2 * Copyright (c) 1989 The Regents of the University of California.
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
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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.
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26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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33 * @(#)slcompress.c 7.7 (Berkeley) 5/7/91
37 * Routines to compress and uncompess tcp packets (for transmission
38 * over low speed serial lines.
40 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
41 * - Initial distribution.
43 * $Id: pppcompress.c,v 1.2 1996/05/24 07:04:14 paulus Exp $
46 #include <sys/types.h>
47 #include <sys/param.h>
48 #include <sys/systm.h>
50 #include <sys/socket.h>
51 #include <sys/socketvar.h>
53 #include <netinet/in.h>
54 #include <netinet/in_systm.h>
55 #include <netinet/ip.h>
56 #include <netinet/tcp.h>
58 #include <net/pppcompress.h>
61 #define INCR(counter) ++comp->counter;
66 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n))
67 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n))
73 vj_compress_init(comp, max_state)
74 struct vjcompress *comp;
78 register struct cstate *tstate = comp->tstate;
80 if ((unsigned) max_state > MAX_STATES - 1)
81 max_state = MAX_STATES - 1;
82 bzero((char *)comp, sizeof(*comp));
83 for (i = max_state; i > 0; --i) {
85 tstate[i].cs_next = &tstate[i - 1];
87 tstate[0].cs_next = &tstate[max_state];
89 comp->last_cs = &tstate[0];
90 comp->last_recv = 255;
91 comp->last_xmit = 255;
92 comp->flags = SLF_TOSS;
96 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ
97 * checks for zero (since zero has to be encoded in the long, 3 byte
100 #define ENCODE(n) { \
101 if ((u_short)(n) >= 256) { \
110 #define ENCODEZ(n) { \
111 if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \
121 #define DECODEL(f) { \
123 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
126 (f) = htonl(ntohl(f) + (u_long)*cp++); \
130 #define DECODES(f) { \
132 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
135 (f) = htons(ntohs(f) + (u_long)*cp++); \
139 #define DECODEU(f) { \
141 (f) = htons((cp[1] << 8) | cp[2]); \
144 (f) = htons((u_long)*cp++); \
149 vj_compress_tcp(m, ip, comp, compress_cid)
151 register struct ip *ip;
152 struct vjcompress *comp;
155 register struct cstate *cs = comp->last_cs->cs_next;
156 register u_int hlen = ip->ip_hl;
157 register struct tcphdr *oth;
158 register struct tcphdr *th;
159 register u_int deltaS, deltaA;
160 register u_int changes = 0;
162 register u_char *cp = new_seq;
165 * Bail if this is an IP fragment or if the TCP packet isn't
166 * `compressible' (i.e., ACK isn't set or some other control bit is
167 * set). (We assume that the caller has already made sure the
168 * packet is IP proto TCP).
170 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40)
173 th = (struct tcphdr *)&((int *)ip)[hlen];
174 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
177 * Packet is compressible -- we're going to send either a
178 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
179 * to locate (or create) the connection state. Special case the
180 * most recently used connection since it's most likely to be used
181 * again & we don't have to do any reordering if it's used.
184 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
185 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
186 *(int *)th != ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
188 * Wasn't the first -- search for it.
190 * States are kept in a circularly linked list with
191 * last_cs pointing to the end of the list. The
192 * list is kept in lru order by moving a state to the
193 * head of the list whenever it is referenced. Since
194 * the list is short and, empirically, the connection
195 * we want is almost always near the front, we locate
196 * states via linear search. If we don't find a state
197 * for the datagram, the oldest state is (re-)used.
199 register struct cstate *lcs;
200 register struct cstate *lastcs = comp->last_cs;
203 lcs = cs; cs = cs->cs_next;
205 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
206 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
207 && *(int *)th == ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl])
209 } while (cs != lastcs);
212 * Didn't find it -- re-use oldest cstate. Send an
213 * uncompressed packet that tells the other side what
214 * connection number we're using for this conversation.
215 * Note that since the state list is circular, the oldest
216 * state points to the newest and we only need to set
217 * last_cs to update the lru linkage.
227 * Found it -- move to the front on the connection list.
232 lcs->cs_next = cs->cs_next;
233 cs->cs_next = lastcs->cs_next;
234 lastcs->cs_next = cs;
239 * Make sure that only what we expect to change changed. The first
240 * line of the `if' checks the IP protocol version, header length &
241 * type of service. The 2nd line checks the "Don't fragment" bit.
242 * The 3rd line checks the time-to-live and protocol (the protocol
243 * check is unnecessary but costless). The 4th line checks the TCP
244 * header length. The 5th line checks IP options, if any. The 6th
245 * line checks TCP options, if any. If any of these things are
246 * different between the previous & current datagram, we send the
247 * current datagram `uncompressed'.
249 oth = (struct tcphdr *)&((int *)&cs->cs_ip)[hlen];
254 if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0] ||
255 ((u_short *)ip)[3] != ((u_short *)&cs->cs_ip)[3] ||
256 ((u_short *)ip)[4] != ((u_short *)&cs->cs_ip)[4] ||
257 th->th_off != oth->th_off ||
259 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
261 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
265 * Figure out which of the changing fields changed. The
266 * receiver expects changes in the order: urgent, window,
267 * ack, seq (the order minimizes the number of temporaries
268 * needed in this section of code).
270 if (th->th_flags & TH_URG) {
271 deltaS = ntohs(th->th_urp);
274 } else if (th->th_urp != oth->th_urp)
275 /* argh! URG not set but urp changed -- a sensible
276 * implementation should never do this but RFC793
277 * doesn't prohibit the change so we have to deal
281 if (deltaS = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win))) {
286 if (deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack)) {
293 if (deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq)) {
304 * Nothing changed. If this packet contains data and the
305 * last one didn't, this is probably a data packet following
306 * an ack (normal on an interactive connection) and we send
307 * it compressed. Otherwise it's probably a retransmit,
308 * retransmitted ack or window probe. Send it uncompressed
309 * in case the other side missed the compressed version.
311 if (ip->ip_len != cs->cs_ip.ip_len &&
312 ntohs(cs->cs_ip.ip_len) == hlen)
320 * actual changes match one of our special case encodings --
321 * send packet uncompressed.
326 if (deltaS == deltaA &&
327 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
328 /* special case for echoed terminal traffic */
335 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
336 /* special case for data xfer */
343 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
348 if (th->th_flags & TH_PUSH)
349 changes |= TCP_PUSH_BIT;
351 * Grab the cksum before we overwrite it below. Then update our
352 * state with this packet's header.
354 deltaA = ntohs(th->th_sum);
355 BCOPY(ip, &cs->cs_ip, hlen);
358 * We want to use the original packet as our compressed packet.
359 * (cp - new_seq) is the number of bytes we need for compressed
360 * sequence numbers. In addition we need one byte for the change
361 * mask, one for the connection id and two for the tcp checksum.
362 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
363 * many bytes of the original packet to toss so subtract the two to
364 * get the new packet size.
366 deltaS = cp - new_seq;
368 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
369 comp->last_xmit = cs->cs_id;
372 *cp++ = changes | NEW_C;
383 BCOPY(new_seq, cp, deltaS);
385 return (TYPE_COMPRESSED_TCP);
388 * Update connection state cs & send uncompressed packet ('uncompressed'
389 * means a regular ip/tcp packet but with the 'conversation id' we hope
390 * to use on future compressed packets in the protocol field).
393 BCOPY(ip, &cs->cs_ip, hlen);
394 ip->ip_p = cs->cs_id;
395 comp->last_xmit = cs->cs_id;
396 return (TYPE_UNCOMPRESSED_TCP);
401 vj_uncompress_tcp(bufp, len, type, comp)
405 struct vjcompress *comp;
410 cp = bufp? *bufp: NULL;
411 vjlen = vj_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen);
413 return (0); /* error */
415 return (len); /* was uncompressed already */
421 * At this point, cp points to the first byte of data in the
422 * packet. If we're not aligned on a 4-byte boundary, copy the
423 * data down so the ip & tcp headers will be aligned. Then back up
424 * cp by the tcp/ip header length to make room for the reconstructed
425 * header (we assume the packet we were handed has enough space to
426 * prepend 128 bytes of header).
430 (void) ovbcopy(cp, (caddr_t)((int)cp &~ 3), len);
431 cp = (u_char *)((int)cp &~ 3);
435 BCOPY(hdr, cp, hlen);
442 * Uncompress a packet of total length total_len. The first buflen
443 * bytes are at buf; this must include the entire (compressed or
444 * uncompressed) TCP/IP header. This procedure returns the length
445 * of the VJ header, with a pointer to the uncompressed IP header
446 * in *hdrp and its length in *hlenp.
449 vj_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp)
451 int buflen, total_len;
453 struct vjcompress *comp;
458 register u_int hlen, changes;
459 register struct tcphdr *th;
460 register struct cstate *cs;
461 register struct ip *ip;
462 register u_short *bp;
463 register u_int vjlen;
467 case TYPE_UNCOMPRESSED_TCP:
468 ip = (struct ip *) buf;
469 if (ip->ip_p >= MAX_STATES)
471 cs = &comp->rstate[comp->last_recv = ip->ip_p];
472 comp->flags &=~ SLF_TOSS;
473 ip->ip_p = IPPROTO_TCP;
475 * Calculate the size of the TCP/IP header and make sure that
476 * we don't overflow the space we have available for it.
478 hlen = ip->ip_hl << 2;
479 if (hlen + sizeof(struct tcphdr) > buflen)
481 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2;
482 if (hlen > MAX_HDR || hlen > buflen)
484 BCOPY(ip, &cs->cs_ip, hlen);
486 INCR(sls_uncompressedin)
487 *hdrp = (u_char *) &cs->cs_ip;
494 case TYPE_COMPRESSED_TCP:
497 /* We've got a compressed packet. */
498 INCR(sls_compressedin)
501 if (changes & NEW_C) {
502 /* Make sure the state index is in range, then grab the state.
503 * If we have a good state index, clear the 'discard' flag. */
504 if (*cp >= MAX_STATES)
507 comp->flags &=~ SLF_TOSS;
508 comp->last_recv = *cp++;
510 /* this packet has an implicit state index. If we've
511 * had a line error since the last time we got an
512 * explicit state index, we have to toss the packet. */
513 if (comp->flags & SLF_TOSS) {
518 cs = &comp->rstate[comp->last_recv];
519 hlen = cs->cs_ip.ip_hl << 2;
520 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
521 th->th_sum = htons((*cp << 8) | cp[1]);
523 if (changes & TCP_PUSH_BIT)
524 th->th_flags |= TH_PUSH;
526 th->th_flags &=~ TH_PUSH;
528 switch (changes & SPECIALS_MASK) {
531 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
532 th->th_ack = htonl(ntohl(th->th_ack) + i);
533 th->th_seq = htonl(ntohl(th->th_seq) + i);
538 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
543 if (changes & NEW_U) {
544 th->th_flags |= TH_URG;
547 th->th_flags &=~ TH_URG;
556 if (changes & NEW_I) {
557 DECODES(cs->cs_ip.ip_id)
559 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
562 * At this point, cp points to the first byte of data in the
563 * packet. Fill in the IP total length and update the IP
569 /* we must have dropped some characters (crc should detect
570 * this but the old slip framing won't) */
573 total_len += cs->cs_hlen - vjlen;
574 cs->cs_ip.ip_len = htons(total_len);
576 /* recompute the ip header checksum */
577 bp = (u_short *) &cs->cs_ip;
578 cs->cs_ip.ip_sum = 0;
579 for (changes = 0; hlen > 0; hlen -= 2)
581 changes = (changes & 0xffff) + (changes >> 16);
582 changes = (changes & 0xffff) + (changes >> 16);
583 cs->cs_ip.ip_sum = ~ changes;
585 *hdrp = (u_char *) &cs->cs_ip;
586 *hlenp = cs->cs_hlen;
590 comp->flags |= SLF_TOSS;