1 /* $NetBSD: slcompress.c,v 1.15 1996/03/15 02:28:12 paulus Exp $ */
2 /* Id: slcompress.c,v 1.3 1996/05/24 07:04:47 paulus Exp */
5 * Copyright (c) 1989, 1993, 1994
6 * The Regents of the University of California. All rights reserved.
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
16 * 3. All advertising materials mentioning features or use of this software
17 * must display the following acknowledgement:
18 * This product includes software developed by the University of
19 * California, Berkeley and its contributors.
20 * 4. Neither the name of the University nor the names of its contributors
21 * may be used to endorse or promote products derived from this software
22 * without specific prior written permission.
24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
27 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
36 * @(#)slcompress.c 8.2 (Berkeley) 4/16/94
40 * Routines to compress and uncompess tcp packets (for transmission
41 * over low speed serial lines.
43 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
44 * - Initial distribution.
47 #include <sys/param.h>
49 #include <sys/systm.h>
51 #include <netinet/in.h>
52 #include <netinet/in_systm.h>
53 #include <netinet/ip.h>
54 #include <netinet/tcp.h>
56 #include <net/slcompress.h>
59 #define INCR(counter) ++comp->counter;
64 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n))
65 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n))
71 sl_compress_init(comp, max_state)
72 struct slcompress *comp;
76 register struct cstate *tstate = comp->tstate;
78 if (max_state == -1) {
79 max_state = MAX_STATES - 1;
80 bzero((char *)comp, sizeof(*comp));
82 /* Don't reset statistics */
83 bzero((char *)comp->tstate, sizeof(comp->tstate));
84 bzero((char *)comp->rstate, sizeof(comp->rstate));
86 for (i = max_state; i > 0; --i) {
88 tstate[i].cs_next = &tstate[i - 1];
90 tstate[0].cs_next = &tstate[max_state];
92 comp->last_cs = &tstate[0];
93 comp->last_recv = 255;
94 comp->last_xmit = 255;
95 comp->flags = SLF_TOSS;
99 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ
100 * checks for zero (since zero has to be encoded in the long, 3 byte
103 #define ENCODE(n) { \
104 if ((u_int16_t)(n) >= 256) { \
113 #define ENCODEZ(n) { \
114 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \
124 #define DECODEL(f) { \
126 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
129 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \
133 #define DECODES(f) { \
135 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
138 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \
142 #define DECODEU(f) { \
144 (f) = htons((cp[1] << 8) | cp[2]); \
147 (f) = htons((u_int32_t)*cp++); \
152 sl_compress_tcp(m, ip, comp, compress_cid)
154 register struct ip *ip;
155 struct slcompress *comp;
158 register struct cstate *cs = comp->last_cs->cs_next;
159 register u_int hlen = ip->ip_hl;
160 register struct tcphdr *oth;
161 register struct tcphdr *th;
162 register u_int deltaS, deltaA;
163 register u_int changes = 0;
165 register u_char *cp = new_seq;
168 * Bail if this is an IP fragment or if the TCP packet isn't
169 * `compressible' (i.e., ACK isn't set or some other control bit is
170 * set). (We assume that the caller has already made sure the
171 * packet is IP proto TCP).
173 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40)
176 th = (struct tcphdr *)&((int32_t *)ip)[hlen];
177 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
180 * Packet is compressible -- we're going to send either a
181 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
182 * to locate (or create) the connection state. Special case the
183 * most recently used connection since it's most likely to be used
184 * again & we don't have to do any reordering if it's used.
187 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
188 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
189 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
191 * Wasn't the first -- search for it.
193 * States are kept in a circularly linked list with
194 * last_cs pointing to the end of the list. The
195 * list is kept in lru order by moving a state to the
196 * head of the list whenever it is referenced. Since
197 * the list is short and, empirically, the connection
198 * we want is almost always near the front, we locate
199 * states via linear search. If we don't find a state
200 * for the datagram, the oldest state is (re-)used.
202 register struct cstate *lcs;
203 register struct cstate *lastcs = comp->last_cs;
206 lcs = cs; cs = cs->cs_next;
208 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
209 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
211 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl])
213 } while (cs != lastcs);
216 * Didn't find it -- re-use oldest cstate. Send an
217 * uncompressed packet that tells the other side what
218 * connection number we're using for this conversation.
219 * Note that since the state list is circular, the oldest
220 * state points to the newest and we only need to set
221 * last_cs to update the lru linkage.
231 * Found it -- move to the front on the connection list.
236 lcs->cs_next = cs->cs_next;
237 cs->cs_next = lastcs->cs_next;
238 lastcs->cs_next = cs;
243 * Make sure that only what we expect to change changed. The first
244 * line of the `if' checks the IP protocol version, header length &
245 * type of service. The 2nd line checks the "Don't fragment" bit.
246 * The 3rd line checks the time-to-live and protocol (the protocol
247 * check is unnecessary but costless). The 4th line checks the TCP
248 * header length. The 5th line checks IP options, if any. The 6th
249 * line checks TCP options, if any. If any of these things are
250 * different between the previous & current datagram, we send the
251 * current datagram `uncompressed'.
253 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen];
258 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] ||
259 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] ||
260 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] ||
261 th->th_off != oth->th_off ||
263 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
265 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
269 * Figure out which of the changing fields changed. The
270 * receiver expects changes in the order: urgent, window,
271 * ack, seq (the order minimizes the number of temporaries
272 * needed in this section of code).
274 if (th->th_flags & TH_URG) {
275 deltaS = ntohs(th->th_urp);
278 } else if (th->th_urp != oth->th_urp)
279 /* argh! URG not set but urp changed -- a sensible
280 * implementation should never do this but RFC793
281 * doesn't prohibit the change so we have to deal
285 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win));
291 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack);
299 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq);
311 * Nothing changed. If this packet contains data and the
312 * last one didn't, this is probably a data packet following
313 * an ack (normal on an interactive connection) and we send
314 * it compressed. Otherwise it's probably a retransmit,
315 * retransmitted ack or window probe. Send it uncompressed
316 * in case the other side missed the compressed version.
318 if (ip->ip_len != cs->cs_ip.ip_len &&
319 ntohs(cs->cs_ip.ip_len) == hlen)
327 * actual changes match one of our special case encodings --
328 * send packet uncompressed.
333 if (deltaS == deltaA &&
334 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
335 /* special case for echoed terminal traffic */
342 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
343 /* special case for data xfer */
350 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
355 if (th->th_flags & TH_PUSH)
356 changes |= TCP_PUSH_BIT;
358 * Grab the cksum before we overwrite it below. Then update our
359 * state with this packet's header.
361 deltaA = ntohs(th->th_sum);
362 BCOPY(ip, &cs->cs_ip, hlen);
365 * We want to use the original packet as our compressed packet.
366 * (cp - new_seq) is the number of bytes we need for compressed
367 * sequence numbers. In addition we need one byte for the change
368 * mask, one for the connection id and two for the tcp checksum.
369 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
370 * many bytes of the original packet to toss so subtract the two to
371 * get the new packet size.
373 deltaS = cp - new_seq;
375 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
376 comp->last_xmit = cs->cs_id;
379 *cp++ = changes | NEW_C;
390 BCOPY(new_seq, cp, deltaS);
392 return (TYPE_COMPRESSED_TCP);
395 * Update connection state cs & send uncompressed packet ('uncompressed'
396 * means a regular ip/tcp packet but with the 'conversation id' we hope
397 * to use on future compressed packets in the protocol field).
400 BCOPY(ip, &cs->cs_ip, hlen);
401 ip->ip_p = cs->cs_id;
402 comp->last_xmit = cs->cs_id;
403 return (TYPE_UNCOMPRESSED_TCP);
408 sl_uncompress_tcp(bufp, len, type, comp)
412 struct slcompress *comp;
417 cp = bufp? *bufp: NULL;
418 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen);
420 return (0); /* error */
422 return (len); /* was uncompressed already */
428 * At this point, cp points to the first byte of data in the
429 * packet. If we're not aligned on a 4-byte boundary, copy the
430 * data down so the ip & tcp headers will be aligned. Then back up
431 * cp by the tcp/ip header length to make room for the reconstructed
432 * header (we assume the packet we were handed has enough space to
433 * prepend 128 bytes of header).
437 (void) ovbcopy(cp, (caddr_t)((long)cp &~ 3), len);
438 cp = (u_char *)((long)cp &~ 3);
442 BCOPY(hdr, cp, hlen);
449 * Uncompress a packet of total length total_len. The first buflen
450 * bytes are at buf; this must include the entire (compressed or
451 * uncompressed) TCP/IP header. This procedure returns the length
452 * of the VJ header, with a pointer to the uncompressed IP header
453 * in *hdrp and its length in *hlenp.
456 sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp)
458 int buflen, total_len;
460 struct slcompress *comp;
465 register u_int hlen, changes;
466 register struct tcphdr *th;
467 register struct cstate *cs;
468 register struct ip *ip;
469 register u_int16_t *bp;
470 register u_int vjlen;
474 case TYPE_UNCOMPRESSED_TCP:
475 ip = (struct ip *) buf;
476 if (ip->ip_p >= MAX_STATES)
478 cs = &comp->rstate[comp->last_recv = ip->ip_p];
479 comp->flags &=~ SLF_TOSS;
480 ip->ip_p = IPPROTO_TCP;
482 * Calculate the size of the TCP/IP header and make sure that
483 * we don't overflow the space we have available for it.
485 hlen = ip->ip_hl << 2;
486 if (hlen + sizeof(struct tcphdr) > buflen)
488 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2;
489 if (hlen > MAX_HDR || hlen > buflen)
491 BCOPY(ip, &cs->cs_ip, hlen);
493 INCR(sls_uncompressedin)
494 *hdrp = (u_char *) &cs->cs_ip;
501 case TYPE_COMPRESSED_TCP:
504 /* We've got a compressed packet. */
505 INCR(sls_compressedin)
508 if (changes & NEW_C) {
509 /* Make sure the state index is in range, then grab the state.
510 * If we have a good state index, clear the 'discard' flag. */
511 if (*cp >= MAX_STATES)
514 comp->flags &=~ SLF_TOSS;
515 comp->last_recv = *cp++;
517 /* this packet has an implicit state index. If we've
518 * had a line error since the last time we got an
519 * explicit state index, we have to toss the packet. */
520 if (comp->flags & SLF_TOSS) {
525 cs = &comp->rstate[comp->last_recv];
526 hlen = cs->cs_ip.ip_hl << 2;
527 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
528 th->th_sum = htons((*cp << 8) | cp[1]);
530 if (changes & TCP_PUSH_BIT)
531 th->th_flags |= TH_PUSH;
533 th->th_flags &=~ TH_PUSH;
535 switch (changes & SPECIALS_MASK) {
538 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
539 th->th_ack = htonl(ntohl(th->th_ack) + i);
540 th->th_seq = htonl(ntohl(th->th_seq) + i);
545 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
550 if (changes & NEW_U) {
551 th->th_flags |= TH_URG;
554 th->th_flags &=~ TH_URG;
563 if (changes & NEW_I) {
564 DECODES(cs->cs_ip.ip_id)
566 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
569 * At this point, cp points to the first byte of data in the
570 * packet. Fill in the IP total length and update the IP
576 /* we must have dropped some characters (crc should detect
577 * this but the old slip framing won't) */
580 total_len += cs->cs_hlen - vjlen;
581 cs->cs_ip.ip_len = htons(total_len);
583 /* recompute the ip header checksum */
584 bp = (u_int16_t *) &cs->cs_ip;
585 cs->cs_ip.ip_sum = 0;
586 for (changes = 0; hlen > 0; hlen -= 2)
588 changes = (changes & 0xffff) + (changes >> 16);
589 changes = (changes & 0xffff) + (changes >> 16);
590 cs->cs_ip.ip_sum = ~ changes;
592 *hdrp = (u_char *) &cs->cs_ip;
593 *hlenp = cs->cs_hlen;
597 comp->flags |= SLF_TOSS;