![[BACK]](/cvsweb/icons/back.gif){kind=icon}
Return to slcompress.c CVS log ![[TXT]](/cvsweb/icons/text.gif){kind=icon}
![[DIR]](/cvsweb/icons/dir.gif){kind=icon}
Up to [Net/2] / Net2 / net|
Return to slcompress.c CVS log | Up to [Net/2] / Net2 / net |
1.1 root 1: /*-
2: * Copyright (c) 1989 The Regents of the University of California.
3: * 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 7.7 (Berkeley) 5/7/91
34: */
35:
36: /*
37: * Routines to compress and uncompess tcp packets (for transmission
38: * over low speed serial lines.
39: *
40: * Van Jacobson ([email protected]), Dec 31, 1989:
41: * - Initial distribution.
42: *
43: * static char rcsid[] =
44: * "$Header: slcompress.c,v 1.19 89/12/31 08:52:59 van Exp $";
45: */
46:
47: #include <sys/param.h>
48: #include <sys/mbuf.h>
49: #include <netinet/in.h>
50: #include <netinet/in_systm.h>
51: #include <netinet/ip.h>
52: #include <netinet/tcp.h>
53:
54: #include "slcompress.h"
55:
56: #ifndef SL_NO_STATS
57: #define INCR(counter) ++comp->counter;
58: #else
59: #define INCR(counter)
60: #endif
61:
62: #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n))
63: #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n))
64: #ifndef KERNEL
65: #define ovbcopy bcopy
66: #endif
67:
68:
69: void
70: sl_compress_init(comp)
71: struct slcompress *comp;
72: {
73: register u_int i;
74: register struct cstate *tstate = comp->tstate;
75:
76: bzero((char *)comp, sizeof(*comp));
77: for (i = MAX_STATES - 1; i > 0; --i) {
78: tstate[i].cs_id = i;
79: tstate[i].cs_next = &tstate[i - 1];
80: }
81: tstate[0].cs_next = &tstate[MAX_STATES - 1];
82: tstate[0].cs_id = 0;
83: comp->last_cs = &tstate[0];
84: comp->last_recv = 255;
85: comp->last_xmit = 255;
86: }
87:
88:
89: /* ENCODE encodes a number that is known to be non-zero. ENCODEZ
90: * checks for zero (since zero has to be encoded in the long, 3 byte
91: * form).
92: */
93: #define ENCODE(n) { \
94: if ((u_short)(n) >= 256) { \
95: *cp++ = 0; \
96: cp[1] = (n); \
97: cp[0] = (n) >> 8; \
98: cp += 2; \
99: } else { \
100: *cp++ = (n); \
101: } \
102: }
103: #define ENCODEZ(n) { \
104: if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \
105: *cp++ = 0; \
106: cp[1] = (n); \
107: cp[0] = (n) >> 8; \
108: cp += 2; \
109: } else { \
110: *cp++ = (n); \
111: } \
112: }
113:
114: #define DECODEL(f) { \
115: if (*cp == 0) {\
116: (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
117: cp += 3; \
118: } else { \
119: (f) = htonl(ntohl(f) + (u_long)*cp++); \
120: } \
121: }
122:
123: #define DECODES(f) { \
124: if (*cp == 0) {\
125: (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
126: cp += 3; \
127: } else { \
128: (f) = htons(ntohs(f) + (u_long)*cp++); \
129: } \
130: }
131:
132: #define DECODEU(f) { \
133: if (*cp == 0) {\
134: (f) = htons((cp[1] << 8) | cp[2]); \
135: cp += 3; \
136: } else { \
137: (f) = htons((u_long)*cp++); \
138: } \
139: }
140:
141:
142: u_char
143: sl_compress_tcp(m, ip, comp, compress_cid)
144: struct mbuf *m;
145: register struct ip *ip;
146: struct slcompress *comp;
147: int compress_cid;
148: {
149: register struct cstate *cs = comp->last_cs->cs_next;
150: register u_int hlen = ip->ip_hl;
151: register struct tcphdr *oth;
152: register struct tcphdr *th;
153: register u_int deltaS, deltaA;
154: register u_int changes = 0;
155: u_char new_seq[16];
156: register u_char *cp = new_seq;
157:
158: /*
159: * Bail if this is an IP fragment or if the TCP packet isn't
160: * `compressible' (i.e., ACK isn't set or some other control bit is
161: * set). (We assume that the caller has already made sure the
162: * packet is IP proto TCP).
163: */
164: if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40)
165: return (TYPE_IP);
166:
167: th = (struct tcphdr *)&((int *)ip)[hlen];
168: if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
169: return (TYPE_IP);
170: /*
171: * Packet is compressible -- we're going to send either a
172: * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
173: * to locate (or create) the connection state. Special case the
174: * most recently used connection since it's most likely to be used
175: * again & we don't have to do any reordering if it's used.
176: */
177: INCR(sls_packets)
178: if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
179: ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
180: *(int *)th != ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
181: /*
182: * Wasn't the first -- search for it.
183: *
184: * States are kept in a circularly linked list with
185: * last_cs pointing to the end of the list. The
186: * list is kept in lru order by moving a state to the
187: * head of the list whenever it is referenced. Since
188: * the list is short and, empirically, the connection
189: * we want is almost always near the front, we locate
190: * states via linear search. If we don't find a state
191: * for the datagram, the oldest state is (re-)used.
192: */
193: register struct cstate *lcs;
194: register struct cstate *lastcs = comp->last_cs;
195:
196: do {
197: lcs = cs; cs = cs->cs_next;
198: INCR(sls_searches)
199: if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
200: && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
201: && *(int *)th == ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl])
202: goto found;
203: } while (cs != lastcs);
204:
205: /*
206: * Didn't find it -- re-use oldest cstate. Send an
207: * uncompressed packet that tells the other side what
208: * connection number we're using for this conversation.
209: * Note that since the state list is circular, the oldest
210: * state points to the newest and we only need to set
211: * last_cs to update the lru linkage.
212: */
213: INCR(sls_misses)
214: comp->last_cs = lcs;
215: hlen += th->th_off;
216: hlen <<= 2;
217: goto uncompressed;
218:
219: found:
220: /*
221: * Found it -- move to the front on the connection list.
222: */
223: if (cs == lastcs)
224: comp->last_cs = lcs;
225: else {
226: lcs->cs_next = cs->cs_next;
227: cs->cs_next = lastcs->cs_next;
228: lastcs->cs_next = cs;
229: }
230: }
231:
232: /*
233: * Make sure that only what we expect to change changed. The first
234: * line of the `if' checks the IP protocol version, header length &
235: * type of service. The 2nd line checks the "Don't fragment" bit.
236: * The 3rd line checks the time-to-live and protocol (the protocol
237: * check is unnecessary but costless). The 4th line checks the TCP
238: * header length. The 5th line checks IP options, if any. The 6th
239: * line checks TCP options, if any. If any of these things are
240: * different between the previous & current datagram, we send the
241: * current datagram `uncompressed'.
242: */
243: oth = (struct tcphdr *)&((int *)&cs->cs_ip)[hlen];
244: deltaS = hlen;
245: hlen += th->th_off;
246: hlen <<= 2;
247:
248: if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0] ||
249: ((u_short *)ip)[3] != ((u_short *)&cs->cs_ip)[3] ||
250: ((u_short *)ip)[4] != ((u_short *)&cs->cs_ip)[4] ||
251: th->th_off != oth->th_off ||
252: (deltaS > 5 &&
253: BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
254: (th->th_off > 5 &&
255: BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
256: goto uncompressed;
257:
258: /*
259: * Figure out which of the changing fields changed. The
260: * receiver expects changes in the order: urgent, window,
261: * ack, seq (the order minimizes the number of temporaries
262: * needed in this section of code).
263: */
264: if (th->th_flags & TH_URG) {
265: deltaS = ntohs(th->th_urp);
266: ENCODEZ(deltaS);
267: changes |= NEW_U;
268: } else if (th->th_urp != oth->th_urp)
269: /* argh! URG not set but urp changed -- a sensible
270: * implementation should never do this but RFC793
271: * doesn't prohibit the change so we have to deal
272: * with it. */
273: goto uncompressed;
274:
275: if (deltaS = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win))) {
276: ENCODE(deltaS);
277: changes |= NEW_W;
278: }
279:
280: if (deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack)) {
281: if (deltaA > 0xffff)
282: goto uncompressed;
283: ENCODE(deltaA);
284: changes |= NEW_A;
285: }
286:
287: if (deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq)) {
288: if (deltaS > 0xffff)
289: goto uncompressed;
290: ENCODE(deltaS);
291: changes |= NEW_S;
292: }
293:
294: switch(changes) {
295:
296: case 0:
297: /*
298: * Nothing changed. If this packet contains data and the
299: * last one didn't, this is probably a data packet following
300: * an ack (normal on an interactive connection) and we send
301: * it compressed. Otherwise it's probably a retransmit,
302: * retransmitted ack or window probe. Send it uncompressed
303: * in case the other side missed the compressed version.
304: */
305: if (ip->ip_len != cs->cs_ip.ip_len &&
306: ntohs(cs->cs_ip.ip_len) == hlen)
307: break;
308:
309: /* (fall through) */
310:
311: case SPECIAL_I:
312: case SPECIAL_D:
313: /*
314: * actual changes match one of our special case encodings --
315: * send packet uncompressed.
316: */
317: goto uncompressed;
318:
319: case NEW_S|NEW_A:
320: if (deltaS == deltaA &&
321: deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
322: /* special case for echoed terminal traffic */
323: changes = SPECIAL_I;
324: cp = new_seq;
325: }
326: break;
327:
328: case NEW_S:
329: if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
330: /* special case for data xfer */
331: changes = SPECIAL_D;
332: cp = new_seq;
333: }
334: break;
335: }
336:
337: deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
338: if (deltaS != 1) {
339: ENCODEZ(deltaS);
340: changes |= NEW_I;
341: }
342: if (th->th_flags & TH_PUSH)
343: changes |= TCP_PUSH_BIT;
344: /*
345: * Grab the cksum before we overwrite it below. Then update our
346: * state with this packet's header.
347: */
348: deltaA = ntohs(th->th_sum);
349: BCOPY(ip, &cs->cs_ip, hlen);
350:
351: /*
352: * We want to use the original packet as our compressed packet.
353: * (cp - new_seq) is the number of bytes we need for compressed
354: * sequence numbers. In addition we need one byte for the change
355: * mask, one for the connection id and two for the tcp checksum.
356: * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
357: * many bytes of the original packet to toss so subtract the two to
358: * get the new packet size.
359: */
360: deltaS = cp - new_seq;
361: cp = (u_char *)ip;
362: if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
363: comp->last_xmit = cs->cs_id;
364: hlen -= deltaS + 4;
365: cp += hlen;
366: *cp++ = changes | NEW_C;
367: *cp++ = cs->cs_id;
368: } else {
369: hlen -= deltaS + 3;
370: cp += hlen;
371: *cp++ = changes;
372: }
373: m->m_len -= hlen;
374: m->m_data += hlen;
375: *cp++ = deltaA >> 8;
376: *cp++ = deltaA;
377: BCOPY(new_seq, cp, deltaS);
378: INCR(sls_compressed)
379: return (TYPE_COMPRESSED_TCP);
380:
381: /*
382: * Update connection state cs & send uncompressed packet ('uncompressed'
383: * means a regular ip/tcp packet but with the 'conversation id' we hope
384: * to use on future compressed packets in the protocol field).
385: */
386: uncompressed:
387: BCOPY(ip, &cs->cs_ip, hlen);
388: ip->ip_p = cs->cs_id;
389: comp->last_xmit = cs->cs_id;
390: return (TYPE_UNCOMPRESSED_TCP);
391: }
392:
393:
394: int
395: sl_uncompress_tcp(bufp, len, type, comp)
396: u_char **bufp;
397: int len;
398: u_int type;
399: struct slcompress *comp;
400: {
401: register u_char *cp;
402: register u_int hlen, changes;
403: register struct tcphdr *th;
404: register struct cstate *cs;
405: register struct ip *ip;
406:
407: switch (type) {
408:
409: case TYPE_UNCOMPRESSED_TCP:
410: ip = (struct ip *) *bufp;
411: if (ip->ip_p >= MAX_STATES)
412: goto bad;
413: cs = &comp->rstate[comp->last_recv = ip->ip_p];
414: comp->flags &=~ SLF_TOSS;
415: ip->ip_p = IPPROTO_TCP;
416: hlen = ip->ip_hl;
417: hlen += ((struct tcphdr *)&((int *)ip)[hlen])->th_off;
418: hlen <<= 2;
419: BCOPY(ip, &cs->cs_ip, hlen);
420: cs->cs_ip.ip_sum = 0;
421: cs->cs_hlen = hlen;
422: INCR(sls_uncompressedin)
423: return (len);
424:
425: default:
426: goto bad;
427:
428: case TYPE_COMPRESSED_TCP:
429: break;
430: }
431: /* We've got a compressed packet. */
432: INCR(sls_compressedin)
433: cp = *bufp;
434: changes = *cp++;
435: if (changes & NEW_C) {
436: /* Make sure the state index is in range, then grab the state.
437: * If we have a good state index, clear the 'discard' flag. */
438: if (*cp >= MAX_STATES)
439: goto bad;
440:
441: comp->flags &=~ SLF_TOSS;
442: comp->last_recv = *cp++;
443: } else {
444: /* this packet has an implicit state index. If we've
445: * had a line error since the last time we got an
446: * explicit state index, we have to toss the packet. */
447: if (comp->flags & SLF_TOSS) {
448: INCR(sls_tossed)
449: return (0);
450: }
451: }
452: cs = &comp->rstate[comp->last_recv];
453: hlen = cs->cs_ip.ip_hl << 2;
454: th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
455: th->th_sum = htons((*cp << 8) | cp[1]);
456: cp += 2;
457: if (changes & TCP_PUSH_BIT)
458: th->th_flags |= TH_PUSH;
459: else
460: th->th_flags &=~ TH_PUSH;
461:
462: switch (changes & SPECIALS_MASK) {
463: case SPECIAL_I:
464: {
465: register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
466: th->th_ack = htonl(ntohl(th->th_ack) + i);
467: th->th_seq = htonl(ntohl(th->th_seq) + i);
468: }
469: break;
470:
471: case SPECIAL_D:
472: th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
473: - cs->cs_hlen);
474: break;
475:
476: default:
477: if (changes & NEW_U) {
478: th->th_flags |= TH_URG;
479: DECODEU(th->th_urp)
480: } else
481: th->th_flags &=~ TH_URG;
482: if (changes & NEW_W)
483: DECODES(th->th_win)
484: if (changes & NEW_A)
485: DECODEL(th->th_ack)
486: if (changes & NEW_S)
487: DECODEL(th->th_seq)
488: break;
489: }
490: if (changes & NEW_I) {
491: DECODES(cs->cs_ip.ip_id)
492: } else
493: cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
494:
495: /*
496: * At this point, cp points to the first byte of data in the
497: * packet. If we're not aligned on a 4-byte boundary, copy the
498: * data down so the ip & tcp headers will be aligned. Then back up
499: * cp by the tcp/ip header length to make room for the reconstructed
500: * header (we assume the packet we were handed has enough space to
501: * prepend 128 bytes of header). Adjust the length to account for
502: * the new header & fill in the IP total length.
503: */
504: len -= (cp - *bufp);
505: if (len < 0)
506: /* we must have dropped some characters (crc should detect
507: * this but the old slip framing won't) */
508: goto bad;
509:
510: if ((int)cp & 3) {
511: if (len > 0)
512: (void) ovbcopy(cp, (caddr_t)((int)cp &~ 3), len);
513: cp = (u_char *)((int)cp &~ 3);
514: }
515: cp -= cs->cs_hlen;
516: len += cs->cs_hlen;
517: cs->cs_ip.ip_len = htons(len);
518: BCOPY(&cs->cs_ip, cp, cs->cs_hlen);
519: *bufp = cp;
520:
521: /* recompute the ip header checksum */
522: {
523: register u_short *bp = (u_short *)cp;
524: for (changes = 0; hlen > 0; hlen -= 2)
525: changes += *bp++;
526: changes = (changes & 0xffff) + (changes >> 16);
527: changes = (changes & 0xffff) + (changes >> 16);
528: ((struct ip *)cp)->ip_sum = ~ changes;
529: }
530: return (len);
531: bad:
532: comp->flags |= SLF_TOSS;
533: INCR(sls_errorin)
534: return (0);
535: }
This archive runs on limited infrastructure. Preserving old code on modern bandwidth. Automated agents are requested to crawl responsibly.