Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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sys/net/slcompress.c
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1 /*- 2 * Copyright (c) 1989, 1993, 1994 3 * The Regents of the University of California. 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 8.2 (Berkeley) 4/16/94 34 * $FreeBSD: src/sys/net/slcompress.c,v 1.7.2.3 1999/09/05 08:18:03 peter Exp $ 35 */ 36 37 /* 38 * Routines to compress and uncompess tcp packets (for transmission 39 * over low speed serial lines. 40 * 41 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989: 42 * - Initial distribution. 43 * 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 if (hlen > m->m_len) 227 return TYPE_IP; 228 goto uncompressed; 229 230 found: 231 /* 232 * Found it -- move to the front on the connection list. 233 */ 234 if (cs == lastcs) 235 comp->last_cs = lcs; 236 else { 237 lcs->cs_next = cs->cs_next; 238 cs->cs_next = lastcs->cs_next; 239 lastcs->cs_next = cs; 240 } 241 } 242 243 /* 244 * Make sure that only what we expect to change changed. The first 245 * line of the `if' checks the IP protocol version, header length & 246 * type of service. The 2nd line checks the "Don't fragment" bit. 247 * The 3rd line checks the time-to-live and protocol (the protocol 248 * check is unnecessary but costless). The 4th line checks the TCP 249 * header length. The 5th line checks IP options, if any. The 6th 250 * line checks TCP options, if any. If any of these things are 251 * different between the previous & current datagram, we send the 252 * current datagram `uncompressed'. 253 */ 254 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen]; 255 deltaS = hlen; 256 hlen += th->th_off; 257 hlen <<= 2; 258 if (hlen > m->m_len) 259 return TYPE_IP; 260 261 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] || 262 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] || 263 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] || 264 th->th_off != oth->th_off || 265 (deltaS > 5 && 266 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 267 (th->th_off > 5 && 268 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 269 goto uncompressed; 270 271 /* 272 * Figure out which of the changing fields changed. The 273 * receiver expects changes in the order: urgent, window, 274 * ack, seq (the order minimizes the number of temporaries 275 * needed in this section of code). 276 */ 277 if (th->th_flags & TH_URG) { 278 deltaS = ntohs(th->th_urp); 279 ENCODEZ(deltaS); 280 changes |= NEW_U; 281 } else if (th->th_urp != oth->th_urp) 282 /* argh! URG not set but urp changed -- a sensible 283 * implementation should never do this but RFC793 284 * doesn't prohibit the change so we have to deal 285 * with it. */ 286 goto uncompressed; 287 288 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win)); 289 if (deltaS) { 290 ENCODE(deltaS); 291 changes |= NEW_W; 292 } 293 294 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack); 295 if (deltaA) { 296 if (deltaA > 0xffff) 297 goto uncompressed; 298 ENCODE(deltaA); 299 changes |= NEW_A; 300 } 301 302 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq); 303 if (deltaS) { 304 if (deltaS > 0xffff) 305 goto uncompressed; 306 ENCODE(deltaS); 307 changes |= NEW_S; 308 } 309 310 switch(changes) { 311 312 case 0: 313 /* 314 * Nothing changed. If this packet contains data and the 315 * last one didn't, this is probably a data packet following 316 * an ack (normal on an interactive connection) and we send 317 * it compressed. Otherwise it's probably a retransmit, 318 * retransmitted ack or window probe. Send it uncompressed 319 * in case the other side missed the compressed version. 320 */ 321 if (ip->ip_len != cs->cs_ip.ip_len && 322 ntohs(cs->cs_ip.ip_len) == hlen) 323 break; 324 325 /* (fall through) */ 326 327 case SPECIAL_I: 328 case SPECIAL_D: 329 /* 330 * actual changes match one of our special case encodings -- 331 * send packet uncompressed. 332 */ 333 goto uncompressed; 334 335 case NEW_S|NEW_A: 336 if (deltaS == deltaA && 337 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 338 /* special case for echoed terminal traffic */ 339 changes = SPECIAL_I; 340 cp = new_seq; 341 } 342 break; 343 344 case NEW_S: 345 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 346 /* special case for data xfer */ 347 changes = SPECIAL_D; 348 cp = new_seq; 349 } 350 break; 351 } 352 353 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 354 if (deltaS != 1) { 355 ENCODEZ(deltaS); 356 changes |= NEW_I; 357 } 358 if (th->th_flags & TH_PUSH) 359 changes |= TCP_PUSH_BIT; 360 /* 361 * Grab the cksum before we overwrite it below. Then update our 362 * state with this packet's header. 363 */ 364 deltaA = ntohs(th->th_sum); 365 BCOPY(ip, &cs->cs_ip, hlen); 366 367 /* 368 * We want to use the original packet as our compressed packet. 369 * (cp - new_seq) is the number of bytes we need for compressed 370 * sequence numbers. In addition we need one byte for the change 371 * mask, one for the connection id and two for the tcp checksum. 372 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 373 * many bytes of the original packet to toss so subtract the two to 374 * get the new packet size. 375 */ 376 deltaS = cp - new_seq; 377 cp = (u_char *)ip; 378 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 379 comp->last_xmit = cs->cs_id; 380 hlen -= deltaS + 4; 381 cp += hlen; 382 *cp++ = changes | NEW_C; 383 *cp++ = cs->cs_id; 384 } else { 385 hlen -= deltaS + 3; 386 cp += hlen; 387 *cp++ = changes; 388 } 389 m->m_len -= hlen; 390 m->m_data += hlen; 391 *cp++ = deltaA >> 8; 392 *cp++ = deltaA; 393 BCOPY(new_seq, cp, deltaS); 394 INCR(sls_compressed) 395 return (TYPE_COMPRESSED_TCP); 396 397 /* 398 * Update connection state cs & send uncompressed packet ('uncompressed' 399 * means a regular ip/tcp packet but with the 'conversation id' we hope 400 * to use on future compressed packets in the protocol field). 401 */ 402 uncompressed: 403 BCOPY(ip, &cs->cs_ip, hlen); 404 ip->ip_p = cs->cs_id; 405 comp->last_xmit = cs->cs_id; 406 return (TYPE_UNCOMPRESSED_TCP); 407 } 408 409 410 int 411 sl_uncompress_tcp(bufp, len, type, comp) 412 u_char **bufp; 413 int len; 414 u_int type; 415 struct slcompress *comp; 416 { 417 u_char *hdr, *cp; 418 int hlen, vjlen; 419 420 cp = bufp? *bufp: NULL; 421 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen); 422 if (vjlen < 0) 423 return (0); /* error */ 424 if (vjlen == 0) 425 return (len); /* was uncompressed already */ 426 427 cp += vjlen; 428 len -= vjlen; 429 430 /* 431 * At this point, cp points to the first byte of data in the 432 * packet. If we're not aligned on a 4-byte boundary, copy the 433 * data down so the ip & tcp headers will be aligned. Then back up 434 * cp by the tcp/ip header length to make room for the reconstructed 435 * header (we assume the packet we were handed has enough space to 436 * prepend 128 bytes of header). 437 */ 438 if ((long)cp & 3) { 439 if (len > 0) 440 (void) ovbcopy(cp, (caddr_t)((long)cp &~ 3), len); 441 cp = (u_char *)((long)cp &~ 3); 442 } 443 cp -= hlen; 444 len += hlen; 445 BCOPY(hdr, cp, hlen); 446 447 *bufp = cp; 448 return (len); 449 } 450 451 /* 452 * Uncompress a packet of total length total_len. The first buflen 453 * bytes are at buf; this must include the entire (compressed or 454 * uncompressed) TCP/IP header. This procedure returns the length 455 * of the VJ header, with a pointer to the uncompressed IP header 456 * in *hdrp and its length in *hlenp. 457 */ 458 int 459 sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp) 460 u_char *buf; 461 int buflen, total_len; 462 u_int type; 463 struct slcompress *comp; 464 u_char **hdrp; 465 u_int *hlenp; 466 { 467 register u_char *cp; 468 register u_int hlen, changes; 469 register struct tcphdr *th; 470 register struct cstate *cs; 471 register struct ip *ip; 472 register u_int16_t *bp; 473 register u_int vjlen; 474 475 switch (type) { 476 477 case TYPE_UNCOMPRESSED_TCP: 478 ip = (struct ip *) buf; 479 if (ip->ip_p >= MAX_STATES) 480 goto bad; 481 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 482 comp->flags &=~ SLF_TOSS; 483 ip->ip_p = IPPROTO_TCP; 484 /* 485 * Calculate the size of the TCP/IP header and make sure that 486 * we don't overflow the space we have available for it. 487 */ 488 hlen = ip->ip_hl << 2; 489 if (hlen + sizeof(struct tcphdr) > buflen) 490 goto bad; 491 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2; 492 if (hlen > MAX_HDR || hlen > buflen) 493 goto bad; 494 BCOPY(ip, &cs->cs_ip, hlen); 495 cs->cs_hlen = hlen; 496 INCR(sls_uncompressedin) 497 *hdrp = (u_char *) &cs->cs_ip; 498 *hlenp = hlen; 499 return (0); 500 501 default: 502 goto bad; 503 504 case TYPE_COMPRESSED_TCP: 505 break; 506 } 507 /* We've got a compressed packet. */ 508 INCR(sls_compressedin) 509 cp = buf; 510 changes = *cp++; 511 if (changes & NEW_C) { 512 /* Make sure the state index is in range, then grab the state. 513 * If we have a good state index, clear the 'discard' flag. */ 514 if (*cp >= MAX_STATES) 515 goto bad; 516 517 comp->flags &=~ SLF_TOSS; 518 comp->last_recv = *cp++; 519 } else { 520 /* this packet has an implicit state index. If we've 521 * had a line error since the last time we got an 522 * explicit state index, we have to toss the packet. */ 523 if (comp->flags & SLF_TOSS) { 524 INCR(sls_tossed) 525 return (-1); 526 } 527 } 528 cs = &comp->rstate[comp->last_recv]; 529 hlen = cs->cs_ip.ip_hl << 2; 530 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 531 th->th_sum = htons((*cp << 8) | cp[1]); 532 cp += 2; 533 if (changes & TCP_PUSH_BIT) 534 th->th_flags |= TH_PUSH; 535 else 536 th->th_flags &=~ TH_PUSH; 537 538 switch (changes & SPECIALS_MASK) { 539 case SPECIAL_I: 540 { 541 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 542 th->th_ack = htonl(ntohl(th->th_ack) + i); 543 th->th_seq = htonl(ntohl(th->th_seq) + i); 544 } 545 break; 546 547 case SPECIAL_D: 548 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 549 - cs->cs_hlen); 550 break; 551 552 default: 553 if (changes & NEW_U) { 554 th->th_flags |= TH_URG; 555 DECODEU(th->th_urp) 556 } else 557 th->th_flags &=~ TH_URG; 558 if (changes & NEW_W) 559 DECODES(th->th_win) 560 if (changes & NEW_A) 561 DECODEL(th->th_ack) 562 if (changes & NEW_S) 563 DECODEL(th->th_seq) 564 break; 565 } 566 if (changes & NEW_I) { 567 DECODES(cs->cs_ip.ip_id) 568 } else 569 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 570 571 /* 572 * At this point, cp points to the first byte of data in the 573 * packet. Fill in the IP total length and update the IP 574 * header checksum. 575 */ 576 vjlen = cp - buf; 577 buflen -= vjlen; 578 if (buflen < 0) 579 /* we must have dropped some characters (crc should detect 580 * this but the old slip framing won't) */ 581 goto bad; 582 583 total_len += cs->cs_hlen - vjlen; 584 cs->cs_ip.ip_len = htons(total_len); 585 586 /* recompute the ip header checksum */ 587 bp = (u_int16_t *) &cs->cs_ip; 588 cs->cs_ip.ip_sum = 0; 589 for (changes = 0; hlen > 0; hlen -= 2) 590 changes += *bp++; 591 changes = (changes & 0xffff) + (changes >> 16); 592 changes = (changes & 0xffff) + (changes >> 16); 593 cs->cs_ip.ip_sum = ~ changes; 594 595 *hdrp = (u_char *) &cs->cs_ip; 596 *hlenp = cs->cs_hlen; 597 return vjlen; 598 599 bad: 600 comp->flags |= SLF_TOSS; 601 INCR(sls_errorin) 602 return (-1); 603 }
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