1 /* $Id: slcompress.c,v 1.3 1996/05/24 07:04:47 paulus Exp $ */
4 * Copyright (c) 1989, 1993, 1994
5 * The Regents of the University of California. All rights reserved.
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17 * This product includes software developed by the University of
18 * California, Berkeley and its contributors.
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35 * @(#)slcompress.c 8.2 (Berkeley) 4/16/94
39 * Routines to compress and uncompess tcp packets (for transmission
40 * over low speed serial lines.
42 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
43 * - Initial distribution.
46 #include <sys/param.h>
48 #include <sys/systm.h>
50 #include <netinet/in.h>
51 #include <netinet/in_systm.h>
52 #include <netinet/ip.h>
53 #include <netinet/tcp.h>
55 #include <net/slcompress.h>
58 #define INCR(counter) ++comp->counter;
63 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n))
64 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n))
70 sl_compress_init(comp, max_state)
71 struct slcompress *comp;
75 register struct cstate *tstate = comp->tstate;
77 if (max_state == -1) {
78 max_state = MAX_STATES - 1;
79 bzero((char *)comp, sizeof(*comp));
81 /* Don't reset statistics */
82 bzero((char *)comp->tstate, sizeof(comp->tstate));
83 bzero((char *)comp->rstate, sizeof(comp->rstate));
85 for (i = max_state; i > 0; --i) {
87 tstate[i].cs_next = &tstate[i - 1];
89 tstate[0].cs_next = &tstate[max_state];
91 comp->last_cs = &tstate[0];
92 comp->last_recv = 255;
93 comp->last_xmit = 255;
94 comp->flags = SLF_TOSS;
98 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ
99 * checks for zero (since zero has to be encoded in the long, 3 byte
102 #define ENCODE(n) { \
103 if ((u_int16_t)(n) >= 256) { \
112 #define ENCODEZ(n) { \
113 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \
123 #define DECODEL(f) { \
125 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
128 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \
132 #define DECODES(f) { \
134 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
137 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \
141 #define DECODEU(f) { \
143 (f) = htons((cp[1] << 8) | cp[2]); \
146 (f) = htons((u_int32_t)*cp++); \
151 sl_compress_tcp(m, ip, comp, compress_cid)
153 register struct ip *ip;
154 struct slcompress *comp;
157 register struct cstate *cs = comp->last_cs->cs_next;
158 register u_int hlen = ip->ip_hl;
159 register struct tcphdr *oth;
160 register struct tcphdr *th;
161 register u_int deltaS, deltaA;
162 register u_int changes = 0;
164 register u_char *cp = new_seq;
167 * Bail if this is an IP fragment or if the TCP packet isn't
168 * `compressible' (i.e., ACK isn't set or some other control bit is
169 * set). (We assume that the caller has already made sure the
170 * packet is IP proto TCP).
172 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40)
175 th = (struct tcphdr *)&((int32_t *)ip)[hlen];
176 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
179 * Packet is compressible -- we're going to send either a
180 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
181 * to locate (or create) the connection state. Special case the
182 * most recently used connection since it's most likely to be used
183 * again & we don't have to do any reordering if it's used.
186 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
187 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
188 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
190 * Wasn't the first -- search for it.
192 * States are kept in a circularly linked list with
193 * last_cs pointing to the end of the list. The
194 * list is kept in lru order by moving a state to the
195 * head of the list whenever it is referenced. Since
196 * the list is short and, empirically, the connection
197 * we want is almost always near the front, we locate
198 * states via linear search. If we don't find a state
199 * for the datagram, the oldest state is (re-)used.
201 register struct cstate *lcs;
202 register struct cstate *lastcs = comp->last_cs;
205 lcs = cs; cs = cs->cs_next;
207 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
208 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
210 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl])
212 } while (cs != lastcs);
215 * Didn't find it -- re-use oldest cstate. Send an
216 * uncompressed packet that tells the other side what
217 * connection number we're using for this conversation.
218 * Note that since the state list is circular, the oldest
219 * state points to the newest and we only need to set
220 * last_cs to update the lru linkage.
230 * Found it -- move to the front on the connection list.
235 lcs->cs_next = cs->cs_next;
236 cs->cs_next = lastcs->cs_next;
237 lastcs->cs_next = cs;
242 * Make sure that only what we expect to change changed. The first
243 * line of the `if' checks the IP protocol version, header length &
244 * type of service. The 2nd line checks the "Don't fragment" bit.
245 * The 3rd line checks the time-to-live and protocol (the protocol
246 * check is unnecessary but costless). The 4th line checks the TCP
247 * header length. The 5th line checks IP options, if any. The 6th
248 * line checks TCP options, if any. If any of these things are
249 * different between the previous & current datagram, we send the
250 * current datagram `uncompressed'.
252 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen];
257 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] ||
258 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] ||
259 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] ||
260 th->th_off != oth->th_off ||
262 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
264 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
268 * Figure out which of the changing fields changed. The
269 * receiver expects changes in the order: urgent, window,
270 * ack, seq (the order minimizes the number of temporaries
271 * needed in this section of code).
273 if (th->th_flags & TH_URG) {
274 deltaS = ntohs(th->th_urp);
277 } else if (th->th_urp != oth->th_urp)
278 /* argh! URG not set but urp changed -- a sensible
279 * implementation should never do this but RFC793
280 * doesn't prohibit the change so we have to deal
284 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win));
290 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack);
298 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq);
310 * Nothing changed. If this packet contains data and the
311 * last one didn't, this is probably a data packet following
312 * an ack (normal on an interactive connection) and we send
313 * it compressed. Otherwise it's probably a retransmit,
314 * retransmitted ack or window probe. Send it uncompressed
315 * in case the other side missed the compressed version.
317 if (ip->ip_len != cs->cs_ip.ip_len &&
318 ntohs(cs->cs_ip.ip_len) == hlen)
326 * actual changes match one of our special case encodings --
327 * send packet uncompressed.
332 if (deltaS == deltaA &&
333 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
334 /* special case for echoed terminal traffic */
341 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
342 /* special case for data xfer */
349 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
354 if (th->th_flags & TH_PUSH)
355 changes |= TCP_PUSH_BIT;
357 * Grab the cksum before we overwrite it below. Then update our
358 * state with this packet's header.
360 deltaA = ntohs(th->th_sum);
361 BCOPY(ip, &cs->cs_ip, hlen);
364 * We want to use the original packet as our compressed packet.
365 * (cp - new_seq) is the number of bytes we need for compressed
366 * sequence numbers. In addition we need one byte for the change
367 * mask, one for the connection id and two for the tcp checksum.
368 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
369 * many bytes of the original packet to toss so subtract the two to
370 * get the new packet size.
372 deltaS = cp - new_seq;
374 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
375 comp->last_xmit = cs->cs_id;
378 *cp++ = changes | NEW_C;
389 BCOPY(new_seq, cp, deltaS);
391 return (TYPE_COMPRESSED_TCP);
394 * Update connection state cs & send uncompressed packet ('uncompressed'
395 * means a regular ip/tcp packet but with the 'conversation id' we hope
396 * to use on future compressed packets in the protocol field).
399 BCOPY(ip, &cs->cs_ip, hlen);
400 ip->ip_p = cs->cs_id;
401 comp->last_xmit = cs->cs_id;
402 return (TYPE_UNCOMPRESSED_TCP);
407 sl_uncompress_tcp(bufp, len, type, comp)
411 struct slcompress *comp;
416 cp = bufp? *bufp: NULL;
417 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen);
419 return (0); /* error */
421 return (len); /* was uncompressed already */
427 * At this point, cp points to the first byte of data in the
428 * packet. If we're not aligned on a 4-byte boundary, copy the
429 * data down so the ip & tcp headers will be aligned. Then back up
430 * cp by the tcp/ip header length to make room for the reconstructed
431 * header (we assume the packet we were handed has enough space to
432 * prepend 128 bytes of header).
436 (void) ovbcopy(cp, (caddr_t)((long)cp &~ 3), len);
437 cp = (u_char *)((long)cp &~ 3);
441 BCOPY(hdr, cp, hlen);
448 * Uncompress a packet of total length total_len. The first buflen
449 * bytes are at buf; this must include the entire (compressed or
450 * uncompressed) TCP/IP header. This procedure returns the length
451 * of the VJ header, with a pointer to the uncompressed IP header
452 * in *hdrp and its length in *hlenp.
455 sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp)
457 int buflen, total_len;
459 struct slcompress *comp;
464 register u_int hlen, changes;
465 register struct tcphdr *th;
466 register struct cstate *cs;
467 register struct ip *ip;
468 register u_int16_t *bp;
469 register u_int vjlen;
473 case TYPE_UNCOMPRESSED_TCP:
474 ip = (struct ip *) buf;
475 if (ip->ip_p >= MAX_STATES)
477 cs = &comp->rstate[comp->last_recv = ip->ip_p];
478 comp->flags &=~ SLF_TOSS;
479 ip->ip_p = IPPROTO_TCP;
481 * Calculate the size of the TCP/IP header and make sure that
482 * we don't overflow the space we have available for it.
484 hlen = ip->ip_hl << 2;
485 if (hlen + sizeof(struct tcphdr) > buflen)
487 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2;
488 if (hlen > MAX_HDR || hlen > buflen)
490 BCOPY(ip, &cs->cs_ip, hlen);
492 INCR(sls_uncompressedin)
493 *hdrp = (u_char *) &cs->cs_ip;
500 case TYPE_COMPRESSED_TCP:
503 /* We've got a compressed packet. */
504 INCR(sls_compressedin)
507 if (changes & NEW_C) {
508 /* Make sure the state index is in range, then grab the state.
509 * If we have a good state index, clear the 'discard' flag. */
510 if (*cp >= MAX_STATES)
513 comp->flags &=~ SLF_TOSS;
514 comp->last_recv = *cp++;
516 /* this packet has an implicit state index. If we've
517 * had a line error since the last time we got an
518 * explicit state index, we have to toss the packet. */
519 if (comp->flags & SLF_TOSS) {
524 cs = &comp->rstate[comp->last_recv];
525 hlen = cs->cs_ip.ip_hl << 2;
526 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
527 th->th_sum = htons((*cp << 8) | cp[1]);
529 if (changes & TCP_PUSH_BIT)
530 th->th_flags |= TH_PUSH;
532 th->th_flags &=~ TH_PUSH;
534 switch (changes & SPECIALS_MASK) {
537 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
538 th->th_ack = htonl(ntohl(th->th_ack) + i);
539 th->th_seq = htonl(ntohl(th->th_seq) + i);
544 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
549 if (changes & NEW_U) {
550 th->th_flags |= TH_URG;
553 th->th_flags &=~ TH_URG;
562 if (changes & NEW_I) {
563 DECODES(cs->cs_ip.ip_id)
565 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
568 * At this point, cp points to the first byte of data in the
569 * packet. Fill in the IP total length and update the IP
575 /* we must have dropped some characters (crc should detect
576 * this but the old slip framing won't) */
579 total_len += cs->cs_hlen - vjlen;
580 cs->cs_ip.ip_len = htons(total_len);
582 /* recompute the ip header checksum */
583 bp = (u_int16_t *) &cs->cs_ip;
584 cs->cs_ip.ip_sum = 0;
585 for (changes = 0; hlen > 0; hlen -= 2)
587 changes = (changes & 0xffff) + (changes >> 16);
588 changes = (changes & 0xffff) + (changes >> 16);
589 cs->cs_ip.ip_sum = ~ changes;
591 *hdrp = (u_char *) &cs->cs_ip;
592 *hlenp = cs->cs_hlen;
596 comp->flags |= SLF_TOSS;