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 #include <config.h>
  32
  33 #include <pcap-types.h>
  34 #ifdef _WIN32
  35 #include <io.h>
  36 #include <fcntl.h>
  37 #endif /* _WIN32 */
  38
  39 #include <errno.h>
  40 #include <memory.h>
  41 #include <stdio.h>
  42 #include <stdlib.h>
  43 #include <string.h>
  44 #include <limits.h> /* for INT_MAX */
  45
  46 #include "pcap-int.h"
  47
  48 #ifdef HAVE_OS_PROTO_H
  49 #include "os-proto.h"
  50 #endif
  51
  52 #include "sf-pcap.h"
  53 #include "sf-pcapng.h"
  54 #include "pcap-common.h"
  55 #include "charconv.h"
  56
  57 #ifdef _WIN32
  58 /*
  59  * This isn't exported on Windows, because it would only work if both
  60  * WinPcap/Npcap and the code using it were to use the Universal CRT; otherwise,
  61  * a FILE structure in WinPcap/Npcap and a FILE structure in the code using it
  62  * could be different if they're using different versions of the C runtime.
  63  *
  64  * Instead, pcap/pcap.h defines it as a macro that wraps the hopen version,
  65  * with the wrapper calling _fileno() and _get_osfhandle() themselves,
  66  * so that it convert the appropriate CRT version's FILE structure to
  67  * a HANDLE (which is OS-defined, not CRT-defined, and is part of the Win32
  68  * and Win64 ABIs).
  69  */
  70 static pcap_t *pcap_fopen_offline_with_tstamp_precision(FILE *, u_int, char *);
  71 #endif
  72
  73 /*
  74  * Setting O_BINARY on Windows is a bit tricky.
  75  */
  76 #if defined(_WIN32)
  77   #define SET_BINMODE(f)  _setmode(_fileno(f), _O_BINARY)
  78 #endif
  79
  80 static int
  81 sf_getnonblock(pcap_t *p _U_)
  82 {
  83         /*
  84          * This is a savefile, not a live capture file, so never say
  85          * it's in non-blocking mode.
  86          */
  87         return (0);
  88 }
  89
  90 static int
  91 sf_setnonblock(pcap_t *p, int nonblock _U_)
  92 {
  93         /*
  94          * This is a savefile, not a live capture file, so reject
  95          * requests to put it in non-blocking mode.  (If it's a
  96          * pipe, it could be put in non-blocking mode, but that
  97          * would significantly complicate the code to read packets,
  98          * as it would have to handle reading partial packets and
  99          * keeping the state of the read.)
 100          */
 101         snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 102             "Savefiles cannot be put into non-blocking mode");
 103         return (-1);
 104 }
 105
 106 static int
 107 sf_cant_set_rfmon(pcap_t *p _U_)
 108 {
 109         /*
 110          * This is a savefile, not a device on which you can capture,
 111          * so never say it supports being put into monitor mode.
 112          */
 113         return (0);
 114 }
 115
 116 static int
 117 sf_stats(pcap_t *p, struct pcap_stat *ps _U_)
 118 {
 119         snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 120             "Statistics aren't available from savefiles");
 121         return (-1);
 122 }
 123
 124 #ifdef _WIN32
 125 static struct pcap_stat *
 126 sf_stats_ex(pcap_t *p, int *size _U_)
 127 {
 128         snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 129             "Statistics aren't available from savefiles");
 130         return (NULL);
 131 }
 132
 133 static int
 134 sf_setbuff(pcap_t *p, int dim _U_)
 135 {
 136         snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 137             "The kernel buffer size cannot be set while reading from a file");
 138         return (-1);
 139 }
 140
 141 static int
 142 sf_setmode(pcap_t *p, int mode _U_)
 143 {
 144         snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 145             "impossible to set mode while reading from a file");
 146         return (-1);
 147 }
 148
 149 static int
 150 sf_setmintocopy(pcap_t *p, int size _U_)
 151 {
 152         snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 153             "The mintocopy parameter cannot be set while reading from a file");
 154         return (-1);
 155 }
 156
 157 static HANDLE
 158 sf_getevent(pcap_t *pcap)
 159 {
 160         (void)snprintf(pcap->errbuf, sizeof(pcap->errbuf),
 161             "The read event cannot be retrieved while reading from a file");
 162         return (INVALID_HANDLE_VALUE);
 163 }
 164
 165 static int
 166 sf_oid_get_request(pcap_t *p, bpf_u_int32 oid _U_, void *data _U_,
 167     size_t *lenp _U_)
 168 {
 169         snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 170             "An OID get request cannot be performed on a file");
 171         return (PCAP_ERROR);
 172 }
 173
 174 static int
 175 sf_oid_set_request(pcap_t *p, bpf_u_int32 oid _U_, const void *data _U_,
 176     size_t *lenp _U_)
 177 {
 178         snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 179             "An OID set request cannot be performed on a file");
 180         return (PCAP_ERROR);
 181 }
 182
 183 static u_int
 184 sf_sendqueue_transmit(pcap_t *p, pcap_send_queue *queue _U_, int sync _U_)
 185 {
 186         pcapint_strlcpy(p->errbuf, "Sending packets isn't supported on savefiles",
 187             PCAP_ERRBUF_SIZE);
 188         return (0);
 189 }
 190
 191 static int
 192 sf_setuserbuffer(pcap_t *p, int size _U_)
 193 {
 194         snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 195             "The user buffer cannot be set when reading from a file");
 196         return (-1);
 197 }
 198
 199 static int
 200 sf_live_dump(pcap_t *p, char *filename _U_, int maxsize _U_, int maxpacks _U_)
 201 {
 202         snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 203             "Live packet dumping cannot be performed when reading from a file");
 204         return (-1);
 205 }
 206
 207 static int
 208 sf_live_dump_ended(pcap_t *p, int sync _U_)
 209 {
 210         snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 211             "Live packet dumping cannot be performed on a pcap_open_dead pcap_t");
 212         return (-1);
 213 }
 214
 215 static PAirpcapHandle
 216 sf_get_airpcap_handle(pcap_t *pcap _U_)
 217 {
 218         return (NULL);
 219 }
 220 #endif
 221
 222 static int
 223 sf_inject(pcap_t *p, const void *buf _U_, int size _U_)
 224 {
 225         pcapint_strlcpy(p->errbuf, "Sending packets isn't supported on savefiles",
 226             PCAP_ERRBUF_SIZE);
 227         return (-1);
 228 }
 229
 230 /*
 231  * Set direction flag: Which packets do we accept on a forwarding
 232  * single device? IN, OUT or both?
 233  */
 234 static int
 235 sf_setdirection(pcap_t *p, pcap_direction_t d _U_)
 236 {
 237         snprintf(p->errbuf, sizeof(p->errbuf),
 238             "Setting direction is not supported on savefiles");
 239         return (-1);
 240 }
 241
 242 void
 243 pcapint_sf_cleanup(pcap_t *p)
 244 {
 245         if (p->rfile != stdin)
 246                 (void)fclose(p->rfile);
 247         if (p->buffer != NULL)
 248                 free(p->buffer);
 249         pcap_freecode(&p->fcode);
 250 }
 251
 252 #ifdef _WIN32
 253 /*
 254  * Wrapper for fopen() and _wfopen().
 255  *
 256  * If we're in UTF-8 mode, map the pathname from UTF-8 to UTF-16LE and
 257  * call _wfopen().
 258  *
 259  * If we're not, just use fopen(); that'll treat it as being in the
 260  * local code page.
 261  */
 262 FILE *
 263 pcapint_charset_fopen(const char *path, const char *mode)
 264 {
 265         wchar_t *utf16_path;
 266 #define MAX_MODE_LEN    16
 267         wchar_t utf16_mode[MAX_MODE_LEN+1];
 268         int i;
 269         char c;
 270         FILE *fp;
 271         int save_errno;
 272
 273         if (pcapint_utf_8_mode) {
 274                 /*
 275                  * Map from UTF-8 to UTF-16LE.
 276                  * Fail if there are invalid characters in the input
 277                  * string, rather than converting them to REPLACEMENT
 278                  * CHARACTER; the latter is appropriate for strings
 279                  * to be displayed to the user, but for file names
 280                  * you just want the attempt to open the file to fail.
 281                  */
 282                 utf16_path = cp_to_utf_16le(CP_UTF8, path,
 283                     MB_ERR_INVALID_CHARS);
 284                 if (utf16_path == NULL) {
 285                         /*
 286                          * Error.  Assume errno has been set.
 287                          *
 288                          * XXX - what about Windows errors?
 289                          */
 290                         return (NULL);
 291                 }
 292
 293                 /*
 294                  * Now convert the mode to UTF-16LE as well.
 295                  * We assume the mode is ASCII, and that
 296                  * it's short, so that's easy.
 297                  */
 298                 for (i = 0; (c = *mode) != '\0'; i++, mode++) {
 299                         if (c > 0x7F) {
 300                                 /* Not an ASCII character; fail with EINVAL. */
 301                                 free(utf16_path);
 302                                 errno = EINVAL;
 303                                 return (NULL);
 304                         }
 305                         if (i >= MAX_MODE_LEN) {
 306                                 /* The mode string is longer than we allow. */
 307                                 free(utf16_path);
 308                                 errno = EINVAL;
 309                                 return (NULL);
 310                         }
 311                         utf16_mode[i] = c;
 312                 }
 313                 utf16_mode[i] = '\0';
 314
 315                 /*
 316                  * OK, we have UTF-16LE strings; hand them to
 317                  * _wfopen().
 318                  */
 319                 fp = _wfopen(utf16_path, utf16_mode);
 320
 321                 /*
 322                  * Make sure freeing the UTF-16LE string doesn't
 323                  * overwrite the error code we got from _wfopen().
 324                  */
 325                 save_errno = errno;
 326                 free(utf16_path);
 327                 errno = save_errno;
 328
 329                 return (fp);
 330         } else {
 331                 /*
 332                  * This takes strings in the local code page as an
 333                  * argument.
 334                  */
 335                 return (fopen(path, mode));
 336         }
 337 }
 338 #endif
 339
 340 pcap_t *
 341 pcap_open_offline_with_tstamp_precision(const char *fname, u_int precision,
 342                                         char *errbuf)
 343 {
 344         FILE *fp;
 345         pcap_t *p;
 346
 347         if (fname == NULL) {
 348                 snprintf(errbuf, PCAP_ERRBUF_SIZE,
 349                     "A null pointer was supplied as the file name");
 350                 return (NULL);
 351         }
 352         if (fname[0] == '-' && fname[1] == '\0')
 353         {
 354                 fp = stdin;
 355                 if (fp == NULL) {
 356                         snprintf(errbuf, PCAP_ERRBUF_SIZE,
 357                             "The standard input is not open");
 358                         return (NULL);
 359                 }
 360 #if defined(_WIN32)
 361                 /*
 362                  * We're reading from the standard input, so put it in binary
 363                  * mode, as savefiles are binary files.
 364                  */
 365                 SET_BINMODE(fp);
 366 #endif
 367         }
 368         else {
 369                 /*
 370                  * Use pcapint_charset_fopen(); on Windows, it tests whether we're
 371                  * in "local code page" or "UTF-8" mode, and treats the
 372                  * pathname appropriately, and on other platforms, it just
 373                  * wraps fopen().
 374                  *
 375                  * "b" is supported as of C90, so *all* UN*Xes should
 376                  * support it, even though it does nothing.
 377                  */
 378                 fp = pcapint_charset_fopen(fname, "rb");
 379                 if (fp == NULL) {
 380                         pcapint_fmt_errmsg_for_errno(errbuf, PCAP_ERRBUF_SIZE,
 381                             errno, "%s", fname);
 382                         return (NULL);
 383                 }
 384         }
 385         p = pcap_fopen_offline_with_tstamp_precision(fp, precision, errbuf);
 386         if (p == NULL) {
 387                 if (fp != stdin)
 388                         fclose(fp);
 389         }
 390         return (p);
 391 }
 392
 393 pcap_t *
 394 pcap_open_offline(const char *fname, char *errbuf)
 395 {
 396         return (pcap_open_offline_with_tstamp_precision(fname,
 397             PCAP_TSTAMP_PRECISION_MICRO, errbuf));
 398 }
 399
 400 #ifdef _WIN32
 401 pcap_t* pcap_hopen_offline_with_tstamp_precision(intptr_t osfd, u_int precision,
 402     char *errbuf)
 403 {
 404         int fd;
 405         FILE *file;
 406
 407         fd = _open_osfhandle(osfd, _O_RDONLY);
 408         if ( fd < 0 )
 409         {
 410                 pcapint_fmt_errmsg_for_errno(errbuf, PCAP_ERRBUF_SIZE,
 411                     errno, "_open_osfhandle");
 412                 return NULL;
 413         }
 414
 415         file = _fdopen(fd, "rb");
 416         if ( file == NULL )
 417         {
 418                 pcapint_fmt_errmsg_for_errno(errbuf, PCAP_ERRBUF_SIZE,
 419                     errno, "_fdopen");
 420                 _close(fd);
 421                 return NULL;
 422         }
 423
 424         return pcap_fopen_offline_with_tstamp_precision(file, precision,
 425             errbuf);
 426 }
 427
 428 pcap_t* pcap_hopen_offline(intptr_t osfd, char *errbuf)
 429 {
 430         return pcap_hopen_offline_with_tstamp_precision(osfd,
 431             PCAP_TSTAMP_PRECISION_MICRO, errbuf);
 432 }
 433 #endif
 434
 435 /*
 436  * Given a link-layer header type and snapshot length, return a
 437  * snapshot length to use when reading the file; it's guaranteed
 438  * to be > 0 and <= INT_MAX.
 439  *
 440  * XXX - the only reason why we limit it to <= INT_MAX is so that
 441  * it fits in p->snapshot, and the only reason that p->snapshot is
 442  * signed is that pcap_snapshot() returns an int, not an unsigned int.
 443  */
 444 bpf_u_int32
 445 pcapint_adjust_snapshot(bpf_u_int32 linktype, bpf_u_int32 snaplen)
 446 {
 447         if (snaplen == 0 || snaplen > INT_MAX) {
 448                 /*
 449                  * Bogus snapshot length; use the maximum for this
 450                  * link-layer type as a fallback.
 451                  *
 452                  * XXX - we don't clamp snapshot lengths that are
 453                  * <= INT_MAX but > max_snaplen_for_dlt(linktype),
 454                  * so a capture file could cause us to allocate
 455                  * a Really Big Buffer.
 456                  */
 457                 snaplen = max_snaplen_for_dlt(linktype);
 458         }
 459         return snaplen;
 460 }
 461
 462 static pcap_t *(*check_headers[])(const uint8_t *, FILE *, u_int, char *, int *) = {
 463         pcap_check_header,
 464         pcap_ng_check_header
 465 };
 466
 467 #define N_FILE_TYPES    (sizeof check_headers / sizeof check_headers[0])
 468
 469 #ifdef _WIN32
 470 static
 471 #endif
 472 pcap_t *
 473 pcap_fopen_offline_with_tstamp_precision(FILE *fp, u_int precision,
 474     char *errbuf)
 475 {
 476         register pcap_t *p;
 477         uint8_t magic[4];
 478         size_t amt_read;
 479         u_int i;
 480         int err;
 481
 482         /*
 483          * Fail if we were passed a NULL fp.
 484          *
 485          * That shouldn't happen if we're opening with a path name, but
 486          * it could happen if buggy code is opening with a FILE * and
 487          * didn't bother to make sure the FILE * isn't null.
 488          */
 489         if (fp == NULL) {
 490                 snprintf(errbuf, PCAP_ERRBUF_SIZE,
 491                     "Null FILE * pointer provided to savefile open routine");
 492                 return (NULL);
 493         }
 494
 495         /*
 496          * Read the first 4 bytes of the file; the network analyzer dump
 497          * file formats we support (pcap and pcapng), and several other
 498          * formats we might support in the future (such as snoop, DOS and
 499          * Windows Sniffer, and Microsoft Network Monitor) all have magic
 500          * numbers that are unique in their first 4 bytes.
 501          */
 502         amt_read = fread(&magic, 1, sizeof(magic), fp);
 503         if (amt_read != sizeof(magic)) {
 504                 if (ferror(fp)) {
 505                         pcapint_fmt_errmsg_for_errno(errbuf, PCAP_ERRBUF_SIZE,
 506                             errno, "error reading dump file");
 507                 } else {
 508                         snprintf(errbuf, PCAP_ERRBUF_SIZE,
 509                             "truncated dump file; tried to read %zu file header bytes, only got %zu",
 510                             sizeof(magic), amt_read);
 511                 }
 512                 return (NULL);
 513         }
 514
 515         /*
 516          * Try all file types.
 517          */
 518         for (i = 0; i < N_FILE_TYPES; i++) {
 519                 p = (*check_headers[i])(magic, fp, precision, errbuf, &err);
 520                 if (p != NULL) {
 521                         /* Yup, that's it. */
 522                         goto found;
 523                 }
 524                 if (err) {
 525                         /*
 526                          * Error trying to read the header.
 527                          */
 528                         return (NULL);
 529                 }
 530         }
 531
 532         /*
 533          * Well, who knows what this mess is....
 534          */
 535         snprintf(errbuf, PCAP_ERRBUF_SIZE, "unknown file format");
 536         return (NULL);
 537
 538 found:
 539         p->rfile = fp;
 540
 541         /* Padding only needed for live capture fcode */
 542         p->fddipad = 0;
 543
 544 #if !defined(_WIN32)
 545         /*
 546          * You can do "select()" and "poll()" on plain files on most
 547          * platforms, and should be able to do so on pipes.
 548          *
 549          * You can't do "select()" on anything other than sockets in
 550          * Windows, so, on Win32 systems, we don't have "selectable_fd".
 551          */
 552         p->selectable_fd = fileno(fp);
 553 #endif
 554
 555         p->can_set_rfmon_op = sf_cant_set_rfmon;
 556         p->read_op = pcapint_offline_read;
 557         p->inject_op = sf_inject;
 558         p->setfilter_op = pcapint_install_bpf_program;
 559         p->setdirection_op = sf_setdirection;
 560         p->set_datalink_op = NULL;      /* we don't support munging link-layer headers */
 561         p->getnonblock_op = sf_getnonblock;
 562         p->setnonblock_op = sf_setnonblock;
 563         p->stats_op = sf_stats;
 564 #ifdef _WIN32
 565         p->stats_ex_op = sf_stats_ex;
 566         p->setbuff_op = sf_setbuff;
 567         p->setmode_op = sf_setmode;
 568         p->setmintocopy_op = sf_setmintocopy;
 569         p->getevent_op = sf_getevent;
 570         p->oid_get_request_op = sf_oid_get_request;
 571         p->oid_set_request_op = sf_oid_set_request;
 572         p->sendqueue_transmit_op = sf_sendqueue_transmit;
 573         p->setuserbuffer_op = sf_setuserbuffer;
 574         p->live_dump_op = sf_live_dump;
 575         p->live_dump_ended_op = sf_live_dump_ended;
 576         p->get_airpcap_handle_op = sf_get_airpcap_handle;
 577 #endif
 578
 579         /*
 580          * For offline captures, the standard one-shot callback can
 581          * be used for pcap_next()/pcap_next_ex().
 582          */
 583         p->oneshot_callback = pcapint_oneshot;
 584
 585         /*
 586          * Default breakloop operation.
 587          */
 588         p->breakloop_op = pcapint_breakloop_common;
 589
 590         /*
 591          * Savefiles never require special BPF code generation.
 592          */
 593         p->bpf_codegen_flags = 0;
 594
 595         p->activated = 1;
 596
 597         return (p);
 598 }
 599
 600 /*
 601  * This isn't needed on Windows; we #define pcap_fopen_offline() as
 602  * a wrapper around pcap_hopen_offline(), and we don't call it from
 603  * inside this file, so it's unused.
 604  */
 605 #ifndef _WIN32
 606 pcap_t *
 607 pcap_fopen_offline(FILE *fp, char *errbuf)
 608 {
 609         return (pcap_fopen_offline_with_tstamp_precision(fp,
 610             PCAP_TSTAMP_PRECISION_MICRO, errbuf));
 611 }
 612 #endif
 613
 614 /*
 615  * Read packets from a capture file, and call the callback for each
 616  * packet.
 617  * If cnt > 0, return after 'cnt' packets, otherwise continue until eof.
 618  */
 619 int
 620 pcapint_offline_read(pcap_t *p, int cnt, pcap_handler callback, u_char *user)
 621 {
 622         struct bpf_insn *fcode;
 623         int n = 0;
 624         u_char *data;
 625
 626         /*
 627          * This can conceivably process more than INT_MAX packets,
 628          * which would overflow the packet count, causing it either
 629          * to look like a negative number, and thus cause us to
 630          * return a value that looks like an error, or overflow
 631          * back into positive territory, and thus cause us to
 632          * return a too-low count.
 633          *
 634          * Therefore, if the packet count is unlimited, we clip
 635          * it at INT_MAX; this routine is not expected to
 636          * process packets indefinitely, so that's not an issue.
 637          */
 638         if (PACKET_COUNT_IS_UNLIMITED(cnt))
 639                 cnt = INT_MAX;
 640
 641         for (;;) {
 642                 struct pcap_pkthdr h;
 643                 int status;
 644
 645                 /*
 646                  * Has "pcap_breakloop()" been called?
 647                  * If so, return immediately - if we haven't read any
 648                  * packets, clear the flag and return -2 to indicate
 649                  * that we were told to break out of the loop, otherwise
 650                  * leave the flag set, so that the *next* call will break
 651                  * out of the loop without having read any packets, and
 652                  * return the number of packets we've processed so far.
 653                  */
 654                 if (p->break_loop) {
 655                         if (n == 0) {
 656                                 p->break_loop = 0;
 657                                 return (-2);
 658                         } else
 659                                 return (n);
 660                 }
 661
 662                 status = p->next_packet_op(p, &h, &data);
 663                 if (status < 0) {
 664                         /*
 665                          * Error.  Pass it back to the caller.
 666                          */
 667                         return (status);
 668                 }
 669                 if (status == 0) {
 670                         /*
 671                          * EOF.  Nothing more to process;
 672                          */
 673                         break;
 674                 }
 675
 676                 /*
 677                  * OK, we've read a packet; run it through the filter
 678                  * and, if it passes, process it.
 679                  */
 680                 if ((fcode = p->fcode.bf_insns) == NULL ||
 681                     pcapint_filter(fcode, data, h.len, h.caplen)) {
 682                         (*callback)(user, &h, data);
 683                         n++;    /* count the packet */
 684                         if (n >= cnt)
 685                                 break;
 686                 }
 687         }
 688         /*XXX this breaks semantics tcpslice expects */
 689         return (n);
 690 }