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 /* $NetBSD: slcompress.c,v 1.25 2003/08/07 16:32:58 agc Exp $ */ 2 /* Id: slcompress.c,v 1.3 1996/05/24 07:04:47 paulus Exp */ 3 4 /* 5 * Copyright (c) 1989, 1993, 1994 6 * The Regents of the University of California. All rights reserved. 7 * 8 * Redistribution and use in source and binary forms, with or without 9 * modification, are permitted provided that the following conditions 10 * are met: 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice, this list of conditions and the following disclaimer in the 15 * documentation and/or other materials provided with the distribution. 16 * 3. Neither the name of the University nor the names of its contributors 17 * may be used to endorse or promote products derived from this software 18 * without specific prior written permission. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30 * SUCH DAMAGE. 31 * 32 * @(#)slcompress.c 8.2 (Berkeley) 4/16/94 33 */ 34 35 /* 36 * Routines to compress and uncompess tcp packets (for transmission 37 * over low speed serial lines. 38 * 39 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989: 40 * - Initial distribution. 41 */ 42 43 #include <sys/cdefs.h> 44 __KERNEL_RCSID(0, "$NetBSD: slcompress.c,v 1.25 2003/08/07 16:32:58 agc Exp $"); 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 66 67 void 68 sl_compress_init(comp) 69 struct slcompress *comp; 70 { 71 u_int i; 72 struct cstate *tstate = comp->tstate; 73 74 memset((char *)comp, 0, sizeof(*comp)); 75 for (i = MAX_STATES - 1; i > 0; --i) { 76 tstate[i].cs_id = i; 77 tstate[i].cs_next = &tstate[i - 1]; 78 } 79 tstate[0].cs_next = &tstate[MAX_STATES - 1]; 80 tstate[0].cs_id = 0; 81 comp->last_cs = &tstate[0]; 82 comp->last_recv = 255; 83 comp->last_xmit = 255; 84 comp->flags = SLF_TOSS; 85 } 86 87 88 /* 89 * Like sl_compress_init, but we get to specify the maximum connection 90 * ID to use on transmission. 91 */ 92 void 93 sl_compress_setup(comp, max_state) 94 struct slcompress *comp; 95 int max_state; 96 { 97 u_int i; 98 struct cstate *tstate = comp->tstate; 99 100 if (max_state == -1) { 101 max_state = MAX_STATES - 1; 102 memset((char *)comp, 0, sizeof(*comp)); 103 } else { 104 /* Don't reset statistics */ 105 memset((char *)comp->tstate, 0, sizeof(comp->tstate)); 106 memset((char *)comp->rstate, 0, sizeof(comp->rstate)); 107 } 108 for (i = max_state; i > 0; --i) { 109 tstate[i].cs_id = i; 110 tstate[i].cs_next = &tstate[i - 1]; 111 } 112 tstate[0].cs_next = &tstate[max_state]; 113 tstate[0].cs_id = 0; 114 comp->last_cs = &tstate[0]; 115 comp->last_recv = 255; 116 comp->last_xmit = 255; 117 comp->flags = SLF_TOSS; 118 } 119 120 121 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ 122 * checks for zero (since zero has to be encoded in the long, 3 byte 123 * form). 124 */ 125 #define ENCODE(n) { \ 126 if ((u_int16_t)(n) >= 256) { \ 127 *cp++ = 0; \ 128 cp[1] = (n); \ 129 cp[0] = (n) >> 8; \ 130 cp += 2; \ 131 } else { \ 132 *cp++ = (n); \ 133 } \ 134 } 135 #define ENCODEZ(n) { \ 136 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \ 137 *cp++ = 0; \ 138 cp[1] = (n); \ 139 cp[0] = (n) >> 8; \ 140 cp += 2; \ 141 } else { \ 142 *cp++ = (n); \ 143 } \ 144 } 145 146 #define DECODEL(f) { \ 147 if (*cp == 0) {\ 148 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 149 cp += 3; \ 150 } else { \ 151 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \ 152 } \ 153 } 154 155 #define DECODES(f) { \ 156 if (*cp == 0) {\ 157 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 158 cp += 3; \ 159 } else { \ 160 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \ 161 } \ 162 } 163 164 #define DECODEU(f) { \ 165 if (*cp == 0) {\ 166 (f) = htons((cp[1] << 8) | cp[2]); \ 167 cp += 3; \ 168 } else { \ 169 (f) = htons((u_int32_t)*cp++); \ 170 } \ 171 } 172 173 u_int 174 sl_compress_tcp(m, ip, comp, compress_cid) 175 struct mbuf *m; 176 struct ip *ip; 177 struct slcompress *comp; 178 int compress_cid; 179 { 180 struct cstate *cs = comp->last_cs->cs_next; 181 u_int hlen = ip->ip_hl; 182 struct tcphdr *oth; 183 struct tcphdr *th; 184 u_int deltaS, deltaA; 185 u_int changes = 0; 186 u_char new_seq[16]; 187 u_char *cp = new_seq; 188 189 /* 190 * Bail if this is an IP fragment or if the TCP packet isn't 191 * `compressible' (i.e., ACK isn't set or some other control bit is 192 * set). (We assume that the caller has already made sure the 193 * packet is IP proto TCP). 194 */ 195 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 196 return (TYPE_IP); 197 198 th = (struct tcphdr *)&((int32_t *)ip)[hlen]; 199 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 200 return (TYPE_IP); 201 /* 202 * Packet is compressible -- we're going to send either a 203 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 204 * to locate (or create) the connection state. Special case the 205 * most recently used connection since it's most likely to be used 206 * again & we don't have to do any reordering if it's used. 207 */ 208 INCR(sls_packets) 209 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 210 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 211 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 212 /* 213 * Wasn't the first -- search for it. 214 * 215 * States are kept in a circularly linked list with 216 * last_cs pointing to the end of the list. The 217 * list is kept in lru order by moving a state to the 218 * head of the list whenever it is referenced. Since 219 * the list is short and, empirically, the connection 220 * we want is almost always near the front, we locate 221 * states via linear search. If we don't find a state 222 * for the datagram, the oldest state is (re-)used. 223 */ 224 struct cstate *lcs; 225 struct cstate *lastcs = comp->last_cs; 226 227 do { 228 lcs = cs; cs = cs->cs_next; 229 INCR(sls_searches) 230 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 231 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 232 && *(int32_t *)th == 233 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 234 goto found; 235 } while (cs != lastcs); 236 237 /* 238 * Didn't find it -- re-use oldest cstate. Send an 239 * uncompressed packet that tells the other side what 240 * connection number we're using for this conversation. 241 * Note that since the state list is circular, the oldest 242 * state points to the newest and we only need to set 243 * last_cs to update the lru linkage. 244 */ 245 INCR(sls_misses) 246 comp->last_cs = lcs; 247 hlen += th->th_off; 248 hlen <<= 2; 249 if (hlen > m->m_len) 250 return (TYPE_IP); 251 goto uncompressed; 252 253 found: 254 /* 255 * Found it -- move to the front on the connection list. 256 */ 257 if (cs == lastcs) 258 comp->last_cs = lcs; 259 else { 260 lcs->cs_next = cs->cs_next; 261 cs->cs_next = lastcs->cs_next; 262 lastcs->cs_next = cs; 263 } 264 } 265 266 /* 267 * Make sure that only what we expect to change changed. The first 268 * line of the `if' checks the IP protocol version, header length & 269 * type of service. The 2nd line checks the "Don't fragment" bit. 270 * The 3rd line checks the time-to-live and protocol (the protocol 271 * check is unnecessary but costless). The 4th line checks the TCP 272 * header length. The 5th line checks IP options, if any. The 6th 273 * line checks TCP options, if any. If any of these things are 274 * different between the previous & current datagram, we send the 275 * current datagram `uncompressed'. 276 */ 277 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen]; 278 deltaS = hlen; 279 hlen += th->th_off; 280 hlen <<= 2; 281 if (hlen > m->m_len) 282 return (TYPE_IP); 283 284 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] || 285 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] || 286 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] || 287 th->th_off != oth->th_off || 288 (deltaS > 5 && 289 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 290 (th->th_off > 5 && 291 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 292 goto uncompressed; 293 294 /* 295 * Figure out which of the changing fields changed. The 296 * receiver expects changes in the order: urgent, window, 297 * ack, seq (the order minimizes the number of temporaries 298 * needed in this section of code). 299 */ 300 if (th->th_flags & TH_URG) { 301 deltaS = ntohs(th->th_urp); 302 ENCODEZ(deltaS); 303 changes |= NEW_U; 304 } else if (th->th_urp != oth->th_urp) 305 /* argh! URG not set but urp changed -- a sensible 306 * implementation should never do this but RFC793 307 * doesn't prohibit the change so we have to deal 308 * with it. */ 309 goto uncompressed; 310 311 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win)); 312 if (deltaS) { 313 ENCODE(deltaS); 314 changes |= NEW_W; 315 } 316 317 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack); 318 if (deltaA) { 319 if (deltaA > 0xffff) 320 goto uncompressed; 321 ENCODE(deltaA); 322 changes |= NEW_A; 323 } 324 325 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq); 326 if (deltaS) { 327 if (deltaS > 0xffff) 328 goto uncompressed; 329 ENCODE(deltaS); 330 changes |= NEW_S; 331 } 332 333 switch (changes) { 334 335 case 0: 336 /* 337 * Nothing changed. If this packet contains data and the 338 * last one didn't, this is probably a data packet following 339 * an ack (normal on an interactive connection) and we send 340 * it compressed. Otherwise it's probably a retransmit, 341 * retransmitted ack or window probe. Send it uncompressed 342 * in case the other side missed the compressed version. 343 */ 344 if (ip->ip_len != cs->cs_ip.ip_len && 345 ntohs(cs->cs_ip.ip_len) == hlen) 346 break; 347 348 /* (fall through) */ 349 350 case SPECIAL_I: 351 case SPECIAL_D: 352 /* 353 * actual changes match one of our special case encodings -- 354 * send packet uncompressed. 355 */ 356 goto uncompressed; 357 358 case NEW_S|NEW_A: 359 if (deltaS == deltaA && 360 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 361 /* special case for echoed terminal traffic */ 362 changes = SPECIAL_I; 363 cp = new_seq; 364 } 365 break; 366 367 case NEW_S: 368 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 369 /* special case for data xfer */ 370 changes = SPECIAL_D; 371 cp = new_seq; 372 } 373 break; 374 } 375 376 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 377 if (deltaS != 1) { 378 ENCODEZ(deltaS); 379 changes |= NEW_I; 380 } 381 if (th->th_flags & TH_PUSH) 382 changes |= TCP_PUSH_BIT; 383 /* 384 * Grab the cksum before we overwrite it below. Then update our 385 * state with this packet's header. 386 */ 387 deltaA = ntohs(th->th_sum); 388 BCOPY(ip, &cs->cs_ip, hlen); 389 390 /* 391 * We want to use the original packet as our compressed packet. 392 * (cp - new_seq) is the number of bytes we need for compressed 393 * sequence numbers. In addition we need one byte for the change 394 * mask, one for the connection id and two for the tcp checksum. 395 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 396 * many bytes of the original packet to toss so subtract the two to 397 * get the new packet size. 398 */ 399 deltaS = cp - new_seq; 400 cp = (u_char *)ip; 401 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 402 comp->last_xmit = cs->cs_id; 403 hlen -= deltaS + 4; 404 cp += hlen; 405 *cp++ = changes | NEW_C; 406 *cp++ = cs->cs_id; 407 } else { 408 hlen -= deltaS + 3; 409 cp += hlen; 410 *cp++ = changes; 411 } 412 m->m_len -= hlen; 413 m->m_data += hlen; 414 *cp++ = deltaA >> 8; 415 *cp++ = deltaA; 416 BCOPY(new_seq, cp, deltaS); 417 INCR(sls_compressed) 418 return (TYPE_COMPRESSED_TCP); 419 420 /* 421 * Update connection state cs & send uncompressed packet ('uncompressed' 422 * means a regular ip/tcp packet but with the 'conversation id' we hope 423 * to use on future compressed packets in the protocol field). 424 */ 425 uncompressed: 426 BCOPY(ip, &cs->cs_ip, hlen); 427 ip->ip_p = cs->cs_id; 428 comp->last_xmit = cs->cs_id; 429 return (TYPE_UNCOMPRESSED_TCP); 430 } 431 432 433 int 434 sl_uncompress_tcp(bufp, len, type, comp) 435 u_char **bufp; 436 int len; 437 u_int type; 438 struct slcompress *comp; 439 { 440 u_char *hdr, *cp; 441 int vjlen; 442 u_int hlen; 443 444 cp = bufp? *bufp: NULL; 445 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen); 446 if (vjlen < 0) 447 return (0); /* error */ 448 if (vjlen == 0) 449 return (len); /* was uncompressed already */ 450 451 cp += vjlen; 452 len -= vjlen; 453 454 /* 455 * At this point, cp points to the first byte of data in the 456 * packet. If we're not aligned on a 4-byte boundary, copy the 457 * data down so the ip & tcp headers will be aligned. Then back up 458 * cp by the tcp/ip header length to make room for the reconstructed 459 * header (we assume the packet we were handed has enough space to 460 * prepend 128 bytes of header). 461 */ 462 if ((long)cp & 3) { 463 if (len > 0) 464 memmove((caddr_t)((long)cp &~ 3), cp, len); 465 cp = (u_char *)((long)cp &~ 3); 466 } 467 cp -= hlen; 468 len += hlen; 469 BCOPY(hdr, cp, hlen); 470 471 *bufp = cp; 472 return (len); 473 } 474 475 /* 476 * Uncompress a packet of total length total_len. The first buflen 477 * bytes are at buf; this must include the entire (compressed or 478 * uncompressed) TCP/IP header. This procedure returns the length 479 * of the VJ header, with a pointer to the uncompressed IP header 480 * in *hdrp and its length in *hlenp. 481 */ 482 int 483 sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp) 484 u_char *buf; 485 int buflen, total_len; 486 u_int type; 487 struct slcompress *comp; 488 u_char **hdrp; 489 u_int *hlenp; 490 { 491 u_char *cp; 492 u_int hlen, changes; 493 struct tcphdr *th; 494 struct cstate *cs; 495 struct ip *ip; 496 u_int16_t *bp; 497 u_int vjlen; 498 499 switch (type) { 500 501 case TYPE_UNCOMPRESSED_TCP: 502 ip = (struct ip *) buf; 503 if (ip->ip_p >= MAX_STATES) 504 goto bad; 505 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 506 comp->flags &=~ SLF_TOSS; 507 ip->ip_p = IPPROTO_TCP; 508 /* 509 * Calculate the size of the TCP/IP header and make sure that 510 * we don't overflow the space we have available for it. 511 */ 512 hlen = ip->ip_hl << 2; 513 if (hlen + sizeof(struct tcphdr) > buflen) 514 goto bad; 515 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2; 516 if (hlen > MAX_HDR || hlen > buflen) 517 goto bad; 518 BCOPY(ip, &cs->cs_ip, hlen); 519 cs->cs_hlen = hlen; 520 INCR(sls_uncompressedin) 521 *hdrp = (u_char *) &cs->cs_ip; 522 *hlenp = hlen; 523 return (0); 524 525 default: 526 goto bad; 527 528 case TYPE_COMPRESSED_TCP: 529 break; 530 } 531 /* We've got a compressed packet. */ 532 INCR(sls_compressedin) 533 cp = buf; 534 changes = *cp++; 535 if (changes & NEW_C) { 536 /* Make sure the state index is in range, then grab the state. 537 * If we have a good state index, clear the 'discard' flag. */ 538 if (*cp >= MAX_STATES) 539 goto bad; 540 541 comp->flags &=~ SLF_TOSS; 542 comp->last_recv = *cp++; 543 } else { 544 /* this packet has an implicit state index. If we've 545 * had a line error since the last time we got an 546 * explicit state index, we have to toss the packet. */ 547 if (comp->flags & SLF_TOSS) { 548 INCR(sls_tossed) 549 return (-1); 550 } 551 } 552 cs = &comp->rstate[comp->last_recv]; 553 hlen = cs->cs_ip.ip_hl << 2; 554 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 555 th->th_sum = htons((*cp << 8) | cp[1]); 556 cp += 2; 557 if (changes & TCP_PUSH_BIT) 558 th->th_flags |= TH_PUSH; 559 else 560 th->th_flags &=~ TH_PUSH; 561 562 switch (changes & SPECIALS_MASK) { 563 case SPECIAL_I: 564 { 565 u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 566 th->th_ack = htonl(ntohl(th->th_ack) + i); 567 th->th_seq = htonl(ntohl(th->th_seq) + i); 568 } 569 break; 570 571 case SPECIAL_D: 572 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 573 - cs->cs_hlen); 574 break; 575 576 default: 577 if (changes & NEW_U) { 578 th->th_flags |= TH_URG; 579 DECODEU(th->th_urp) 580 } else 581 th->th_flags &=~ TH_URG; 582 if (changes & NEW_W) 583 DECODES(th->th_win) 584 if (changes & NEW_A) 585 DECODEL(th->th_ack) 586 if (changes & NEW_S) 587 DECODEL(th->th_seq) 588 break; 589 } 590 if (changes & NEW_I) { 591 DECODES(cs->cs_ip.ip_id) 592 } else 593 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 594 595 /* 596 * At this point, cp points to the first byte of data in the 597 * packet. Fill in the IP total length and update the IP 598 * header checksum. 599 */ 600 vjlen = cp - buf; 601 buflen -= vjlen; 602 if (buflen < 0) 603 /* we must have dropped some characters (crc should detect 604 * this but the old slip framing won't) */ 605 goto bad; 606 607 total_len += cs->cs_hlen - vjlen; 608 cs->cs_ip.ip_len = htons(total_len); 609 610 /* recompute the ip header checksum */ 611 bp = (u_int16_t *) &cs->cs_ip; 612 cs->cs_ip.ip_sum = 0; 613 for (changes = 0; hlen > 0; hlen -= 2) 614 changes += *bp++; 615 changes = (changes & 0xffff) + (changes >> 16); 616 changes = (changes & 0xffff) + (changes >> 16); 617 cs->cs_ip.ip_sum = ~ changes; 618 619 *hdrp = (u_char *) &cs->cs_ip; 620 *hlenp = cs->cs_hlen; 621 return vjlen; 622 623 bad: 624 comp->flags |= SLF_TOSS; 625 INCR(sls_errorin) 626 return (-1); 627 }
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