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
34 * $FreeBSD: src/sys/net/slcompress.c,v 1.16 1999/12/29 04:38:37 peter Exp $
35 * $DragonFly: src/sys/net/ppp_layer/slcompress.c,v 1.4 2005/12/11 13:00:17 swildner Exp $
39 * Routines to compress and uncompess tcp packets (for transmission
40 * over low speed serial lines.
42 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
43 * - Initial distribution.
47 #include <sys/param.h>
49 #include <sys/systm.h>
51 #include <netinet/in.h>
52 #include <netinet/in_systm.h>
53 #include <netinet/ip.h>
54 #include <netinet/tcp.h>
56 #include <net/slcompress.h>
59 #define INCR(counter) ++comp->counter;
64 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n))
65 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n))
71 sl_compress_init(struct slcompress *comp, int max_state)
74 struct cstate *tstate = comp->tstate;
76 if (max_state == -1) {
77 max_state = MAX_STATES - 1;
78 bzero((char *)comp, sizeof(*comp));
80 /* Don't reset statistics */
81 bzero((char *)comp->tstate, sizeof(comp->tstate));
82 bzero((char *)comp->rstate, sizeof(comp->rstate));
84 for (i = max_state; i > 0; --i) {
86 tstate[i].cs_next = &tstate[i - 1];
88 tstate[0].cs_next = &tstate[max_state];
90 comp->last_cs = &tstate[0];
91 comp->last_recv = 255;
92 comp->last_xmit = 255;
93 comp->flags = SLF_TOSS;
97 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ
98 * checks for zero (since zero has to be encoded in the long, 3 byte
101 #define ENCODE(n) { \
102 if ((u_int16_t)(n) >= 256) { \
111 #define ENCODEZ(n) { \
112 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \
122 #define DECODEL(f) { \
124 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
127 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \
131 #define DECODES(f) { \
133 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
136 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \
140 #define DECODEU(f) { \
142 (f) = htons((cp[1] << 8) | cp[2]); \
145 (f) = htons((u_int32_t)*cp++); \
150 * Attempt to compress an outgoing TCP packet and return the type of
151 * the result. The caller must have already verified that the protocol
152 * is TCP. The first mbuf must contain the complete IP and TCP headers,
153 * and "ip" must be == mtod(m, struct ip *). "comp" supplies the
154 * compression state, and "compress_cid" tells us whether it is OK
155 * to leave out the CID field when feasible.
157 * The caller is responsible for adjusting m->m_pkthdr.len upon return,
158 * if m is an M_PKTHDR mbuf.
161 sl_compress_tcp(struct mbuf *m, struct ip *ip, struct slcompress *comp,
164 struct cstate *cs = comp->last_cs->cs_next;
165 u_int hlen = ip->ip_hl;
168 u_int deltaS, deltaA;
171 u_char *cp = new_seq;
174 * Bail if this is an IP fragment or if the TCP packet isn't
175 * `compressible' (i.e., ACK isn't set or some other control bit is
176 * set). (We assume that the caller has already made sure the
177 * packet is IP proto TCP).
179 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40)
182 th = (struct tcphdr *)&((int32_t *)ip)[hlen];
183 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
186 * Packet is compressible -- we're going to send either a
187 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
188 * to locate (or create) the connection state. Special case the
189 * most recently used connection since it's most likely to be used
190 * again & we don't have to do any reordering if it's used.
193 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
194 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
195 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
197 * Wasn't the first -- search for it.
199 * States are kept in a circularly linked list with
200 * last_cs pointing to the end of the list. The
201 * list is kept in lru order by moving a state to the
202 * head of the list whenever it is referenced. Since
203 * the list is short and, empirically, the connection
204 * we want is almost always near the front, we locate
205 * states via linear search. If we don't find a state
206 * for the datagram, the oldest state is (re-)used.
209 struct cstate *lastcs = comp->last_cs;
212 lcs = cs; cs = cs->cs_next;
214 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
215 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
217 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl])
219 } while (cs != lastcs);
222 * Didn't find it -- re-use oldest cstate. Send an
223 * uncompressed packet that tells the other side what
224 * connection number we're using for this conversation.
225 * Note that since the state list is circular, the oldest
226 * state points to the newest and we only need to set
227 * last_cs to update the lru linkage.
239 * Found it -- move to the front on the connection list.
244 lcs->cs_next = cs->cs_next;
245 cs->cs_next = lastcs->cs_next;
246 lastcs->cs_next = cs;
251 * Make sure that only what we expect to change changed. The first
252 * line of the `if' checks the IP protocol version, header length &
253 * type of service. The 2nd line checks the "Don't fragment" bit.
254 * The 3rd line checks the time-to-live and protocol (the protocol
255 * check is unnecessary but costless). The 4th line checks the TCP
256 * header length. The 5th line checks IP options, if any. The 6th
257 * line checks TCP options, if any. If any of these things are
258 * different between the previous & current datagram, we send the
259 * current datagram `uncompressed'.
261 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen];
268 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] ||
269 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] ||
270 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] ||
271 th->th_off != oth->th_off ||
273 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
275 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
279 * Figure out which of the changing fields changed. The
280 * receiver expects changes in the order: urgent, window,
281 * ack, seq (the order minimizes the number of temporaries
282 * needed in this section of code).
284 if (th->th_flags & TH_URG) {
285 deltaS = ntohs(th->th_urp);
288 } else if (th->th_urp != oth->th_urp)
289 /* argh! URG not set but urp changed -- a sensible
290 * implementation should never do this but RFC793
291 * doesn't prohibit the change so we have to deal
295 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win));
301 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack);
309 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq);
321 * Nothing changed. If this packet contains data and the
322 * last one didn't, this is probably a data packet following
323 * an ack (normal on an interactive connection) and we send
324 * it compressed. Otherwise it's probably a retransmit,
325 * retransmitted ack or window probe. Send it uncompressed
326 * in case the other side missed the compressed version.
328 if (ip->ip_len != cs->cs_ip.ip_len &&
329 ntohs(cs->cs_ip.ip_len) == hlen)
337 * actual changes match one of our special case encodings --
338 * send packet uncompressed.
343 if (deltaS == deltaA &&
344 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
345 /* special case for echoed terminal traffic */
352 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
353 /* special case for data xfer */
360 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
365 if (th->th_flags & TH_PUSH)
366 changes |= TCP_PUSH_BIT;
368 * Grab the cksum before we overwrite it below. Then update our
369 * state with this packet's header.
371 deltaA = ntohs(th->th_sum);
372 BCOPY(ip, &cs->cs_ip, hlen);
375 * We want to use the original packet as our compressed packet.
376 * (cp - new_seq) is the number of bytes we need for compressed
377 * sequence numbers. In addition we need one byte for the change
378 * mask, one for the connection id and two for the tcp checksum.
379 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
380 * many bytes of the original packet to toss so subtract the two to
381 * get the new packet size.
383 deltaS = cp - new_seq;
385 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
386 comp->last_xmit = cs->cs_id;
389 *cp++ = changes | NEW_C;
400 BCOPY(new_seq, cp, deltaS);
402 return (TYPE_COMPRESSED_TCP);
405 * Update connection state cs & send uncompressed packet ('uncompressed'
406 * means a regular ip/tcp packet but with the 'conversation id' we hope
407 * to use on future compressed packets in the protocol field).
410 BCOPY(ip, &cs->cs_ip, hlen);
411 ip->ip_p = cs->cs_id;
412 comp->last_xmit = cs->cs_id;
413 return (TYPE_UNCOMPRESSED_TCP);
418 sl_uncompress_tcp(u_char **bufp, int len, u_int type, struct slcompress *comp)
423 cp = bufp? *bufp: NULL;
424 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen);
426 return (0); /* error */
428 return (len); /* was uncompressed already */
434 * At this point, cp points to the first byte of data in the
435 * packet. If we're not aligned on a 4-byte boundary, copy the
436 * data down so the ip & tcp headers will be aligned. Then back up
437 * cp by the tcp/ip header length to make room for the reconstructed
438 * header (we assume the packet we were handed has enough space to
439 * prepend 128 bytes of header).
441 if ((intptr_t)cp & 3) {
443 (void) ovbcopy(cp, (caddr_t)((intptr_t)cp &~ 3), len);
444 cp = (u_char *)((intptr_t)cp &~ 3);
448 BCOPY(hdr, cp, hlen);
455 * Uncompress a packet of total length total_len. The first buflen
456 * bytes are at buf; this must include the entire (compressed or
457 * uncompressed) TCP/IP header. This procedure returns the length
458 * of the VJ header, with a pointer to the uncompressed IP header
459 * in *hdrp and its length in *hlenp.
462 sl_uncompress_tcp_core(u_char *buf, int buflen, int total_len, u_int type,
463 struct slcompress *comp, u_char **hdrp, u_int *hlenp)
475 case TYPE_UNCOMPRESSED_TCP:
476 ip = (struct ip *) buf;
477 if (ip->ip_p >= MAX_STATES)
479 cs = &comp->rstate[comp->last_recv = ip->ip_p];
480 comp->flags &=~ SLF_TOSS;
481 ip->ip_p = IPPROTO_TCP;
483 * Calculate the size of the TCP/IP header and make sure that
484 * we don't overflow the space we have available for it.
486 hlen = ip->ip_hl << 2;
487 if (hlen + sizeof(struct tcphdr) > buflen)
489 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2;
490 if (hlen > MAX_HDR || hlen > buflen)
492 BCOPY(ip, &cs->cs_ip, hlen);
494 INCR(sls_uncompressedin)
495 *hdrp = (u_char *) &cs->cs_ip;
502 case TYPE_COMPRESSED_TCP:
505 /* We've got a compressed packet. */
506 INCR(sls_compressedin)
509 if (changes & NEW_C) {
510 /* Make sure the state index is in range, then grab the state.
511 * If we have a good state index, clear the 'discard' flag. */
512 if (*cp >= MAX_STATES)
515 comp->flags &=~ SLF_TOSS;
516 comp->last_recv = *cp++;
518 /* this packet has an implicit state index. If we've
519 * had a line error since the last time we got an
520 * explicit state index, we have to toss the packet. */
521 if (comp->flags & SLF_TOSS) {
526 cs = &comp->rstate[comp->last_recv];
527 hlen = cs->cs_ip.ip_hl << 2;
528 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
529 th->th_sum = htons((*cp << 8) | cp[1]);
531 if (changes & TCP_PUSH_BIT)
532 th->th_flags |= TH_PUSH;
534 th->th_flags &=~ TH_PUSH;
536 switch (changes & SPECIALS_MASK) {
539 u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
540 th->th_ack = htonl(ntohl(th->th_ack) + i);
541 th->th_seq = htonl(ntohl(th->th_seq) + i);
546 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
551 if (changes & NEW_U) {
552 th->th_flags |= TH_URG;
555 th->th_flags &=~ TH_URG;
564 if (changes & NEW_I) {
565 DECODES(cs->cs_ip.ip_id)
567 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
570 * At this point, cp points to the first byte of data in the
571 * packet. Fill in the IP total length and update the IP
577 /* we must have dropped some characters (crc should detect
578 * this but the old slip framing won't) */
581 total_len += cs->cs_hlen - vjlen;
582 cs->cs_ip.ip_len = htons(total_len);
584 /* recompute the ip header checksum */
585 bp = (u_int16_t *) &cs->cs_ip;
586 cs->cs_ip.ip_sum = 0;
587 for (changes = 0; hlen > 0; hlen -= 2)
589 changes = (changes & 0xffff) + (changes >> 16);
590 changes = (changes & 0xffff) + (changes >> 16);
591 cs->cs_ip.ip_sum = ~ changes;
593 *hdrp = (u_char *) &cs->cs_ip;
594 *hlenp = cs->cs_hlen;
598 comp->flags |= SLF_TOSS;