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 1.1 1994/09/16 06:58:24 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>
43 #include <net/vjcompress.h>
46 #define INCR(counter) ++comp->counter
51 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n))
53 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n))
59 vj_compress_init(comp, max_state)
60 struct vjcompress *comp;
64 register struct cstate *tstate = comp->tstate;
67 max_state = MAX_STATES - 1;
68 bzero((char *)comp, sizeof(*comp));
69 for (i = max_state; i > 0; --i) {
71 tstate[i].cs_next = &tstate[i - 1];
73 tstate[0].cs_next = &tstate[max_state];
75 comp->last_cs = &tstate[0];
76 comp->last_recv = 255;
77 comp->last_xmit = 255;
78 comp->flags = VJF_TOSS;
82 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ
83 * checks for zero (since zero has to be encoded in the long, 3 byte
87 if ((u_short)(n) >= 256) { \
96 #define ENCODEZ(n) { \
97 if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \
107 #define DECODEL(f) { \
109 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
112 (f) = htonl(ntohl(f) + (u_long)*cp++); \
116 #define DECODES(f) { \
118 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
121 (f) = htons(ntohs(f) + (u_long)*cp++); \
125 #define DECODEU(f) { \
127 (f) = htons((cp[1] << 8) | cp[2]); \
130 (f) = htons((u_long)*cp++); \
135 vj_compress_tcp(ip, mlen, comp, compress_cid, vjhdrp)
136 register struct ip *ip;
138 struct vjcompress *comp;
142 register struct cstate *cs = comp->last_cs->cs_next;
143 register u_int hlen = ip->ip_hl;
144 register struct tcphdr *oth;
145 register struct tcphdr *th;
146 register u_int deltaS, deltaA;
147 register u_int changes = 0;
149 register u_char *cp = new_seq;
152 * Bail if this is an IP fragment or if the TCP packet isn't
153 * `compressible' (i.e., ACK isn't set or some other control bit is
154 * set). (We assume that the caller has already made sure the
155 * packet is IP proto TCP).
157 if ((ip->ip_off & htons(0x3fff)) || mlen < 40)
160 th = (struct tcphdr *)&((int *)ip)[hlen];
161 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
164 * Packet is compressible -- we're going to send either a
165 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
166 * to locate (or create) the connection state. Special case the
167 * most recently used connection since it's most likely to be used
168 * again & we don't have to do any reordering if it's used.
171 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
172 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
173 *(int *)th != ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
175 * Wasn't the first -- search for it.
177 * States are kept in a circularly linked list with
178 * last_cs pointing to the end of the list. The
179 * list is kept in lru order by moving a state to the
180 * head of the list whenever it is referenced. Since
181 * the list is short and, empirically, the connection
182 * we want is almost always near the front, we locate
183 * states via linear search. If we don't find a state
184 * for the datagram, the oldest state is (re-)used.
186 register struct cstate *lcs;
187 register struct cstate *lastcs = comp->last_cs;
190 lcs = cs; cs = cs->cs_next;
192 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
193 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
194 && *(int *)th == ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl])
196 } while (cs != lastcs);
199 * Didn't find it -- re-use oldest cstate. Send an
200 * uncompressed packet that tells the other side what
201 * connection number we're using for this conversation.
202 * Note that since the state list is circular, the oldest
203 * state points to the newest and we only need to set
204 * last_cs to update the lru linkage.
216 * Found it -- move to the front on the connection list.
221 lcs->cs_next = cs->cs_next;
222 cs->cs_next = lastcs->cs_next;
223 lastcs->cs_next = cs;
228 * Make sure that only what we expect to change changed. The first
229 * line of the `if' checks the IP protocol version, header length &
230 * type of service. The 2nd line checks the "Don't fragment" bit.
231 * The 3rd line checks the time-to-live and protocol (the protocol
232 * check is unnecessary but costless). The 4th line checks the TCP
233 * header length. The 5th line checks IP options, if any. The 6th
234 * line checks TCP options, if any. If any of these things are
235 * different between the previous & current datagram, we send the
236 * current datagram `uncompressed'.
238 oth = (struct tcphdr *)&((int *)&cs->cs_ip)[hlen];
245 if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0] ||
246 ((u_short *)ip)[3] != ((u_short *)&cs->cs_ip)[3] ||
247 ((u_short *)ip)[4] != ((u_short *)&cs->cs_ip)[4] ||
248 th->th_off != oth->th_off ||
249 (deltaS > 5 && BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
250 (th->th_off > 5 && BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
254 * Figure out which of the changing fields changed. The
255 * receiver expects changes in the order: urgent, window,
256 * ack, seq (the order minimizes the number of temporaries
257 * needed in this section of code).
259 if (th->th_flags & TH_URG) {
260 deltaS = ntohs(th->th_urp);
263 } else if (th->th_urp != oth->th_urp)
264 /* argh! URG not set but urp changed -- a sensible
265 * implementation should never do this but RFC793
266 * doesn't prohibit the change so we have to deal
270 if (deltaS = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win))) {
275 if (deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack)) {
282 if (deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq)) {
293 * Nothing changed. If this packet contains data and the
294 * last one didn't, this is probably a data packet following
295 * an ack (normal on an interactive connection) and we send
296 * it compressed. Otherwise it's probably a retransmit,
297 * retransmitted ack or window probe. Send it uncompressed
298 * in case the other side missed the compressed version.
300 if (ip->ip_len != cs->cs_ip.ip_len &&
301 ntohs(cs->cs_ip.ip_len) == hlen)
309 * actual changes match one of our special case encodings --
310 * send packet uncompressed.
315 if (deltaS == deltaA && deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
316 /* special case for echoed terminal traffic */
323 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
324 /* special case for data xfer */
331 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
336 if (th->th_flags & TH_PUSH)
337 changes |= TCP_PUSH_BIT;
339 * Grab the cksum before we overwrite it below. Then update our
340 * state with this packet's header.
342 deltaA = ntohs(th->th_sum);
343 BCOPY(ip, &cs->cs_ip, hlen);
346 * We want to use the original packet as our compressed packet.
347 * (cp - new_seq) is the number of bytes we need for compressed
348 * sequence numbers. In addition we need one byte for the change
349 * mask, one for the connection id and two for the tcp checksum.
350 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
351 * many bytes of the original packet to toss so subtract the two to
352 * get the new packet size.
354 deltaS = cp - new_seq;
356 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
357 comp->last_xmit = cs->cs_id;
359 *vjhdrp = (cp += hlen);
360 *cp++ = changes | NEW_C;
364 *vjhdrp = (cp += hlen);
369 BCOPY(new_seq, cp, deltaS);
370 INCR(vjs_compressed);
371 return (TYPE_COMPRESSED_TCP);
374 * Update connection state cs & send uncompressed packet (that is,
375 * a regular ip/tcp packet but with the 'conversation id' we hope
376 * to use on future compressed packets in the protocol field).
379 BCOPY(ip, &cs->cs_ip, hlen);
380 ip->ip_p = cs->cs_id;
381 comp->last_xmit = cs->cs_id;
382 return (TYPE_UNCOMPRESSED_TCP);
386 * Called when we may have missed a packet.
389 vj_uncompress_err(comp)
390 struct vjcompress *comp;
392 comp->flags |= VJF_TOSS;
397 * "Uncompress" a packet of type TYPE_UNCOMPRESSED_TCP.
400 vj_uncompress_uncomp(buf, comp)
402 struct vjcompress *comp;
405 register struct cstate *cs;
406 register struct ip *ip;
408 ip = (struct ip *) buf;
409 if (ip->ip_p >= MAX_STATES) {
410 comp->flags |= VJF_TOSS;
414 cs = &comp->rstate[comp->last_recv = ip->ip_p];
415 comp->flags &=~ VJF_TOSS;
416 ip->ip_p = IPPROTO_TCP;
418 hlen += ((struct tcphdr *)&((int *)ip)[hlen])->th_off;
420 BCOPY(ip, &cs->cs_ip, hlen);
422 INCR(vjs_uncompressedin);
427 * Uncompress a packet of type TYPE_COMPRESSED_TCP.
428 * The packet starts at buf and is of total length total_len.
429 * The first buflen bytes are at buf; this must include the entire
430 * compressed TCP/IP header. This procedure returns the length
431 * of the VJ header, with a pointer to the uncompressed IP header
432 * in *hdrp and its length in *hlenp.
435 vj_uncompress_tcp(buf, buflen, total_len, comp, hdrp, hlenp)
437 int buflen, total_len;
438 struct vjcompress *comp;
443 register u_int hlen, changes;
444 register struct tcphdr *th;
445 register struct cstate *cs;
446 register struct ip *ip;
447 register u_short *bp;
448 register u_int vjlen;
450 INCR(vjs_compressedin);
453 if (changes & NEW_C) {
454 /* Make sure the state index is in range, then grab the state.
455 * If we have a good state index, clear the 'discard' flag. */
456 if (*cp >= MAX_STATES)
459 comp->flags &=~ VJF_TOSS;
460 comp->last_recv = *cp++;
462 /* this packet has an implicit state index. If we've
463 * had a line error since the last time we got an
464 * explicit state index, we have to toss the packet. */
465 if (comp->flags & VJF_TOSS) {
470 cs = &comp->rstate[comp->last_recv];
471 hlen = cs->cs_ip.ip_hl << 2;
472 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
473 th->th_sum = htons((*cp << 8) | cp[1]);
475 if (changes & TCP_PUSH_BIT)
476 th->th_flags |= TH_PUSH;
478 th->th_flags &=~ TH_PUSH;
480 switch (changes & SPECIALS_MASK) {
483 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
484 th->th_ack = htonl(ntohl(th->th_ack) + i);
485 th->th_seq = htonl(ntohl(th->th_seq) + i);
490 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
495 if (changes & NEW_U) {
496 th->th_flags |= TH_URG;
499 th->th_flags &=~ TH_URG;
508 if (changes & NEW_I) {
509 DECODES(cs->cs_ip.ip_id);
511 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
514 * At this point, cp points to the first byte of data in the
515 * packet. Fill in the IP total length and update the IP
521 /* we must have dropped some characters (crc should detect
522 * this but the old slip framing won't) */
525 total_len += cs->cs_hlen - vjlen;
526 cs->cs_ip.ip_len = htons(total_len);
528 /* recompute the ip header checksum */
529 bp = (u_short *) &cs->cs_ip;
530 cs->cs_ip.ip_sum = 0;
531 for (changes = 0; hlen > 0; hlen -= 2)
533 changes = (changes & 0xffff) + (changes >> 16);
534 changes = (changes & 0xffff) + (changes >> 16);
535 cs->cs_ip.ip_sum = ~ changes;
537 *hdrp = (u_char *) &cs->cs_ip;
538 *hlenp = cs->cs_hlen;
542 comp->flags |= VJF_TOSS;