2 * Copyright (c) 1989, 1993, 1994
3 * The Regents of the University of California. All rights reserved.
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 * 3. All advertising materials mentioning features or use of this software
14 * must display the following acknowledgement:
15 * This product includes software developed by the University of
16 * California, Berkeley and its contributors.
17 * 4. Neither the name of the University nor the names of its contributors
18 * may be used to endorse or promote products derived from this software
19 * without specific prior written permission.
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 * @(#)slcompress.c 8.2 (Berkeley) 4/16/94
38 * Routines to compress and uncompess tcp packets (for transmission
39 * over low speed serial lines.
41 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
42 * - 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((void *)(p1), (void *)(p2), (int)(n))
64 #define BCOPY(p1, p2, n) bcopy((void *)(p1), (void *)(p2), (int)(n))
67 sl_compress_init(comp, max_state)
68 struct slcompress *comp;
72 register struct cstate *tstate = comp->tstate;
74 if (max_state == -1) {
75 max_state = MAX_STATES - 1;
76 bzero((char *)comp, sizeof(*comp));
78 /* Don't reset statistics */
79 bzero((char *)comp->tstate, sizeof(comp->tstate));
80 bzero((char *)comp->rstate, sizeof(comp->rstate));
82 for (i = max_state; i > 0; --i) {
84 tstate[i].cs_next = &tstate[i - 1];
86 tstate[0].cs_next = &tstate[max_state];
88 comp->last_cs = &tstate[0];
89 comp->last_recv = 255;
90 comp->last_xmit = 255;
91 comp->flags = SLF_TOSS;
95 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ
96 * checks for zero (since zero has to be encoded in the long, 3 byte
100 if ((u_int16_t)(n) >= 256) { \
109 #define ENCODEZ(n) { \
110 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \
120 #define DECODEL(f) { \
122 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
125 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \
129 #define DECODES(f) { \
131 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
134 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \
138 #define DECODEU(f) { \
140 (f) = htons((cp[1] << 8) | cp[2]); \
143 (f) = htons((u_int32_t)*cp++); \
148 * Attempt to compress an outgoing TCP packet and return the type of
149 * the result. The caller must have already verified that the protocol
150 * is TCP. The first mbuf must contain the complete IP and TCP headers,
151 * and "ip" must be == mtod(m, struct ip *). "comp" supplies the
152 * compression state, and "compress_cid" tells us whether it is OK
153 * to leave out the CID field when feasible.
155 * The caller is responsible for adjusting m->m_pkthdr.len upon return,
156 * if m is an M_PKTHDR mbuf.
159 sl_compress_tcp(m, ip, comp, compress_cid)
161 register struct ip *ip;
162 struct slcompress *comp;
165 register struct cstate *cs = comp->last_cs->cs_next;
166 register u_int hlen = ip->ip_hl;
167 register struct tcphdr *oth;
168 register struct tcphdr *th;
169 register u_int deltaS, deltaA;
170 register u_int changes = 0;
172 register u_char *cp = new_seq;
175 * Bail if this is an IP fragment or if the TCP packet isn't
176 * `compressible' (i.e., ACK isn't set or some other control bit is
177 * set). (We assume that the caller has already made sure the
178 * packet is IP proto TCP).
180 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40)
183 th = (struct tcphdr *)&((int32_t *)ip)[hlen];
184 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
187 * Packet is compressible -- we're going to send either a
188 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
189 * to locate (or create) the connection state. Special case the
190 * most recently used connection since it's most likely to be used
191 * again & we don't have to do any reordering if it's used.
194 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
195 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
196 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
198 * Wasn't the first -- search for it.
200 * States are kept in a circularly linked list with
201 * last_cs pointing to the end of the list. The
202 * list is kept in lru order by moving a state to the
203 * head of the list whenever it is referenced. Since
204 * the list is short and, empirically, the connection
205 * we want is almost always near the front, we locate
206 * states via linear search. If we don't find a state
207 * for the datagram, the oldest state is (re-)used.
209 register struct cstate *lcs;
210 register struct cstate *lastcs = comp->last_cs;
213 lcs = cs; cs = cs->cs_next;
215 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
216 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
218 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl])
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.
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 *)&((int32_t *)&cs->cs_ip)[hlen];
269 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] ||
270 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] ||
271 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] ||
272 th->th_off != oth->th_off ||
274 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
276 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
280 * Figure out which of the changing fields changed. The
281 * receiver expects changes in the order: urgent, window,
282 * ack, seq (the order minimizes the number of temporaries
283 * needed in this section of code).
285 if (th->th_flags & TH_URG) {
286 deltaS = ntohs(th->th_urp);
289 } else if (th->th_urp != oth->th_urp)
290 /* argh! URG not set but urp changed -- a sensible
291 * implementation should never do this but RFC793
292 * doesn't prohibit the change so we have to deal
296 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win));
302 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack);
310 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq);
322 * Nothing changed. If this packet contains data and the
323 * last one didn't, this is probably a data packet following
324 * an ack (normal on an interactive connection) and we send
325 * it compressed. Otherwise it's probably a retransmit,
326 * retransmitted ack or window probe. Send it uncompressed
327 * in case the other side missed the compressed version.
329 if (ip->ip_len != cs->cs_ip.ip_len &&
330 ntohs(cs->cs_ip.ip_len) == hlen)
338 * actual changes match one of our special case encodings --
339 * send packet uncompressed.
344 if (deltaS == deltaA &&
345 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
346 /* special case for echoed terminal traffic */
353 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
354 /* special case for data xfer */
361 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
366 if (th->th_flags & TH_PUSH)
367 changes |= TCP_PUSH_BIT;
369 * Grab the cksum before we overwrite it below. Then update our
370 * state with this packet's header.
372 deltaA = ntohs(th->th_sum);
373 BCOPY(ip, &cs->cs_ip, hlen);
376 * We want to use the original packet as our compressed packet.
377 * (cp - new_seq) is the number of bytes we need for compressed
378 * sequence numbers. In addition we need one byte for the change
379 * mask, one for the connection id and two for the tcp checksum.
380 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
381 * many bytes of the original packet to toss so subtract the two to
382 * get the new packet size.
384 deltaS = cp - new_seq;
386 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
387 comp->last_xmit = cs->cs_id;
390 *cp++ = changes | NEW_C;
401 BCOPY(new_seq, cp, deltaS);
403 return (TYPE_COMPRESSED_TCP);
406 * Update connection state cs & send uncompressed packet ('uncompressed'
407 * means a regular ip/tcp packet but with the 'conversation id' we hope
408 * to use on future compressed packets in the protocol field).
411 BCOPY(ip, &cs->cs_ip, hlen);
412 ip->ip_p = cs->cs_id;
413 comp->last_xmit = cs->cs_id;
414 return (TYPE_UNCOMPRESSED_TCP);
419 sl_uncompress_tcp(bufp, len, type, comp)
423 struct slcompress *comp;
428 cp = bufp? *bufp: NULL;
429 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen);
431 return (0); /* error */
433 return (len); /* was uncompressed already */
439 * At this point, cp points to the first byte of data in the
440 * packet. If we're not aligned on a 4-byte boundary, copy the
441 * data down so the ip & tcp headers will be aligned. Then back up
442 * cp by the tcp/ip header length to make room for the reconstructed
443 * header (we assume the packet we were handed has enough space to
444 * prepend 128 bytes of header).
446 if ((intptr_t)cp & 3) {
448 BCOPY(cp, ((intptr_t)cp &~ 3), len);
449 cp = (u_char *)((intptr_t)cp &~ 3);
453 BCOPY(hdr, cp, hlen);
460 * Uncompress a packet of total length total_len. The first buflen
461 * bytes are at buf; this must include the entire (compressed or
462 * uncompressed) TCP/IP header. This procedure returns the length
463 * of the VJ header, with a pointer to the uncompressed IP header
464 * in *hdrp and its length in *hlenp.
467 sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp)
469 int buflen, total_len;
471 struct slcompress *comp;
476 register u_int hlen, changes;
477 register struct tcphdr *th;
478 register struct cstate *cs;
479 register struct ip *ip;
480 register u_int16_t *bp;
481 register u_int vjlen;
485 case TYPE_UNCOMPRESSED_TCP:
486 ip = (struct ip *) buf;
487 if (ip->ip_p >= MAX_STATES)
489 cs = &comp->rstate[comp->last_recv = ip->ip_p];
490 comp->flags &=~ SLF_TOSS;
491 ip->ip_p = IPPROTO_TCP;
493 * Calculate the size of the TCP/IP header and make sure that
494 * we don't overflow the space we have available for it.
496 hlen = ip->ip_hl << 2;
497 if (hlen + sizeof(struct tcphdr) > buflen)
499 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2;
500 if (hlen > MAX_HDR || hlen > buflen)
502 BCOPY(ip, &cs->cs_ip, hlen);
504 INCR(sls_uncompressedin)
505 *hdrp = (u_char *) &cs->cs_ip;
512 case TYPE_COMPRESSED_TCP:
515 /* We've got a compressed packet. */
516 INCR(sls_compressedin)
519 if (changes & NEW_C) {
520 /* Make sure the state index is in range, then grab the state.
521 * If we have a good state index, clear the 'discard' flag. */
522 if (*cp >= MAX_STATES)
525 comp->flags &=~ SLF_TOSS;
526 comp->last_recv = *cp++;
528 /* this packet has an implicit state index. If we've
529 * had a line error since the last time we got an
530 * explicit state index, we have to toss the packet. */
531 if (comp->flags & SLF_TOSS) {
536 cs = &comp->rstate[comp->last_recv];
537 hlen = cs->cs_ip.ip_hl << 2;
538 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
539 th->th_sum = htons((*cp << 8) | cp[1]);
541 if (changes & TCP_PUSH_BIT)
542 th->th_flags |= TH_PUSH;
544 th->th_flags &=~ TH_PUSH;
546 switch (changes & SPECIALS_MASK) {
549 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
550 th->th_ack = htonl(ntohl(th->th_ack) + i);
551 th->th_seq = htonl(ntohl(th->th_seq) + i);
556 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
561 if (changes & NEW_U) {
562 th->th_flags |= TH_URG;
565 th->th_flags &=~ TH_URG;
574 if (changes & NEW_I) {
575 DECODES(cs->cs_ip.ip_id)
577 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
580 * At this point, cp points to the first byte of data in the
581 * packet. Fill in the IP total length and update the IP
587 /* we must have dropped some characters (crc should detect
588 * this but the old slip framing won't) */
591 total_len += cs->cs_hlen - vjlen;
592 cs->cs_ip.ip_len = htons(total_len);
594 /* recompute the ip header checksum */
595 bp = (u_int16_t *) &cs->cs_ip;
596 cs->cs_ip.ip_sum = 0;
597 for (changes = 0; hlen > 0; hlen -= 2)
599 changes = (changes & 0xffff) + (changes >> 16);
600 changes = (changes & 0xffff) + (changes >> 16);
601 cs->cs_ip.ip_sum = ~ changes;
603 *hdrp = (u_char *) &cs->cs_ip;
604 *hlenp = cs->cs_hlen;
608 comp->flags |= SLF_TOSS;