FreeBSD/Linux Kernel Cross Reference
sys/net/slcompress.c
1 /*-
2 * Copyright (c) 1989, 1993, 1994
3 * The Regents of the University of California. All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
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.
20 *
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
31 * SUCH DAMAGE.
32 *
33 * @(#)slcompress.c 8.2 (Berkeley) 4/16/94
34 * $FreeBSD$
35 */
36
37 /*
38 * Routines to compress and uncompess tcp packets (for transmission
39 * over low speed serial lines.
40 *
41 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
42 * - Initial distribution.
43 *
44 */
45
46 #include <sys/param.h>
47 #include <sys/mbuf.h>
48 #include <sys/systm.h>
49
50 #include <netinet/in.h>
51 #include <netinet/in_systm.h>
52 #include <netinet/ip.h>
53 #include <netinet/tcp.h>
54
55 #include <net/slcompress.h>
56
57 #ifndef SL_NO_STATS
58 #define INCR(counter) ++comp->counter;
59 #else
60 #define INCR(counter)
61 #endif
62
63 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n))
64 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n))
65 #ifndef _KERNEL
66 #define ovbcopy bcopy
67 #endif
68
69 void
70 sl_compress_init(comp, max_state)
71 struct slcompress *comp;
72 int max_state;
73 {
74 register u_int i;
75 register struct cstate *tstate = comp->tstate;
76
77 if (max_state == -1) {
78 max_state = MAX_STATES - 1;
79 bzero((char *)comp, sizeof(*comp));
80 } else {
81 /* Don't reset statistics */
82 bzero((char *)comp->tstate, sizeof(comp->tstate));
83 bzero((char *)comp->rstate, sizeof(comp->rstate));
84 }
85 for (i = max_state; i > 0; --i) {
86 tstate[i].cs_id = i;
87 tstate[i].cs_next = &tstate[i - 1];
88 }
89 tstate[0].cs_next = &tstate[max_state];
90 tstate[0].cs_id = 0;
91 comp->last_cs = &tstate[0];
92 comp->last_recv = 255;
93 comp->last_xmit = 255;
94 comp->flags = SLF_TOSS;
95 }
96
97
98 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ
99 * checks for zero (since zero has to be encoded in the long, 3 byte
100 * form).
101 */
102 #define ENCODE(n) { \
103 if ((u_int16_t)(n) >= 256) { \
104 *cp++ = 0; \
105 cp[1] = (n); \
106 cp[0] = (n) >> 8; \
107 cp += 2; \
108 } else { \
109 *cp++ = (n); \
110 } \
111 }
112 #define ENCODEZ(n) { \
113 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \
114 *cp++ = 0; \
115 cp[1] = (n); \
116 cp[0] = (n) >> 8; \
117 cp += 2; \
118 } else { \
119 *cp++ = (n); \
120 } \
121 }
122
123 #define DECODEL(f) { \
124 if (*cp == 0) {\
125 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
126 cp += 3; \
127 } else { \
128 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \
129 } \
130 }
131
132 #define DECODES(f) { \
133 if (*cp == 0) {\
134 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
135 cp += 3; \
136 } else { \
137 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \
138 } \
139 }
140
141 #define DECODEU(f) { \
142 if (*cp == 0) {\
143 (f) = htons((cp[1] << 8) | cp[2]); \
144 cp += 3; \
145 } else { \
146 (f) = htons((u_int32_t)*cp++); \
147 } \
148 }
149
150 /*
151 * Attempt to compress an outgoing TCP packet and return the type of
152 * the result. The caller must have already verified that the protocol
153 * is TCP. The first mbuf must contain the complete IP and TCP headers,
154 * and "ip" must be == mtod(m, struct ip *). "comp" supplies the
155 * compression state, and "compress_cid" tells us whether it is OK
156 * to leave out the CID field when feasible.
157 *
158 * The caller is responsible for adjusting m->m_pkthdr.len upon return,
159 * if m is an M_PKTHDR mbuf.
160 */
161 u_int
162 sl_compress_tcp(m, ip, comp, compress_cid)
163 struct mbuf *m;
164 register struct ip *ip;
165 struct slcompress *comp;
166 int compress_cid;
167 {
168 register struct cstate *cs = comp->last_cs->cs_next;
169 register u_int hlen = ip->ip_hl;
170 register struct tcphdr *oth;
171 register struct tcphdr *th;
172 register u_int deltaS, deltaA;
173 register u_int changes = 0;
174 u_char new_seq[16];
175 register u_char *cp = new_seq;
176
177 /*
178 * Bail if this is an IP fragment or if the TCP packet isn't
179 * `compressible' (i.e., ACK isn't set or some other control bit is
180 * set). (We assume that the caller has already made sure the
181 * packet is IP proto TCP).
182 */
183 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40)
184 return (TYPE_IP);
185
186 th = (struct tcphdr *)&((int32_t *)ip)[hlen];
187 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
188 return (TYPE_IP);
189 /*
190 * Packet is compressible -- we're going to send either a
191 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
192 * to locate (or create) the connection state. Special case the
193 * most recently used connection since it's most likely to be used
194 * again & we don't have to do any reordering if it's used.
195 */
196 INCR(sls_packets)
197 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
198 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
199 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
200 /*
201 * Wasn't the first -- search for it.
202 *
203 * States are kept in a circularly linked list with
204 * last_cs pointing to the end of the list. The
205 * list is kept in lru order by moving a state to the
206 * head of the list whenever it is referenced. Since
207 * the list is short and, empirically, the connection
208 * we want is almost always near the front, we locate
209 * states via linear search. If we don't find a state
210 * for the datagram, the oldest state is (re-)used.
211 */
212 register struct cstate *lcs;
213 register struct cstate *lastcs = comp->last_cs;
214
215 do {
216 lcs = cs; cs = cs->cs_next;
217 INCR(sls_searches)
218 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
219 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
220 && *(int32_t *)th ==
221 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl])
222 goto found;
223 } while (cs != lastcs);
224
225 /*
226 * Didn't find it -- re-use oldest cstate. Send an
227 * uncompressed packet that tells the other side what
228 * connection number we're using for this conversation.
229 * Note that since the state list is circular, the oldest
230 * state points to the newest and we only need to set
231 * last_cs to update the lru linkage.
232 */
233 INCR(sls_misses)
234 comp->last_cs = lcs;
235 hlen += th->th_off;
236 hlen <<= 2;
237 if (hlen > m->m_len)
238 return TYPE_IP;
239 goto uncompressed;
240
241 found:
242 /*
243 * Found it -- move to the front on the connection list.
244 */
245 if (cs == lastcs)
246 comp->last_cs = lcs;
247 else {
248 lcs->cs_next = cs->cs_next;
249 cs->cs_next = lastcs->cs_next;
250 lastcs->cs_next = cs;
251 }
252 }
253
254 /*
255 * Make sure that only what we expect to change changed. The first
256 * line of the `if' checks the IP protocol version, header length &
257 * type of service. The 2nd line checks the "Don't fragment" bit.
258 * The 3rd line checks the time-to-live and protocol (the protocol
259 * check is unnecessary but costless). The 4th line checks the TCP
260 * header length. The 5th line checks IP options, if any. The 6th
261 * line checks TCP options, if any. If any of these things are
262 * different between the previous & current datagram, we send the
263 * current datagram `uncompressed'.
264 */
265 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen];
266 deltaS = hlen;
267 hlen += th->th_off;
268 hlen <<= 2;
269 if (hlen > m->m_len)
270 return TYPE_IP;
271
272 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] ||
273 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] ||
274 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] ||
275 th->th_off != oth->th_off ||
276 (deltaS > 5 &&
277 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
278 (th->th_off > 5 &&
279 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
280 goto uncompressed;
281
282 /*
283 * Figure out which of the changing fields changed. The
284 * receiver expects changes in the order: urgent, window,
285 * ack, seq (the order minimizes the number of temporaries
286 * needed in this section of code).
287 */
288 if (th->th_flags & TH_URG) {
289 deltaS = ntohs(th->th_urp);
290 ENCODEZ(deltaS);
291 changes |= NEW_U;
292 } else if (th->th_urp != oth->th_urp)
293 /* argh! URG not set but urp changed -- a sensible
294 * implementation should never do this but RFC793
295 * doesn't prohibit the change so we have to deal
296 * with it. */
297 goto uncompressed;
298
299 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win));
300 if (deltaS) {
301 ENCODE(deltaS);
302 changes |= NEW_W;
303 }
304
305 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack);
306 if (deltaA) {
307 if (deltaA > 0xffff)
308 goto uncompressed;
309 ENCODE(deltaA);
310 changes |= NEW_A;
311 }
312
313 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq);
314 if (deltaS) {
315 if (deltaS > 0xffff)
316 goto uncompressed;
317 ENCODE(deltaS);
318 changes |= NEW_S;
319 }
320
321 switch(changes) {
322
323 case 0:
324 /*
325 * Nothing changed. If this packet contains data and the
326 * last one didn't, this is probably a data packet following
327 * an ack (normal on an interactive connection) and we send
328 * it compressed. Otherwise it's probably a retransmit,
329 * retransmitted ack or window probe. Send it uncompressed
330 * in case the other side missed the compressed version.
331 */
332 if (ip->ip_len != cs->cs_ip.ip_len &&
333 ntohs(cs->cs_ip.ip_len) == hlen)
334 break;
335
336 /* (fall through) */
337
338 case SPECIAL_I:
339 case SPECIAL_D:
340 /*
341 * actual changes match one of our special case encodings --
342 * send packet uncompressed.
343 */
344 goto uncompressed;
345
346 case NEW_S|NEW_A:
347 if (deltaS == deltaA &&
348 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
349 /* special case for echoed terminal traffic */
350 changes = SPECIAL_I;
351 cp = new_seq;
352 }
353 break;
354
355 case NEW_S:
356 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
357 /* special case for data xfer */
358 changes = SPECIAL_D;
359 cp = new_seq;
360 }
361 break;
362 }
363
364 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
365 if (deltaS != 1) {
366 ENCODEZ(deltaS);
367 changes |= NEW_I;
368 }
369 if (th->th_flags & TH_PUSH)
370 changes |= TCP_PUSH_BIT;
371 /*
372 * Grab the cksum before we overwrite it below. Then update our
373 * state with this packet's header.
374 */
375 deltaA = ntohs(th->th_sum);
376 BCOPY(ip, &cs->cs_ip, hlen);
377
378 /*
379 * We want to use the original packet as our compressed packet.
380 * (cp - new_seq) is the number of bytes we need for compressed
381 * sequence numbers. In addition we need one byte for the change
382 * mask, one for the connection id and two for the tcp checksum.
383 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
384 * many bytes of the original packet to toss so subtract the two to
385 * get the new packet size.
386 */
387 deltaS = cp - new_seq;
388 cp = (u_char *)ip;
389 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
390 comp->last_xmit = cs->cs_id;
391 hlen -= deltaS + 4;
392 cp += hlen;
393 *cp++ = changes | NEW_C;
394 *cp++ = cs->cs_id;
395 } else {
396 hlen -= deltaS + 3;
397 cp += hlen;
398 *cp++ = changes;
399 }
400 m->m_len -= hlen;
401 m->m_data += hlen;
402 *cp++ = deltaA >> 8;
403 *cp++ = deltaA;
404 BCOPY(new_seq, cp, deltaS);
405 INCR(sls_compressed)
406 return (TYPE_COMPRESSED_TCP);
407
408 /*
409 * Update connection state cs & send uncompressed packet ('uncompressed'
410 * means a regular ip/tcp packet but with the 'conversation id' we hope
411 * to use on future compressed packets in the protocol field).
412 */
413 uncompressed:
414 BCOPY(ip, &cs->cs_ip, hlen);
415 ip->ip_p = cs->cs_id;
416 comp->last_xmit = cs->cs_id;
417 return (TYPE_UNCOMPRESSED_TCP);
418 }
419
420
421 int
422 sl_uncompress_tcp(bufp, len, type, comp)
423 u_char **bufp;
424 int len;
425 u_int type;
426 struct slcompress *comp;
427 {
428 u_char *hdr, *cp;
429 int hlen, vjlen;
430
431 cp = bufp? *bufp: NULL;
432 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen);
433 if (vjlen < 0)
434 return (0); /* error */
435 if (vjlen == 0)
436 return (len); /* was uncompressed already */
437
438 cp += vjlen;
439 len -= vjlen;
440
441 /*
442 * At this point, cp points to the first byte of data in the
443 * packet. If we're not aligned on a 4-byte boundary, copy the
444 * data down so the ip & tcp headers will be aligned. Then back up
445 * cp by the tcp/ip header length to make room for the reconstructed
446 * header (we assume the packet we were handed has enough space to
447 * prepend 128 bytes of header).
448 */
449 if ((intptr_t)cp & 3) {
450 if (len > 0)
451 (void) ovbcopy(cp, (caddr_t)((intptr_t)cp &~ 3), len);
452 cp = (u_char *)((intptr_t)cp &~ 3);
453 }
454 cp -= hlen;
455 len += hlen;
456 BCOPY(hdr, cp, hlen);
457
458 *bufp = cp;
459 return (len);
460 }
461
462 /*
463 * Uncompress a packet of total length total_len. The first buflen
464 * bytes are at buf; this must include the entire (compressed or
465 * uncompressed) TCP/IP header. This procedure returns the length
466 * of the VJ header, with a pointer to the uncompressed IP header
467 * in *hdrp and its length in *hlenp.
468 */
469 int
470 sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp)
471 u_char *buf;
472 int buflen, total_len;
473 u_int type;
474 struct slcompress *comp;
475 u_char **hdrp;
476 u_int *hlenp;
477 {
478 register u_char *cp;
479 register u_int hlen, changes;
480 register struct tcphdr *th;
481 register struct cstate *cs;
482 register struct ip *ip;
483 register u_int16_t *bp;
484 register u_int vjlen;
485
486 switch (type) {
487
488 case TYPE_UNCOMPRESSED_TCP:
489 ip = (struct ip *) buf;
490 if (ip->ip_p >= MAX_STATES)
491 goto bad;
492 cs = &comp->rstate[comp->last_recv = ip->ip_p];
493 comp->flags &=~ SLF_TOSS;
494 ip->ip_p = IPPROTO_TCP;
495 /*
496 * Calculate the size of the TCP/IP header and make sure that
497 * we don't overflow the space we have available for it.
498 */
499 hlen = ip->ip_hl << 2;
500 if (hlen + sizeof(struct tcphdr) > buflen)
501 goto bad;
502 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2;
503 if (hlen > MAX_HDR || hlen > buflen)
504 goto bad;
505 BCOPY(ip, &cs->cs_ip, hlen);
506 cs->cs_hlen = hlen;
507 INCR(sls_uncompressedin)
508 *hdrp = (u_char *) &cs->cs_ip;
509 *hlenp = hlen;
510 return (0);
511
512 default:
513 goto bad;
514
515 case TYPE_COMPRESSED_TCP:
516 break;
517 }
518 /* We've got a compressed packet. */
519 INCR(sls_compressedin)
520 cp = buf;
521 changes = *cp++;
522 if (changes & NEW_C) {
523 /* Make sure the state index is in range, then grab the state.
524 * If we have a good state index, clear the 'discard' flag. */
525 if (*cp >= MAX_STATES)
526 goto bad;
527
528 comp->flags &=~ SLF_TOSS;
529 comp->last_recv = *cp++;
530 } else {
531 /* this packet has an implicit state index. If we've
532 * had a line error since the last time we got an
533 * explicit state index, we have to toss the packet. */
534 if (comp->flags & SLF_TOSS) {
535 INCR(sls_tossed)
536 return (-1);
537 }
538 }
539 cs = &comp->rstate[comp->last_recv];
540 hlen = cs->cs_ip.ip_hl << 2;
541 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
542 th->th_sum = htons((*cp << 8) | cp[1]);
543 cp += 2;
544 if (changes & TCP_PUSH_BIT)
545 th->th_flags |= TH_PUSH;
546 else
547 th->th_flags &=~ TH_PUSH;
548
549 switch (changes & SPECIALS_MASK) {
550 case SPECIAL_I:
551 {
552 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
553 th->th_ack = htonl(ntohl(th->th_ack) + i);
554 th->th_seq = htonl(ntohl(th->th_seq) + i);
555 }
556 break;
557
558 case SPECIAL_D:
559 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
560 - cs->cs_hlen);
561 break;
562
563 default:
564 if (changes & NEW_U) {
565 th->th_flags |= TH_URG;
566 DECODEU(th->th_urp)
567 } else
568 th->th_flags &=~ TH_URG;
569 if (changes & NEW_W)
570 DECODES(th->th_win)
571 if (changes & NEW_A)
572 DECODEL(th->th_ack)
573 if (changes & NEW_S)
574 DECODEL(th->th_seq)
575 break;
576 }
577 if (changes & NEW_I) {
578 DECODES(cs->cs_ip.ip_id)
579 } else
580 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
581
582 /*
583 * At this point, cp points to the first byte of data in the
584 * packet. Fill in the IP total length and update the IP
585 * header checksum.
586 */
587 vjlen = cp - buf;
588 buflen -= vjlen;
589 if (buflen < 0)
590 /* we must have dropped some characters (crc should detect
591 * this but the old slip framing won't) */
592 goto bad;
593
594 total_len += cs->cs_hlen - vjlen;
595 cs->cs_ip.ip_len = htons(total_len);
596
597 /* recompute the ip header checksum */
598 bp = (u_int16_t *) &cs->cs_ip;
599 cs->cs_ip.ip_sum = 0;
600 for (changes = 0; hlen > 0; hlen -= 2)
601 changes += *bp++;
602 changes = (changes & 0xffff) + (changes >> 16);
603 changes = (changes & 0xffff) + (changes >> 16);
604 cs->cs_ip.ip_sum = ~ changes;
605
606 *hdrp = (u_char *) &cs->cs_ip;
607 *hlenp = cs->cs_hlen;
608 return vjlen;
609
610 bad:
611 comp->flags |= SLF_TOSS;
612 INCR(sls_errorin)
613 return (-1);
614 }
Cache object: 595d6dc99f3780cbcb20771823b7bd62
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