1 /* $Id: slcompress.c,v 1.1 1995/12/11 05:17:11 paulus Exp $ */
4 * Copyright (c) 1989, 1993, 1994
5 * The Regents of the University of California. All rights reserved.
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35 * @(#)slcompress.c 8.2 (Berkeley) 4/16/94
39 * Routines to compress and uncompess tcp packets (for transmission
40 * over low speed serial lines.
42 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
43 * - Initial distribution.
46 #include <sys/param.h>
49 #include <netinet/in.h>
50 #include <netinet/in_systm.h>
51 #include <netinet/ip.h>
52 #include <netinet/tcp.h>
54 #include <net/slcompress.h>
57 #define INCR(counter) ++comp->counter;
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))
69 sl_compress_init(comp, max_state)
70 struct slcompress *comp;
74 register struct cstate *tstate = comp->tstate;
77 max_state = MAX_STATES - 1;
78 bzero((char *)comp, sizeof(*comp));
79 for (i = max_state; i > 0; --i) {
81 tstate[i].cs_next = &tstate[i - 1];
83 tstate[0].cs_next = &tstate[max_state];
85 comp->last_cs = &tstate[0];
86 comp->last_recv = 255;
87 comp->last_xmit = 255;
88 comp->flags = SLF_TOSS;
92 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ
93 * checks for zero (since zero has to be encoded in the long, 3 byte
97 if ((u_int16_t)(n) >= 256) { \
106 #define ENCODEZ(n) { \
107 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \
117 #define DECODEL(f) { \
119 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
122 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \
126 #define DECODES(f) { \
128 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
131 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \
135 #define DECODEU(f) { \
137 (f) = htons((cp[1] << 8) | cp[2]); \
140 (f) = htons((u_int32_t)*cp++); \
145 sl_compress_tcp(m, ip, comp, compress_cid)
147 register struct ip *ip;
148 struct slcompress *comp;
151 register struct cstate *cs = comp->last_cs->cs_next;
152 register u_int hlen = ip->ip_hl;
153 register struct tcphdr *oth;
154 register struct tcphdr *th;
155 register u_int deltaS, deltaA;
156 register u_int changes = 0;
158 register u_char *cp = new_seq;
161 * Bail if this is an IP fragment or if the TCP packet isn't
162 * `compressible' (i.e., ACK isn't set or some other control bit is
163 * set). (We assume that the caller has already made sure the
164 * packet is IP proto TCP).
166 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40)
169 th = (struct tcphdr *)&((int32_t *)ip)[hlen];
170 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
173 * Packet is compressible -- we're going to send either a
174 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
175 * to locate (or create) the connection state. Special case the
176 * most recently used connection since it's most likely to be used
177 * again & we don't have to do any reordering if it's used.
180 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
181 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
182 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
184 * Wasn't the first -- search for it.
186 * States are kept in a circularly linked list with
187 * last_cs pointing to the end of the list. The
188 * list is kept in lru order by moving a state to the
189 * head of the list whenever it is referenced. Since
190 * the list is short and, empirically, the connection
191 * we want is almost always near the front, we locate
192 * states via linear search. If we don't find a state
193 * for the datagram, the oldest state is (re-)used.
195 register struct cstate *lcs;
196 register struct cstate *lastcs = comp->last_cs;
199 lcs = cs; cs = cs->cs_next;
201 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
202 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
204 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl])
206 } while (cs != lastcs);
209 * Didn't find it -- re-use oldest cstate. Send an
210 * uncompressed packet that tells the other side what
211 * connection number we're using for this conversation.
212 * Note that since the state list is circular, the oldest
213 * state points to the newest and we only need to set
214 * last_cs to update the lru linkage.
224 * Found it -- move to the front on the connection list.
229 lcs->cs_next = cs->cs_next;
230 cs->cs_next = lastcs->cs_next;
231 lastcs->cs_next = cs;
236 * Make sure that only what we expect to change changed. The first
237 * line of the `if' checks the IP protocol version, header length &
238 * type of service. The 2nd line checks the "Don't fragment" bit.
239 * The 3rd line checks the time-to-live and protocol (the protocol
240 * check is unnecessary but costless). The 4th line checks the TCP
241 * header length. The 5th line checks IP options, if any. The 6th
242 * line checks TCP options, if any. If any of these things are
243 * different between the previous & current datagram, we send the
244 * current datagram `uncompressed'.
246 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen];
251 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] ||
252 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] ||
253 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] ||
254 th->th_off != oth->th_off ||
256 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
258 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
262 * Figure out which of the changing fields changed. The
263 * receiver expects changes in the order: urgent, window,
264 * ack, seq (the order minimizes the number of temporaries
265 * needed in this section of code).
267 if (th->th_flags & TH_URG) {
268 deltaS = ntohs(th->th_urp);
271 } else if (th->th_urp != oth->th_urp)
272 /* argh! URG not set but urp changed -- a sensible
273 * implementation should never do this but RFC793
274 * doesn't prohibit the change so we have to deal
278 if (deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win))) {
283 if (deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack)) {
290 if (deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq)) {
301 * Nothing changed. If this packet contains data and the
302 * last one didn't, this is probably a data packet following
303 * an ack (normal on an interactive connection) and we send
304 * it compressed. Otherwise it's probably a retransmit,
305 * retransmitted ack or window probe. Send it uncompressed
306 * in case the other side missed the compressed version.
308 if (ip->ip_len != cs->cs_ip.ip_len &&
309 ntohs(cs->cs_ip.ip_len) == hlen)
317 * actual changes match one of our special case encodings --
318 * send packet uncompressed.
323 if (deltaS == deltaA &&
324 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
325 /* special case for echoed terminal traffic */
332 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
333 /* special case for data xfer */
340 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
345 if (th->th_flags & TH_PUSH)
346 changes |= TCP_PUSH_BIT;
348 * Grab the cksum before we overwrite it below. Then update our
349 * state with this packet's header.
351 deltaA = ntohs(th->th_sum);
352 BCOPY(ip, &cs->cs_ip, hlen);
355 * We want to use the original packet as our compressed packet.
356 * (cp - new_seq) is the number of bytes we need for compressed
357 * sequence numbers. In addition we need one byte for the change
358 * mask, one for the connection id and two for the tcp checksum.
359 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
360 * many bytes of the original packet to toss so subtract the two to
361 * get the new packet size.
363 deltaS = cp - new_seq;
365 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
366 comp->last_xmit = cs->cs_id;
369 *cp++ = changes | NEW_C;
380 BCOPY(new_seq, cp, deltaS);
382 return (TYPE_COMPRESSED_TCP);
385 * Update connection state cs & send uncompressed packet ('uncompressed'
386 * means a regular ip/tcp packet but with the 'conversation id' we hope
387 * to use on future compressed packets in the protocol field).
390 BCOPY(ip, &cs->cs_ip, hlen);
391 ip->ip_p = cs->cs_id;
392 comp->last_xmit = cs->cs_id;
393 return (TYPE_UNCOMPRESSED_TCP);
398 sl_uncompress_tcp(bufp, len, type, comp)
402 struct slcompress *comp;
407 cp = bufp? *bufp: NULL;
408 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen);
410 return (0); /* error */
412 return (len); /* was uncompressed already */
418 * At this point, cp points to the first byte of data in the
419 * packet. If we're not aligned on a 4-byte boundary, copy the
420 * data down so the ip & tcp headers will be aligned. Then back up
421 * cp by the tcp/ip header length to make room for the reconstructed
422 * header (we assume the packet we were handed has enough space to
423 * prepend 128 bytes of header).
427 (void) ovbcopy(cp, (caddr_t)((int)cp &~ 3), len);
428 cp = (u_char *)((int)cp &~ 3);
432 BCOPY(hdr, cp, hlen);
439 * Uncompress a packet of total length total_len. The first buflen
440 * bytes are at buf; this must include the entire (compressed or
441 * uncompressed) TCP/IP header. This procedure returns the length
442 * of the VJ header, with a pointer to the uncompressed IP header
443 * in *hdrp and its length in *hlenp.
446 sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp)
448 int buflen, total_len;
450 struct slcompress *comp;
455 register u_int hlen, changes;
456 register struct tcphdr *th;
457 register struct cstate *cs;
458 register struct ip *ip;
459 register u_int16_t *bp;
460 register u_int vjlen;
464 case TYPE_UNCOMPRESSED_TCP:
465 ip = (struct ip *) buf;
466 if (ip->ip_p >= MAX_STATES)
468 cs = &comp->rstate[comp->last_recv = ip->ip_p];
469 comp->flags &=~ SLF_TOSS;
470 ip->ip_p = IPPROTO_TCP;
472 hlen += ((struct tcphdr *)&((int32_t *)ip)[hlen])->th_off;
474 BCOPY(ip, &cs->cs_ip, hlen);
476 INCR(sls_uncompressedin)
477 *hdrp = (u_char *) &cs->cs_ip;
484 case TYPE_COMPRESSED_TCP:
487 /* We've got a compressed packet. */
488 INCR(sls_compressedin)
491 if (changes & NEW_C) {
492 /* Make sure the state index is in range, then grab the state.
493 * If we have a good state index, clear the 'discard' flag. */
494 if (*cp >= MAX_STATES)
497 comp->flags &=~ SLF_TOSS;
498 comp->last_recv = *cp++;
500 /* this packet has an implicit state index. If we've
501 * had a line error since the last time we got an
502 * explicit state index, we have to toss the packet. */
503 if (comp->flags & SLF_TOSS) {
508 cs = &comp->rstate[comp->last_recv];
509 hlen = cs->cs_ip.ip_hl << 2;
510 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
511 th->th_sum = htons((*cp << 8) | cp[1]);
513 if (changes & TCP_PUSH_BIT)
514 th->th_flags |= TH_PUSH;
516 th->th_flags &=~ TH_PUSH;
518 switch (changes & SPECIALS_MASK) {
521 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
522 th->th_ack = htonl(ntohl(th->th_ack) + i);
523 th->th_seq = htonl(ntohl(th->th_seq) + i);
528 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
533 if (changes & NEW_U) {
534 th->th_flags |= TH_URG;
537 th->th_flags &=~ TH_URG;
546 if (changes & NEW_I) {
547 DECODES(cs->cs_ip.ip_id)
549 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
552 * At this point, cp points to the first byte of data in the
553 * packet. Fill in the IP total length and update the IP
559 /* we must have dropped some characters (crc should detect
560 * this but the old slip framing won't) */
563 total_len += cs->cs_hlen - vjlen;
564 cs->cs_ip.ip_len = htons(total_len);
566 /* recompute the ip header checksum */
567 bp = (u_int16_t *) &cs->cs_ip;
568 cs->cs_ip.ip_sum = 0;
569 for (changes = 0; hlen > 0; hlen -= 2)
571 changes = (changes & 0xffff) + (changes >> 16);
572 changes = (changes & 0xffff) + (changes >> 16);
573 cs->cs_ip.ip_sum = ~ changes;
575 *hdrp = (u_char *) &cs->cs_ip;
576 *hlenp = cs->cs_hlen;
580 comp->flags |= SLF_TOSS;