Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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sys/bsd/net/slcompress.c
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1 /* 2 * Copyright (c) 2000 Apple Computer, Inc. All rights reserved. 3 * 4 * @APPLE_LICENSE_HEADER_START@ 5 * 6 * Copyright (c) 1999-2003 Apple Computer, Inc. All Rights Reserved. 7 * 8 * This file contains Original Code and/or Modifications of Original Code 9 * as defined in and that are subject to the Apple Public Source License 10 * Version 2.0 (the 'License'). You may not use this file except in 11 * compliance with the License. Please obtain a copy of the License at 12 * http://www.opensource.apple.com/apsl/ and read it before using this 13 * file. 14 * 15 * The Original Code and all software distributed under the License are 16 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER 17 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, 18 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, 19 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. 20 * Please see the License for the specific language governing rights and 21 * limitations under the License. 22 * 23 * @APPLE_LICENSE_HEADER_END@ 24 */ 25 /*- 26 * Copyright (c) 1989, 1993, 1994 27 * The Regents of the University of California. All rights reserved. 28 * 29 * Redistribution and use in source and binary forms, with or without 30 * modification, are permitted provided that the following conditions 31 * are met: 32 * 1. Redistributions of source code must retain the above copyright 33 * notice, this list of conditions and the following disclaimer. 34 * 2. Redistributions in binary form must reproduce the above copyright 35 * notice, this list of conditions and the following disclaimer in the 36 * documentation and/or other materials provided with the distribution. 37 * 3. All advertising materials mentioning features or use of this software 38 * must display the following acknowledgement: 39 * This product includes software developed by the University of 40 * California, Berkeley and its contributors. 41 * 4. Neither the name of the University nor the names of its contributors 42 * may be used to endorse or promote products derived from this software 43 * without specific prior written permission. 44 * 45 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 46 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 47 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 48 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 49 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 50 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 51 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 52 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 53 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 54 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 55 * SUCH DAMAGE. 56 * 57 * @(#)slcompress.c 8.2 (Berkeley) 4/16/94 58 * $FreeBSD: src/sys/net/slcompress.c,v 1.16 1999/12/29 04:38:37 peter Exp $ 59 */ 60 61 /* 62 * Routines to compress and uncompess tcp packets (for transmission 63 * over low speed serial lines. 64 * 65 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989: 66 * - Initial distribution. 67 * 68 */ 69 70 #include <sys/param.h> 71 #include <sys/mbuf.h> 72 #include <sys/systm.h> 73 74 #include <netinet/in.h> 75 #include <netinet/in_systm.h> 76 #include <netinet/ip.h> 77 #include <netinet/tcp.h> 78 79 #include <net/slcompress.h> 80 81 #ifndef SL_NO_STATS 82 #define INCR(counter) ++comp->counter; 83 #else 84 #define INCR(counter) 85 #endif 86 87 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n)) 88 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n)) 89 #ifndef KERNEL 90 #define ovbcopy bcopy 91 #endif 92 93 void 94 sl_compress_init(comp, max_state) 95 struct slcompress *comp; 96 int max_state; 97 { 98 register u_int i; 99 register struct cstate *tstate = comp->tstate; 100 101 if (max_state == -1) { 102 max_state = MAX_STATES - 1; 103 bzero((char *)comp, sizeof(*comp)); 104 } else { 105 /* Don't reset statistics */ 106 bzero((char *)comp->tstate, sizeof(comp->tstate)); 107 bzero((char *)comp->rstate, sizeof(comp->rstate)); 108 } 109 for (i = max_state; i > 0; --i) { 110 tstate[i].cs_id = i; 111 tstate[i].cs_next = &tstate[i - 1]; 112 } 113 tstate[0].cs_next = &tstate[max_state]; 114 tstate[0].cs_id = 0; 115 comp->last_cs = &tstate[0]; 116 comp->last_recv = 255; 117 comp->last_xmit = 255; 118 comp->flags = SLF_TOSS; 119 } 120 121 122 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ 123 * checks for zero (since zero has to be encoded in the long, 3 byte 124 * form). 125 */ 126 #define ENCODE(n) { \ 127 if ((u_int16_t)(n) >= 256) { \ 128 *cp++ = 0; \ 129 cp[1] = (n); \ 130 cp[0] = (n) >> 8; \ 131 cp += 2; \ 132 } else { \ 133 *cp++ = (n); \ 134 } \ 135 } 136 #define ENCODEZ(n) { \ 137 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \ 138 *cp++ = 0; \ 139 cp[1] = (n); \ 140 cp[0] = (n) >> 8; \ 141 cp += 2; \ 142 } else { \ 143 *cp++ = (n); \ 144 } \ 145 } 146 147 #define DECODEL(f) { \ 148 if (*cp == 0) {\ 149 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 150 cp += 3; \ 151 } else { \ 152 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \ 153 } \ 154 } 155 156 #define DECODES(f) { \ 157 if (*cp == 0) {\ 158 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 159 cp += 3; \ 160 } else { \ 161 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \ 162 } \ 163 } 164 165 #define DECODEU(f) { \ 166 if (*cp == 0) {\ 167 (f) = htons((cp[1] << 8) | cp[2]); \ 168 cp += 3; \ 169 } else { \ 170 (f) = htons((u_int32_t)*cp++); \ 171 } \ 172 } 173 174 /* 175 * Attempt to compress an outgoing TCP packet and return the type of 176 * the result. The caller must have already verified that the protocol 177 * is TCP. The first mbuf must contain the complete IP and TCP headers, 178 * and "ip" must be == mtod(m, struct ip *). "comp" supplies the 179 * compression state, and "compress_cid" tells us whether it is OK 180 * to leave out the CID field when feasible. 181 * 182 * The caller is responsible for adjusting m->m_pkthdr.len upon return, 183 * if m is an M_PKTHDR mbuf. 184 */ 185 u_int 186 sl_compress_tcp(m, ip, comp, compress_cid) 187 struct mbuf *m; 188 register struct ip *ip; 189 struct slcompress *comp; 190 int compress_cid; 191 { 192 register struct cstate *cs = comp->last_cs->cs_next; 193 register u_int hlen = ip->ip_hl; 194 register struct tcphdr *oth; 195 register struct tcphdr *th; 196 register u_int deltaS, deltaA; 197 register u_int changes = 0; 198 u_char new_seq[16]; 199 register u_char *cp = new_seq; 200 201 /* 202 * Bail if this is an IP fragment or if the TCP packet isn't 203 * `compressible' (i.e., ACK isn't set or some other control bit is 204 * set). (We assume that the caller has already made sure the 205 * packet is IP proto TCP). 206 */ 207 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 208 return (TYPE_IP); 209 210 th = (struct tcphdr *)&((int32_t *)ip)[hlen]; 211 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 212 return (TYPE_IP); 213 /* 214 * Packet is compressible -- we're going to send either a 215 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 216 * to locate (or create) the connection state. Special case the 217 * most recently used connection since it's most likely to be used 218 * again & we don't have to do any reordering if it's used. 219 */ 220 INCR(sls_packets) 221 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 222 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 223 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 224 /* 225 * Wasn't the first -- search for it. 226 * 227 * States are kept in a circularly linked list with 228 * last_cs pointing to the end of the list. The 229 * list is kept in lru order by moving a state to the 230 * head of the list whenever it is referenced. Since 231 * the list is short and, empirically, the connection 232 * we want is almost always near the front, we locate 233 * states via linear search. If we don't find a state 234 * for the datagram, the oldest state is (re-)used. 235 */ 236 register struct cstate *lcs; 237 register struct cstate *lastcs = comp->last_cs; 238 239 do { 240 lcs = cs; cs = cs->cs_next; 241 INCR(sls_searches) 242 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 243 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 244 && *(int32_t *)th == 245 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 246 goto found; 247 } while (cs != lastcs); 248 249 /* 250 * Didn't find it -- re-use oldest cstate. Send an 251 * uncompressed packet that tells the other side what 252 * connection number we're using for this conversation. 253 * Note that since the state list is circular, the oldest 254 * state points to the newest and we only need to set 255 * last_cs to update the lru linkage. 256 */ 257 INCR(sls_misses) 258 comp->last_cs = lcs; 259 hlen += th->th_off; 260 hlen <<= 2; 261 if (hlen > m->m_len) 262 return TYPE_IP; 263 goto uncompressed; 264 265 found: 266 /* 267 * Found it -- move to the front on the connection list. 268 */ 269 if (cs == lastcs) 270 comp->last_cs = lcs; 271 else { 272 lcs->cs_next = cs->cs_next; 273 cs->cs_next = lastcs->cs_next; 274 lastcs->cs_next = cs; 275 } 276 } 277 278 /* 279 * Make sure that only what we expect to change changed. The first 280 * line of the `if' checks the IP protocol version, header length & 281 * type of service. The 2nd line checks the "Don't fragment" bit. 282 * The 3rd line checks the time-to-live and protocol (the protocol 283 * check is unnecessary but costless). The 4th line checks the TCP 284 * header length. The 5th line checks IP options, if any. The 6th 285 * line checks TCP options, if any. If any of these things are 286 * different between the previous & current datagram, we send the 287 * current datagram `uncompressed'. 288 */ 289 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen]; 290 deltaS = hlen; 291 hlen += th->th_off; 292 hlen <<= 2; 293 if (hlen > m->m_len) 294 return TYPE_IP; 295 296 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] || 297 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] || 298 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] || 299 th->th_off != oth->th_off || 300 (deltaS > 5 && 301 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 302 (th->th_off > 5 && 303 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 304 goto uncompressed; 305 306 /* 307 * Figure out which of the changing fields changed. The 308 * receiver expects changes in the order: urgent, window, 309 * ack, seq (the order minimizes the number of temporaries 310 * needed in this section of code). 311 */ 312 if (th->th_flags & TH_URG) { 313 deltaS = ntohs(th->th_urp); 314 ENCODEZ(deltaS); 315 changes |= NEW_U; 316 } else if (th->th_urp != oth->th_urp) 317 /* argh! URG not set but urp changed -- a sensible 318 * implementation should never do this but RFC793 319 * doesn't prohibit the change so we have to deal 320 * with it. */ 321 goto uncompressed; 322 323 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win)); 324 if (deltaS) { 325 ENCODE(deltaS); 326 changes |= NEW_W; 327 } 328 329 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack); 330 if (deltaA) { 331 if (deltaA > 0xffff) 332 goto uncompressed; 333 ENCODE(deltaA); 334 changes |= NEW_A; 335 } 336 337 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq); 338 if (deltaS) { 339 if (deltaS > 0xffff) 340 goto uncompressed; 341 ENCODE(deltaS); 342 changes |= NEW_S; 343 } 344 345 switch(changes) { 346 347 case 0: 348 /* 349 * Nothing changed. If this packet contains data and the 350 * last one didn't, this is probably a data packet following 351 * an ack (normal on an interactive connection) and we send 352 * it compressed. Otherwise it's probably a retransmit, 353 * retransmitted ack or window probe. Send it uncompressed 354 * in case the other side missed the compressed version. 355 */ 356 if (ip->ip_len != cs->cs_ip.ip_len && 357 ntohs(cs->cs_ip.ip_len) == hlen) 358 break; 359 360 /* (fall through) */ 361 362 case SPECIAL_I: 363 case SPECIAL_D: 364 /* 365 * actual changes match one of our special case encodings -- 366 * send packet uncompressed. 367 */ 368 goto uncompressed; 369 370 case NEW_S|NEW_A: 371 if (deltaS == deltaA && 372 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 373 /* special case for echoed terminal traffic */ 374 changes = SPECIAL_I; 375 cp = new_seq; 376 } 377 break; 378 379 case NEW_S: 380 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 381 /* special case for data xfer */ 382 changes = SPECIAL_D; 383 cp = new_seq; 384 } 385 break; 386 } 387 388 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 389 if (deltaS != 1) { 390 ENCODEZ(deltaS); 391 changes |= NEW_I; 392 } 393 if (th->th_flags & TH_PUSH) 394 changes |= TCP_PUSH_BIT; 395 /* 396 * Grab the cksum before we overwrite it below. Then update our 397 * state with this packet's header. 398 */ 399 deltaA = ntohs(th->th_sum); 400 BCOPY(ip, &cs->cs_ip, hlen); 401 402 /* 403 * We want to use the original packet as our compressed packet. 404 * (cp - new_seq) is the number of bytes we need for compressed 405 * sequence numbers. In addition we need one byte for the change 406 * mask, one for the connection id and two for the tcp checksum. 407 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 408 * many bytes of the original packet to toss so subtract the two to 409 * get the new packet size. 410 */ 411 deltaS = cp - new_seq; 412 cp = (u_char *)ip; 413 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 414 comp->last_xmit = cs->cs_id; 415 hlen -= deltaS + 4; 416 cp += hlen; 417 *cp++ = changes | NEW_C; 418 *cp++ = cs->cs_id; 419 } else { 420 hlen -= deltaS + 3; 421 cp += hlen; 422 *cp++ = changes; 423 } 424 m->m_len -= hlen; 425 m->m_data += hlen; 426 *cp++ = deltaA >> 8; 427 *cp++ = deltaA; 428 BCOPY(new_seq, cp, deltaS); 429 INCR(sls_compressed) 430 return (TYPE_COMPRESSED_TCP); 431 432 /* 433 * Update connection state cs & send uncompressed packet ('uncompressed' 434 * means a regular ip/tcp packet but with the 'conversation id' we hope 435 * to use on future compressed packets in the protocol field). 436 */ 437 uncompressed: 438 BCOPY(ip, &cs->cs_ip, hlen); 439 ip->ip_p = cs->cs_id; 440 comp->last_xmit = cs->cs_id; 441 return (TYPE_UNCOMPRESSED_TCP); 442 } 443 444 445 int 446 sl_uncompress_tcp(bufp, len, type, comp) 447 u_char **bufp; 448 int len; 449 u_int type; 450 struct slcompress *comp; 451 { 452 u_char *hdr, *cp; 453 int hlen, vjlen; 454 455 cp = bufp? *bufp: NULL; 456 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen); 457 if (vjlen < 0) 458 return (0); /* error */ 459 if (vjlen == 0) 460 return (len); /* was uncompressed already */ 461 462 cp += vjlen; 463 len -= vjlen; 464 465 /* 466 * At this point, cp points to the first byte of data in the 467 * packet. If we're not aligned on a 4-byte boundary, copy the 468 * data down so the ip & tcp headers will be aligned. Then back up 469 * cp by the tcp/ip header length to make room for the reconstructed 470 * header (we assume the packet we were handed has enough space to 471 * prepend 128 bytes of header). 472 */ 473 if ((intptr_t)cp & 3) { 474 if (len > 0) 475 (void) ovbcopy(cp, (caddr_t)((intptr_t)cp &~ 3), len); 476 cp = (u_char *)((intptr_t)cp &~ 3); 477 } 478 cp -= hlen; 479 len += hlen; 480 BCOPY(hdr, cp, hlen); 481 482 *bufp = cp; 483 return (len); 484 } 485 486 /* 487 * Uncompress a packet of total length total_len. The first buflen 488 * bytes are at buf; this must include the entire (compressed or 489 * uncompressed) TCP/IP header. This procedure returns the length 490 * of the VJ header, with a pointer to the uncompressed IP header 491 * in *hdrp and its length in *hlenp. 492 */ 493 int 494 sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp) 495 u_char *buf; 496 int buflen, total_len; 497 u_int type; 498 struct slcompress *comp; 499 u_char **hdrp; 500 u_int *hlenp; 501 { 502 register u_char *cp; 503 register u_int hlen, changes; 504 register struct tcphdr *th; 505 register struct cstate *cs; 506 register struct ip *ip; 507 register u_int16_t *bp; 508 register u_int vjlen; 509 510 switch (type) { 511 512 case TYPE_UNCOMPRESSED_TCP: 513 ip = (struct ip *) buf; 514 if (ip->ip_p >= MAX_STATES) 515 goto bad; 516 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 517 comp->flags &=~ SLF_TOSS; 518 ip->ip_p = IPPROTO_TCP; 519 /* 520 * Calculate the size of the TCP/IP header and make sure that 521 * we don't overflow the space we have available for it. 522 */ 523 hlen = ip->ip_hl << 2; 524 if (hlen + sizeof(struct tcphdr) > buflen) 525 goto bad; 526 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2; 527 if (hlen > MAX_HDR || hlen > buflen) 528 goto bad; 529 BCOPY(ip, &cs->cs_ip, hlen); 530 cs->cs_hlen = hlen; 531 INCR(sls_uncompressedin) 532 *hdrp = (u_char *) &cs->cs_ip; 533 *hlenp = hlen; 534 return (0); 535 536 default: 537 goto bad; 538 539 case TYPE_COMPRESSED_TCP: 540 break; 541 } 542 /* We've got a compressed packet. */ 543 INCR(sls_compressedin) 544 cp = buf; 545 changes = *cp++; 546 if (changes & NEW_C) { 547 /* Make sure the state index is in range, then grab the state. 548 * If we have a good state index, clear the 'discard' flag. */ 549 if (*cp >= MAX_STATES) 550 goto bad; 551 552 comp->flags &=~ SLF_TOSS; 553 comp->last_recv = *cp++; 554 } else { 555 /* this packet has an implicit state index. If we've 556 * had a line error since the last time we got an 557 * explicit state index, we have to toss the packet. */ 558 if (comp->flags & SLF_TOSS) { 559 INCR(sls_tossed) 560 return (-1); 561 } 562 } 563 cs = &comp->rstate[comp->last_recv]; 564 hlen = cs->cs_ip.ip_hl << 2; 565 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 566 th->th_sum = htons((*cp << 8) | cp[1]); 567 cp += 2; 568 if (changes & TCP_PUSH_BIT) 569 th->th_flags |= TH_PUSH; 570 else 571 th->th_flags &=~ TH_PUSH; 572 573 switch (changes & SPECIALS_MASK) { 574 case SPECIAL_I: 575 { 576 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 577 th->th_ack = htonl(ntohl(th->th_ack) + i); 578 th->th_seq = htonl(ntohl(th->th_seq) + i); 579 } 580 break; 581 582 case SPECIAL_D: 583 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 584 - cs->cs_hlen); 585 break; 586 587 default: 588 if (changes & NEW_U) { 589 th->th_flags |= TH_URG; 590 DECODEU(th->th_urp) 591 } else 592 th->th_flags &=~ TH_URG; 593 if (changes & NEW_W) 594 DECODES(th->th_win) 595 if (changes & NEW_A) 596 DECODEL(th->th_ack) 597 if (changes & NEW_S) 598 DECODEL(th->th_seq) 599 break; 600 } 601 if (changes & NEW_I) { 602 DECODES(cs->cs_ip.ip_id) 603 } else 604 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 605 606 /* 607 * At this point, cp points to the first byte of data in the 608 * packet. Fill in the IP total length and update the IP 609 * header checksum. 610 */ 611 vjlen = cp - buf; 612 buflen -= vjlen; 613 if (buflen < 0) 614 /* we must have dropped some characters (crc should detect 615 * this but the old slip framing won't) */ 616 goto bad; 617 618 total_len += cs->cs_hlen - vjlen; 619 cs->cs_ip.ip_len = htons(total_len); 620 621 /* recompute the ip header checksum */ 622 bp = (u_int16_t *) &cs->cs_ip; 623 cs->cs_ip.ip_sum = 0; 624 for (changes = 0; hlen > 0; hlen -= 2) 625 changes += *bp++; 626 changes = (changes & 0xffff) + (changes >> 16); 627 changes = (changes & 0xffff) + (changes >> 16); 628 cs->cs_ip.ip_sum = ~ changes; 629 630 *hdrp = (u_char *) &cs->cs_ip; 631 *hlenp = cs->cs_hlen; 632 return vjlen; 633 634 bad: 635 comp->flags |= SLF_TOSS; 636 INCR(sls_errorin) 637 return (-1); 638 }
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