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: releng/5.2/sys/net/slcompress.c 113072 2003-04-04 12:11:46Z des $
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((void *)(p1), (void *)(p2), (int)(n))
64 #define BCOPY(p1, p2, n) bcopy((void *)(p1), (void *)(p2), (int)(n))
65
66 void
67 sl_compress_init(comp, max_state)
68 struct slcompress *comp;
69 int max_state;
70 {
71 register u_int i;
72 register struct cstate *tstate = comp->tstate;
73
74 if (max_state == -1) {
75 max_state = MAX_STATES - 1;
76 bzero((char *)comp, sizeof(*comp));
77 } else {
78 /* Don't reset statistics */
79 bzero((char *)comp->tstate, sizeof(comp->tstate));
80 bzero((char *)comp->rstate, sizeof(comp->rstate));
81 }
82 for (i = max_state; i > 0; --i) {
83 tstate[i].cs_id = i;
84 tstate[i].cs_next = &tstate[i - 1];
85 }
86 tstate[0].cs_next = &tstate[max_state];
87 tstate[0].cs_id = 0;
88 comp->last_cs = &tstate[0];
89 comp->last_recv = 255;
90 comp->last_xmit = 255;
91 comp->flags = SLF_TOSS;
92 }
93
94
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
97 * form).
98 */
99 #define ENCODE(n) { \
100 if ((u_int16_t)(n) >= 256) { \
101 *cp++ = 0; \
102 cp[1] = (n); \
103 cp[0] = (n) >> 8; \
104 cp += 2; \
105 } else { \
106 *cp++ = (n); \
107 } \
108 }
109 #define ENCODEZ(n) { \
110 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \
111 *cp++ = 0; \
112 cp[1] = (n); \
113 cp[0] = (n) >> 8; \
114 cp += 2; \
115 } else { \
116 *cp++ = (n); \
117 } \
118 }
119
120 #define DECODEL(f) { \
121 if (*cp == 0) {\
122 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
123 cp += 3; \
124 } else { \
125 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \
126 } \
127 }
128
129 #define DECODES(f) { \
130 if (*cp == 0) {\
131 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
132 cp += 3; \
133 } else { \
134 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \
135 } \
136 }
137
138 #define DECODEU(f) { \
139 if (*cp == 0) {\
140 (f) = htons((cp[1] << 8) | cp[2]); \
141 cp += 3; \
142 } else { \
143 (f) = htons((u_int32_t)*cp++); \
144 } \
145 }
146
147 /*
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.
154 *
155 * The caller is responsible for adjusting m->m_pkthdr.len upon return,
156 * if m is an M_PKTHDR mbuf.
157 */
158 u_int
159 sl_compress_tcp(m, ip, comp, compress_cid)
160 struct mbuf *m;
161 register struct ip *ip;
162 struct slcompress *comp;
163 int compress_cid;
164 {
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;
171 u_char new_seq[16];
172 register u_char *cp = new_seq;
173
174 /*
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).
179 */
180 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40)
181 return (TYPE_IP);
182
183 th = (struct tcphdr *)&((int32_t *)ip)[hlen];
184 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
185 return (TYPE_IP);
186 /*
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.
192 */
193 INCR(sls_packets)
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]) {
197 /*
198 * Wasn't the first -- search for it.
199 *
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.
208 */
209 register struct cstate *lcs;
210 register struct cstate *lastcs = comp->last_cs;
211
212 do {
213 lcs = cs; cs = cs->cs_next;
214 INCR(sls_searches)
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
217 && *(int32_t *)th ==
218 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl])
219 goto found;
220 } while (cs != lastcs);
221
222 /*
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.
229 */
230 INCR(sls_misses)
231 comp->last_cs = lcs;
232 hlen += th->th_off;
233 hlen <<= 2;
234 if (hlen > m->m_len)
235 return TYPE_IP;
236 goto uncompressed;
237
238 found:
239 /*
240 * Found it -- move to the front on the connection list.
241 */
242 if (cs == lastcs)
243 comp->last_cs = lcs;
244 else {
245 lcs->cs_next = cs->cs_next;
246 cs->cs_next = lastcs->cs_next;
247 lastcs->cs_next = cs;
248 }
249 }
250
251 /*
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'.
261 */
262 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen];
263 deltaS = hlen;
264 hlen += th->th_off;
265 hlen <<= 2;
266 if (hlen > m->m_len)
267 return TYPE_IP;
268
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 ||
273 (deltaS > 5 &&
274 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
275 (th->th_off > 5 &&
276 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
277 goto uncompressed;
278
279 /*
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).
284 */
285 if (th->th_flags & TH_URG) {
286 deltaS = ntohs(th->th_urp);
287 ENCODEZ(deltaS);
288 changes |= NEW_U;
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
293 * with it. */
294 goto uncompressed;
295
296 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win));
297 if (deltaS) {
298 ENCODE(deltaS);
299 changes |= NEW_W;
300 }
301
302 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack);
303 if (deltaA) {
304 if (deltaA > 0xffff)
305 goto uncompressed;
306 ENCODE(deltaA);
307 changes |= NEW_A;
308 }
309
310 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq);
311 if (deltaS) {
312 if (deltaS > 0xffff)
313 goto uncompressed;
314 ENCODE(deltaS);
315 changes |= NEW_S;
316 }
317
318 switch(changes) {
319
320 case 0:
321 /*
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.
328 */
329 if (ip->ip_len != cs->cs_ip.ip_len &&
330 ntohs(cs->cs_ip.ip_len) == hlen)
331 break;
332
333 /* FALLTHROUGH */
334
335 case SPECIAL_I:
336 case SPECIAL_D:
337 /*
338 * actual changes match one of our special case encodings --
339 * send packet uncompressed.
340 */
341 goto uncompressed;
342
343 case NEW_S|NEW_A:
344 if (deltaS == deltaA &&
345 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
346 /* special case for echoed terminal traffic */
347 changes = SPECIAL_I;
348 cp = new_seq;
349 }
350 break;
351
352 case NEW_S:
353 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
354 /* special case for data xfer */
355 changes = SPECIAL_D;
356 cp = new_seq;
357 }
358 break;
359 }
360
361 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
362 if (deltaS != 1) {
363 ENCODEZ(deltaS);
364 changes |= NEW_I;
365 }
366 if (th->th_flags & TH_PUSH)
367 changes |= TCP_PUSH_BIT;
368 /*
369 * Grab the cksum before we overwrite it below. Then update our
370 * state with this packet's header.
371 */
372 deltaA = ntohs(th->th_sum);
373 BCOPY(ip, &cs->cs_ip, hlen);
374
375 /*
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.
383 */
384 deltaS = cp - new_seq;
385 cp = (u_char *)ip;
386 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
387 comp->last_xmit = cs->cs_id;
388 hlen -= deltaS + 4;
389 cp += hlen;
390 *cp++ = changes | NEW_C;
391 *cp++ = cs->cs_id;
392 } else {
393 hlen -= deltaS + 3;
394 cp += hlen;
395 *cp++ = changes;
396 }
397 m->m_len -= hlen;
398 m->m_data += hlen;
399 *cp++ = deltaA >> 8;
400 *cp++ = deltaA;
401 BCOPY(new_seq, cp, deltaS);
402 INCR(sls_compressed)
403 return (TYPE_COMPRESSED_TCP);
404
405 /*
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).
409 */
410 uncompressed:
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);
415 }
416
417
418 int
419 sl_uncompress_tcp(bufp, len, type, comp)
420 u_char **bufp;
421 int len;
422 u_int type;
423 struct slcompress *comp;
424 {
425 u_char *hdr, *cp;
426 int hlen, vjlen;
427
428 cp = bufp? *bufp: NULL;
429 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen);
430 if (vjlen < 0)
431 return (0); /* error */
432 if (vjlen == 0)
433 return (len); /* was uncompressed already */
434
435 cp += vjlen;
436 len -= vjlen;
437
438 /*
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).
445 */
446 if ((intptr_t)cp & 3) {
447 if (len > 0)
448 BCOPY(cp, ((intptr_t)cp &~ 3), len);
449 cp = (u_char *)((intptr_t)cp &~ 3);
450 }
451 cp -= hlen;
452 len += hlen;
453 BCOPY(hdr, cp, hlen);
454
455 *bufp = cp;
456 return (len);
457 }
458
459 /*
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.
465 */
466 int
467 sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp)
468 u_char *buf;
469 int buflen, total_len;
470 u_int type;
471 struct slcompress *comp;
472 u_char **hdrp;
473 u_int *hlenp;
474 {
475 register u_char *cp;
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;
482
483 switch (type) {
484
485 case TYPE_UNCOMPRESSED_TCP:
486 ip = (struct ip *) buf;
487 if (ip->ip_p >= MAX_STATES)
488 goto bad;
489 cs = &comp->rstate[comp->last_recv = ip->ip_p];
490 comp->flags &=~ SLF_TOSS;
491 ip->ip_p = IPPROTO_TCP;
492 /*
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.
495 */
496 hlen = ip->ip_hl << 2;
497 if (hlen + sizeof(struct tcphdr) > buflen)
498 goto bad;
499 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2;
500 if (hlen > MAX_HDR || hlen > buflen)
501 goto bad;
502 BCOPY(ip, &cs->cs_ip, hlen);
503 cs->cs_hlen = hlen;
504 INCR(sls_uncompressedin)
505 *hdrp = (u_char *) &cs->cs_ip;
506 *hlenp = hlen;
507 return (0);
508
509 default:
510 goto bad;
511
512 case TYPE_COMPRESSED_TCP:
513 break;
514 }
515 /* We've got a compressed packet. */
516 INCR(sls_compressedin)
517 cp = buf;
518 changes = *cp++;
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)
523 goto bad;
524
525 comp->flags &=~ SLF_TOSS;
526 comp->last_recv = *cp++;
527 } else {
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) {
532 INCR(sls_tossed)
533 return (-1);
534 }
535 }
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]);
540 cp += 2;
541 if (changes & TCP_PUSH_BIT)
542 th->th_flags |= TH_PUSH;
543 else
544 th->th_flags &=~ TH_PUSH;
545
546 switch (changes & SPECIALS_MASK) {
547 case SPECIAL_I:
548 {
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);
552 }
553 break;
554
555 case SPECIAL_D:
556 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
557 - cs->cs_hlen);
558 break;
559
560 default:
561 if (changes & NEW_U) {
562 th->th_flags |= TH_URG;
563 DECODEU(th->th_urp)
564 } else
565 th->th_flags &=~ TH_URG;
566 if (changes & NEW_W)
567 DECODES(th->th_win)
568 if (changes & NEW_A)
569 DECODEL(th->th_ack)
570 if (changes & NEW_S)
571 DECODEL(th->th_seq)
572 break;
573 }
574 if (changes & NEW_I) {
575 DECODES(cs->cs_ip.ip_id)
576 } else
577 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
578
579 /*
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
582 * header checksum.
583 */
584 vjlen = cp - buf;
585 buflen -= vjlen;
586 if (buflen < 0)
587 /* we must have dropped some characters (crc should detect
588 * this but the old slip framing won't) */
589 goto bad;
590
591 total_len += cs->cs_hlen - vjlen;
592 cs->cs_ip.ip_len = htons(total_len);
593
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)
598 changes += *bp++;
599 changes = (changes & 0xffff) + (changes >> 16);
600 changes = (changes & 0xffff) + (changes >> 16);
601 cs->cs_ip.ip_sum = ~ changes;
602
603 *hdrp = (u_char *) &cs->cs_ip;
604 *hlenp = cs->cs_hlen;
605 return vjlen;
606
607 bad:
608 comp->flags |= SLF_TOSS;
609 INCR(sls_errorin)
610 return (-1);
611 }
Cache object: 04c5ee545215a2383fffff8b930d62f3
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