2 * Routines to compress and uncompess tcp packets (for transmission
3 * over low speed serial lines.
5 * Copyright (c) 1989 Regents of the University of California.
8 * Redistribution and use in source and binary forms are permitted
9 * provided that the above copyright notice and this paragraph are
10 * duplicated in all such forms and that any documentation,
11 * advertising materials, and other materials related to such
12 * distribution and use acknowledge that the software was developed
13 * by the University of California, Berkeley. The name of the
14 * University may not be used to endorse or promote products derived
15 * from this software without specific prior written permission.
16 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
17 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
18 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
20 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
21 * - Initial distribution.
23 * Modified June 1993 by Paul Mackerras, paulus@cs.anu.edu.au,
24 * so that the entire packet being decompressed doesn't have
25 * to be in contiguous memory (just the compressed header).
27 * $Id: vjcompress.c,v 1.4 1994/12/08 00:35:33 paulus Exp $
30 #include <sys/types.h>
31 #include <sys/param.h>
34 #include <net/net_globals.h>
36 #include <netinet/in.h>
39 #define _NETINET_IN_SYSTM_H_
40 typedef u_long n_long;
42 #include <netinet/in_systm.h>
45 #include <netinet/ip.h>
46 #include <netinet/tcp.h>
48 #include <net/ppp_defs.h>
49 #include <net/vjcompress.h>
52 #define INCR(counter) ++comp->stats.counter
57 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n))
59 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n))
65 #define getip_hl(base) (((base).ip_vhl)&0xf)
66 #define getth_off(base) ((((base).th_xoff)&0xf0)>>4)
69 #define getip_hl(base) ((base).ip_hl)
70 #define getth_off(base) ((base).th_off)
74 vj_compress_init(comp, max_state)
75 struct vjcompress *comp;
79 register struct cstate *tstate = comp->tstate;
82 max_state = MAX_STATES - 1;
83 bzero((char *)comp, sizeof(*comp));
84 for (i = max_state; i > 0; --i) {
86 tstate[i].cs_next = &tstate[i - 1];
88 tstate[0].cs_next = &tstate[max_state];
90 comp->last_cs = &tstate[0];
91 comp->last_recv = 255;
92 comp->last_xmit = 255;
93 comp->flags = VJF_TOSS;
97 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ
98 * checks for zero (since zero has to be encoded in the long, 3 byte
101 #define ENCODE(n) { \
102 if ((u_short)(n) >= 256) { \
111 #define ENCODEZ(n) { \
112 if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \
122 #define DECODEL(f) { \
124 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
127 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \
131 #define DECODES(f) { \
133 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
136 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \
140 #define DECODEU(f) { \
142 (f) = htons((cp[1] << 8) | cp[2]); \
145 (f) = htons((u_int32_t)*cp++); \
150 vj_compress_tcp(ip, mlen, comp, compress_cid, vjhdrp)
151 register struct ip *ip;
153 struct vjcompress *comp;
157 register struct cstate *cs = comp->last_cs->cs_next;
158 register u_int hlen = getip_hl(*ip);
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)) || mlen < 40)
175 th = (struct tcphdr *)&((int *)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 *(int *)th != ((int *)&cs->cs_ip)[getip_hl(cs->cs_ip)]) {
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
209 && *(int *)th == ((int *)&cs->cs_ip)[getip_hl(cs->cs_ip)])
211 } while (cs != lastcs);
214 * Didn't find it -- re-use oldest cstate. Send an
215 * uncompressed packet that tells the other side what
216 * connection number we're using for this conversation.
217 * Note that since the state list is circular, the oldest
218 * state points to the newest and we only need to set
219 * last_cs to update the lru linkage.
223 hlen += getth_off(*th);
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 *)&((int *)&cs->cs_ip)[hlen];
255 hlen += getth_off(*th);
260 if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0] ||
261 ((u_short *)ip)[3] != ((u_short *)&cs->cs_ip)[3] ||
262 ((u_short *)ip)[4] != ((u_short *)&cs->cs_ip)[4] ||
263 getth_off(*th) != getth_off(*oth) ||
264 (deltaS > 5 && BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
265 (getth_off(*th) > 5 && BCMP(th + 1, oth + 1, (getth_off(*th) - 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 if (deltaS = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win))) {
290 if (deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack)) {
297 if (deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq)) {
308 * Nothing changed. If this packet contains data and the
309 * last one didn't, this is probably a data packet following
310 * an ack (normal on an interactive connection) and we send
311 * it compressed. Otherwise it's probably a retransmit,
312 * retransmitted ack or window probe. Send it uncompressed
313 * in case the other side missed the compressed version.
315 if (ip->ip_len != cs->cs_ip.ip_len &&
316 ntohs(cs->cs_ip.ip_len) == hlen)
324 * actual changes match one of our special case encodings --
325 * send packet uncompressed.
330 if (deltaS == deltaA && deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
331 /* special case for echoed terminal traffic */
338 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
339 /* special case for data xfer */
346 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
351 if (th->th_flags & TH_PUSH)
352 changes |= TCP_PUSH_BIT;
354 * Grab the cksum before we overwrite it below. Then update our
355 * state with this packet's header.
357 deltaA = ntohs(th->th_sum);
358 BCOPY(ip, &cs->cs_ip, hlen);
361 * We want to use the original packet as our compressed packet.
362 * (cp - new_seq) is the number of bytes we need for compressed
363 * sequence numbers. In addition we need one byte for the change
364 * mask, one for the connection id and two for the tcp checksum.
365 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
366 * many bytes of the original packet to toss so subtract the two to
367 * get the new packet size.
369 deltaS = cp - new_seq;
371 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
372 comp->last_xmit = cs->cs_id;
374 *vjhdrp = (cp += hlen);
375 *cp++ = changes | NEW_C;
379 *vjhdrp = (cp += hlen);
384 BCOPY(new_seq, cp, deltaS);
385 INCR(vjs_compressed);
386 return (TYPE_COMPRESSED_TCP);
389 * Update connection state cs & send uncompressed packet (that is,
390 * a regular ip/tcp packet but with the 'conversation id' we hope
391 * to use on future compressed packets in the protocol field).
394 BCOPY(ip, &cs->cs_ip, hlen);
395 ip->ip_p = cs->cs_id;
396 comp->last_xmit = cs->cs_id;
397 return (TYPE_UNCOMPRESSED_TCP);
401 * Called when we may have missed a packet.
404 vj_uncompress_err(comp)
405 struct vjcompress *comp;
407 comp->flags |= VJF_TOSS;
412 * "Uncompress" a packet of type TYPE_UNCOMPRESSED_TCP.
415 vj_uncompress_uncomp(buf, comp)
417 struct vjcompress *comp;
420 register struct cstate *cs;
421 register struct ip *ip;
423 ip = (struct ip *) buf;
424 if (ip->ip_p >= MAX_STATES) {
425 comp->flags |= VJF_TOSS;
429 cs = &comp->rstate[comp->last_recv = ip->ip_p];
430 comp->flags &=~ VJF_TOSS;
431 ip->ip_p = IPPROTO_TCP;
432 hlen = getip_hl(*ip);
433 hlen += getth_off(*((struct tcphdr *)&((int *)ip)[hlen]));
435 BCOPY(ip, &cs->cs_ip, hlen);
437 INCR(vjs_uncompressedin);
442 * Uncompress a packet of type TYPE_COMPRESSED_TCP.
443 * The packet starts at buf and is of total length total_len.
444 * The first buflen bytes are at buf; this must include the entire
445 * compressed TCP/IP header. This procedure returns the length
446 * of the VJ header, with a pointer to the uncompressed IP header
447 * in *hdrp and its length in *hlenp.
450 vj_uncompress_tcp(buf, buflen, total_len, comp, hdrp, hlenp)
452 int buflen, total_len;
453 struct vjcompress *comp;
458 register u_int hlen, changes;
459 register struct tcphdr *th;
460 register struct cstate *cs;
461 register u_short *bp;
462 register u_int vjlen;
464 INCR(vjs_compressedin);
467 if (changes & NEW_C) {
468 /* Make sure the state index is in range, then grab the state.
469 * If we have a good state index, clear the 'discard' flag. */
470 if (*cp >= MAX_STATES)
473 comp->flags &=~ VJF_TOSS;
474 comp->last_recv = *cp++;
476 /* this packet has an implicit state index. If we've
477 * had a line error since the last time we got an
478 * explicit state index, we have to toss the packet. */
479 if (comp->flags & VJF_TOSS) {
484 cs = &comp->rstate[comp->last_recv];
485 hlen = getip_hl(cs->cs_ip) << 2;
486 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
487 th->th_sum = htons((*cp << 8) | cp[1]);
489 if (changes & TCP_PUSH_BIT)
490 th->th_flags |= TH_PUSH;
492 th->th_flags &=~ TH_PUSH;
494 switch (changes & SPECIALS_MASK) {
497 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
498 th->th_ack = htonl(ntohl(th->th_ack) + i);
499 th->th_seq = htonl(ntohl(th->th_seq) + i);
504 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
509 if (changes & NEW_U) {
510 th->th_flags |= TH_URG;
513 th->th_flags &=~ TH_URG;
522 if (changes & NEW_I) {
523 DECODES(cs->cs_ip.ip_id);
525 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
528 * At this point, cp points to the first byte of data in the
529 * packet. Fill in the IP total length and update the IP
535 /* we must have dropped some characters (crc should detect
536 * this but the old slip framing won't) */
539 total_len += cs->cs_hlen - vjlen;
540 cs->cs_ip.ip_len = htons(total_len);
542 /* recompute the ip header checksum */
543 bp = (u_short *) &cs->cs_ip;
544 cs->cs_ip.ip_sum = 0;
545 for (changes = 0; hlen > 0; hlen -= 2)
547 changes = (changes & 0xffff) + (changes >> 16);
548 changes = (changes & 0xffff) + (changes >> 16);
549 cs->cs_ip.ip_sum = ~ changes;
551 *hdrp = (u_char *) &cs->cs_ip;
552 *hlenp = cs->cs_hlen;
556 comp->flags |= VJF_TOSS;