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 1.2 1994/09/19 04:20:13 paulus Exp $
30 #include <sys/types.h>
31 #include <sys/param.h>
32 #include <netinet/in.h>
33 #include <netinet/in_systm.h>
34 #include <netinet/ip.h>
35 #include <netinet/tcp.h>
37 #include <net/ppp_defs.h>
38 #include <net/vjcompress.h>
41 #define INCR(counter) ++comp->stats.counter
46 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n))
48 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n))
54 vj_compress_init(comp, max_state)
55 struct vjcompress *comp;
59 register struct cstate *tstate = comp->tstate;
62 max_state = MAX_STATES - 1;
63 bzero((char *)comp, sizeof(*comp));
64 for (i = max_state; i > 0; --i) {
66 tstate[i].cs_next = &tstate[i - 1];
68 tstate[0].cs_next = &tstate[max_state];
70 comp->last_cs = &tstate[0];
71 comp->last_recv = 255;
72 comp->last_xmit = 255;
73 comp->flags = VJF_TOSS;
77 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ
78 * checks for zero (since zero has to be encoded in the long, 3 byte
82 if ((u_short)(n) >= 256) { \
91 #define ENCODEZ(n) { \
92 if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \
102 #define DECODEL(f) { \
104 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
107 (f) = htonl(ntohl(f) + (u_long)*cp++); \
111 #define DECODES(f) { \
113 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
116 (f) = htons(ntohs(f) + (u_long)*cp++); \
120 #define DECODEU(f) { \
122 (f) = htons((cp[1] << 8) | cp[2]); \
125 (f) = htons((u_long)*cp++); \
130 vj_compress_tcp(ip, mlen, comp, compress_cid, vjhdrp)
131 register struct ip *ip;
133 struct vjcompress *comp;
137 register struct cstate *cs = comp->last_cs->cs_next;
138 register u_int hlen = ip->ip_hl;
139 register struct tcphdr *oth;
140 register struct tcphdr *th;
141 register u_int deltaS, deltaA;
142 register u_int changes = 0;
144 register u_char *cp = new_seq;
147 * Bail if this is an IP fragment or if the TCP packet isn't
148 * `compressible' (i.e., ACK isn't set or some other control bit is
149 * set). (We assume that the caller has already made sure the
150 * packet is IP proto TCP).
152 if ((ip->ip_off & htons(0x3fff)) || mlen < 40)
155 th = (struct tcphdr *)&((int *)ip)[hlen];
156 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
159 * Packet is compressible -- we're going to send either a
160 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
161 * to locate (or create) the connection state. Special case the
162 * most recently used connection since it's most likely to be used
163 * again & we don't have to do any reordering if it's used.
166 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
167 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
168 *(int *)th != ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
170 * Wasn't the first -- search for it.
172 * States are kept in a circularly linked list with
173 * last_cs pointing to the end of the list. The
174 * list is kept in lru order by moving a state to the
175 * head of the list whenever it is referenced. Since
176 * the list is short and, empirically, the connection
177 * we want is almost always near the front, we locate
178 * states via linear search. If we don't find a state
179 * for the datagram, the oldest state is (re-)used.
181 register struct cstate *lcs;
182 register struct cstate *lastcs = comp->last_cs;
185 lcs = cs; cs = cs->cs_next;
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 && *(int *)th == ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl])
191 } while (cs != lastcs);
194 * Didn't find it -- re-use oldest cstate. Send an
195 * uncompressed packet that tells the other side what
196 * connection number we're using for this conversation.
197 * Note that since the state list is circular, the oldest
198 * state points to the newest and we only need to set
199 * last_cs to update the lru linkage.
211 * Found it -- move to the front on the connection list.
216 lcs->cs_next = cs->cs_next;
217 cs->cs_next = lastcs->cs_next;
218 lastcs->cs_next = cs;
223 * Make sure that only what we expect to change changed. The first
224 * line of the `if' checks the IP protocol version, header length &
225 * type of service. The 2nd line checks the "Don't fragment" bit.
226 * The 3rd line checks the time-to-live and protocol (the protocol
227 * check is unnecessary but costless). The 4th line checks the TCP
228 * header length. The 5th line checks IP options, if any. The 6th
229 * line checks TCP options, if any. If any of these things are
230 * different between the previous & current datagram, we send the
231 * current datagram `uncompressed'.
233 oth = (struct tcphdr *)&((int *)&cs->cs_ip)[hlen];
240 if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0] ||
241 ((u_short *)ip)[3] != ((u_short *)&cs->cs_ip)[3] ||
242 ((u_short *)ip)[4] != ((u_short *)&cs->cs_ip)[4] ||
243 th->th_off != oth->th_off ||
244 (deltaS > 5 && BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
245 (th->th_off > 5 && BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
249 * Figure out which of the changing fields changed. The
250 * receiver expects changes in the order: urgent, window,
251 * ack, seq (the order minimizes the number of temporaries
252 * needed in this section of code).
254 if (th->th_flags & TH_URG) {
255 deltaS = ntohs(th->th_urp);
258 } else if (th->th_urp != oth->th_urp)
259 /* argh! URG not set but urp changed -- a sensible
260 * implementation should never do this but RFC793
261 * doesn't prohibit the change so we have to deal
265 if (deltaS = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win))) {
270 if (deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack)) {
277 if (deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq)) {
288 * Nothing changed. If this packet contains data and the
289 * last one didn't, this is probably a data packet following
290 * an ack (normal on an interactive connection) and we send
291 * it compressed. Otherwise it's probably a retransmit,
292 * retransmitted ack or window probe. Send it uncompressed
293 * in case the other side missed the compressed version.
295 if (ip->ip_len != cs->cs_ip.ip_len &&
296 ntohs(cs->cs_ip.ip_len) == hlen)
304 * actual changes match one of our special case encodings --
305 * send packet uncompressed.
310 if (deltaS == deltaA && deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
311 /* special case for echoed terminal traffic */
318 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
319 /* special case for data xfer */
326 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
331 if (th->th_flags & TH_PUSH)
332 changes |= TCP_PUSH_BIT;
334 * Grab the cksum before we overwrite it below. Then update our
335 * state with this packet's header.
337 deltaA = ntohs(th->th_sum);
338 BCOPY(ip, &cs->cs_ip, hlen);
341 * We want to use the original packet as our compressed packet.
342 * (cp - new_seq) is the number of bytes we need for compressed
343 * sequence numbers. In addition we need one byte for the change
344 * mask, one for the connection id and two for the tcp checksum.
345 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
346 * many bytes of the original packet to toss so subtract the two to
347 * get the new packet size.
349 deltaS = cp - new_seq;
351 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
352 comp->last_xmit = cs->cs_id;
354 *vjhdrp = (cp += hlen);
355 *cp++ = changes | NEW_C;
359 *vjhdrp = (cp += hlen);
364 BCOPY(new_seq, cp, deltaS);
365 INCR(vjs_compressed);
366 return (TYPE_COMPRESSED_TCP);
369 * Update connection state cs & send uncompressed packet (that is,
370 * a regular ip/tcp packet but with the 'conversation id' we hope
371 * to use on future compressed packets in the protocol field).
374 BCOPY(ip, &cs->cs_ip, hlen);
375 ip->ip_p = cs->cs_id;
376 comp->last_xmit = cs->cs_id;
377 return (TYPE_UNCOMPRESSED_TCP);
381 * Called when we may have missed a packet.
384 vj_uncompress_err(comp)
385 struct vjcompress *comp;
387 comp->flags |= VJF_TOSS;
392 * "Uncompress" a packet of type TYPE_UNCOMPRESSED_TCP.
395 vj_uncompress_uncomp(buf, comp)
397 struct vjcompress *comp;
400 register struct cstate *cs;
401 register struct ip *ip;
403 ip = (struct ip *) buf;
404 if (ip->ip_p >= MAX_STATES) {
405 comp->flags |= VJF_TOSS;
409 cs = &comp->rstate[comp->last_recv = ip->ip_p];
410 comp->flags &=~ VJF_TOSS;
411 ip->ip_p = IPPROTO_TCP;
413 hlen += ((struct tcphdr *)&((int *)ip)[hlen])->th_off;
415 BCOPY(ip, &cs->cs_ip, hlen);
417 INCR(vjs_uncompressedin);
422 * Uncompress a packet of type TYPE_COMPRESSED_TCP.
423 * The packet starts at buf and is of total length total_len.
424 * The first buflen bytes are at buf; this must include the entire
425 * compressed TCP/IP header. This procedure returns the length
426 * of the VJ header, with a pointer to the uncompressed IP header
427 * in *hdrp and its length in *hlenp.
430 vj_uncompress_tcp(buf, buflen, total_len, comp, hdrp, hlenp)
432 int buflen, total_len;
433 struct vjcompress *comp;
438 register u_int hlen, changes;
439 register struct tcphdr *th;
440 register struct cstate *cs;
441 register struct ip *ip;
442 register u_short *bp;
443 register u_int vjlen;
445 INCR(vjs_compressedin);
448 if (changes & NEW_C) {
449 /* Make sure the state index is in range, then grab the state.
450 * If we have a good state index, clear the 'discard' flag. */
451 if (*cp >= MAX_STATES)
454 comp->flags &=~ VJF_TOSS;
455 comp->last_recv = *cp++;
457 /* this packet has an implicit state index. If we've
458 * had a line error since the last time we got an
459 * explicit state index, we have to toss the packet. */
460 if (comp->flags & VJF_TOSS) {
465 cs = &comp->rstate[comp->last_recv];
466 hlen = cs->cs_ip.ip_hl << 2;
467 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
468 th->th_sum = htons((*cp << 8) | cp[1]);
470 if (changes & TCP_PUSH_BIT)
471 th->th_flags |= TH_PUSH;
473 th->th_flags &=~ TH_PUSH;
475 switch (changes & SPECIALS_MASK) {
478 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
479 th->th_ack = htonl(ntohl(th->th_ack) + i);
480 th->th_seq = htonl(ntohl(th->th_seq) + i);
485 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
490 if (changes & NEW_U) {
491 th->th_flags |= TH_URG;
494 th->th_flags &=~ TH_URG;
503 if (changes & NEW_I) {
504 DECODES(cs->cs_ip.ip_id);
506 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
509 * At this point, cp points to the first byte of data in the
510 * packet. Fill in the IP total length and update the IP
516 /* we must have dropped some characters (crc should detect
517 * this but the old slip framing won't) */
520 total_len += cs->cs_hlen - vjlen;
521 cs->cs_ip.ip_len = htons(total_len);
523 /* recompute the ip header checksum */
524 bp = (u_short *) &cs->cs_ip;
525 cs->cs_ip.ip_sum = 0;
526 for (changes = 0; hlen > 0; hlen -= 2)
528 changes = (changes & 0xffff) + (changes >> 16);
529 changes = (changes & 0xffff) + (changes >> 16);
530 cs->cs_ip.ip_sum = ~ changes;
532 *hdrp = (u_char *) &cs->cs_ip;
533 *hlenp = cs->cs_hlen;
537 comp->flags |= VJF_TOSS;