netbsd-1.1/slcompress.c

   1 /*      $Id: slcompress.c,v 1.3 1996/05/24 07:04:47 paulus Exp $        */
   2
   3 /*
   4  * Copyright (c) 1989, 1993, 1994
   5  *      The Regents of the University of California.  All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  * 3. All advertising materials mentioning features or use of this software
  16  *    must display the following acknowledgement:
  17  *      This product includes software developed by the University of
  18  *      California, Berkeley and its contributors.
  19  * 4. Neither the name of the University nor the names of its contributors
  20  *    may be used to endorse or promote products derived from this software
  21  *    without specific prior written permission.
  22  *
  23  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  24  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  25  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  26  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  27  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  28  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  29  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  30  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  31  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  32  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  33  * SUCH DAMAGE.
  34  *
  35  *      @(#)slcompress.c        8.2 (Berkeley) 4/16/94
  36  */
  37
  38 /*
  39  * Routines to compress and uncompess tcp packets (for transmission
  40  * over low speed serial lines.
  41  *
  42  * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
  43  *      - Initial distribution.
  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((char *)(p1), (char *)(p2), (int)(n))
  64 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n))
  65 #ifndef _KERNEL
  66 #define ovbcopy bcopy
  67 #endif
  68
  69 void
  70 sl_compress_init(comp, max_state)
  71         struct slcompress *comp;
  72         int max_state;
  73 {
  74         register u_int i;
  75         register struct cstate *tstate = comp->tstate;
  76
  77         if (max_state == -1) {
  78                 max_state = MAX_STATES - 1;
  79                 bzero((char *)comp, sizeof(*comp));
  80         } else {
  81                 /* Don't reset statistics */
  82                 bzero((char *)comp->tstate, sizeof(comp->tstate));
  83                 bzero((char *)comp->rstate, sizeof(comp->rstate));
  84         }
  85         for (i = max_state; i > 0; --i) {
  86                 tstate[i].cs_id = i;
  87                 tstate[i].cs_next = &tstate[i - 1];
  88         }
  89         tstate[0].cs_next = &tstate[max_state];
  90         tstate[0].cs_id = 0;
  91         comp->last_cs = &tstate[0];
  92         comp->last_recv = 255;
  93         comp->last_xmit = 255;
  94         comp->flags = SLF_TOSS;
  95 }
  96
  97
  98 /* ENCODE encodes a number that is known to be non-zero.  ENCODEZ
  99  * checks for zero (since zero has to be encoded in the long, 3 byte
 100  * form).
 101  */
 102 #define ENCODE(n) { \
 103         if ((u_int16_t)(n) >= 256) { \
 104                 *cp++ = 0; \
 105                 cp[1] = (n); \
 106                 cp[0] = (n) >> 8; \
 107                 cp += 2; \
 108         } else { \
 109                 *cp++ = (n); \
 110         } \
 111 }
 112 #define ENCODEZ(n) { \
 113         if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \
 114                 *cp++ = 0; \
 115                 cp[1] = (n); \
 116                 cp[0] = (n) >> 8; \
 117                 cp += 2; \
 118         } else { \
 119                 *cp++ = (n); \
 120         } \
 121 }
 122
 123 #define DECODEL(f) { \
 124         if (*cp == 0) {\
 125                 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
 126                 cp += 3; \
 127         } else { \
 128                 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \
 129         } \
 130 }
 131
 132 #define DECODES(f) { \
 133         if (*cp == 0) {\
 134                 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
 135                 cp += 3; \
 136         } else { \
 137                 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \
 138         } \
 139 }
 140
 141 #define DECODEU(f) { \
 142         if (*cp == 0) {\
 143                 (f) = htons((cp[1] << 8) | cp[2]); \
 144                 cp += 3; \
 145         } else { \
 146                 (f) = htons((u_int32_t)*cp++); \
 147         } \
 148 }
 149
 150 u_int
 151 sl_compress_tcp(m, ip, comp, compress_cid)
 152         struct mbuf *m;
 153         register struct ip *ip;
 154         struct slcompress *comp;
 155         int compress_cid;
 156 {
 157         register struct cstate *cs = comp->last_cs->cs_next;
 158         register u_int hlen = ip->ip_hl;
 159         register struct tcphdr *oth;
 160         register struct tcphdr *th;
 161         register u_int deltaS, deltaA;
 162         register u_int changes = 0;
 163         u_char new_seq[16];
 164         register u_char *cp = new_seq;
 165
 166         /*
 167          * Bail if this is an IP fragment or if the TCP packet isn't
 168          * `compressible' (i.e., ACK isn't set or some other control bit is
 169          * set).  (We assume that the caller has already made sure the
 170          * packet is IP proto TCP).
 171          */
 172         if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40)
 173                 return (TYPE_IP);
 174
 175         th = (struct tcphdr *)&((int32_t *)ip)[hlen];
 176         if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
 177                 return (TYPE_IP);
 178         /*
 179          * Packet is compressible -- we're going to send either a
 180          * COMPRESSED_TCP or UNCOMPRESSED_TCP packet.  Either way we need
 181          * to locate (or create) the connection state.  Special case the
 182          * most recently used connection since it's most likely to be used
 183          * again & we don't have to do any reordering if it's used.
 184          */
 185         INCR(sls_packets)
 186         if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
 187             ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
 188             *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
 189                 /*
 190                  * Wasn't the first -- search for it.
 191                  *
 192                  * States are kept in a circularly linked list with
 193                  * last_cs pointing to the end of the list.  The
 194                  * list is kept in lru order by moving a state to the
 195                  * head of the list whenever it is referenced.  Since
 196                  * the list is short and, empirically, the connection
 197                  * we want is almost always near the front, we locate
 198                  * states via linear search.  If we don't find a state
 199                  * for the datagram, the oldest state is (re-)used.
 200                  */
 201                 register struct cstate *lcs;
 202                 register struct cstate *lastcs = comp->last_cs;
 203
 204                 do {
 205                         lcs = cs; cs = cs->cs_next;
 206                         INCR(sls_searches)
 207                         if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
 208                             && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
 209                             && *(int32_t *)th ==
 210                             ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl])
 211                                 goto found;
 212                 } while (cs != lastcs);
 213
 214                 /*
 215                  * Didn't find it -- re-use oldest cstate.  Send an
 216                  * uncompressed packet that tells the other side what
 217                  * connection number we're using for this conversation.
 218                  * Note that since the state list is circular, the oldest
 219                  * state points to the newest and we only need to set
 220                  * last_cs to update the lru linkage.
 221                  */
 222                 INCR(sls_misses)
 223                 comp->last_cs = lcs;
 224                 hlen += th->th_off;
 225                 hlen <<= 2;
 226                 goto uncompressed;
 227
 228         found:
 229                 /*
 230                  * Found it -- move to the front on the connection list.
 231                  */
 232                 if (cs == lastcs)
 233                         comp->last_cs = lcs;
 234                 else {
 235                         lcs->cs_next = cs->cs_next;
 236                         cs->cs_next = lastcs->cs_next;
 237                         lastcs->cs_next = cs;
 238                 }
 239         }
 240
 241         /*
 242          * Make sure that only what we expect to change changed. The first
 243          * line of the `if' checks the IP protocol version, header length &
 244          * type of service.  The 2nd line checks the "Don't fragment" bit.
 245          * The 3rd line checks the time-to-live and protocol (the protocol
 246          * check is unnecessary but costless).  The 4th line checks the TCP
 247          * header length.  The 5th line checks IP options, if any.  The 6th
 248          * line checks TCP options, if any.  If any of these things are
 249          * different between the previous & current datagram, we send the
 250          * current datagram `uncompressed'.
 251          */
 252         oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen];
 253         deltaS = hlen;
 254         hlen += th->th_off;
 255         hlen <<= 2;
 256
 257         if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] ||
 258             ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] ||
 259             ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] ||
 260             th->th_off != oth->th_off ||
 261             (deltaS > 5 &&
 262              BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
 263             (th->th_off > 5 &&
 264              BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
 265                 goto uncompressed;
 266
 267         /*
 268          * Figure out which of the changing fields changed.  The
 269          * receiver expects changes in the order: urgent, window,
 270          * ack, seq (the order minimizes the number of temporaries
 271          * needed in this section of code).
 272          */
 273         if (th->th_flags & TH_URG) {
 274                 deltaS = ntohs(th->th_urp);
 275                 ENCODEZ(deltaS);
 276                 changes |= NEW_U;
 277         } else if (th->th_urp != oth->th_urp)
 278                 /* argh! URG not set but urp changed -- a sensible
 279                  * implementation should never do this but RFC793
 280                  * doesn't prohibit the change so we have to deal
 281                  * with it. */
 282                  goto uncompressed;
 283
 284         deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win));
 285         if (deltaS) {
 286                 ENCODE(deltaS);
 287                 changes |= NEW_W;
 288         }
 289
 290         deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack);
 291         if (deltaA) {
 292                 if (deltaA > 0xffff)
 293                         goto uncompressed;
 294                 ENCODE(deltaA);
 295                 changes |= NEW_A;
 296         }
 297
 298         deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq);
 299         if (deltaS) {
 300                 if (deltaS > 0xffff)
 301                         goto uncompressed;
 302                 ENCODE(deltaS);
 303                 changes |= NEW_S;
 304         }
 305
 306         switch(changes) {
 307
 308         case 0:
 309                 /*
 310                  * Nothing changed. If this packet contains data and the
 311                  * last one didn't, this is probably a data packet following
 312                  * an ack (normal on an interactive connection) and we send
 313                  * it compressed.  Otherwise it's probably a retransmit,
 314                  * retransmitted ack or window probe.  Send it uncompressed
 315                  * in case the other side missed the compressed version.
 316                  */
 317                 if (ip->ip_len != cs->cs_ip.ip_len &&
 318                     ntohs(cs->cs_ip.ip_len) == hlen)
 319                         break;
 320
 321                 /* (fall through) */
 322
 323         case SPECIAL_I:
 324         case SPECIAL_D:
 325                 /*
 326                  * actual changes match one of our special case encodings --
 327                  * send packet uncompressed.
 328                  */
 329                 goto uncompressed;
 330
 331         case NEW_S|NEW_A:
 332                 if (deltaS == deltaA &&
 333                     deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
 334                         /* special case for echoed terminal traffic */
 335                         changes = SPECIAL_I;
 336                         cp = new_seq;
 337                 }
 338                 break;
 339
 340         case NEW_S:
 341                 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
 342                         /* special case for data xfer */
 343                         changes = SPECIAL_D;
 344                         cp = new_seq;
 345                 }
 346                 break;
 347         }
 348
 349         deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
 350         if (deltaS != 1) {
 351                 ENCODEZ(deltaS);
 352                 changes |= NEW_I;
 353         }
 354         if (th->th_flags & TH_PUSH)
 355                 changes |= TCP_PUSH_BIT;
 356         /*
 357          * Grab the cksum before we overwrite it below.  Then update our
 358          * state with this packet's header.
 359          */
 360         deltaA = ntohs(th->th_sum);
 361         BCOPY(ip, &cs->cs_ip, hlen);
 362
 363         /*
 364          * We want to use the original packet as our compressed packet.
 365          * (cp - new_seq) is the number of bytes we need for compressed
 366          * sequence numbers.  In addition we need one byte for the change
 367          * mask, one for the connection id and two for the tcp checksum.
 368          * So, (cp - new_seq) + 4 bytes of header are needed.  hlen is how
 369          * many bytes of the original packet to toss so subtract the two to
 370          * get the new packet size.
 371          */
 372         deltaS = cp - new_seq;
 373         cp = (u_char *)ip;
 374         if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
 375                 comp->last_xmit = cs->cs_id;
 376                 hlen -= deltaS + 4;
 377                 cp += hlen;
 378                 *cp++ = changes | NEW_C;
 379                 *cp++ = cs->cs_id;
 380         } else {
 381                 hlen -= deltaS + 3;
 382                 cp += hlen;
 383                 *cp++ = changes;
 384         }
 385         m->m_len -= hlen;
 386         m->m_data += hlen;
 387         *cp++ = deltaA >> 8;
 388         *cp++ = deltaA;
 389         BCOPY(new_seq, cp, deltaS);
 390         INCR(sls_compressed)
 391         return (TYPE_COMPRESSED_TCP);
 392
 393         /*
 394          * Update connection state cs & send uncompressed packet ('uncompressed'
 395          * means a regular ip/tcp packet but with the 'conversation id' we hope
 396          * to use on future compressed packets in the protocol field).
 397          */
 398 uncompressed:
 399         BCOPY(ip, &cs->cs_ip, hlen);
 400         ip->ip_p = cs->cs_id;
 401         comp->last_xmit = cs->cs_id;
 402         return (TYPE_UNCOMPRESSED_TCP);
 403 }
 404
 405
 406 int
 407 sl_uncompress_tcp(bufp, len, type, comp)
 408         u_char **bufp;
 409         int len;
 410         u_int type;
 411         struct slcompress *comp;
 412 {
 413         u_char *hdr, *cp;
 414         int hlen, vjlen;
 415
 416         cp = bufp? *bufp: NULL;
 417         vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen);
 418         if (vjlen < 0)
 419                 return (0);     /* error */
 420         if (vjlen == 0)
 421                 return (len);   /* was uncompressed already */
 422
 423         cp += vjlen;
 424         len -= vjlen;
 425
 426         /*
 427          * At this point, cp points to the first byte of data in the
 428          * packet.  If we're not aligned on a 4-byte boundary, copy the
 429          * data down so the ip & tcp headers will be aligned.  Then back up
 430          * cp by the tcp/ip header length to make room for the reconstructed
 431          * header (we assume the packet we were handed has enough space to
 432          * prepend 128 bytes of header).
 433          */
 434         if ((long)cp & 3) {
 435                 if (len > 0)
 436                         (void) ovbcopy(cp, (caddr_t)((long)cp &~ 3), len);
 437                 cp = (u_char *)((long)cp &~ 3);
 438         }
 439         cp -= hlen;
 440         len += hlen;
 441         BCOPY(hdr, cp, hlen);
 442
 443         *bufp = cp;
 444         return (len);
 445 }
 446
 447 /*
 448  * Uncompress a packet of total length total_len.  The first buflen
 449  * bytes are at buf; this must include the entire (compressed or
 450  * uncompressed) TCP/IP header.  This procedure returns the length
 451  * of the VJ header, with a pointer to the uncompressed IP header
 452  * in *hdrp and its length in *hlenp.
 453  */
 454 int
 455 sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp)
 456         u_char *buf;
 457         int buflen, total_len;
 458         u_int type;
 459         struct slcompress *comp;
 460         u_char **hdrp;
 461         u_int *hlenp;
 462 {
 463         register u_char *cp;
 464         register u_int hlen, changes;
 465         register struct tcphdr *th;
 466         register struct cstate *cs;
 467         register struct ip *ip;
 468         register u_int16_t *bp;
 469         register u_int vjlen;
 470
 471         switch (type) {
 472
 473         case TYPE_UNCOMPRESSED_TCP:
 474                 ip = (struct ip *) buf;
 475                 if (ip->ip_p >= MAX_STATES)
 476                         goto bad;
 477                 cs = &comp->rstate[comp->last_recv = ip->ip_p];
 478                 comp->flags &=~ SLF_TOSS;
 479                 ip->ip_p = IPPROTO_TCP;
 480                 /*
 481                  * Calculate the size of the TCP/IP header and make sure that
 482                  * we don't overflow the space we have available for it.
 483                  */
 484                 hlen = ip->ip_hl << 2;
 485                 if (hlen + sizeof(struct tcphdr) > buflen)
 486                         goto bad;
 487                 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2;
 488                 if (hlen > MAX_HDR || hlen > buflen)
 489                         goto bad;
 490                 BCOPY(ip, &cs->cs_ip, hlen);
 491                 cs->cs_hlen = hlen;
 492                 INCR(sls_uncompressedin)
 493                 *hdrp = (u_char *) &cs->cs_ip;
 494                 *hlenp = hlen;
 495                 return (0);
 496
 497         default:
 498                 goto bad;
 499
 500         case TYPE_COMPRESSED_TCP:
 501                 break;
 502         }
 503         /* We've got a compressed packet. */
 504         INCR(sls_compressedin)
 505         cp = buf;
 506         changes = *cp++;
 507         if (changes & NEW_C) {
 508                 /* Make sure the state index is in range, then grab the state.
 509                  * If we have a good state index, clear the 'discard' flag. */
 510                 if (*cp >= MAX_STATES)
 511                         goto bad;
 512
 513                 comp->flags &=~ SLF_TOSS;
 514                 comp->last_recv = *cp++;
 515         } else {
 516                 /* this packet has an implicit state index.  If we've
 517                  * had a line error since the last time we got an
 518                  * explicit state index, we have to toss the packet. */
 519                 if (comp->flags & SLF_TOSS) {
 520                         INCR(sls_tossed)
 521                         return (-1);
 522                 }
 523         }
 524         cs = &comp->rstate[comp->last_recv];
 525         hlen = cs->cs_ip.ip_hl << 2;
 526         th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
 527         th->th_sum = htons((*cp << 8) | cp[1]);
 528         cp += 2;
 529         if (changes & TCP_PUSH_BIT)
 530                 th->th_flags |= TH_PUSH;
 531         else
 532                 th->th_flags &=~ TH_PUSH;
 533
 534         switch (changes & SPECIALS_MASK) {
 535         case SPECIAL_I:
 536                 {
 537                 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
 538                 th->th_ack = htonl(ntohl(th->th_ack) + i);
 539                 th->th_seq = htonl(ntohl(th->th_seq) + i);
 540                 }
 541                 break;
 542
 543         case SPECIAL_D:
 544                 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
 545                                    - cs->cs_hlen);
 546                 break;
 547
 548         default:
 549                 if (changes & NEW_U) {
 550                         th->th_flags |= TH_URG;
 551                         DECODEU(th->th_urp)
 552                 } else
 553                         th->th_flags &=~ TH_URG;
 554                 if (changes & NEW_W)
 555                         DECODES(th->th_win)
 556                 if (changes & NEW_A)
 557                         DECODEL(th->th_ack)
 558                 if (changes & NEW_S)
 559                         DECODEL(th->th_seq)
 560                 break;
 561         }
 562         if (changes & NEW_I) {
 563                 DECODES(cs->cs_ip.ip_id)
 564         } else
 565                 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
 566
 567         /*
 568          * At this point, cp points to the first byte of data in the
 569          * packet.  Fill in the IP total length and update the IP
 570          * header checksum.
 571          */
 572         vjlen = cp - buf;
 573         buflen -= vjlen;
 574         if (buflen < 0)
 575                 /* we must have dropped some characters (crc should detect
 576                  * this but the old slip framing won't) */
 577                 goto bad;
 578
 579         total_len += cs->cs_hlen - vjlen;
 580         cs->cs_ip.ip_len = htons(total_len);
 581
 582         /* recompute the ip header checksum */
 583         bp = (u_int16_t *) &cs->cs_ip;
 584         cs->cs_ip.ip_sum = 0;
 585         for (changes = 0; hlen > 0; hlen -= 2)
 586                 changes += *bp++;
 587         changes = (changes & 0xffff) + (changes >> 16);
 588         changes = (changes & 0xffff) + (changes >> 16);
 589         cs->cs_ip.ip_sum = ~ changes;
 590
 591         *hdrp = (u_char *) &cs->cs_ip;
 592         *hlenp = cs->cs_hlen;
 593         return vjlen;
 594
 595 bad:
 596         comp->flags |= SLF_TOSS;
 597         INCR(sls_errorin)
 598         return (-1);
 599 }