1 /*- 2 * Copyright (c) 1989 The Regents of the University of California. 3 * All rights reserved. 4 * 5 * %sccs.include.redist.c% 6 * 7 * @(#)slcompress.c 7.9 (Berkeley) 06/04/93 8 */ 9 10 /* 11 * Routines to compress and uncompess tcp packets (for transmission 12 * over low speed serial lines. 13 * 14 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989: 15 * - Initial distribution. 16 * 17 * static char rcsid[] = 18 * "$Header: slcompress.c,v 1.19 89/12/31 08:52:59 van Exp $"; 19 */ 20 21 #include <sys/param.h> 22 #include <sys/mbuf.h> 23 24 #include <netinet/in.h> 25 #include <netinet/in_systm.h> 26 #include <netinet/ip.h> 27 #include <netinet/tcp.h> 28 29 #include <net/slcompress.h> 30 31 #ifndef SL_NO_STATS 32 #define INCR(counter) ++comp->counter; 33 #else 34 #define INCR(counter) 35 #endif 36 37 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n)) 38 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n)) 39 #ifndef KERNEL 40 #define ovbcopy bcopy 41 #endif 42 43 void 44 sl_compress_init(comp) 45 struct slcompress *comp; 46 { 47 register u_int i; 48 register struct cstate *tstate = comp->tstate; 49 50 bzero((char *)comp, sizeof(*comp)); 51 for (i = MAX_STATES - 1; i > 0; --i) { 52 tstate[i].cs_id = i; 53 tstate[i].cs_next = &tstate[i - 1]; 54 } 55 tstate[0].cs_next = &tstate[MAX_STATES - 1]; 56 tstate[0].cs_id = 0; 57 comp->last_cs = &tstate[0]; 58 comp->last_recv = 255; 59 comp->last_xmit = 255; 60 } 61 62 63 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ 64 * checks for zero (since zero has to be encoded in the long, 3 byte 65 * form). 66 */ 67 #define ENCODE(n) { \ 68 if ((u_short)(n) >= 256) { \ 69 *cp++ = 0; \ 70 cp[1] = (n); \ 71 cp[0] = (n) >> 8; \ 72 cp += 2; \ 73 } else { \ 74 *cp++ = (n); \ 75 } \ 76 } 77 #define ENCODEZ(n) { \ 78 if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \ 79 *cp++ = 0; \ 80 cp[1] = (n); \ 81 cp[0] = (n) >> 8; \ 82 cp += 2; \ 83 } else { \ 84 *cp++ = (n); \ 85 } \ 86 } 87 88 #define DECODEL(f) { \ 89 if (*cp == 0) {\ 90 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 91 cp += 3; \ 92 } else { \ 93 (f) = htonl(ntohl(f) + (u_long)*cp++); \ 94 } \ 95 } 96 97 #define DECODES(f) { \ 98 if (*cp == 0) {\ 99 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 100 cp += 3; \ 101 } else { \ 102 (f) = htons(ntohs(f) + (u_long)*cp++); \ 103 } \ 104 } 105 106 #define DECODEU(f) { \ 107 if (*cp == 0) {\ 108 (f) = htons((cp[1] << 8) | cp[2]); \ 109 cp += 3; \ 110 } else { \ 111 (f) = htons((u_long)*cp++); \ 112 } \ 113 } 114 115 u_int 116 sl_compress_tcp(m, ip, comp, compress_cid) 117 struct mbuf *m; 118 register struct ip *ip; 119 struct slcompress *comp; 120 int compress_cid; 121 { 122 register struct cstate *cs = comp->last_cs->cs_next; 123 register u_int hlen = ip->ip_hl; 124 register struct tcphdr *oth; 125 register struct tcphdr *th; 126 register u_int deltaS, deltaA; 127 register u_int changes = 0; 128 u_char new_seq[16]; 129 register u_char *cp = new_seq; 130 131 /* 132 * Bail if this is an IP fragment or if the TCP packet isn't 133 * `compressible' (i.e., ACK isn't set or some other control bit is 134 * set). (We assume that the caller has already made sure the 135 * packet is IP proto TCP). 136 */ 137 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 138 return (TYPE_IP); 139 140 th = (struct tcphdr *)&((int *)ip)[hlen]; 141 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 142 return (TYPE_IP); 143 /* 144 * Packet is compressible -- we're going to send either a 145 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 146 * to locate (or create) the connection state. Special case the 147 * most recently used connection since it's most likely to be used 148 * again & we don't have to do any reordering if it's used. 149 */ 150 INCR(sls_packets) 151 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 152 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 153 *(int *)th != ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 154 /* 155 * Wasn't the first -- search for it. 156 * 157 * States are kept in a circularly linked list with 158 * last_cs pointing to the end of the list. The 159 * list is kept in lru order by moving a state to the 160 * head of the list whenever it is referenced. Since 161 * the list is short and, empirically, the connection 162 * we want is almost always near the front, we locate 163 * states via linear search. If we don't find a state 164 * for the datagram, the oldest state is (re-)used. 165 */ 166 register struct cstate *lcs; 167 register struct cstate *lastcs = comp->last_cs; 168 169 do { 170 lcs = cs; cs = cs->cs_next; 171 INCR(sls_searches) 172 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 173 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 174 && *(int *)th == ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 175 goto found; 176 } while (cs != lastcs); 177 178 /* 179 * Didn't find it -- re-use oldest cstate. Send an 180 * uncompressed packet that tells the other side what 181 * connection number we're using for this conversation. 182 * Note that since the state list is circular, the oldest 183 * state points to the newest and we only need to set 184 * last_cs to update the lru linkage. 185 */ 186 INCR(sls_misses) 187 comp->last_cs = lcs; 188 hlen += th->th_off; 189 hlen <<= 2; 190 goto uncompressed; 191 192 found: 193 /* 194 * Found it -- move to the front on the connection list. 195 */ 196 if (cs == lastcs) 197 comp->last_cs = lcs; 198 else { 199 lcs->cs_next = cs->cs_next; 200 cs->cs_next = lastcs->cs_next; 201 lastcs->cs_next = cs; 202 } 203 } 204 205 /* 206 * Make sure that only what we expect to change changed. The first 207 * line of the `if' checks the IP protocol version, header length & 208 * type of service. The 2nd line checks the "Don't fragment" bit. 209 * The 3rd line checks the time-to-live and protocol (the protocol 210 * check is unnecessary but costless). The 4th line checks the TCP 211 * header length. The 5th line checks IP options, if any. The 6th 212 * line checks TCP options, if any. If any of these things are 213 * different between the previous & current datagram, we send the 214 * current datagram `uncompressed'. 215 */ 216 oth = (struct tcphdr *)&((int *)&cs->cs_ip)[hlen]; 217 deltaS = hlen; 218 hlen += th->th_off; 219 hlen <<= 2; 220 221 if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0] || 222 ((u_short *)ip)[3] != ((u_short *)&cs->cs_ip)[3] || 223 ((u_short *)ip)[4] != ((u_short *)&cs->cs_ip)[4] || 224 th->th_off != oth->th_off || 225 (deltaS > 5 && 226 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 227 (th->th_off > 5 && 228 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 229 goto uncompressed; 230 231 /* 232 * Figure out which of the changing fields changed. The 233 * receiver expects changes in the order: urgent, window, 234 * ack, seq (the order minimizes the number of temporaries 235 * needed in this section of code). 236 */ 237 if (th->th_flags & TH_URG) { 238 deltaS = ntohs(th->th_urp); 239 ENCODEZ(deltaS); 240 changes |= NEW_U; 241 } else if (th->th_urp != oth->th_urp) 242 /* argh! URG not set but urp changed -- a sensible 243 * implementation should never do this but RFC793 244 * doesn't prohibit the change so we have to deal 245 * with it. */ 246 goto uncompressed; 247 248 if (deltaS = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win))) { 249 ENCODE(deltaS); 250 changes |= NEW_W; 251 } 252 253 if (deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack)) { 254 if (deltaA > 0xffff) 255 goto uncompressed; 256 ENCODE(deltaA); 257 changes |= NEW_A; 258 } 259 260 if (deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq)) { 261 if (deltaS > 0xffff) 262 goto uncompressed; 263 ENCODE(deltaS); 264 changes |= NEW_S; 265 } 266 267 switch(changes) { 268 269 case 0: 270 /* 271 * Nothing changed. If this packet contains data and the 272 * last one didn't, this is probably a data packet following 273 * an ack (normal on an interactive connection) and we send 274 * it compressed. Otherwise it's probably a retransmit, 275 * retransmitted ack or window probe. Send it uncompressed 276 * in case the other side missed the compressed version. 277 */ 278 if (ip->ip_len != cs->cs_ip.ip_len && 279 ntohs(cs->cs_ip.ip_len) == hlen) 280 break; 281 282 /* (fall through) */ 283 284 case SPECIAL_I: 285 case SPECIAL_D: 286 /* 287 * actual changes match one of our special case encodings -- 288 * send packet uncompressed. 289 */ 290 goto uncompressed; 291 292 case NEW_S|NEW_A: 293 if (deltaS == deltaA && 294 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 295 /* special case for echoed terminal traffic */ 296 changes = SPECIAL_I; 297 cp = new_seq; 298 } 299 break; 300 301 case NEW_S: 302 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 303 /* special case for data xfer */ 304 changes = SPECIAL_D; 305 cp = new_seq; 306 } 307 break; 308 } 309 310 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 311 if (deltaS != 1) { 312 ENCODEZ(deltaS); 313 changes |= NEW_I; 314 } 315 if (th->th_flags & TH_PUSH) 316 changes |= TCP_PUSH_BIT; 317 /* 318 * Grab the cksum before we overwrite it below. Then update our 319 * state with this packet's header. 320 */ 321 deltaA = ntohs(th->th_sum); 322 BCOPY(ip, &cs->cs_ip, hlen); 323 324 /* 325 * We want to use the original packet as our compressed packet. 326 * (cp - new_seq) is the number of bytes we need for compressed 327 * sequence numbers. In addition we need one byte for the change 328 * mask, one for the connection id and two for the tcp checksum. 329 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 330 * many bytes of the original packet to toss so subtract the two to 331 * get the new packet size. 332 */ 333 deltaS = cp - new_seq; 334 cp = (u_char *)ip; 335 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 336 comp->last_xmit = cs->cs_id; 337 hlen -= deltaS + 4; 338 cp += hlen; 339 *cp++ = changes | NEW_C; 340 *cp++ = cs->cs_id; 341 } else { 342 hlen -= deltaS + 3; 343 cp += hlen; 344 *cp++ = changes; 345 } 346 m->m_len -= hlen; 347 m->m_data += hlen; 348 *cp++ = deltaA >> 8; 349 *cp++ = deltaA; 350 BCOPY(new_seq, cp, deltaS); 351 INCR(sls_compressed) 352 return (TYPE_COMPRESSED_TCP); 353 354 /* 355 * Update connection state cs & send uncompressed packet ('uncompressed' 356 * means a regular ip/tcp packet but with the 'conversation id' we hope 357 * to use on future compressed packets in the protocol field). 358 */ 359 uncompressed: 360 BCOPY(ip, &cs->cs_ip, hlen); 361 ip->ip_p = cs->cs_id; 362 comp->last_xmit = cs->cs_id; 363 return (TYPE_UNCOMPRESSED_TCP); 364 } 365 366 367 int 368 sl_uncompress_tcp(bufp, len, type, comp) 369 u_char **bufp; 370 int len; 371 u_int type; 372 struct slcompress *comp; 373 { 374 register u_char *cp; 375 register u_int hlen, changes; 376 register struct tcphdr *th; 377 register struct cstate *cs; 378 register struct ip *ip; 379 380 switch (type) { 381 382 case TYPE_UNCOMPRESSED_TCP: 383 ip = (struct ip *) *bufp; 384 if (ip->ip_p >= MAX_STATES) 385 goto bad; 386 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 387 comp->flags &=~ SLF_TOSS; 388 ip->ip_p = IPPROTO_TCP; 389 hlen = ip->ip_hl; 390 hlen += ((struct tcphdr *)&((int *)ip)[hlen])->th_off; 391 hlen <<= 2; 392 BCOPY(ip, &cs->cs_ip, hlen); 393 cs->cs_ip.ip_sum = 0; 394 cs->cs_hlen = hlen; 395 INCR(sls_uncompressedin) 396 return (len); 397 398 default: 399 goto bad; 400 401 case TYPE_COMPRESSED_TCP: 402 break; 403 } 404 /* We've got a compressed packet. */ 405 INCR(sls_compressedin) 406 cp = *bufp; 407 changes = *cp++; 408 if (changes & NEW_C) { 409 /* Make sure the state index is in range, then grab the state. 410 * If we have a good state index, clear the 'discard' flag. */ 411 if (*cp >= MAX_STATES) 412 goto bad; 413 414 comp->flags &=~ SLF_TOSS; 415 comp->last_recv = *cp++; 416 } else { 417 /* this packet has an implicit state index. If we've 418 * had a line error since the last time we got an 419 * explicit state index, we have to toss the packet. */ 420 if (comp->flags & SLF_TOSS) { 421 INCR(sls_tossed) 422 return (0); 423 } 424 } 425 cs = &comp->rstate[comp->last_recv]; 426 hlen = cs->cs_ip.ip_hl << 2; 427 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 428 th->th_sum = htons((*cp << 8) | cp[1]); 429 cp += 2; 430 if (changes & TCP_PUSH_BIT) 431 th->th_flags |= TH_PUSH; 432 else 433 th->th_flags &=~ TH_PUSH; 434 435 switch (changes & SPECIALS_MASK) { 436 case SPECIAL_I: 437 { 438 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 439 th->th_ack = htonl(ntohl(th->th_ack) + i); 440 th->th_seq = htonl(ntohl(th->th_seq) + i); 441 } 442 break; 443 444 case SPECIAL_D: 445 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 446 - cs->cs_hlen); 447 break; 448 449 default: 450 if (changes & NEW_U) { 451 th->th_flags |= TH_URG; 452 DECODEU(th->th_urp) 453 } else 454 th->th_flags &=~ TH_URG; 455 if (changes & NEW_W) 456 DECODES(th->th_win) 457 if (changes & NEW_A) 458 DECODEL(th->th_ack) 459 if (changes & NEW_S) 460 DECODEL(th->th_seq) 461 break; 462 } 463 if (changes & NEW_I) { 464 DECODES(cs->cs_ip.ip_id) 465 } else 466 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 467 468 /* 469 * At this point, cp points to the first byte of data in the 470 * packet. If we're not aligned on a 4-byte boundary, copy the 471 * data down so the ip & tcp headers will be aligned. Then back up 472 * cp by the tcp/ip header length to make room for the reconstructed 473 * header (we assume the packet we were handed has enough space to 474 * prepend 128 bytes of header). Adjust the length to account for 475 * the new header & fill in the IP total length. 476 */ 477 len -= (cp - *bufp); 478 if (len < 0) 479 /* we must have dropped some characters (crc should detect 480 * this but the old slip framing won't) */ 481 goto bad; 482 483 if ((int)cp & 3) { 484 if (len > 0) 485 (void) ovbcopy(cp, (caddr_t)((int)cp &~ 3), len); 486 cp = (u_char *)((int)cp &~ 3); 487 } 488 cp -= cs->cs_hlen; 489 len += cs->cs_hlen; 490 cs->cs_ip.ip_len = htons(len); 491 BCOPY(&cs->cs_ip, cp, cs->cs_hlen); 492 *bufp = cp; 493 494 /* recompute the ip header checksum */ 495 { 496 register u_short *bp = (u_short *)cp; 497 for (changes = 0; hlen > 0; hlen -= 2) 498 changes += *bp++; 499 changes = (changes & 0xffff) + (changes >> 16); 500 changes = (changes & 0xffff) + (changes >> 16); 501 ((struct ip *)cp)->ip_sum = ~ changes; 502 } 503 return (len); 504 bad: 505 comp->flags |= SLF_TOSS; 506 INCR(sls_errorin) 507 return (0); 508 } 509