Annotation of sys/net/slcompress.c, Revision 1.1.1.1
1.1 nbrk 1: /* $OpenBSD: slcompress.c,v 1.9 2007/02/14 00:53:48 jsg Exp $ */
2: /* $NetBSD: slcompress.c,v 1.17 1997/05/17 21:12:10 christos Exp $ */
3:
4: /*
5: * Copyright (c) 1989, 1993, 1994
6: * The Regents of the University of California. All rights reserved.
7: *
8: * Redistribution and use in source and binary forms, with or without
9: * modification, are permitted provided that the following conditions
10: * are met:
11: * 1. Redistributions of source code must retain the above copyright
12: * notice, this list of conditions and the following disclaimer.
13: * 2. Redistributions in binary form must reproduce the above copyright
14: * notice, this list of conditions and the following disclaimer in the
15: * documentation and/or other materials provided with the distribution.
16: * 3. Neither the name of the University nor the names of its contributors
17: * may be used to endorse or promote products derived from this software
18: * without specific prior written permission.
19: *
20: * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21: * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22: * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23: * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24: * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25: * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26: * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27: * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28: * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29: * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30: * SUCH DAMAGE.
31: *
32: * @(#)slcompress.c 8.2 (Berkeley) 4/16/94
33: */
34:
35: /*
36: * Routines to compress and uncompess tcp packets (for transmission
37: * over low speed serial lines.
38: *
39: * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
40: * - Initial distribution.
41: */
42:
43: #include <sys/param.h>
44: #include <sys/mbuf.h>
45: #include <sys/systm.h>
46:
47: #include <netinet/in.h>
48: #include <netinet/in_systm.h>
49: #include <netinet/ip.h>
50: #include <netinet/tcp.h>
51:
52: #include <net/slcompress.h>
53:
54: #ifndef SL_NO_STATS
55: #define INCR(counter) ++comp->counter;
56: #else
57: #define INCR(counter)
58: #endif
59:
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))
62: #ifndef _KERNEL
63: #define ovbcopy bcopy
64: #endif
65:
66:
67: void
68: sl_compress_init(comp)
69: struct slcompress *comp;
70: {
71: u_int i;
72: struct cstate *tstate = comp->tstate;
73:
74: bzero((char *)comp, sizeof(*comp));
75: for (i = MAX_STATES - 1; i > 0; --i) {
76: tstate[i].cs_id = i;
77: tstate[i].cs_next = &tstate[i - 1];
78: }
79: tstate[0].cs_next = &tstate[MAX_STATES - 1];
80: tstate[0].cs_id = 0;
81: comp->last_cs = &tstate[0];
82: comp->last_recv = 255;
83: comp->last_xmit = 255;
84: comp->flags = SLF_TOSS;
85: }
86:
87:
88: /*
89: * Like sl_compress_init, but we get to specify the maximum connection
90: * ID to use on transmission.
91: */
92: void
93: sl_compress_setup(comp, max_state)
94: struct slcompress *comp;
95: int max_state;
96: {
97: u_int i;
98: struct cstate *tstate = comp->tstate;
99:
100: if (max_state == -1) {
101: max_state = MAX_STATES - 1;
102: bzero((char *)comp, sizeof(*comp));
103: } else {
104: /* Don't reset statistics */
105: bzero((char *)comp->tstate, sizeof(comp->tstate));
106: bzero((char *)comp->rstate, sizeof(comp->rstate));
107: }
108: for (i = max_state; i > 0; --i) {
109: tstate[i].cs_id = i;
110: tstate[i].cs_next = &tstate[i - 1];
111: }
112: tstate[0].cs_next = &tstate[max_state];
113: tstate[0].cs_id = 0;
114: comp->last_cs = &tstate[0];
115: comp->last_recv = 255;
116: comp->last_xmit = 255;
117: comp->flags = SLF_TOSS;
118: }
119:
120:
121: /* ENCODE encodes a number that is known to be non-zero. ENCODEZ
122: * checks for zero (since zero has to be encoded in the long, 3 byte
123: * form).
124: */
125: #define ENCODE(n) { \
126: if ((u_int16_t)(n) >= 256) { \
127: *cp++ = 0; \
128: cp[1] = (n); \
129: cp[0] = (n) >> 8; \
130: cp += 2; \
131: } else { \
132: *cp++ = (n); \
133: } \
134: }
135: #define ENCODEZ(n) { \
136: if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \
137: *cp++ = 0; \
138: cp[1] = (n); \
139: cp[0] = (n) >> 8; \
140: cp += 2; \
141: } else { \
142: *cp++ = (n); \
143: } \
144: }
145:
146: #define DECODEL(f) { \
147: if (*cp == 0) {\
148: (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
149: cp += 3; \
150: } else { \
151: (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \
152: } \
153: }
154:
155: #define DECODES(f) { \
156: if (*cp == 0) {\
157: (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
158: cp += 3; \
159: } else { \
160: (f) = htons(ntohs(f) + (u_int32_t)*cp++); \
161: } \
162: }
163:
164: #define DECODEU(f) { \
165: if (*cp == 0) {\
166: (f) = htons((cp[1] << 8) | cp[2]); \
167: cp += 3; \
168: } else { \
169: (f) = htons((u_int32_t)*cp++); \
170: } \
171: }
172:
173: u_int
174: sl_compress_tcp(m, ip, comp, compress_cid)
175: struct mbuf *m;
176: struct ip *ip;
177: struct slcompress *comp;
178: int compress_cid;
179: {
180: struct cstate *cs = comp->last_cs->cs_next;
181: u_int hlen = ip->ip_hl;
182: struct tcphdr *oth;
183: struct tcphdr *th;
184: u_int deltaS, deltaA;
185: u_int changes = 0;
186: u_char new_seq[16];
187: u_char *cp = new_seq;
188:
189: /*
190: * Bail if this is an IP fragment or if the TCP packet isn't
191: * `compressible' (i.e., ACK isn't set or some other control bit is
192: * set). (We assume that the caller has already made sure the
193: * packet is IP proto TCP).
194: */
195: if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40)
196: return (TYPE_IP);
197:
198: th = (struct tcphdr *)&((int32_t *)ip)[hlen];
199: if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
200: return (TYPE_IP);
201: /*
202: * Packet is compressible -- we're going to send either a
203: * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
204: * to locate (or create) the connection state. Special case the
205: * most recently used connection since it's most likely to be used
206: * again & we don't have to do any reordering if it's used.
207: */
208: INCR(sls_packets)
209: if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
210: ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
211: *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
212: /*
213: * Wasn't the first -- search for it.
214: *
215: * States are kept in a circularly linked list with
216: * last_cs pointing to the end of the list. The
217: * list is kept in lru order by moving a state to the
218: * head of the list whenever it is referenced. Since
219: * the list is short and, empirically, the connection
220: * we want is almost always near the front, we locate
221: * states via linear search. If we don't find a state
222: * for the datagram, the oldest state is (re-)used.
223: */
224: struct cstate *lcs;
225: struct cstate *lastcs = comp->last_cs;
226:
227: do {
228: lcs = cs; cs = cs->cs_next;
229: INCR(sls_searches)
230: if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
231: && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
232: && *(int32_t *)th ==
233: ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl])
234: goto found;
235: } while (cs != lastcs);
236:
237: /*
238: * Didn't find it -- re-use oldest cstate. Send an
239: * uncompressed packet that tells the other side what
240: * connection number we're using for this conversation.
241: * Note that since the state list is circular, the oldest
242: * state points to the newest and we only need to set
243: * last_cs to update the lru linkage.
244: */
245: INCR(sls_misses)
246: comp->last_cs = lcs;
247: hlen += th->th_off;
248: hlen <<= 2;
249: goto uncompressed;
250:
251: found:
252: /*
253: * Found it -- move to the front on the connection list.
254: */
255: if (cs == lastcs)
256: comp->last_cs = lcs;
257: else {
258: lcs->cs_next = cs->cs_next;
259: cs->cs_next = lastcs->cs_next;
260: lastcs->cs_next = cs;
261: }
262: }
263:
264: /*
265: * Make sure that only what we expect to change changed. The first
266: * line of the `if' checks the IP protocol version, header length &
267: * type of service. The 2nd line checks the "Don't fragment" bit.
268: * The 3rd line checks the time-to-live and protocol (the protocol
269: * check is unnecessary but costless). The 4th line checks the TCP
270: * header length. The 5th line checks IP options, if any. The 6th
271: * line checks TCP options, if any. If any of these things are
272: * different between the previous & current datagram, we send the
273: * current datagram `uncompressed'.
274: */
275: oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen];
276: deltaS = hlen;
277: hlen += th->th_off;
278: hlen <<= 2;
279:
280: if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] ||
281: ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] ||
282: ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] ||
283: th->th_off != oth->th_off ||
284: (deltaS > 5 &&
285: BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
286: (th->th_off > 5 &&
287: BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
288: goto uncompressed;
289:
290: /*
291: * Figure out which of the changing fields changed. The
292: * receiver expects changes in the order: urgent, window,
293: * ack, seq (the order minimizes the number of temporaries
294: * needed in this section of code).
295: */
296: if (th->th_flags & TH_URG) {
297: deltaS = ntohs(th->th_urp);
298: ENCODEZ(deltaS);
299: changes |= NEW_U;
300: } else if (th->th_urp != oth->th_urp)
301: /* argh! URG not set but urp changed -- a sensible
302: * implementation should never do this but RFC793
303: * doesn't prohibit the change so we have to deal
304: * with it. */
305: goto uncompressed;
306:
307: deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win));
308: if (deltaS) {
309: ENCODE(deltaS);
310: changes |= NEW_W;
311: }
312:
313: deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack);
314: if (deltaA) {
315: if (deltaA > 0xffff)
316: goto uncompressed;
317: ENCODE(deltaA);
318: changes |= NEW_A;
319: }
320:
321: deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq);
322: if (deltaS) {
323: if (deltaS > 0xffff)
324: goto uncompressed;
325: ENCODE(deltaS);
326: changes |= NEW_S;
327: }
328:
329: switch(changes) {
330:
331: case 0:
332: /*
333: * Nothing changed. If this packet contains data and the
334: * last one didn't, this is probably a data packet following
335: * an ack (normal on an interactive connection) and we send
336: * it compressed. Otherwise it's probably a retransmit,
337: * retransmitted ack or window probe. Send it uncompressed
338: * in case the other side missed the compressed version.
339: */
340: if (ip->ip_len != cs->cs_ip.ip_len &&
341: ntohs(cs->cs_ip.ip_len) == hlen)
342: break;
343:
344: /* FALLTHROUGH */
345:
346: case SPECIAL_I:
347: case SPECIAL_D:
348: /*
349: * actual changes match one of our special case encodings --
350: * send packet uncompressed.
351: */
352: goto uncompressed;
353:
354: case NEW_S|NEW_A:
355: if (deltaS == deltaA &&
356: deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
357: /* special case for echoed terminal traffic */
358: changes = SPECIAL_I;
359: cp = new_seq;
360: }
361: break;
362:
363: case NEW_S:
364: if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
365: /* special case for data xfer */
366: changes = SPECIAL_D;
367: cp = new_seq;
368: }
369: break;
370: }
371:
372: deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
373: if (deltaS != 1) {
374: ENCODEZ(deltaS);
375: changes |= NEW_I;
376: }
377: if (th->th_flags & TH_PUSH)
378: changes |= TCP_PUSH_BIT;
379: /*
380: * Grab the cksum before we overwrite it below. Then update our
381: * state with this packet's header.
382: */
383: deltaA = ntohs(th->th_sum);
384: BCOPY(ip, &cs->cs_ip, hlen);
385:
386: /*
387: * We want to use the original packet as our compressed packet.
388: * (cp - new_seq) is the number of bytes we need for compressed
389: * sequence numbers. In addition we need one byte for the change
390: * mask, one for the connection id and two for the tcp checksum.
391: * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
392: * many bytes of the original packet to toss so subtract the two to
393: * get the new packet size.
394: */
395: deltaS = cp - new_seq;
396: cp = (u_char *)ip;
397: if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
398: comp->last_xmit = cs->cs_id;
399: hlen -= deltaS + 4;
400: cp += hlen;
401: *cp++ = changes | NEW_C;
402: *cp++ = cs->cs_id;
403: } else {
404: hlen -= deltaS + 3;
405: cp += hlen;
406: *cp++ = changes;
407: }
408: m->m_len -= hlen;
409: m->m_data += hlen;
410: *cp++ = deltaA >> 8;
411: *cp++ = deltaA;
412: BCOPY(new_seq, cp, deltaS);
413: INCR(sls_compressed)
414: return (TYPE_COMPRESSED_TCP);
415:
416: /*
417: * Update connection state cs & send uncompressed packet ('uncompressed'
418: * means a regular ip/tcp packet but with the 'conversation id' we hope
419: * to use on future compressed packets in the protocol field).
420: */
421: uncompressed:
422: BCOPY(ip, &cs->cs_ip, hlen);
423: ip->ip_p = cs->cs_id;
424: comp->last_xmit = cs->cs_id;
425: return (TYPE_UNCOMPRESSED_TCP);
426: }
427:
428:
429: int
430: sl_uncompress_tcp(bufp, len, type, comp)
431: u_char **bufp;
432: int len;
433: u_int type;
434: struct slcompress *comp;
435: {
436: u_char *hdr, *cp;
437: int hlen, vjlen;
438:
439: cp = bufp? *bufp: NULL;
440: vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen);
441: if (vjlen < 0)
442: return (0); /* error */
443: if (vjlen == 0)
444: return (len); /* was uncompressed already */
445:
446: cp += vjlen;
447: len -= vjlen;
448:
449: /*
450: * At this point, cp points to the first byte of data in the
451: * packet. If we're not aligned on a 4-byte boundary, copy the
452: * data down so the ip & tcp headers will be aligned. Then back up
453: * cp by the tcp/ip header length to make room for the reconstructed
454: * header (we assume the packet we were handed has enough space to
455: * prepend 128 bytes of header).
456: */
457: if ((long)cp & 3) {
458: if (len > 0)
459: (void) ovbcopy(cp, (caddr_t)((long)cp &~ 3), len);
460: cp = (u_char *)((long)cp &~ 3);
461: }
462: cp -= hlen;
463: len += hlen;
464: BCOPY(hdr, cp, hlen);
465:
466: *bufp = cp;
467: return (len);
468: }
469:
470: /*
471: * Uncompress a packet of total length total_len. The first buflen
472: * bytes are at buf; this must include the entire (compressed or
473: * uncompressed) TCP/IP header. This procedure returns the length
474: * of the VJ header, with a pointer to the uncompressed IP header
475: * in *hdrp and its length in *hlenp.
476: */
477: int
478: sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp)
479: u_char *buf;
480: int buflen, total_len;
481: u_int type;
482: struct slcompress *comp;
483: u_char **hdrp;
484: u_int *hlenp;
485: {
486: u_char *cp;
487: u_int hlen, changes;
488: struct tcphdr *th;
489: struct cstate *cs;
490: struct ip *ip;
491: u_int16_t *bp;
492: u_int vjlen;
493:
494: switch (type) {
495:
496: case TYPE_UNCOMPRESSED_TCP:
497: ip = (struct ip *) buf;
498: if (ip->ip_p >= MAX_STATES)
499: goto bad;
500: cs = &comp->rstate[comp->last_recv = ip->ip_p];
501: comp->flags &=~ SLF_TOSS;
502: ip->ip_p = IPPROTO_TCP;
503: /*
504: * Calculate the size of the TCP/IP header and make sure that
505: * we don't overflow the space we have available for it.
506: */
507: hlen = ip->ip_hl << 2;
508: if (hlen + sizeof(struct tcphdr) > buflen)
509: goto bad;
510: hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2;
511: if (hlen > MAX_HDR || hlen > buflen)
512: goto bad;
513: BCOPY(ip, &cs->cs_ip, hlen);
514: cs->cs_hlen = hlen;
515: INCR(sls_uncompressedin)
516: *hdrp = (u_char *) &cs->cs_ip;
517: *hlenp = hlen;
518: return (0);
519:
520: default:
521: goto bad;
522:
523: case TYPE_COMPRESSED_TCP:
524: break;
525: }
526: /* We've got a compressed packet. */
527: INCR(sls_compressedin)
528: cp = buf;
529: changes = *cp++;
530: if (changes & NEW_C) {
531: /* Make sure the state index is in range, then grab the state.
532: * If we have a good state index, clear the 'discard' flag. */
533: if (*cp >= MAX_STATES)
534: goto bad;
535:
536: comp->flags &=~ SLF_TOSS;
537: comp->last_recv = *cp++;
538: } else {
539: /* this packet has an implicit state index. If we've
540: * had a line error since the last time we got an
541: * explicit state index, we have to toss the packet. */
542: if (comp->flags & SLF_TOSS) {
543: INCR(sls_tossed)
544: return (-1);
545: }
546: }
547: cs = &comp->rstate[comp->last_recv];
548: hlen = cs->cs_ip.ip_hl << 2;
549: th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
550: th->th_sum = htons((*cp << 8) | cp[1]);
551: cp += 2;
552: if (changes & TCP_PUSH_BIT)
553: th->th_flags |= TH_PUSH;
554: else
555: th->th_flags &=~ TH_PUSH;
556:
557: switch (changes & SPECIALS_MASK) {
558: case SPECIAL_I:
559: {
560: u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
561: th->th_ack = htonl(ntohl(th->th_ack) + i);
562: th->th_seq = htonl(ntohl(th->th_seq) + i);
563: }
564: break;
565:
566: case SPECIAL_D:
567: th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
568: - cs->cs_hlen);
569: break;
570:
571: default:
572: if (changes & NEW_U) {
573: th->th_flags |= TH_URG;
574: DECODEU(th->th_urp)
575: } else
576: th->th_flags &=~ TH_URG;
577: if (changes & NEW_W)
578: DECODES(th->th_win)
579: if (changes & NEW_A)
580: DECODEL(th->th_ack)
581: if (changes & NEW_S)
582: DECODEL(th->th_seq)
583: break;
584: }
585: if (changes & NEW_I) {
586: DECODES(cs->cs_ip.ip_id)
587: } else
588: cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
589:
590: /*
591: * At this point, cp points to the first byte of data in the
592: * packet. Fill in the IP total length and update the IP
593: * header checksum.
594: */
595: vjlen = cp - buf;
596: buflen -= vjlen;
597: if (buflen < 0)
598: /* we must have dropped some characters (crc should detect
599: * this but the old slip framing won't) */
600: goto bad;
601:
602: total_len += cs->cs_hlen - vjlen;
603: cs->cs_ip.ip_len = htons(total_len);
604:
605: /* recompute the ip header checksum */
606: bp = (u_int16_t *) &cs->cs_ip;
607: cs->cs_ip.ip_sum = 0;
608: for (changes = 0; hlen > 0; hlen -= 2)
609: changes += *bp++;
610: changes = (changes & 0xffff) + (changes >> 16);
611: changes = (changes & 0xffff) + (changes >> 16);
612: cs->cs_ip.ip_sum = ~ changes;
613:
614: *hdrp = (u_char *) &cs->cs_ip;
615: *hlenp = cs->cs_hlen;
616: return vjlen;
617:
618: bad:
619: comp->flags |= SLF_TOSS;
620: INCR(sls_errorin)
621: return (-1);
622: }
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