1 /* slcompress.c 7.5 90/01/20 */ 2 /* 3 * Routines to compress and uncompess tcp packets (for transmission 4 * over low speed serial lines. 5 * 6 * Copyright (c) 1989 Regents of the University of California. 7 * All rights reserved. 8 * 9 * Redistribution and use in source and binary forms are permitted 10 * provided that the above copyright notice and this paragraph are 11 * duplicated in all such forms and that any documentation, 12 * advertising materials, and other materials related to such 13 * distribution and use acknowledge that the software was developed 14 * by the University of California, Berkeley. The name of the 15 * University may not be used to endorse or promote products derived 16 * from this software without specific prior written permission. 17 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR 18 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED 19 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE. 20 * 21 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989: 22 * - Initial distribution. 23 */ 24 #ifndef lint 25 static char rcsid[] = "$Header: slcompress.c,v 1.19 89/12/31 08:52:59 van Exp $"; 26 #endif 27 28 #include <sys/types.h> 29 #include <sys/param.h> 30 #include <sys/mbuf.h> 31 #include <netinet/in.h> 32 #include <netinet/in_systm.h> 33 #include <netinet/ip.h> 34 #include <netinet/tcp.h> 35 36 #include "slcompress.h" 37 38 #ifndef SL_NO_STATS 39 #define INCR(counter) ++comp->counter; 40 #else 41 #define INCR(counter) 42 #endif 43 44 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n)) 45 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n)) 46 #ifndef KERNEL 47 #define ovbcopy bcopy 48 #endif 49 50 51 void 52 sl_compress_init(comp) 53 struct slcompress *comp; 54 { 55 register u_int i; 56 register struct cstate *tstate = comp->tstate; 57 58 bzero((char *)comp, sizeof(*comp)); 59 for (i = MAX_STATES - 1; i > 0; --i) { 60 tstate[i].cs_id = i; 61 tstate[i].cs_next = &tstate[i - 1]; 62 } 63 tstate[0].cs_next = &tstate[MAX_STATES - 1]; 64 tstate[0].cs_id = 0; 65 comp->last_cs = &tstate[0]; 66 comp->last_recv = 255; 67 comp->last_xmit = 255; 68 } 69 70 71 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ 72 * checks for zero (since zero has to be encoded in the long, 3 byte 73 * form). 74 */ 75 #define ENCODE(n) { \ 76 if ((u_short)(n) >= 256) { \ 77 *cp++ = 0; \ 78 cp[1] = (n); \ 79 cp[0] = (n) >> 8; \ 80 cp += 2; \ 81 } else { \ 82 *cp++ = (n); \ 83 } \ 84 } 85 #define ENCODEZ(n) { \ 86 if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \ 87 *cp++ = 0; \ 88 cp[1] = (n); \ 89 cp[0] = (n) >> 8; \ 90 cp += 2; \ 91 } else { \ 92 *cp++ = (n); \ 93 } \ 94 } 95 96 #define DECODEL(f) { \ 97 if (*cp == 0) {\ 98 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 99 cp += 3; \ 100 } else { \ 101 (f) = htonl(ntohl(f) + (u_long)*cp++); \ 102 } \ 103 } 104 105 #define DECODES(f) { \ 106 if (*cp == 0) {\ 107 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 108 cp += 3; \ 109 } else { \ 110 (f) = htons(ntohs(f) + (u_long)*cp++); \ 111 } \ 112 } 113 114 #define DECODEU(f) { \ 115 if (*cp == 0) {\ 116 (f) = htons((cp[1] << 8) | cp[2]); \ 117 cp += 3; \ 118 } else { \ 119 (f) = htons((u_long)*cp++); \ 120 } \ 121 } 122 123 124 u_char 125 sl_compress_tcp(m, ip, comp, compress_cid) 126 struct mbuf *m; 127 register struct ip *ip; 128 struct slcompress *comp; 129 int compress_cid; 130 { 131 register struct cstate *cs = comp->last_cs->cs_next; 132 register u_int hlen = ip->ip_hl; 133 register struct tcphdr *oth; 134 register struct tcphdr *th; 135 register u_int deltaS, deltaA; 136 register u_int changes = 0; 137 u_char new_seq[16]; 138 register u_char *cp = new_seq; 139 140 /* 141 * Bail if this is an IP fragment or if the TCP packet isn't 142 * `compressible' (i.e., ACK isn't set or some other control bit is 143 * set). (We assume that the caller has already made sure the 144 * packet is IP proto TCP). 145 */ 146 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 147 return (TYPE_IP); 148 149 th = (struct tcphdr *)&((int *)ip)[hlen]; 150 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 151 return (TYPE_IP); 152 /* 153 * Packet is compressible -- we're going to send either a 154 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 155 * to locate (or create) the connection state. Special case the 156 * most recently used connection since it's most likely to be used 157 * again & we don't have to do any reordering if it's used. 158 */ 159 INCR(sls_packets) 160 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 161 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 162 *(int *)th != ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 163 /* 164 * Wasn't the first -- search for it. 165 * 166 * States are kept in a circularly linked list with 167 * last_cs pointing to the end of the list. The 168 * list is kept in lru order by moving a state to the 169 * head of the list whenever it is referenced. Since 170 * the list is short and, empirically, the connection 171 * we want is almost always near the front, we locate 172 * states via linear search. If we don't find a state 173 * for the datagram, the oldest state is (re-)used. 174 */ 175 register struct cstate *lcs; 176 register struct cstate *lastcs = comp->last_cs; 177 178 do { 179 lcs = cs; cs = cs->cs_next; 180 INCR(sls_searches) 181 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 182 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 183 && *(int *)th == ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 184 goto found; 185 } while (cs != lastcs); 186 187 /* 188 * Didn't find it -- re-use oldest cstate. Send an 189 * uncompressed packet that tells the other side what 190 * connection number we're using for this conversation. 191 * Note that since the state list is circular, the oldest 192 * state points to the newest and we only need to set 193 * last_cs to update the lru linkage. 194 */ 195 INCR(sls_misses) 196 comp->last_cs = lcs; 197 hlen += th->th_off; 198 hlen <<= 2; 199 goto uncompressed; 200 201 found: 202 /* 203 * Found it -- move to the front on the connection list. 204 */ 205 if (cs == lastcs) 206 comp->last_cs = lcs; 207 else { 208 lcs->cs_next = cs->cs_next; 209 cs->cs_next = lastcs->cs_next; 210 lastcs->cs_next = cs; 211 } 212 } 213 214 /* 215 * Make sure that only what we expect to change changed. The first 216 * line of the `if' checks the IP protocol version, header length & 217 * type of service. The 2nd line checks the "Don't fragment" bit. 218 * The 3rd line checks the time-to-live and protocol (the protocol 219 * check is unnecessary but costless). The 4th line checks the TCP 220 * header length. The 5th line checks IP options, if any. The 6th 221 * line checks TCP options, if any. If any of these things are 222 * different between the previous & current datagram, we send the 223 * current datagram `uncompressed'. 224 */ 225 oth = (struct tcphdr *)&((int *)&cs->cs_ip)[hlen]; 226 deltaS = hlen; 227 hlen += th->th_off; 228 hlen <<= 2; 229 230 if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0] || 231 ((u_short *)ip)[3] != ((u_short *)&cs->cs_ip)[3] || 232 ((u_short *)ip)[4] != ((u_short *)&cs->cs_ip)[4] || 233 th->th_off != oth->th_off || 234 (deltaS > 5 && 235 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 236 (th->th_off > 5 && 237 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 238 goto uncompressed; 239 240 /* 241 * Figure out which of the changing fields changed. The 242 * receiver expects changes in the order: urgent, window, 243 * ack, seq (the order minimizes the number of temporaries 244 * needed in this section of code). 245 */ 246 if (th->th_flags & TH_URG) { 247 deltaS = ntohs(th->th_urp); 248 ENCODEZ(deltaS); 249 changes |= NEW_U; 250 } else if (th->th_urp != oth->th_urp) 251 /* argh! URG not set but urp changed -- a sensible 252 * implementation should never do this but RFC793 253 * doesn't prohibit the change so we have to deal 254 * with it. */ 255 goto uncompressed; 256 257 if (deltaS = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win))) { 258 ENCODE(deltaS); 259 changes |= NEW_W; 260 } 261 262 if (deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack)) { 263 if (deltaA > 0xffff) 264 goto uncompressed; 265 ENCODE(deltaA); 266 changes |= NEW_A; 267 } 268 269 if (deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq)) { 270 if (deltaS > 0xffff) 271 goto uncompressed; 272 ENCODE(deltaS); 273 changes |= NEW_S; 274 } 275 276 switch(changes) { 277 278 case 0: 279 /* 280 * Nothing changed. If this packet contains data and the 281 * last one didn't, this is probably a data packet following 282 * an ack (normal on an interactive connection) and we send 283 * it compressed. Otherwise it's probably a retransmit, 284 * retransmitted ack or window probe. Send it uncompressed 285 * in case the other side missed the compressed version. 286 */ 287 if (ip->ip_len != cs->cs_ip.ip_len && 288 ntohs(cs->cs_ip.ip_len) == hlen) 289 break; 290 291 /* (fall through) */ 292 293 case SPECIAL_I: 294 case SPECIAL_D: 295 /* 296 * actual changes match one of our special case encodings -- 297 * send packet uncompressed. 298 */ 299 goto uncompressed; 300 301 case NEW_S|NEW_A: 302 if (deltaS == deltaA && 303 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 304 /* special case for echoed terminal traffic */ 305 changes = SPECIAL_I; 306 cp = new_seq; 307 } 308 break; 309 310 case NEW_S: 311 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 312 /* special case for data xfer */ 313 changes = SPECIAL_D; 314 cp = new_seq; 315 } 316 break; 317 } 318 319 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 320 if (deltaS != 1) { 321 ENCODEZ(deltaS); 322 changes |= NEW_I; 323 } 324 if (th->th_flags & TH_PUSH) 325 changes |= TCP_PUSH_BIT; 326 /* 327 * Grab the cksum before we overwrite it below. Then update our 328 * state with this packet's header. 329 */ 330 deltaA = ntohs(th->th_sum); 331 BCOPY(ip, &cs->cs_ip, hlen); 332 333 /* 334 * We want to use the original packet as our compressed packet. 335 * (cp - new_seq) is the number of bytes we need for compressed 336 * sequence numbers. In addition we need one byte for the change 337 * mask, one for the connection id and two for the tcp checksum. 338 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 339 * many bytes of the original packet to toss so subtract the two to 340 * get the new packet size. 341 */ 342 deltaS = cp - new_seq; 343 cp = (u_char *)ip; 344 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 345 comp->last_xmit = cs->cs_id; 346 hlen -= deltaS + 4; 347 cp += hlen; 348 *cp++ = changes | NEW_C; 349 *cp++ = cs->cs_id; 350 } else { 351 hlen -= deltaS + 3; 352 cp += hlen; 353 *cp++ = changes; 354 } 355 m->m_len -= hlen; 356 m->m_data += hlen; 357 *cp++ = deltaA >> 8; 358 *cp++ = deltaA; 359 BCOPY(new_seq, cp, deltaS); 360 INCR(sls_compressed) 361 return (TYPE_COMPRESSED_TCP); 362 363 /* 364 * Update connection state cs & send uncompressed packet ('uncompressed' 365 * means a regular ip/tcp packet but with the 'conversation id' we hope 366 * to use on future compressed packets in the protocol field). 367 */ 368 uncompressed: 369 BCOPY(ip, &cs->cs_ip, hlen); 370 ip->ip_p = cs->cs_id; 371 comp->last_xmit = cs->cs_id; 372 return (TYPE_UNCOMPRESSED_TCP); 373 } 374 375 376 int 377 sl_uncompress_tcp(bufp, len, type, comp) 378 u_char **bufp; 379 int len; 380 u_int type; 381 struct slcompress *comp; 382 { 383 register u_char *cp; 384 register u_int hlen, changes; 385 register struct tcphdr *th; 386 register struct cstate *cs; 387 register struct ip *ip; 388 389 switch (type) { 390 391 case TYPE_UNCOMPRESSED_TCP: 392 ip = (struct ip *) *bufp; 393 if (ip->ip_p >= MAX_STATES) 394 goto bad; 395 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 396 comp->flags &=~ SLF_TOSS; 397 ip->ip_p = IPPROTO_TCP; 398 hlen = ip->ip_hl; 399 hlen += ((struct tcphdr *)&((int *)ip)[hlen])->th_off; 400 hlen <<= 2; 401 BCOPY(ip, &cs->cs_ip, hlen); 402 cs->cs_ip.ip_sum = 0; 403 cs->cs_hlen = hlen; 404 INCR(sls_uncompressedin) 405 return (len); 406 407 default: 408 goto bad; 409 410 case TYPE_COMPRESSED_TCP: 411 break; 412 } 413 /* We've got a compressed packet. */ 414 INCR(sls_compressedin) 415 cp = *bufp; 416 changes = *cp++; 417 if (changes & NEW_C) { 418 /* Make sure the state index is in range, then grab the state. 419 * If we have a good state index, clear the 'discard' flag. */ 420 if (*cp >= MAX_STATES) 421 goto bad; 422 423 comp->flags &=~ SLF_TOSS; 424 comp->last_recv = *cp++; 425 } else { 426 /* this packet has an implicit state index. If we've 427 * had a line error since the last time we got an 428 * explicit state index, we have to toss the packet. */ 429 if (comp->flags & SLF_TOSS) { 430 INCR(sls_tossed) 431 return (0); 432 } 433 } 434 cs = &comp->rstate[comp->last_recv]; 435 hlen = cs->cs_ip.ip_hl << 2; 436 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 437 th->th_sum = htons((*cp << 8) | cp[1]); 438 cp += 2; 439 if (changes & TCP_PUSH_BIT) 440 th->th_flags |= TH_PUSH; 441 else 442 th->th_flags &=~ TH_PUSH; 443 444 switch (changes & SPECIALS_MASK) { 445 case SPECIAL_I: 446 { 447 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 448 th->th_ack = htonl(ntohl(th->th_ack) + i); 449 th->th_seq = htonl(ntohl(th->th_seq) + i); 450 } 451 break; 452 453 case SPECIAL_D: 454 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 455 - cs->cs_hlen); 456 break; 457 458 default: 459 if (changes & NEW_U) { 460 th->th_flags |= TH_URG; 461 DECODEU(th->th_urp) 462 } else 463 th->th_flags &=~ TH_URG; 464 if (changes & NEW_W) 465 DECODES(th->th_win) 466 if (changes & NEW_A) 467 DECODEL(th->th_ack) 468 if (changes & NEW_S) 469 DECODEL(th->th_seq) 470 break; 471 } 472 if (changes & NEW_I) { 473 DECODES(cs->cs_ip.ip_id) 474 } else 475 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 476 477 /* 478 * At this point, cp points to the first byte of data in the 479 * packet. If we're not aligned on a 4-byte boundary, copy the 480 * data down so the ip & tcp headers will be aligned. Then back up 481 * cp by the tcp/ip header length to make room for the reconstructed 482 * header (we assume the packet we were handed has enough space to 483 * prepend 128 bytes of header). Adjust the length to account for 484 * the new header & fill in the IP total length. 485 */ 486 len -= (cp - *bufp); 487 if (len < 0) 488 /* we must have dropped some characters (crc should detect 489 * this but the old slip framing won't) */ 490 goto bad; 491 492 if ((int)cp & 3) { 493 if (len > 0) 494 (void) ovbcopy(cp, (caddr_t)((int)cp &~ 3), len); 495 cp = (u_char *)((int)cp &~ 3); 496 } 497 cp -= cs->cs_hlen; 498 len += cs->cs_hlen; 499 cs->cs_ip.ip_len = htons(len); 500 BCOPY(&cs->cs_ip, cp, cs->cs_hlen); 501 *bufp = cp; 502 503 /* recompute the ip header checksum */ 504 { 505 register u_short *bp = (u_short *)cp; 506 for (changes = 0; hlen > 0; hlen -= 2) 507 changes += *bp++; 508 changes = (changes & 0xffff) + (changes >> 16); 509 changes = (changes & 0xffff) + (changes >> 16); 510 ((struct ip *)cp)->ip_sum = ~ changes; 511 } 512 return (len); 513 bad: 514 comp->flags |= SLF_TOSS; 515 INCR(sls_errorin) 516 return (0); 517 } 518