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. Neither the name of the University nor the names of its contributors
14 * may be used to endorse or promote products derived from this software
15 * without specific prior written permission.
17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 * @(#)slcompress.c 8.2 (Berkeley) 4/16/94
30 * $FreeBSD: src/sys/net/slcompress.c,v 1.16 1999/12/29 04:38:37 peter Exp $
31 * $DragonFly: src/sys/net/ppp_layer/slcompress.c,v 1.5 2006/01/14 11:05:18 swildner Exp $
35 * Routines to compress and uncompess tcp packets (for transmission
36 * over low speed serial lines.
38 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
39 * - Initial distribution.
43 #include <sys/param.h>
45 #include <sys/systm.h>
47 #include <netinet/in.h>
48 #include <netinet/in_systm.h>
49 #include <netinet/ip.h>
50 #include <netinet/tcp.h>
52 #include <net/slcompress.h>
55 #define INCR(counter) ++comp->counter;
60 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n))
61 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n))
67 sl_compress_init(struct slcompress *comp, int max_state)
70 struct cstate *tstate = comp->tstate;
72 if (max_state == -1) {
73 max_state = MAX_STATES - 1;
74 bzero((char *)comp, sizeof(*comp));
76 /* Don't reset statistics */
77 bzero((char *)comp->tstate, sizeof(comp->tstate));
78 bzero((char *)comp->rstate, sizeof(comp->rstate));
80 for (i = max_state; i > 0; --i) {
82 tstate[i].cs_next = &tstate[i - 1];
84 tstate[0].cs_next = &tstate[max_state];
86 comp->last_cs = &tstate[0];
87 comp->last_recv = 255;
88 comp->last_xmit = 255;
89 comp->flags = SLF_TOSS;
93 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ
94 * checks for zero (since zero has to be encoded in the long, 3 byte
98 if ((u_int16_t)(n) >= 256) { \
107 #define ENCODEZ(n) { \
108 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \
118 #define DECODEL(f) { \
120 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
123 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \
127 #define DECODES(f) { \
129 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
132 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \
136 #define DECODEU(f) { \
138 (f) = htons((cp[1] << 8) | cp[2]); \
141 (f) = htons((u_int32_t)*cp++); \
146 * Attempt to compress an outgoing TCP packet and return the type of
147 * the result. The caller must have already verified that the protocol
148 * is TCP. The first mbuf must contain the complete IP and TCP headers,
149 * and "ip" must be == mtod(m, struct ip *). "comp" supplies the
150 * compression state, and "compress_cid" tells us whether it is OK
151 * to leave out the CID field when feasible.
153 * The caller is responsible for adjusting m->m_pkthdr.len upon return,
154 * if m is an M_PKTHDR mbuf.
157 sl_compress_tcp(struct mbuf *m, struct ip *ip, struct slcompress *comp,
160 struct cstate *cs = comp->last_cs->cs_next;
161 u_int hlen = ip->ip_hl;
164 u_int deltaS, deltaA;
167 u_char *cp = new_seq;
170 * Bail if this is an IP fragment or if the TCP packet isn't
171 * `compressible' (i.e., ACK isn't set or some other control bit is
172 * set). (We assume that the caller has already made sure the
173 * packet is IP proto TCP).
175 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40)
178 th = (struct tcphdr *)&((int32_t *)ip)[hlen];
179 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
182 * Packet is compressible -- we're going to send either a
183 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
184 * to locate (or create) the connection state. Special case the
185 * most recently used connection since it's most likely to be used
186 * again & we don't have to do any reordering if it's used.
189 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
190 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
191 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
193 * Wasn't the first -- search for it.
195 * States are kept in a circularly linked list with
196 * last_cs pointing to the end of the list. The
197 * list is kept in lru order by moving a state to the
198 * head of the list whenever it is referenced. Since
199 * the list is short and, empirically, the connection
200 * we want is almost always near the front, we locate
201 * states via linear search. If we don't find a state
202 * for the datagram, the oldest state is (re-)used.
205 struct cstate *lastcs = comp->last_cs;
208 lcs = cs; cs = cs->cs_next;
210 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
211 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
213 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl])
215 } while (cs != lastcs);
218 * Didn't find it -- re-use oldest cstate. Send an
219 * uncompressed packet that tells the other side what
220 * connection number we're using for this conversation.
221 * Note that since the state list is circular, the oldest
222 * state points to the newest and we only need to set
223 * last_cs to update the lru linkage.
235 * Found it -- move to the front on the connection list.
240 lcs->cs_next = cs->cs_next;
241 cs->cs_next = lastcs->cs_next;
242 lastcs->cs_next = cs;
247 * Make sure that only what we expect to change changed. The first
248 * line of the `if' checks the IP protocol version, header length &
249 * type of service. The 2nd line checks the "Don't fragment" bit.
250 * The 3rd line checks the time-to-live and protocol (the protocol
251 * check is unnecessary but costless). The 4th line checks the TCP
252 * header length. The 5th line checks IP options, if any. The 6th
253 * line checks TCP options, if any. If any of these things are
254 * different between the previous & current datagram, we send the
255 * current datagram `uncompressed'.
257 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen];
264 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] ||
265 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] ||
266 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] ||
267 th->th_off != oth->th_off ||
269 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
271 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
275 * Figure out which of the changing fields changed. The
276 * receiver expects changes in the order: urgent, window,
277 * ack, seq (the order minimizes the number of temporaries
278 * needed in this section of code).
280 if (th->th_flags & TH_URG) {
281 deltaS = ntohs(th->th_urp);
284 } else if (th->th_urp != oth->th_urp)
285 /* argh! URG not set but urp changed -- a sensible
286 * implementation should never do this but RFC793
287 * doesn't prohibit the change so we have to deal
291 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win));
297 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack);
305 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 &&
340 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
341 /* special case for echoed terminal traffic */
348 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
349 /* special case for data xfer */
356 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
361 if (th->th_flags & TH_PUSH)
362 changes |= TCP_PUSH_BIT;
364 * Grab the cksum before we overwrite it below. Then update our
365 * state with this packet's header.
367 deltaA = ntohs(th->th_sum);
368 BCOPY(ip, &cs->cs_ip, hlen);
371 * We want to use the original packet as our compressed packet.
372 * (cp - new_seq) is the number of bytes we need for compressed
373 * sequence numbers. In addition we need one byte for the change
374 * mask, one for the connection id and two for the tcp checksum.
375 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
376 * many bytes of the original packet to toss so subtract the two to
377 * get the new packet size.
379 deltaS = cp - new_seq;
381 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
382 comp->last_xmit = cs->cs_id;
385 *cp++ = changes | NEW_C;
396 BCOPY(new_seq, cp, deltaS);
398 return (TYPE_COMPRESSED_TCP);
401 * Update connection state cs & send uncompressed packet ('uncompressed'
402 * means a regular ip/tcp packet but with the 'conversation id' we hope
403 * to use on future compressed packets in the protocol field).
406 BCOPY(ip, &cs->cs_ip, hlen);
407 ip->ip_p = cs->cs_id;
408 comp->last_xmit = cs->cs_id;
409 return (TYPE_UNCOMPRESSED_TCP);
414 sl_uncompress_tcp(u_char **bufp, int len, u_int type, struct slcompress *comp)
419 cp = bufp? *bufp: NULL;
420 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen);
422 return (0); /* error */
424 return (len); /* was uncompressed already */
430 * At this point, cp points to the first byte of data in the
431 * packet. If we're not aligned on a 4-byte boundary, copy the
432 * data down so the ip & tcp headers will be aligned. Then back up
433 * cp by the tcp/ip header length to make room for the reconstructed
434 * header (we assume the packet we were handed has enough space to
435 * prepend 128 bytes of header).
437 if ((intptr_t)cp & 3) {
439 ovbcopy(cp, (caddr_t)((intptr_t)cp &~ 3), len);
440 cp = (u_char *)((intptr_t)cp &~ 3);
444 BCOPY(hdr, cp, hlen);
451 * Uncompress a packet of total length total_len. The first buflen
452 * bytes are at buf; this must include the entire (compressed or
453 * uncompressed) TCP/IP header. This procedure returns the length
454 * of the VJ header, with a pointer to the uncompressed IP header
455 * in *hdrp and its length in *hlenp.
458 sl_uncompress_tcp_core(u_char *buf, int buflen, int total_len, u_int type,
459 struct slcompress *comp, u_char **hdrp, u_int *hlenp)
471 case TYPE_UNCOMPRESSED_TCP:
472 ip = (struct ip *) buf;
473 if (ip->ip_p >= MAX_STATES)
475 cs = &comp->rstate[comp->last_recv = ip->ip_p];
476 comp->flags &=~ SLF_TOSS;
477 ip->ip_p = IPPROTO_TCP;
479 * Calculate the size of the TCP/IP header and make sure that
480 * we don't overflow the space we have available for it.
482 hlen = ip->ip_hl << 2;
483 if (hlen + sizeof(struct tcphdr) > buflen)
485 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2;
486 if (hlen > MAX_HDR || hlen > buflen)
488 BCOPY(ip, &cs->cs_ip, hlen);
490 INCR(sls_uncompressedin)
491 *hdrp = (u_char *) &cs->cs_ip;
498 case TYPE_COMPRESSED_TCP:
501 /* We've got a compressed packet. */
502 INCR(sls_compressedin)
505 if (changes & NEW_C) {
506 /* Make sure the state index is in range, then grab the state.
507 * If we have a good state index, clear the 'discard' flag. */
508 if (*cp >= MAX_STATES)
511 comp->flags &=~ SLF_TOSS;
512 comp->last_recv = *cp++;
514 /* this packet has an implicit state index. If we've
515 * had a line error since the last time we got an
516 * explicit state index, we have to toss the packet. */
517 if (comp->flags & SLF_TOSS) {
522 cs = &comp->rstate[comp->last_recv];
523 hlen = cs->cs_ip.ip_hl << 2;
524 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
525 th->th_sum = htons((*cp << 8) | cp[1]);
527 if (changes & TCP_PUSH_BIT)
528 th->th_flags |= TH_PUSH;
530 th->th_flags &=~ TH_PUSH;
532 switch (changes & SPECIALS_MASK) {
535 u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
536 th->th_ack = htonl(ntohl(th->th_ack) + i);
537 th->th_seq = htonl(ntohl(th->th_seq) + i);
542 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
547 if (changes & NEW_U) {
548 th->th_flags |= TH_URG;
551 th->th_flags &=~ TH_URG;
560 if (changes & NEW_I) {
561 DECODES(cs->cs_ip.ip_id)
563 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
566 * At this point, cp points to the first byte of data in the
567 * packet. Fill in the IP total length and update the IP
573 /* we must have dropped some characters (crc should detect
574 * this but the old slip framing won't) */
577 total_len += cs->cs_hlen - vjlen;
578 cs->cs_ip.ip_len = htons(total_len);
580 /* recompute the ip header checksum */
581 bp = (u_int16_t *) &cs->cs_ip;
582 cs->cs_ip.ip_sum = 0;
583 for (changes = 0; hlen > 0; hlen -= 2)
585 changes = (changes & 0xffff) + (changes >> 16);
586 changes = (changes & 0xffff) + (changes >> 16);
587 cs->cs_ip.ip_sum = ~ changes;
589 *hdrp = (u_char *) &cs->cs_ip;
590 *hlenp = cs->cs_hlen;
594 comp->flags |= SLF_TOSS;