2 * SPDX-License-Identifier: BSD-3-Clause
4 * Copyright (c) 1989, 1993, 1994
5 * The Regents of the University of California. All rights reserved.
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 * 3. Neither the name of the University nor the names of its contributors
16 * may be used to endorse or promote products derived from this software
17 * without specific prior written permission.
19 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 * Routines to compress and uncompess tcp packets (for transmission
34 * over low speed serial lines.
36 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
37 * - Initial distribution.
41 #include <sys/param.h>
43 #include <sys/systm.h>
45 #include <netinet/in.h>
46 #include <netinet/in_systm.h>
47 #include <netinet/ip.h>
48 #include <netinet/tcp.h>
50 #include <net/slcompress.h>
53 #define INCR(counter) ++comp->counter;
58 #define BCMP(p1, p2, n) bcmp((void *)(p1), (void *)(p2), (int)(n))
59 #define BCOPY(p1, p2, n) bcopy((void *)(p1), (void *)(p2), (int)(n))
62 sl_compress_init(struct slcompress *comp, int max_state)
65 struct cstate *tstate = comp->tstate;
67 if (max_state == -1) {
68 max_state = MAX_STATES - 1;
69 bzero((char *)comp, sizeof(*comp));
71 /* Don't reset statistics */
72 bzero((char *)comp->tstate, sizeof(comp->tstate));
73 bzero((char *)comp->rstate, sizeof(comp->rstate));
75 for (i = max_state; i > 0; --i) {
77 tstate[i].cs_next = &tstate[i - 1];
79 tstate[0].cs_next = &tstate[max_state];
81 comp->last_cs = &tstate[0];
82 comp->last_recv = 255;
83 comp->last_xmit = 255;
84 comp->flags = SLF_TOSS;
87 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ
88 * checks for zero (since zero has to be encoded in the long, 3 byte
92 if ((u_int16_t)(n) >= 256) { \
101 #define ENCODEZ(n) { \
102 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \
112 #define DECODEL(f) { \
114 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
117 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \
121 #define DECODES(f) { \
123 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
126 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \
130 #define DECODEU(f) { \
132 (f) = htons((cp[1] << 8) | cp[2]); \
135 (f) = htons((u_int32_t)*cp++); \
140 * Attempt to compress an outgoing TCP packet and return the type of
141 * the result. The caller must have already verified that the protocol
142 * is TCP. The first mbuf must contain the complete IP and TCP headers,
143 * and "ip" must be == mtod(m, struct ip *). "comp" supplies the
144 * compression state, and "compress_cid" tells us whether it is OK
145 * to leave out the CID field when feasible.
147 * The caller is responsible for adjusting m->m_pkthdr.len upon return,
148 * if m is an M_PKTHDR mbuf.
151 sl_compress_tcp(struct mbuf *m, struct ip *ip, struct slcompress *comp,
154 struct cstate *cs = comp->last_cs->cs_next;
155 u_int hlen = ip->ip_hl;
158 u_int deltaS, deltaA;
161 u_char *cp = new_seq;
164 * Bail if this is an IP fragment or if the TCP packet isn't
165 * `compressible' (i.e., ACK isn't set or some other control bit is
166 * set). (We assume that the caller has already made sure the
167 * packet is IP proto TCP).
169 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40)
172 th = (struct tcphdr *)&((int32_t *)ip)[hlen];
173 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
176 * Packet is compressible -- we're going to send either a
177 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
178 * to locate (or create) the connection state. Special case the
179 * most recently used connection since it's most likely to be used
180 * again & we don't have to do any reordering if it's used.
183 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
184 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
185 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
187 * Wasn't the first -- search for it.
189 * States are kept in a circularly linked list with
190 * last_cs pointing to the end of the list. The
191 * list is kept in lru order by moving a state to the
192 * head of the list whenever it is referenced. Since
193 * the list is short and, empirically, the connection
194 * we want is almost always near the front, we locate
195 * states via linear search. If we don't find a state
196 * for the datagram, the oldest state is (re-)used.
199 struct cstate *lastcs = comp->last_cs;
202 lcs = cs; cs = cs->cs_next;
204 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
205 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
207 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl])
209 } while (cs != lastcs);
212 * Didn't find it -- re-use oldest cstate. Send an
213 * uncompressed packet that tells the other side what
214 * connection number we're using for this conversation.
215 * Note that since the state list is circular, the oldest
216 * state points to the newest and we only need to set
217 * last_cs to update the lru linkage.
229 * Found it -- move to the front on the connection list.
234 lcs->cs_next = cs->cs_next;
235 cs->cs_next = lastcs->cs_next;
236 lastcs->cs_next = cs;
241 * Make sure that only what we expect to change changed. The first
242 * line of the `if' checks the IP protocol version, header length &
243 * type of service. The 2nd line checks the "Don't fragment" bit.
244 * The 3rd line checks the time-to-live and protocol (the protocol
245 * check is unnecessary but costless). The 4th line checks the TCP
246 * header length. The 5th line checks IP options, if any. The 6th
247 * line checks TCP options, if any. If any of these things are
248 * different between the previous & current datagram, we send the
249 * current datagram `uncompressed'.
251 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen];
258 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] ||
259 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] ||
260 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] ||
261 th->th_off != oth->th_off ||
263 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
265 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
269 * Figure out which of the changing fields changed. The
270 * receiver expects changes in the order: urgent, window,
271 * ack, seq (the order minimizes the number of temporaries
272 * needed in this section of code).
274 if (th->th_flags & TH_URG) {
275 deltaS = ntohs(th->th_urp);
278 } else if (th->th_urp != oth->th_urp)
279 /* argh! URG not set but urp changed -- a sensible
280 * implementation should never do this but RFC793
281 * doesn't prohibit the change so we have to deal
285 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win));
291 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack);
299 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq);
310 * Nothing changed. If this packet contains data and the
311 * last one didn't, this is probably a data packet following
312 * an ack (normal on an interactive connection) and we send
313 * it compressed. Otherwise it's probably a retransmit,
314 * retransmitted ack or window probe. Send it uncompressed
315 * in case the other side missed the compressed version.
317 if (ip->ip_len != cs->cs_ip.ip_len &&
318 ntohs(cs->cs_ip.ip_len) == hlen)
326 * actual changes match one of our special case encodings --
327 * send packet uncompressed.
332 if (deltaS == deltaA &&
333 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
334 /* special case for echoed terminal traffic */
341 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
342 /* special case for data xfer */
349 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
354 if (th->th_flags & TH_PUSH)
355 changes |= TCP_PUSH_BIT;
357 * Grab the cksum before we overwrite it below. Then update our
358 * state with this packet's header.
360 deltaA = ntohs(th->th_sum);
361 BCOPY(ip, &cs->cs_ip, hlen);
364 * We want to use the original packet as our compressed packet.
365 * (cp - new_seq) is the number of bytes we need for compressed
366 * sequence numbers. In addition we need one byte for the change
367 * mask, one for the connection id and two for the tcp checksum.
368 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
369 * many bytes of the original packet to toss so subtract the two to
370 * get the new packet size.
372 deltaS = cp - new_seq;
374 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
375 comp->last_xmit = cs->cs_id;
378 *cp++ = changes | NEW_C;
389 BCOPY(new_seq, cp, deltaS);
391 return (TYPE_COMPRESSED_TCP);
394 * Update connection state cs & send uncompressed packet ('uncompressed'
395 * means a regular ip/tcp packet but with the 'conversation id' we hope
396 * to use on future compressed packets in the protocol field).
399 BCOPY(ip, &cs->cs_ip, hlen);
400 ip->ip_p = cs->cs_id;
401 comp->last_xmit = cs->cs_id;
402 return (TYPE_UNCOMPRESSED_TCP);
406 sl_uncompress_tcp(u_char **bufp, int len, u_int type, struct slcompress *comp)
411 cp = bufp? *bufp: NULL;
412 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen);
414 return (0); /* error */
416 return (len); /* was uncompressed already */
422 * At this point, cp points to the first byte of data in the
423 * packet. If we're not aligned on a 4-byte boundary, copy the
424 * data down so the ip & tcp headers will be aligned. Then back up
425 * cp by the tcp/ip header length to make room for the reconstructed
426 * header (we assume the packet we were handed has enough space to
427 * prepend 128 bytes of header).
429 if ((intptr_t)cp & 3) {
431 BCOPY(cp, ((intptr_t)cp &~ 3), len);
432 cp = (u_char *)((intptr_t)cp &~ 3);
436 BCOPY(hdr, cp, hlen);
443 * Uncompress a packet of total length total_len. The first buflen
444 * bytes are at buf; this must include the entire (compressed or
445 * uncompressed) TCP/IP header. This procedure returns the length
446 * of the VJ header, with a pointer to the uncompressed IP header
447 * in *hdrp and its length in *hlenp.
450 sl_uncompress_tcp_core(u_char *buf, int buflen, int total_len, u_int type,
451 struct slcompress *comp, u_char **hdrp, u_int *hlenp)
462 case TYPE_UNCOMPRESSED_TCP:
463 ip = (struct ip *) buf;
464 if (ip->ip_p >= MAX_STATES)
466 cs = &comp->rstate[comp->last_recv = ip->ip_p];
467 comp->flags &=~ SLF_TOSS;
468 ip->ip_p = IPPROTO_TCP;
470 * Calculate the size of the TCP/IP header and make sure that
471 * we don't overflow the space we have available for it.
473 hlen = ip->ip_hl << 2;
474 if (hlen + sizeof(struct tcphdr) > buflen)
476 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2;
477 if (hlen > MAX_HDR || hlen > buflen)
479 BCOPY(ip, &cs->cs_ip, hlen);
481 INCR(sls_uncompressedin)
482 *hdrp = (u_char *) &cs->cs_ip;
489 case TYPE_COMPRESSED_TCP:
492 /* We've got a compressed packet. */
493 INCR(sls_compressedin)
496 if (changes & NEW_C) {
497 /* Make sure the state index is in range, then grab the state.
498 * If we have a good state index, clear the 'discard' flag. */
499 if (*cp >= MAX_STATES)
502 comp->flags &=~ SLF_TOSS;
503 comp->last_recv = *cp++;
505 /* this packet has an implicit state index. If we've
506 * had a line error since the last time we got an
507 * explicit state index, we have to toss the packet. */
508 if (comp->flags & SLF_TOSS) {
513 cs = &comp->rstate[comp->last_recv];
514 hlen = cs->cs_ip.ip_hl << 2;
515 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
516 th->th_sum = htons((*cp << 8) | cp[1]);
518 if (changes & TCP_PUSH_BIT)
519 th->th_flags |= TH_PUSH;
521 th->th_flags &=~ TH_PUSH;
523 switch (changes & SPECIALS_MASK) {
526 u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
527 th->th_ack = htonl(ntohl(th->th_ack) + i);
528 th->th_seq = htonl(ntohl(th->th_seq) + i);
533 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
538 if (changes & NEW_U) {
539 th->th_flags |= TH_URG;
542 th->th_flags &=~ TH_URG;
551 if (changes & NEW_I) {
552 DECODES(cs->cs_ip.ip_id)
554 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
557 * At this point, cp points to the first byte of data in the
558 * packet. Fill in the IP total length and update the IP
564 /* we must have dropped some characters (crc should detect
565 * this but the old slip framing won't) */
568 total_len += cs->cs_hlen - vjlen;
569 cs->cs_ip.ip_len = htons(total_len);
571 /* recompute the ip header checksum */
572 bp = (u_int16_t *) &cs->cs_ip;
573 cs->cs_ip.ip_sum = 0;
574 for (changes = 0; hlen > 0; hlen -= 2)
576 changes = (changes & 0xffff) + (changes >> 16);
577 changes = (changes & 0xffff) + (changes >> 16);
578 cs->cs_ip.ip_sum = ~ changes;
580 *hdrp = (u_char *) &cs->cs_ip;
581 *hlenp = cs->cs_hlen;
585 comp->flags |= SLF_TOSS;