|= NEW_W;
278	}
279
280	if (deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack)) {
281	if (deltaA > 0xffff)
282	goto uncompressed;
283	ENCODE(deltaA);
284	changes \|= NEW_A;
285	}
286
287	if (deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq)) {
288	if (deltaS > 0xffff)
289	goto uncompressed;
290	ENCODE(deltaS);
291	changes \|= NEW_S;
292	}
293
294	switch(changes) {
295
296	case 0:
297	/*
298	* Nothing changed. If this packet contains data and the
299	* last one didn't, this is probably a data packet following
300	* an ack (normal on an interactive connection) and we send
301	* it compressed. Otherwise it's probably a retransmit,
302	* retransmitted ack or window probe. Send it uncompressed
303	* in case the other side missed the compressed version.
304	*/
305	if (ip->ip_len != cs->cs_ip.ip_len &&
306	ntohs(cs->cs_ip.ip_len) == hlen)
307	break;
308
309	/* (fall through) */
310
311	case SPECIAL_I:
312	case SPECIAL_D:
313	/*
314	* actual changes match one of our special case encodings --
315	* send packet uncompressed.
316	*/
317	goto uncompressed;
318
319	case NEW_S\|NEW_A:
320	if (deltaS == deltaA &&
321	deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
322	/* special case for echoed terminal traffic */
323	changes = SPECIAL_I;
324	cp = new_seq;
325	}
326	break;
327
328	case NEW_S:
329	if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
330	/* special case for data xfer */
331	changes = SPECIAL_D;
332	cp = new_seq;
333	}
334	break;
335	}
336
337	deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
338	if (deltaS != 1) {
339	ENCODEZ(deltaS);
340	changes \|= NEW_I;
341	}
342	if (th->th_flags & TH_PUSH)
343	changes \|= TCP_PUSH_BIT;
344	/*
345	* Grab the cksum before we overwrite it below. Then update our
346	* state with this packet's header.
347	*/
348	deltaA = ntohs(th->th_sum);
349	BCOPY(ip, &cs->cs_ip, hlen);
350
351	/*
352	* We want to use the original packet as our compressed packet.
353	* (cp - new_seq) is the number of bytes we need for compressed
354	* sequence numbers. In addition we need one byte for the change
355	* mask, one for the connection id and two for the tcp checksum.
356	* So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
357	* many bytes of the original packet to toss so subtract the two to
358	* get the new packet size.
359	*/
360	deltaS = cp - new_seq;
361	cp = (u_char *)ip;
362	if (compress_cid == 0 \|\| comp->last_xmit != cs->cs_id) {
363	comp->last_xmit = cs->cs_id;
364	hlen -= deltaS + 4;
365	cp += hlen;
366	*cp++ = changes \| NEW_C;
367	*cp++ = cs->cs_id;
368	} else {
369	hlen -= deltaS + 3;
370	cp += hlen;
371	*cp++ = changes;
372	}
373	m->m_len -= hlen;
374	m->m_data += hlen;
375	*cp++ = deltaA >> 8;
376	*cp++ = deltaA;
377	BCOPY(new_seq, cp, deltaS);
378	INCR(sls_compressed)
379	return (TYPE_COMPRESSED_TCP);
380
381	/*
382	* Update connection state cs & send uncompressed packet ('uncompressed'
383	* means a regular ip/tcp packet but with the 'conversation id' we hope
384	* to use on future compressed packets in the protocol field).
385	*/
386	uncompressed:
387	BCOPY(ip, &cs->cs_ip, hlen);
388	ip->ip_p = cs->cs_id;
389	comp->last_xmit = cs->cs_id;
390	return (TYPE_UNCOMPRESSED_TCP);
391	}
392
393
394	int
395	sl_uncompress_tcp(bufp, len, type, comp)
396	u_char **bufp;
397	int len;
398	u_int type;
399	struct slcompress *comp;
400	{
401	register u_char *cp;
402	register u_int hlen, changes;
403	register struct tcphdr *th;
404	register struct cstate *cs;
405	register struct ip *ip;
406
407	switch (type) {
408
409	case TYPE_UNCOMPRESSED_TCP:
410	ip = (struct ip ) bufp;
411	if (ip->ip_p >= MAX_STATES)
412	goto bad;
413	cs = &comp->rstate[comp->last_recv = ip->ip_p];
414	comp->flags &=~ SLF_TOSS;
415	ip->ip_p = IPPROTO_TCP;
416	hlen = ip->ip_hl;
417	hlen += ((struct tcphdr )&((int )ip)[hlen])->th_off;
418	hlen <<= 2;
419	BCOPY(ip, &cs->cs_ip, hlen);
420	cs->cs_ip.ip_sum = 0;
421	cs->cs_hlen = hlen;
422	INCR(sls_uncompressedin)
423	return (len);
424
425	default:
426	goto bad;
427
428	case TYPE_COMPRESSED_TCP:
429	break;
430	}
431	/* We've got a compressed packet. */
432	INCR(sls_compressedin)
433	cp = *bufp;
434	changes = *cp++;
435	if (changes & NEW_C) {
436	/* Make sure the state index is in range, then grab the state.
437	* If we have a good state index, clear the 'discard' flag. */
438	if (*cp >= MAX_STATES)
439	goto bad;
440
441	comp->flags &=~ SLF_TOSS;
442	comp->last_recv = *cp++;
443	} else {
444	/* this packet has an implicit state index. If we've
445	* had a line error since the last time we got an
446	* explicit state index, we have to toss the packet. */
447	if (comp->flags & SLF_TOSS) {
448	INCR(sls_tossed)
449	return (0);
450	}
451	}
452	cs = &comp->rstate[comp->last_recv];
453	hlen = cs->cs_ip.ip_hl << 2;
454	th = (struct tcphdr )&((u_char )&cs->cs_ip)[hlen];
455	th->th_sum = htons((*cp << 8) \| cp[1]);
456	cp += 2;
457	if (changes & TCP_PUSH_BIT)
458	th->th_flags \|= TH_PUSH;
459	else
460	th->th_flags &=~ TH_PUSH;
461
462	switch (changes & SPECIALS_MASK) {
463	case SPECIAL_I:
464	{
465	register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
466	th->th_ack = htonl(ntohl(th->th_ack) + i);
467	th->th_seq = htonl(ntohl(th->th_seq) + i);
468	}
469	break;
470
471	case SPECIAL_D:
472	th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
473	- cs->cs_hlen);
474	break;
475
476	default:
477	if (changes & NEW_U) {
478	th->th_flags \|= TH_URG;
479	DECODEU(th->th_urp)
480	} else
481	th->th_flags &=~ TH_URG;
482	if (changes & NEW_W)
483	DECODES(th->th_win)
484	if (changes & NEW_A)
485	DECODEL(th->th_ack)
486	if (changes & NEW_S)
487	DECODEL(th->th_seq)
488	break;
489	}
490	if (changes & NEW_I) {
491	DECODES(cs->cs_ip.ip_id)
492	} else
493	cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
494
495	/*
496	* At this point, cp points to the first byte of data in the
497	* packet. If we're not aligned on a 4-byte boundary, copy the
498	* data down so the ip & tcp headers will be aligned. Then back up
499	* cp by the tcp/ip header length to make room for the reconstructed
500	* header (we assume the packet we were handed has enough space to
501	* prepend 128 bytes of header). Adjust the length to account for
502	* the new header & fill in the IP total length.
503	*/
504	len -= (cp - *bufp);
505	if (len < 0)
506	/* we must have dropped some characters (crc should detect
507	* this but the old slip framing won't) */
508	goto bad;
509
510	if ((int)cp & 3) {
511	if (len > 0)
512	(void) ovbcopy(cp, (caddr_t)((int)cp &~ 3), len);
513	cp = (u_char *)((int)cp &~ 3);
514	}
515	cp -= cs->cs_hlen;
516	len += cs->cs_hlen;
517	cs->cs_ip.ip_len = htons(len);
518	BCOPY(&cs->cs_ip, cp, cs->cs_hlen);
519	*bufp = cp;
520
521	/* recompute the ip header checksum */
522	{
523	register u_short bp = (u_short )cp;
524	for (changes = 0; hlen > 0; hlen -= 2)
525	changes += *bp++;
526	changes = (changes & 0xffff) + (changes >> 16);
527	changes = (changes & 0xffff) + (changes >> 16);
528	((struct ip *)cp)->ip_sum = ~ changes;
529	}
530	return (len);
531	bad:
532	comp->flags \|= SLF_TOSS;
533	INCR(sls_errorin)
534	return (0);
535	}