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 1.5 1995/05/19 03:48:34 paulus Exp $
30 #include <sys/types.h>
31 #include <sys/param.h>
35 #include <sys/byteorder.h> /* for ntohl, etc. */
37 /* make sure we don't get the gnu "fixed" one! */
38 #include "/usr/include/sys/byteorder.h"
43 #include <net/net_globals.h>
45 #include <netinet/in.h>
48 #define _NETINET_IN_SYSTM_H_
49 typedef u_long n_long;
51 #include <netinet/in_systm.h>
54 #include <netinet/ip.h>
55 #include <netinet/tcp.h>
57 #include <net/ppp_defs.h>
58 #include <net/vjcompress.h>
61 #define INCR(counter) ++comp->stats.counter
66 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n))
68 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n))
74 #define getip_hl(base) (((base).ip_vhl)&0xf)
75 #define getth_off(base) ((((base).th_xoff)&0xf0)>>4)
78 #define getip_hl(base) ((base).ip_hl)
79 #define getth_off(base) ((base).th_off)
83 vj_compress_init(comp, max_state)
84 struct vjcompress *comp;
88 register struct cstate *tstate = comp->tstate;
91 max_state = MAX_STATES - 1;
92 bzero((char *)comp, sizeof(*comp));
93 for (i = max_state; i > 0; --i) {
95 tstate[i].cs_next = &tstate[i - 1];
97 tstate[0].cs_next = &tstate[max_state];
99 comp->last_cs = &tstate[0];
100 comp->last_recv = 255;
101 comp->last_xmit = 255;
102 comp->flags = VJF_TOSS;
106 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ
107 * checks for zero (since zero has to be encoded in the long, 3 byte
110 #define ENCODE(n) { \
111 if ((u_short)(n) >= 256) { \
120 #define ENCODEZ(n) { \
121 if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \
131 #define DECODEL(f) { \
133 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
136 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \
140 #define DECODES(f) { \
142 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
145 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \
149 #define DECODEU(f) { \
151 (f) = htons((cp[1] << 8) | cp[2]); \
154 (f) = htons((u_int32_t)*cp++); \
159 vj_compress_tcp(ip, mlen, comp, compress_cid, vjhdrp)
160 register struct ip *ip;
162 struct vjcompress *comp;
166 register struct cstate *cs = comp->last_cs->cs_next;
167 register u_int hlen = getip_hl(*ip);
168 register struct tcphdr *oth;
169 register struct tcphdr *th;
170 register u_int deltaS, deltaA;
171 register u_int changes = 0;
173 register u_char *cp = new_seq;
176 * Bail if this is an IP fragment or if the TCP packet isn't
177 * `compressible' (i.e., ACK isn't set or some other control bit is
178 * set). (We assume that the caller has already made sure the
179 * packet is IP proto TCP).
181 if ((ip->ip_off & htons(0x3fff)) || mlen < 40)
184 th = (struct tcphdr *)&((int *)ip)[hlen];
185 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
188 * Packet is compressible -- we're going to send either a
189 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
190 * to locate (or create) the connection state. Special case the
191 * most recently used connection since it's most likely to be used
192 * again & we don't have to do any reordering if it's used.
195 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
196 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
197 *(int *)th != ((int *)&cs->cs_ip)[getip_hl(cs->cs_ip)]) {
199 * Wasn't the first -- search for it.
201 * States are kept in a circularly linked list with
202 * last_cs pointing to the end of the list. The
203 * list is kept in lru order by moving a state to the
204 * head of the list whenever it is referenced. Since
205 * the list is short and, empirically, the connection
206 * we want is almost always near the front, we locate
207 * states via linear search. If we don't find a state
208 * for the datagram, the oldest state is (re-)used.
210 register struct cstate *lcs;
211 register struct cstate *lastcs = comp->last_cs;
214 lcs = cs; cs = cs->cs_next;
216 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
217 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
218 && *(int *)th == ((int *)&cs->cs_ip)[getip_hl(cs->cs_ip)])
220 } while (cs != lastcs);
223 * Didn't find it -- re-use oldest cstate. Send an
224 * uncompressed packet that tells the other side what
225 * connection number we're using for this conversation.
226 * Note that since the state list is circular, the oldest
227 * state points to the newest and we only need to set
228 * last_cs to update the lru linkage.
232 hlen += getth_off(*th);
240 * Found it -- move to the front on the connection list.
245 lcs->cs_next = cs->cs_next;
246 cs->cs_next = lastcs->cs_next;
247 lastcs->cs_next = cs;
252 * Make sure that only what we expect to change changed. The first
253 * line of the `if' checks the IP protocol version, header length &
254 * type of service. The 2nd line checks the "Don't fragment" bit.
255 * The 3rd line checks the time-to-live and protocol (the protocol
256 * check is unnecessary but costless). The 4th line checks the TCP
257 * header length. The 5th line checks IP options, if any. The 6th
258 * line checks TCP options, if any. If any of these things are
259 * different between the previous & current datagram, we send the
260 * current datagram `uncompressed'.
262 oth = (struct tcphdr *)&((int *)&cs->cs_ip)[hlen];
264 hlen += getth_off(*th);
269 if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0] ||
270 ((u_short *)ip)[3] != ((u_short *)&cs->cs_ip)[3] ||
271 ((u_short *)ip)[4] != ((u_short *)&cs->cs_ip)[4] ||
272 getth_off(*th) != getth_off(*oth) ||
273 (deltaS > 5 && BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
274 (getth_off(*th) > 5 && BCMP(th + 1, oth + 1, (getth_off(*th) - 5) << 2)))
278 * Figure out which of the changing fields changed. The
279 * receiver expects changes in the order: urgent, window,
280 * ack, seq (the order minimizes the number of temporaries
281 * needed in this section of code).
283 if (th->th_flags & TH_URG) {
284 deltaS = ntohs(th->th_urp);
287 } else if (th->th_urp != oth->th_urp)
288 /* argh! URG not set but urp changed -- a sensible
289 * implementation should never do this but RFC793
290 * doesn't prohibit the change so we have to deal
294 if (deltaS = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win))) {
299 if (deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack)) {
306 if (deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq)) {
317 * Nothing changed. If this packet contains data and the
318 * last one didn't, this is probably a data packet following
319 * an ack (normal on an interactive connection) and we send
320 * it compressed. Otherwise it's probably a retransmit,
321 * retransmitted ack or window probe. Send it uncompressed
322 * in case the other side missed the compressed version.
324 if (ip->ip_len != cs->cs_ip.ip_len &&
325 ntohs(cs->cs_ip.ip_len) == hlen)
333 * actual changes match one of our special case encodings --
334 * send packet uncompressed.
339 if (deltaS == deltaA && deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
340 /* special case for echoed terminal traffic */
347 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
348 /* special case for data xfer */
355 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
360 if (th->th_flags & TH_PUSH)
361 changes |= TCP_PUSH_BIT;
363 * Grab the cksum before we overwrite it below. Then update our
364 * state with this packet's header.
366 deltaA = ntohs(th->th_sum);
367 BCOPY(ip, &cs->cs_ip, hlen);
370 * We want to use the original packet as our compressed packet.
371 * (cp - new_seq) is the number of bytes we need for compressed
372 * sequence numbers. In addition we need one byte for the change
373 * mask, one for the connection id and two for the tcp checksum.
374 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
375 * many bytes of the original packet to toss so subtract the two to
376 * get the new packet size.
378 deltaS = cp - new_seq;
380 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
381 comp->last_xmit = cs->cs_id;
383 *vjhdrp = (cp += hlen);
384 *cp++ = changes | NEW_C;
388 *vjhdrp = (cp += hlen);
393 BCOPY(new_seq, cp, deltaS);
394 INCR(vjs_compressed);
395 return (TYPE_COMPRESSED_TCP);
398 * Update connection state cs & send uncompressed packet (that is,
399 * a regular ip/tcp packet but with the 'conversation id' we hope
400 * to use on future compressed packets in the protocol field).
403 BCOPY(ip, &cs->cs_ip, hlen);
404 ip->ip_p = cs->cs_id;
405 comp->last_xmit = cs->cs_id;
406 return (TYPE_UNCOMPRESSED_TCP);
410 * Called when we may have missed a packet.
413 vj_uncompress_err(comp)
414 struct vjcompress *comp;
416 comp->flags |= VJF_TOSS;
421 * "Uncompress" a packet of type TYPE_UNCOMPRESSED_TCP.
424 vj_uncompress_uncomp(buf, comp)
426 struct vjcompress *comp;
429 register struct cstate *cs;
430 register struct ip *ip;
432 ip = (struct ip *) buf;
433 if (ip->ip_p >= MAX_STATES) {
434 comp->flags |= VJF_TOSS;
438 cs = &comp->rstate[comp->last_recv = ip->ip_p];
439 comp->flags &=~ VJF_TOSS;
440 ip->ip_p = IPPROTO_TCP;
441 hlen = getip_hl(*ip);
442 hlen += getth_off(*((struct tcphdr *)&((int *)ip)[hlen]));
444 BCOPY(ip, &cs->cs_ip, hlen);
446 INCR(vjs_uncompressedin);
451 * Uncompress a packet of type TYPE_COMPRESSED_TCP.
452 * The packet starts at buf and is of total length total_len.
453 * The first buflen bytes are at buf; this must include the entire
454 * compressed TCP/IP header. This procedure returns the length
455 * of the VJ header, with a pointer to the uncompressed IP header
456 * in *hdrp and its length in *hlenp.
459 vj_uncompress_tcp(buf, buflen, total_len, comp, hdrp, hlenp)
461 int buflen, total_len;
462 struct vjcompress *comp;
467 register u_int hlen, changes;
468 register struct tcphdr *th;
469 register struct cstate *cs;
470 register u_short *bp;
471 register u_int vjlen;
473 INCR(vjs_compressedin);
476 if (changes & NEW_C) {
477 /* Make sure the state index is in range, then grab the state.
478 * If we have a good state index, clear the 'discard' flag. */
479 if (*cp >= MAX_STATES)
482 comp->flags &=~ VJF_TOSS;
483 comp->last_recv = *cp++;
485 /* this packet has an implicit state index. If we've
486 * had a line error since the last time we got an
487 * explicit state index, we have to toss the packet. */
488 if (comp->flags & VJF_TOSS) {
493 cs = &comp->rstate[comp->last_recv];
494 hlen = getip_hl(cs->cs_ip) << 2;
495 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
496 th->th_sum = htons((*cp << 8) | cp[1]);
498 if (changes & TCP_PUSH_BIT)
499 th->th_flags |= TH_PUSH;
501 th->th_flags &=~ TH_PUSH;
503 switch (changes & SPECIALS_MASK) {
506 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
507 th->th_ack = htonl(ntohl(th->th_ack) + i);
508 th->th_seq = htonl(ntohl(th->th_seq) + i);
513 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
518 if (changes & NEW_U) {
519 th->th_flags |= TH_URG;
522 th->th_flags &=~ TH_URG;
531 if (changes & NEW_I) {
532 DECODES(cs->cs_ip.ip_id);
534 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
537 * At this point, cp points to the first byte of data in the
538 * packet. Fill in the IP total length and update the IP
544 /* we must have dropped some characters (crc should detect
545 * this but the old slip framing won't) */
548 total_len += cs->cs_hlen - vjlen;
549 cs->cs_ip.ip_len = htons(total_len);
551 /* recompute the ip header checksum */
552 bp = (u_short *) &cs->cs_ip;
553 cs->cs_ip.ip_sum = 0;
554 for (changes = 0; hlen > 0; hlen -= 2)
556 changes = (changes & 0xffff) + (changes >> 16);
557 changes = (changes & 0xffff) + (changes >> 16);
558 cs->cs_ip.ip_sum = ~ changes;
560 *hdrp = (u_char *) &cs->cs_ip;
561 *hlenp = cs->cs_hlen;
565 comp->flags |= VJF_TOSS;