The Tcpdump Group git mirrors - libpcap/blob - savefile.c

   1 /*
   2  * Copyright (c) 1993, 1994, 1995, 1996, 1997
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that: (1) source code distributions
   7  * retain the above copyright notice and this paragraph in its entirety, (2)
   8  * distributions including binary code include the above copyright notice and
   9  * this paragraph in its entirety in the documentation or other materials
  10  * provided with the distribution, and (3) all advertising materials mentioning
  11  * features or use of this software display the following acknowledgement:
  12  * ``This product includes software developed by the University of California,
  13  * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
  14  * the University nor the names of its contributors may be used to endorse
  15  * or promote products derived from this software without specific prior
  16  * written permission.
  17  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
  18  * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
  19  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  20  *
  21  * savefile.c - supports offline use of tcpdump
  22  *      Extraction/creation by Jeffrey Mogul, DECWRL
  23  *      Modified by Steve McCanne, LBL.
  24  *
  25  * Used to save the received packet headers, after filtering, to
  26  * a file, and then read them later.
  27  * The first record in the file contains saved values for the machine
  28  * dependent values so we can print the dump file on any architecture.
  29  */
  30
  31 #ifdef HAVE_CONFIG_H
  32 #include <config.h>
  33 #endif
  34
  35 #include <pcap-types.h>
  36 #ifdef _WIN32
  37 #include <io.h>
  38 #include <fcntl.h>
  39 #endif /* _WIN32 */
  40
  41 #include <errno.h>
  42 #include <memory.h>
  43 #include <stdio.h>
  44 #include <stdlib.h>
  45 #include <string.h>
  46 #include <limits.h> /* for INT_MAX */
  47
  48 #include "pcap-int.h"
  49
  50 #ifdef HAVE_OS_PROTO_H
  51 #include "os-proto.h"
  52 #endif
  53
  54 #include "sf-pcap.h"
  55 #include "sf-pcapng.h"
  56 #include "pcap-common.h"
  57 #include "charconv.h"
  58
  59 #ifdef _WIN32
  60 /*
  61  * This isn't exported on Windows, because it would only work if both
  62  * WinPcap/Npcap and the code using it were to use the Universal CRT; otherwise,
  63  * a FILE structure in WinPcap/Npcap and a FILE structure in the code using it
  64  * could be different if they're using different versions of the C runtime.
  65  *
  66  * Instead, pcap/pcap.h defines it as a macro that wraps the hopen version,
  67  * with the wrapper calling _fileno() and _get_osfhandle() themselves,
  68  * so that it convert the appropriate CRT version's FILE structure to
  69  * a HANDLE (which is OS-defined, not CRT-defined, and is part of the Win32
  70  * and Win64 ABIs).
  71  */
  72 static pcap_t *pcap_fopen_offline_with_tstamp_precision(FILE *, u_int, char *);
  73 #endif
  74
  75 /*
  76  * Setting O_BINARY on DOS/Windows is a bit tricky
  77  */
  78 #if defined(_WIN32)
  79   #define SET_BINMODE(f)  _setmode(_fileno(f), _O_BINARY)
  80 #elif defined(MSDOS)
  81   #if defined(__HIGHC__)
  82   #define SET_BINMODE(f)  setmode(f, O_BINARY)
  83   #else
  84   #define SET_BINMODE(f)  setmode(fileno(f), O_BINARY)
  85   #endif
  86 #endif
  87
  88 static int
  89 sf_getnonblock(pcap_t *p _U_)
  90 {
  91         /*
  92          * This is a savefile, not a live capture file, so never say
  93          * it's in non-blocking mode.
  94          */
  95         return (0);
  96 }
  97
  98 static int
  99 sf_setnonblock(pcap_t *p, int nonblock _U_)
 100 {
 101         /*
 102          * This is a savefile, not a live capture file, so reject
 103          * requests to put it in non-blocking mode.  (If it's a
 104          * pipe, it could be put in non-blocking mode, but that
 105          * would significantly complicate the code to read packets,
 106          * as it would have to handle reading partial packets and
 107          * keeping the state of the read.)
 108          */
 109         snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 110             "Savefiles cannot be put into non-blocking mode");
 111         return (-1);
 112 }
 113
 114 static int
 115 sf_cant_set_rfmon(pcap_t *p _U_)
 116 {
 117         /*
 118          * This is a savefile, not a device on which you can capture,
 119          * so never say it supports being put into monitor mode.
 120          */
 121         return (0);
 122 }
 123
 124 static int
 125 sf_stats(pcap_t *p, struct pcap_stat *ps _U_)
 126 {
 127         snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 128             "Statistics aren't available from savefiles");
 129         return (-1);
 130 }
 131
 132 #ifdef _WIN32
 133 static struct pcap_stat *
 134 sf_stats_ex(pcap_t *p, int *size _U_)
 135 {
 136         snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 137             "Statistics aren't available from savefiles");
 138         return (NULL);
 139 }
 140
 141 static int
 142 sf_setbuff(pcap_t *p, int dim _U_)
 143 {
 144         snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 145             "The kernel buffer size cannot be set while reading from a file");
 146         return (-1);
 147 }
 148
 149 static int
 150 sf_setmode(pcap_t *p, int mode _U_)
 151 {
 152         snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 153             "impossible to set mode while reading from a file");
 154         return (-1);
 155 }
 156
 157 static int
 158 sf_setmintocopy(pcap_t *p, int size _U_)
 159 {
 160         snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 161             "The mintocopy parameter cannot be set while reading from a file");
 162         return (-1);
 163 }
 164
 165 static HANDLE
 166 sf_getevent(pcap_t *pcap)
 167 {
 168         (void)snprintf(pcap->errbuf, sizeof(pcap->errbuf),
 169             "The read event cannot be retrieved while reading from a file");
 170         return (INVALID_HANDLE_VALUE);
 171 }
 172
 173 static int
 174 sf_oid_get_request(pcap_t *p, bpf_u_int32 oid _U_, void *data _U_,
 175     size_t *lenp _U_)
 176 {
 177         snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 178             "An OID get request cannot be performed on a file");
 179         return (PCAP_ERROR);
 180 }
 181
 182 static int
 183 sf_oid_set_request(pcap_t *p, bpf_u_int32 oid _U_, const void *data _U_,
 184     size_t *lenp _U_)
 185 {
 186         snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 187             "An OID set request cannot be performed on a file");
 188         return (PCAP_ERROR);
 189 }
 190
 191 static u_int
 192 sf_sendqueue_transmit(pcap_t *p, pcap_send_queue *queue _U_, int sync _U_)
 193 {
 194         pcap_strlcpy(p->errbuf, "Sending packets isn't supported on savefiles",
 195             PCAP_ERRBUF_SIZE);
 196         return (0);
 197 }
 198
 199 static int
 200 sf_setuserbuffer(pcap_t *p, int size _U_)
 201 {
 202         snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 203             "The user buffer cannot be set when reading from a file");
 204         return (-1);
 205 }
 206
 207 static int
 208 sf_live_dump(pcap_t *p, char *filename _U_, int maxsize _U_, int maxpacks _U_)
 209 {
 210         snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 211             "Live packet dumping cannot be performed when reading from a file");
 212         return (-1);
 213 }
 214
 215 static int
 216 sf_live_dump_ended(pcap_t *p, int sync _U_)
 217 {
 218         snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 219             "Live packet dumping cannot be performed on a pcap_open_dead pcap_t");
 220         return (-1);
 221 }
 222
 223 static PAirpcapHandle
 224 sf_get_airpcap_handle(pcap_t *pcap _U_)
 225 {
 226         return (NULL);
 227 }
 228 #endif
 229
 230 static int
 231 sf_inject(pcap_t *p, const void *buf _U_, int size _U_)
 232 {
 233         pcap_strlcpy(p->errbuf, "Sending packets isn't supported on savefiles",
 234             PCAP_ERRBUF_SIZE);
 235         return (-1);
 236 }
 237
 238 /*
 239  * Set direction flag: Which packets do we accept on a forwarding
 240  * single device? IN, OUT or both?
 241  */
 242 static int
 243 sf_setdirection(pcap_t *p, pcap_direction_t d _U_)
 244 {
 245         snprintf(p->errbuf, sizeof(p->errbuf),
 246             "Setting direction is not supported on savefiles");
 247         return (-1);
 248 }
 249
 250 void
 251 sf_cleanup(pcap_t *p)
 252 {
 253         if (p->rfile != stdin)
 254                 (void)fclose(p->rfile);
 255         if (p->buffer != NULL)
 256                 free(p->buffer);
 257         pcap_freecode(&p->fcode);
 258 }
 259
 260 #ifdef _WIN32
 261 /*
 262  * Wrapper for fopen() and _wfopen().
 263  *
 264  * If we're in UTF-8 mode, map the pathname from UTF-8 to UTF-16LE and
 265  * call _wfopen().
 266  *
 267  * If we're not, just use fopen(); that'll treat it as being in the
 268  * local code page.
 269  */
 270 FILE *
 271 charset_fopen(const char *path, const char *mode)
 272 {
 273         wchar_t *utf16_path;
 274 #define MAX_MODE_LEN    16
 275         wchar_t utf16_mode[MAX_MODE_LEN+1];
 276         int i;
 277         char c;
 278         FILE *fp;
 279         int save_errno;
 280
 281         if (pcap_utf_8_mode) {
 282                 /*
 283                  * Map from UTF-8 to UTF-16LE.
 284                  * Fail if there are invalid characters in the input
 285                  * string, rather than converting them to REPLACEMENT
 286                  * CHARACTER; the latter is appropriate for strings
 287                  * to be displayed to the user, but for file names
 288                  * you just want the attempt to open the file to fail.
 289                  */
 290                 utf16_path = cp_to_utf_16le(CP_UTF8, path,
 291                     MB_ERR_INVALID_CHARS);
 292                 if (utf16_path == NULL) {
 293                         /*
 294                          * Error.  Assume errno has been set.
 295                          *
 296                          * XXX - what about Windows errors?
 297                          */
 298                         return (NULL);
 299                 }
 300
 301                 /*
 302                  * Now convert the mode to UTF-16LE as well.
 303                  * We assume the mode is ASCII, and that
 304                  * it's short, so that's easy.
 305                  */
 306                 for (i = 0; (c = *mode) != '\0'; i++, mode++) {
 307                         if (c > 0x7F) {
 308                                 /* Not an ASCII character; fail with EINVAL. */
 309                                 free(utf16_path);
 310                                 errno = EINVAL;
 311                                 return (NULL);
 312                         }
 313                         if (i >= MAX_MODE_LEN) {
 314                                 /* The mode string is longer than we allow. */
 315                                 free(utf16_path);
 316                                 errno = EINVAL;
 317                                 return (NULL);
 318                         }
 319                         utf16_mode[i] = c;
 320                 }
 321                 utf16_mode[i] = '\0';
 322
 323                 /*
 324                  * OK, we have UTF-16LE strings; hand them to
 325                  * _wfopen().
 326                  */
 327                 fp = _wfopen(utf16_path, utf16_mode);
 328
 329                 /*
 330                  * Make sure freeing the UTF-16LE string doesn't
 331                  * overwrite the error code we got from _wfopen().
 332                  */
 333                 save_errno = errno;
 334                 free(utf16_path);
 335                 errno = save_errno;
 336
 337                 return (fp);
 338         } else {
 339                 /*
 340                  * This takes strings in the local code page as an
 341                  * argument.
 342                  */
 343                 return (fopen(path, mode));
 344         }
 345 }
 346 #endif
 347
 348 pcap_t *
 349 pcap_open_offline_with_tstamp_precision(const char *fname, u_int precision,
 350                                         char *errbuf)
 351 {
 352         FILE *fp;
 353         pcap_t *p;
 354
 355         if (fname == NULL) {
 356                 snprintf(errbuf, PCAP_ERRBUF_SIZE,
 357                     "A null pointer was supplied as the file name");
 358                 return (NULL);
 359         }
 360         if (fname[0] == '-' && fname[1] == '\0')
 361         {
 362                 fp = stdin;
 363                 if (fp == NULL) {
 364                         snprintf(errbuf, PCAP_ERRBUF_SIZE,
 365                             "The standard input is not open");
 366                         return (NULL);
 367                 }
 368 #if defined(_WIN32) || defined(MSDOS)
 369                 /*
 370                  * We're reading from the standard input, so put it in binary
 371                  * mode, as savefiles are binary files.
 372                  */
 373                 SET_BINMODE(fp);
 374 #endif
 375         }
 376         else {
 377                 /*
 378                  * Use charset_fopen(); on Windows, it tests whether we're
 379                  * in "local code page" or "UTF-8" mode, and treats the
 380                  * pathname appropriately, and on other platforms, it just
 381                  * wraps fopen().
 382                  *
 383                  * "b" is supported as of C90, so *all* UN*Xes should
 384                  * support it, even though it does nothing.  For MS-DOS,
 385                  * we again need it.
 386                  */
 387                 fp = charset_fopen(fname, "rb");
 388                 if (fp == NULL) {
 389                         pcap_fmt_errmsg_for_errno(errbuf, PCAP_ERRBUF_SIZE,
 390                             errno, "%s", fname);
 391                         return (NULL);
 392                 }
 393         }
 394         p = pcap_fopen_offline_with_tstamp_precision(fp, precision, errbuf);
 395         if (p == NULL) {
 396                 if (fp != stdin)
 397                         fclose(fp);
 398         }
 399         return (p);
 400 }
 401
 402 pcap_t *
 403 pcap_open_offline(const char *fname, char *errbuf)
 404 {
 405         return (pcap_open_offline_with_tstamp_precision(fname,
 406             PCAP_TSTAMP_PRECISION_MICRO, errbuf));
 407 }
 408
 409 #ifdef _WIN32
 410 pcap_t* pcap_hopen_offline_with_tstamp_precision(intptr_t osfd, u_int precision,
 411     char *errbuf)
 412 {
 413         int fd;
 414         FILE *file;
 415
 416         fd = _open_osfhandle(osfd, _O_RDONLY);
 417         if ( fd < 0 )
 418         {
 419                 pcap_fmt_errmsg_for_errno(errbuf, PCAP_ERRBUF_SIZE,
 420                     errno, "_open_osfhandle");
 421                 return NULL;
 422         }
 423
 424         file = _fdopen(fd, "rb");
 425         if ( file == NULL )
 426         {
 427                 pcap_fmt_errmsg_for_errno(errbuf, PCAP_ERRBUF_SIZE,
 428                     errno, "_fdopen");
 429                 _close(fd);
 430                 return NULL;
 431         }
 432
 433         return pcap_fopen_offline_with_tstamp_precision(file, precision,
 434             errbuf);
 435 }
 436
 437 pcap_t* pcap_hopen_offline(intptr_t osfd, char *errbuf)
 438 {
 439         return pcap_hopen_offline_with_tstamp_precision(osfd,
 440             PCAP_TSTAMP_PRECISION_MICRO, errbuf);
 441 }
 442 #endif
 443
 444 /*
 445  * Given a link-layer header type and snapshot length, return a
 446  * snapshot length to use when reading the file; it's guaranteed
 447  * to be > 0 and <= INT_MAX.
 448  *
 449  * XXX - the only reason why we limit it to <= INT_MAX is so that
 450  * it fits in p->snapshot, and the only reason that p->snapshot is
 451  * signed is that pcap_snapshot() returns an int, not an unsigned int.
 452  */
 453 bpf_u_int32
 454 pcap_adjust_snapshot(bpf_u_int32 linktype, bpf_u_int32 snaplen)
 455 {
 456         if (snaplen == 0 || snaplen > INT_MAX) {
 457                 /*
 458                  * Bogus snapshot length; use the maximum for this
 459                  * link-layer type as a fallback.
 460                  *
 461                  * XXX - we don't clamp snapshot lengths that are
 462                  * <= INT_MAX but > max_snaplen_for_dlt(linktype),
 463                  * so a capture file could cause us to allocate
 464                  * a Really Big Buffer.
 465                  */
 466                 snaplen = max_snaplen_for_dlt(linktype);
 467         }
 468         return snaplen;
 469 }
 470
 471 static pcap_t *(*check_headers[])(const uint8_t *, FILE *, u_int, char *, int *) = {
 472         pcap_check_header,
 473         pcap_ng_check_header
 474 };
 475
 476 #define N_FILE_TYPES    (sizeof check_headers / sizeof check_headers[0])
 477
 478 #ifdef _WIN32
 479 static
 480 #endif
 481 pcap_t *
 482 pcap_fopen_offline_with_tstamp_precision(FILE *fp, u_int precision,
 483     char *errbuf)
 484 {
 485         register pcap_t *p;
 486         uint8_t magic[4];
 487         size_t amt_read;
 488         u_int i;
 489         int err;
 490
 491         /*
 492          * Fail if we were passed a NULL fp.
 493          *
 494          * That shouldn't happen if we're opening with a path name, but
 495          * it could happen if buggy code is opening with a FILE * and
 496          * didn't bother to make sure the FILE * isn't null.
 497          */
 498         if (fp == NULL) {
 499                 snprintf(errbuf, PCAP_ERRBUF_SIZE,
 500                     "Null FILE * pointer provided to savefile open routine");
 501                 return (NULL);
 502         }
 503
 504         /*
 505          * Read the first 4 bytes of the file; the network analyzer dump
 506          * file formats we support (pcap and pcapng), and several other
 507          * formats we might support in the future (such as snoop, DOS and
 508          * Windows Sniffer, and Microsoft Network Monitor) all have magic
 509          * numbers that are unique in their first 4 bytes.
 510          */
 511         amt_read = fread(&magic, 1, sizeof(magic), fp);
 512         if (amt_read != sizeof(magic)) {
 513                 if (ferror(fp)) {
 514                         pcap_fmt_errmsg_for_errno(errbuf, PCAP_ERRBUF_SIZE,
 515                             errno, "error reading dump file");
 516                 } else {
 517                         snprintf(errbuf, PCAP_ERRBUF_SIZE,
 518                             "truncated dump file; tried to read %zu file header bytes, only got %zu",
 519                             sizeof(magic), amt_read);
 520                 }
 521                 return (NULL);
 522         }
 523
 524         /*
 525          * Try all file types.
 526          */
 527         for (i = 0; i < N_FILE_TYPES; i++) {
 528                 p = (*check_headers[i])(magic, fp, precision, errbuf, &err);
 529                 if (p != NULL) {
 530                         /* Yup, that's it. */
 531                         goto found;
 532                 }
 533                 if (err) {
 534                         /*
 535                          * Error trying to read the header.
 536                          */
 537                         return (NULL);
 538                 }
 539         }
 540
 541         /*
 542          * Well, who knows what this mess is....
 543          */
 544         snprintf(errbuf, PCAP_ERRBUF_SIZE, "unknown file format");
 545         return (NULL);
 546
 547 found:
 548         p->rfile = fp;
 549
 550         /* Padding only needed for live capture fcode */
 551         p->fddipad = 0;
 552
 553 #if !defined(_WIN32) && !defined(MSDOS)
 554         /*
 555          * You can do "select()" and "poll()" on plain files on most
 556          * platforms, and should be able to do so on pipes.
 557          *
 558          * You can't do "select()" on anything other than sockets in
 559          * Windows, so, on Win32 systems, we don't have "selectable_fd".
 560          */
 561         p->selectable_fd = fileno(fp);
 562 #endif
 563
 564         p->can_set_rfmon_op = sf_cant_set_rfmon;
 565         p->read_op = pcap_offline_read;
 566         p->inject_op = sf_inject;
 567         p->setfilter_op = install_bpf_program;
 568         p->setdirection_op = sf_setdirection;
 569         p->set_datalink_op = NULL;      /* we don't support munging link-layer headers */
 570         p->getnonblock_op = sf_getnonblock;
 571         p->setnonblock_op = sf_setnonblock;
 572         p->stats_op = sf_stats;
 573 #ifdef _WIN32
 574         p->stats_ex_op = sf_stats_ex;
 575         p->setbuff_op = sf_setbuff;
 576         p->setmode_op = sf_setmode;
 577         p->setmintocopy_op = sf_setmintocopy;
 578         p->getevent_op = sf_getevent;
 579         p->oid_get_request_op = sf_oid_get_request;
 580         p->oid_set_request_op = sf_oid_set_request;
 581         p->sendqueue_transmit_op = sf_sendqueue_transmit;
 582         p->setuserbuffer_op = sf_setuserbuffer;
 583         p->live_dump_op = sf_live_dump;
 584         p->live_dump_ended_op = sf_live_dump_ended;
 585         p->get_airpcap_handle_op = sf_get_airpcap_handle;
 586 #endif
 587
 588         /*
 589          * For offline captures, the standard one-shot callback can
 590          * be used for pcap_next()/pcap_next_ex().
 591          */
 592         p->oneshot_callback = pcap_oneshot;
 593
 594         /*
 595          * Default breakloop operation.
 596          */
 597         p->breakloop_op = pcap_breakloop_common;
 598
 599         /*
 600          * Savefiles never require special BPF code generation.
 601          */
 602         p->bpf_codegen_flags = 0;
 603
 604         p->activated = 1;
 605
 606         return (p);
 607 }
 608
 609 /*
 610  * This isn't needed on Windows; we #define pcap_fopen_offline() as
 611  * a wrapper around pcap_hopen_offline(), and we don't call it from
 612  * inside this file, so it's unused.
 613  */
 614 #ifndef _WIN32
 615 pcap_t *
 616 pcap_fopen_offline(FILE *fp, char *errbuf)
 617 {
 618         return (pcap_fopen_offline_with_tstamp_precision(fp,
 619             PCAP_TSTAMP_PRECISION_MICRO, errbuf));
 620 }
 621 #endif
 622
 623 /*
 624  * Read packets from a capture file, and call the callback for each
 625  * packet.
 626  * If cnt > 0, return after 'cnt' packets, otherwise continue until eof.
 627  */
 628 int
 629 pcap_offline_read(pcap_t *p, int cnt, pcap_handler callback, u_char *user)
 630 {
 631         struct bpf_insn *fcode;
 632         int n = 0;
 633         u_char *data;
 634
 635         /*
 636          * This can conceivably process more than INT_MAX packets,
 637          * which would overflow the packet count, causing it either
 638          * to look like a negative number, and thus cause us to
 639          * return a value that looks like an error, or overflow
 640          * back into positive territory, and thus cause us to
 641          * return a too-low count.
 642          *
 643          * Therefore, if the packet count is unlimited, we clip
 644          * it at INT_MAX; this routine is not expected to
 645          * process packets indefinitely, so that's not an issue.
 646          */
 647         if (PACKET_COUNT_IS_UNLIMITED(cnt))
 648                 cnt = INT_MAX;
 649
 650         for (;;) {
 651                 struct pcap_pkthdr h;
 652                 int status;
 653
 654                 /*
 655                  * Has "pcap_breakloop()" been called?
 656                  * If so, return immediately - if we haven't read any
 657                  * packets, clear the flag and return -2 to indicate
 658                  * that we were told to break out of the loop, otherwise
 659                  * leave the flag set, so that the *next* call will break
 660                  * out of the loop without having read any packets, and
 661                  * return the number of packets we've processed so far.
 662                  */
 663                 if (p->break_loop) {
 664                         if (n == 0) {
 665                                 p->break_loop = 0;
 666                                 return (-2);
 667                         } else
 668                                 return (n);
 669                 }
 670
 671                 status = p->next_packet_op(p, &h, &data);
 672                 if (status < 0) {
 673                         /*
 674                          * Error.  Pass it back to the caller.
 675                          */
 676                         return (status);
 677                 }
 678                 if (status == 0) {
 679                         /*
 680                          * EOF.  Nothing more to process;
 681                          */
 682                         break;
 683                 }
 684
 685                 /*
 686                  * OK, we've read a packet; run it through the filter
 687                  * and, if it passes, process it.
 688                  */
 689                 if ((fcode = p->fcode.bf_insns) == NULL ||
 690                     pcap_filter(fcode, data, h.len, h.caplen)) {
 691                         (*callback)(user, &h, data);
 692                         n++;    /* count the packet */
 693                         if (n >= cnt)
 694                                 break;
 695                 }
 696         }
 697         /*XXX this breaks semantics tcpslice expects */
 698         return (n);
 699 }