netbsd-1.2/ppp-deflate.c

   1 /*      $NetBSD: ppp-deflate.c,v 1.6 1998/05/02 14:34:25 christos Exp $ */
   2 /*      Id: ppp-deflate.c,v 1.5 1997/03/04 03:33:28 paulus Exp  */
   3
   4 /*
   5  * ppp_deflate.c - interface the zlib procedures for Deflate compression
   6  * and decompression (as used by gzip) to the PPP code.
   7  * This version is for use with mbufs on BSD-derived systems.
   8  *
   9  * Copyright (c) 1994 Paul Mackerras. All rights reserved.
  10  *
  11  * Redistribution and use in source and binary forms, with or without
  12  * modification, are permitted provided that the following conditions
  13  * are met:
  14  *
  15  * 1. Redistributions of source code must retain the above copyright
  16  *    notice, this list of conditions and the following disclaimer.
  17  *
  18  * 2. Redistributions in binary form must reproduce the above copyright
  19  *    notice, this list of conditions and the following disclaimer in
  20  *    the documentation and/or other materials provided with the
  21  *    distribution.
  22  *
  23  * 3. The name(s) of the authors of this software must not be used to
  24  *    endorse or promote products derived from this software without
  25  *    prior written permission.
  26  *
  27  * 4. Redistributions of any form whatsoever must retain the following
  28  *    acknowledgment:
  29  *    "This product includes software developed by Paul Mackerras
  30  *     <paulus@samba.org>".
  31  *
  32  * THE AUTHORS OF THIS SOFTWARE DISCLAIM ALL WARRANTIES WITH REGARD TO
  33  * THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
  34  * AND FITNESS, IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
  35  * SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  36  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
  37  * AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
  38  * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  39  */
  40
  41 #include <sys/param.h>
  42 #include <sys/types.h>
  43 #include <sys/systm.h>
  44 #include <sys/mbuf.h>
  45 #include <net/ppp_defs.h>
  46 #include <net/zlib.h>
  47
  48 #define PACKETPTR       struct mbuf *
  49 #include <net/ppp-comp.h>
  50
  51 #if DO_DEFLATE
  52
  53 #define DEFLATE_DEBUG   1
  54
  55 /*
  56  * State for a Deflate (de)compressor.
  57  */
  58 struct deflate_state {
  59     int         seqno;
  60     int         w_size;
  61     int         unit;
  62     int         hdrlen;
  63     int         mru;
  64     int         debug;
  65     z_stream    strm;
  66     struct compstat stats;
  67 };
  68
  69 #define DEFLATE_OVHD    2               /* Deflate overhead/packet */
  70
  71 static void     *zalloc __P((void *, u_int items, u_int size));
  72 static void     zfree __P((void *, void *ptr));
  73 static void     *z_comp_alloc __P((u_char *options, int opt_len));
  74 static void     *z_decomp_alloc __P((u_char *options, int opt_len));
  75 static void     z_comp_free __P((void *state));
  76 static void     z_decomp_free __P((void *state));
  77 static int      z_comp_init __P((void *state, u_char *options, int opt_len,
  78                                  int unit, int hdrlen, int debug));
  79 static int      z_decomp_init __P((void *state, u_char *options, int opt_len,
  80                                      int unit, int hdrlen, int mru, int debug));
  81 static int      z_compress __P((void *state, struct mbuf **mret,
  82                                   struct mbuf *mp, int slen, int maxolen));
  83 static void     z_incomp __P((void *state, struct mbuf *dmsg));
  84 static int      z_decompress __P((void *state, struct mbuf *cmp,
  85                                     struct mbuf **dmpp));
  86 static void     z_comp_reset __P((void *state));
  87 static void     z_decomp_reset __P((void *state));
  88 static void     z_comp_stats __P((void *state, struct compstat *stats));
  89
  90 /*
  91  * Procedures exported to if_ppp.c.
  92  */
  93 struct compressor ppp_deflate = {
  94     CI_DEFLATE,                 /* compress_proto */
  95     z_comp_alloc,               /* comp_alloc */
  96     z_comp_free,                /* comp_free */
  97     z_comp_init,                /* comp_init */
  98     z_comp_reset,               /* comp_reset */
  99     z_compress,                 /* compress */
 100     z_comp_stats,               /* comp_stat */
 101     z_decomp_alloc,             /* decomp_alloc */
 102     z_decomp_free,              /* decomp_free */
 103     z_decomp_init,              /* decomp_init */
 104     z_decomp_reset,             /* decomp_reset */
 105     z_decompress,               /* decompress */
 106     z_incomp,                   /* incomp */
 107     z_comp_stats,               /* decomp_stat */
 108 };
 109
 110 struct compressor ppp_deflate_draft = {
 111     CI_DEFLATE_DRAFT,           /* compress_proto */
 112     z_comp_alloc,               /* comp_alloc */
 113     z_comp_free,                /* comp_free */
 114     z_comp_init,                /* comp_init */
 115     z_comp_reset,               /* comp_reset */
 116     z_compress,                 /* compress */
 117     z_comp_stats,               /* comp_stat */
 118     z_decomp_alloc,             /* decomp_alloc */
 119     z_decomp_free,              /* decomp_free */
 120     z_decomp_init,              /* decomp_init */
 121     z_decomp_reset,             /* decomp_reset */
 122     z_decompress,               /* decompress */
 123     z_incomp,                   /* incomp */
 124     z_comp_stats,               /* decomp_stat */
 125 };
 126 /*
 127  * Space allocation and freeing routines for use by zlib routines.
 128  */
 129 void *
 130 zalloc(notused, items, size)
 131     void *notused;
 132     u_int items, size;
 133 {
 134     void *ptr;
 135
 136     MALLOC(ptr, void *, items * size, M_DEVBUF, M_NOWAIT);
 137     return ptr;
 138 }
 139
 140 void
 141 zfree(notused, ptr)
 142     void *notused;
 143     void *ptr;
 144 {
 145     FREE(ptr, M_DEVBUF);
 146 }
 147
 148 /*
 149  * Allocate space for a compressor.
 150  */
 151 static void *
 152 z_comp_alloc(options, opt_len)
 153     u_char *options;
 154     int opt_len;
 155 {
 156     struct deflate_state *state;
 157     int w_size;
 158
 159     if (opt_len != CILEN_DEFLATE
 160         || (options[0] != CI_DEFLATE && options[0] != CI_DEFLATE_DRAFT)
 161         || options[1] != CILEN_DEFLATE
 162         || DEFLATE_METHOD(options[2]) != DEFLATE_METHOD_VAL
 163         || options[3] != DEFLATE_CHK_SEQUENCE)
 164         return NULL;
 165     w_size = DEFLATE_SIZE(options[2]);
 166     if (w_size < DEFLATE_MIN_SIZE || w_size > DEFLATE_MAX_SIZE)
 167         return NULL;
 168
 169     MALLOC(state, struct deflate_state *, sizeof(struct deflate_state),
 170            M_DEVBUF, M_NOWAIT);
 171     if (state == NULL)
 172         return NULL;
 173
 174     state->strm.next_in = NULL;
 175     state->strm.zalloc = zalloc;
 176     state->strm.zfree = zfree;
 177     if (deflateInit2(&state->strm, Z_DEFAULT_COMPRESSION, DEFLATE_METHOD_VAL,
 178                      -w_size, 8, Z_DEFAULT_STRATEGY) != Z_OK) {
 179         FREE(state, M_DEVBUF);
 180         return NULL;
 181     }
 182
 183     state->w_size = w_size;
 184     bzero(&state->stats, sizeof(state->stats));
 185     return (void *) state;
 186 }
 187
 188 static void
 189 z_comp_free(arg)
 190     void *arg;
 191 {
 192     struct deflate_state *state = (struct deflate_state *) arg;
 193
 194     deflateEnd(&state->strm);
 195     FREE(state, M_DEVBUF);
 196 }
 197
 198 static int
 199 z_comp_init(arg, options, opt_len, unit, hdrlen, debug)
 200     void *arg;
 201     u_char *options;
 202     int opt_len, unit, hdrlen, debug;
 203 {
 204     struct deflate_state *state = (struct deflate_state *) arg;
 205
 206     if (opt_len < CILEN_DEFLATE
 207         || (options[0] != CI_DEFLATE && options[0] != CI_DEFLATE_DRAFT)
 208         || options[1] != CILEN_DEFLATE
 209         || DEFLATE_METHOD(options[2]) != DEFLATE_METHOD_VAL
 210         || DEFLATE_SIZE(options[2]) != state->w_size
 211         || options[3] != DEFLATE_CHK_SEQUENCE)
 212         return 0;
 213
 214     state->seqno = 0;
 215     state->unit = unit;
 216     state->hdrlen = hdrlen;
 217     state->debug = debug;
 218
 219     deflateReset(&state->strm);
 220
 221     return 1;
 222 }
 223
 224 static void
 225 z_comp_reset(arg)
 226     void *arg;
 227 {
 228     struct deflate_state *state = (struct deflate_state *) arg;
 229
 230     state->seqno = 0;
 231     deflateReset(&state->strm);
 232 }
 233
 234 int
 235 z_compress(arg, mret, mp, orig_len, maxolen)
 236     void *arg;
 237     struct mbuf **mret;         /* compressed packet (out) */
 238     struct mbuf *mp;            /* uncompressed packet (in) */
 239     int orig_len, maxolen;
 240 {
 241     struct deflate_state *state = (struct deflate_state *) arg;
 242     u_char *rptr, *wptr;
 243     int proto, olen, wspace, r, flush;
 244     struct mbuf *m;
 245
 246     /*
 247      * Check that the protocol is in the range we handle.
 248      */
 249     rptr = mtod(mp, u_char *);
 250     proto = PPP_PROTOCOL(rptr);
 251     if (proto > 0x3fff || proto == 0xfd || proto == 0xfb) {
 252         *mret = NULL;
 253         return orig_len;
 254     }
 255
 256     /* Allocate one mbuf initially. */
 257     if (maxolen > orig_len)
 258         maxolen = orig_len;
 259     MGET(m, M_DONTWAIT, MT_DATA);
 260     *mret = m;
 261     if (m != NULL) {
 262         m->m_len = 0;
 263         if (maxolen + state->hdrlen > MLEN)
 264             MCLGET(m, M_DONTWAIT);
 265         wspace = M_TRAILINGSPACE(m);
 266         if (state->hdrlen + PPP_HDRLEN + 2 < wspace) {
 267             m->m_data += state->hdrlen;
 268             wspace -= state->hdrlen;
 269         }
 270         wptr = mtod(m, u_char *);
 271
 272         /*
 273          * Copy over the PPP header and store the 2-byte sequence number.
 274          */
 275         wptr[0] = PPP_ADDRESS(rptr);
 276         wptr[1] = PPP_CONTROL(rptr);
 277         wptr[2] = PPP_COMP >> 8;
 278         wptr[3] = PPP_COMP;
 279         wptr += PPP_HDRLEN;
 280         wptr[0] = state->seqno >> 8;
 281         wptr[1] = state->seqno;
 282         wptr += 2;
 283         state->strm.next_out = wptr;
 284         state->strm.avail_out = wspace - (PPP_HDRLEN + 2);
 285     } else {
 286         state->strm.next_out = NULL;
 287         state->strm.avail_out = 1000000;
 288         wptr = NULL;
 289         wspace = 0;
 290     }
 291     ++state->seqno;
 292
 293     rptr += (proto > 0xff)? 2: 3;       /* skip 1st proto byte if 0 */
 294     state->strm.next_in = rptr;
 295     state->strm.avail_in = mtod(mp, u_char *) + mp->m_len - rptr;
 296     mp = mp->m_next;
 297     flush = (mp == NULL)? Z_PACKET_FLUSH: Z_NO_FLUSH;
 298     olen = 0;
 299     for (;;) {
 300         r = deflate(&state->strm, flush);
 301         if (r != Z_OK) {
 302             printf("z_compress: deflate returned %d (%s)\n",
 303                    r, (state->strm.msg? state->strm.msg: ""));
 304             break;
 305         }
 306         if (flush != Z_NO_FLUSH && state->strm.avail_out != 0)
 307             break;              /* all done */
 308         if (state->strm.avail_in == 0 && mp != NULL) {
 309             state->strm.next_in = mtod(mp, u_char *);
 310             state->strm.avail_in = mp->m_len;
 311             mp = mp->m_next;
 312             if (mp == NULL)
 313                 flush = Z_PACKET_FLUSH;
 314         }
 315         if (state->strm.avail_out == 0) {
 316             if (m != NULL) {
 317                 m->m_len = wspace;
 318                 olen += wspace;
 319                 MGET(m->m_next, M_DONTWAIT, MT_DATA);
 320                 m = m->m_next;
 321                 if (m != NULL) {
 322                     m->m_len = 0;
 323                     if (maxolen - olen > MLEN)
 324                         MCLGET(m, M_DONTWAIT);
 325                     state->strm.next_out = mtod(m, u_char *);
 326                     state->strm.avail_out = wspace = M_TRAILINGSPACE(m);
 327                 }
 328             }
 329             if (m == NULL) {
 330                 state->strm.next_out = NULL;
 331                 state->strm.avail_out = 1000000;
 332             }
 333         }
 334     }
 335     if (m != NULL)
 336         olen += (m->m_len = wspace - state->strm.avail_out);
 337
 338     /*
 339      * See if we managed to reduce the size of the packet.
 340      */
 341     if (m != NULL && olen < orig_len) {
 342         state->stats.comp_bytes += olen;
 343         state->stats.comp_packets++;
 344     } else {
 345         if (*mret != NULL) {
 346             m_freem(*mret);
 347             *mret = NULL;
 348         }
 349         state->stats.inc_bytes += orig_len;
 350         state->stats.inc_packets++;
 351         olen = orig_len;
 352     }
 353     state->stats.unc_bytes += orig_len;
 354     state->stats.unc_packets++;
 355
 356     return olen;
 357 }
 358
 359 static void
 360 z_comp_stats(arg, stats)
 361     void *arg;
 362     struct compstat *stats;
 363 {
 364     struct deflate_state *state = (struct deflate_state *) arg;
 365     u_int out;
 366
 367     *stats = state->stats;
 368     stats->ratio = stats->unc_bytes;
 369     out = stats->comp_bytes + stats->inc_bytes;
 370     if (stats->ratio <= 0x7ffffff)
 371         stats->ratio <<= 8;
 372     else
 373         out >>= 8;
 374     if (out != 0)
 375         stats->ratio /= out;
 376 }
 377
 378 /*
 379  * Allocate space for a decompressor.
 380  */
 381 static void *
 382 z_decomp_alloc(options, opt_len)
 383     u_char *options;
 384     int opt_len;
 385 {
 386     struct deflate_state *state;
 387     int w_size;
 388
 389     if (opt_len != CILEN_DEFLATE
 390         || (options[0] != CI_DEFLATE && options[0] != CI_DEFLATE_DRAFT)
 391         || options[1] != CILEN_DEFLATE
 392         || DEFLATE_METHOD(options[2]) != DEFLATE_METHOD_VAL
 393         || options[3] != DEFLATE_CHK_SEQUENCE)
 394         return NULL;
 395     w_size = DEFLATE_SIZE(options[2]);
 396     if (w_size < DEFLATE_MIN_SIZE || w_size > DEFLATE_MAX_SIZE)
 397         return NULL;
 398
 399     MALLOC(state, struct deflate_state *, sizeof(struct deflate_state),
 400            M_DEVBUF, M_NOWAIT);
 401     if (state == NULL)
 402         return NULL;
 403
 404     state->strm.next_out = NULL;
 405     state->strm.zalloc = zalloc;
 406     state->strm.zfree = zfree;
 407     if (inflateInit2(&state->strm, -w_size) != Z_OK) {
 408         FREE(state, M_DEVBUF);
 409         return NULL;
 410     }
 411
 412     state->w_size = w_size;
 413     bzero(&state->stats, sizeof(state->stats));
 414     return (void *) state;
 415 }
 416
 417 static void
 418 z_decomp_free(arg)
 419     void *arg;
 420 {
 421     struct deflate_state *state = (struct deflate_state *) arg;
 422
 423     inflateEnd(&state->strm);
 424     FREE(state, M_DEVBUF);
 425 }
 426
 427 static int
 428 z_decomp_init(arg, options, opt_len, unit, hdrlen, mru, debug)
 429     void *arg;
 430     u_char *options;
 431     int opt_len, unit, hdrlen, mru, debug;
 432 {
 433     struct deflate_state *state = (struct deflate_state *) arg;
 434
 435     if (opt_len < CILEN_DEFLATE
 436         || (options[0] != CI_DEFLATE && options[0] != CI_DEFLATE_DRAFT)
 437         || options[1] != CILEN_DEFLATE
 438         || DEFLATE_METHOD(options[2]) != DEFLATE_METHOD_VAL
 439         || DEFLATE_SIZE(options[2]) != state->w_size
 440         || options[3] != DEFLATE_CHK_SEQUENCE)
 441         return 0;
 442
 443     state->seqno = 0;
 444     state->unit = unit;
 445     state->hdrlen = hdrlen;
 446     state->debug = debug;
 447     state->mru = mru;
 448
 449     inflateReset(&state->strm);
 450
 451     return 1;
 452 }
 453
 454 static void
 455 z_decomp_reset(arg)
 456     void *arg;
 457 {
 458     struct deflate_state *state = (struct deflate_state *) arg;
 459
 460     state->seqno = 0;
 461     inflateReset(&state->strm);
 462 }
 463
 464 /*
 465  * Decompress a Deflate-compressed packet.
 466  *
 467  * Because of patent problems, we return DECOMP_ERROR for errors
 468  * found by inspecting the input data and for system problems, but
 469  * DECOMP_FATALERROR for any errors which could possibly be said to
 470  * be being detected "after" decompression.  For DECOMP_ERROR,
 471  * we can issue a CCP reset-request; for DECOMP_FATALERROR, we may be
 472  * infringing a patent of Motorola's if we do, so we take CCP down
 473  * instead.
 474  *
 475  * Given that the frame has the correct sequence number and a good FCS,
 476  * errors such as invalid codes in the input most likely indicate a
 477  * bug, so we return DECOMP_FATALERROR for them in order to turn off
 478  * compression, even though they are detected by inspecting the input.
 479  */
 480 int
 481 z_decompress(arg, mi, mop)
 482     void *arg;
 483     struct mbuf *mi, **mop;
 484 {
 485     struct deflate_state *state = (struct deflate_state *) arg;
 486     struct mbuf *mo, *mo_head;
 487     u_char *rptr, *wptr;
 488     int rlen, olen, ospace;
 489     int seq, i, flush, r, decode_proto;
 490     u_char hdr[PPP_HDRLEN + DEFLATE_OVHD];
 491
 492     *mop = NULL;
 493     rptr = mtod(mi, u_char *);
 494     rlen = mi->m_len;
 495     for (i = 0; i < PPP_HDRLEN + DEFLATE_OVHD; ++i) {
 496         while (rlen <= 0) {
 497             mi = mi->m_next;
 498             if (mi == NULL)
 499                 return DECOMP_ERROR;
 500             rptr = mtod(mi, u_char *);
 501             rlen = mi->m_len;
 502         }
 503         hdr[i] = *rptr++;
 504         --rlen;
 505     }
 506
 507     /* Check the sequence number. */
 508     seq = (hdr[PPP_HDRLEN] << 8) + hdr[PPP_HDRLEN+1];
 509     if (seq != state->seqno) {
 510         if (state->debug)
 511             printf("z_decompress%d: bad seq # %d, expected %d\n",
 512                    state->unit, seq, state->seqno);
 513         return DECOMP_ERROR;
 514     }
 515     ++state->seqno;
 516
 517     /* Allocate an output mbuf. */
 518     MGETHDR(mo, M_DONTWAIT, MT_DATA);
 519     if (mo == NULL)
 520         return DECOMP_ERROR;
 521     mo_head = mo;
 522     mo->m_len = 0;
 523     mo->m_next = NULL;
 524     MCLGET(mo, M_DONTWAIT);
 525     ospace = M_TRAILINGSPACE(mo);
 526     if (state->hdrlen + PPP_HDRLEN < ospace) {
 527         mo->m_data += state->hdrlen;
 528         ospace -= state->hdrlen;
 529     }
 530
 531     /*
 532      * Fill in the first part of the PPP header.  The protocol field
 533      * comes from the decompressed data.
 534      */
 535     wptr = mtod(mo, u_char *);
 536     wptr[0] = PPP_ADDRESS(hdr);
 537     wptr[1] = PPP_CONTROL(hdr);
 538     wptr[2] = 0;
 539
 540     /*
 541      * Set up to call inflate.  We set avail_out to 1 initially so we can
 542      * look at the first byte of the output and decide whether we have
 543      * a 1-byte or 2-byte protocol field.
 544      */
 545     state->strm.next_in = rptr;
 546     state->strm.avail_in = rlen;
 547     mi = mi->m_next;
 548     flush = (mi == NULL)? Z_PACKET_FLUSH: Z_NO_FLUSH;
 549     rlen += PPP_HDRLEN + DEFLATE_OVHD;
 550     state->strm.next_out = wptr + 3;
 551     state->strm.avail_out = 1;
 552     decode_proto = 1;
 553     olen = PPP_HDRLEN;
 554
 555     /*
 556      * Call inflate, supplying more input or output as needed.
 557      */
 558     for (;;) {
 559         r = inflate(&state->strm, flush);
 560         if (r != Z_OK) {
 561 #if !DEFLATE_DEBUG
 562             if (state->debug)
 563 #endif
 564                 printf("z_decompress%d: inflate returned %d (%s)\n",
 565                        state->unit, r, (state->strm.msg? state->strm.msg: ""));
 566             m_freem(mo_head);
 567             return DECOMP_FATALERROR;
 568         }
 569         if (flush != Z_NO_FLUSH && state->strm.avail_out != 0)
 570             break;              /* all done */
 571         if (state->strm.avail_in == 0 && mi != NULL) {
 572             state->strm.next_in = mtod(mi, u_char *);
 573             state->strm.avail_in = mi->m_len;
 574             rlen += mi->m_len;
 575             mi = mi->m_next;
 576             if (mi == NULL)
 577                 flush = Z_PACKET_FLUSH;
 578         }
 579         if (state->strm.avail_out == 0) {
 580             if (decode_proto) {
 581                 state->strm.avail_out = ospace - PPP_HDRLEN;
 582                 if ((wptr[3] & 1) == 0) {
 583                     /* 2-byte protocol field */
 584                     wptr[2] = wptr[3];
 585                     --state->strm.next_out;
 586                     ++state->strm.avail_out;
 587                     --olen;
 588                 }
 589                 decode_proto = 0;
 590             } else {
 591                 mo->m_len = ospace;
 592                 olen += ospace;
 593                 MGET(mo->m_next, M_DONTWAIT, MT_DATA);
 594                 mo = mo->m_next;
 595                 if (mo == NULL) {
 596                     m_freem(mo_head);
 597                     return DECOMP_ERROR;
 598                 }
 599                 MCLGET(mo, M_DONTWAIT);
 600                 state->strm.next_out = mtod(mo, u_char *);
 601                 state->strm.avail_out = ospace = M_TRAILINGSPACE(mo);
 602             }
 603         }
 604     }
 605     if (decode_proto) {
 606         m_freem(mo_head);
 607         return DECOMP_ERROR;
 608     }
 609     olen += (mo->m_len = ospace - state->strm.avail_out);
 610 #if DEFLATE_DEBUG
 611     if (olen > state->mru + PPP_HDRLEN)
 612         printf("ppp_deflate%d: exceeded mru (%d > %d)\n",
 613                state->unit, olen, state->mru + PPP_HDRLEN);
 614 #endif
 615
 616     state->stats.unc_bytes += olen;
 617     state->stats.unc_packets++;
 618     state->stats.comp_bytes += rlen;
 619     state->stats.comp_packets++;
 620
 621     *mop = mo_head;
 622     return DECOMP_OK;
 623 }
 624
 625 /*
 626  * Incompressible data has arrived - add it to the history.
 627  */
 628 static void
 629 z_incomp(arg, mi)
 630     void *arg;
 631     struct mbuf *mi;
 632 {
 633     struct deflate_state *state = (struct deflate_state *) arg;
 634     u_char *rptr;
 635     int rlen, proto, r;
 636
 637     /*
 638      * Check that the protocol is one we handle.
 639      */
 640     rptr = mtod(mi, u_char *);
 641     proto = PPP_PROTOCOL(rptr);
 642     if (proto > 0x3fff || proto == 0xfd || proto == 0xfb)
 643         return;
 644
 645     ++state->seqno;
 646
 647     /*
 648      * Iterate through the mbufs, adding the characters in them
 649      * to the decompressor's history.  For the first mbuf, we start
 650      * at the either the 1st or 2nd byte of the protocol field,
 651      * depending on whether the protocol value is compressible.
 652      */
 653     rlen = mi->m_len;
 654     state->strm.next_in = rptr + 3;
 655     state->strm.avail_in = rlen - 3;
 656     if (proto > 0xff) {
 657         --state->strm.next_in;
 658         ++state->strm.avail_in;
 659     }
 660     for (;;) {
 661         r = inflateIncomp(&state->strm);
 662         if (r != Z_OK) {
 663             /* gak! */
 664 #if !DEFLATE_DEBUG
 665             if (state->debug)
 666 #endif
 667                 printf("z_incomp%d: inflateIncomp returned %d (%s)\n",
 668                        state->unit, r, (state->strm.msg? state->strm.msg: ""));
 669             return;
 670         }
 671         mi = mi->m_next;
 672         if (mi == NULL)
 673             break;
 674         state->strm.next_in = mtod(mi, u_char *);
 675         state->strm.avail_in = mi->m_len;
 676         rlen += mi->m_len;
 677     }
 678
 679     /*
 680      * Update stats.
 681      */
 682     state->stats.inc_bytes += rlen;
 683     state->stats.inc_packets++;
 684     state->stats.unc_bytes += rlen;
 685     state->stats.unc_packets++;
 686 }
 687
 688 #endif /* DO_DEFLATE */