The Tcpdump Group git mirrors - tcpdump/blob - print-tcp.c

   1 /*
   2  * Copyright (c) 1988, 1989, 1990, 1991, 1992, 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
  22 #ifndef lint
  23 static const char rcsid[] =
  24     "@(#) $Header: /tcpdump/master/tcpdump/print-tcp.c,v 1.104 2002-12-11 07:14:09 guy Exp $ (LBL)";
  25 #endif
  26
  27 #ifdef HAVE_CONFIG_H
  28 #include "config.h"
  29 #endif
  30
  31 #include <tcpdump-stdinc.h>
  32
  33 #include <rpc/rpc.h>
  34
  35 #include <stdio.h>
  36 #include <stdlib.h>
  37 #include <string.h>
  38
  39 #include "interface.h"
  40 #include "addrtoname.h"
  41 #include "extract.h"
  42
  43 #include "tcp.h"
  44
  45 #include "ip.h"
  46 #ifdef INET6
  47 #include "ip6.h"
  48 #endif
  49
  50 #include "nameser.h"
  51
  52 static void print_tcp_rst_data(register const u_char *sp, u_int length);
  53
  54 #define MAX_RST_DATA_LEN        30
  55
  56
  57 struct tha {
  58 #ifndef INET6
  59         struct in_addr src;
  60         struct in_addr dst;
  61 #else
  62         struct in6_addr src;
  63         struct in6_addr dst;
  64 #endif /*INET6*/
  65         u_int port;
  66 };
  67
  68 struct tcp_seq_hash {
  69         struct tcp_seq_hash *nxt;
  70         struct tha addr;
  71         tcp_seq seq;
  72         tcp_seq ack;
  73 };
  74
  75 #define TSEQ_HASHSIZE 919
  76
  77 /* These tcp optinos do not have the size octet */
  78 #define ZEROLENOPT(o) ((o) == TCPOPT_EOL || (o) == TCPOPT_NOP)
  79
  80 static struct tcp_seq_hash tcp_seq_hash[TSEQ_HASHSIZE];
  81
  82
  83 #ifndef TELNET_PORT
  84 #define TELNET_PORT     23
  85 #endif
  86 #ifndef BGP_PORT
  87 #define BGP_PORT        179
  88 #endif
  89 #define NETBIOS_SSN_PORT 139
  90 #ifndef PPTP_PORT
  91 #define PPTP_PORT       1723
  92 #endif
  93 #define BEEP_PORT        10288
  94 #ifndef NFS_PORT
  95 #define NFS_PORT        2049
  96 #endif
  97 #define MSDP_PORT       639
  98 #define LDP_PORT        646
  99
 100 static int tcp_cksum(register const struct ip *ip,
 101                      register const struct tcphdr *tp,
 102                      register int len)
 103 {
 104         union phu {
 105                 struct phdr {
 106                         u_int32_t src;
 107                         u_int32_t dst;
 108                         u_char mbz;
 109                         u_char proto;
 110                         u_int16_t len;
 111                 } ph;
 112                 u_int16_t pa[6];
 113         } phu;
 114         const u_int16_t *sp;
 115
 116         /* pseudo-header.. */
 117         phu.ph.len = htons(len);        /* XXX */
 118         phu.ph.mbz = 0;
 119         phu.ph.proto = IPPROTO_TCP;
 120         memcpy(&phu.ph.src, &ip->ip_src.s_addr, sizeof(u_int32_t));
 121         if (IP_HL(ip) == 5)
 122                 memcpy(&phu.ph.dst, &ip->ip_dst.s_addr, sizeof(u_int32_t));
 123         else
 124                 phu.ph.dst = ip_finddst(ip);
 125
 126         sp = &phu.pa[0];
 127         return in_cksum((u_short *)tp, len,
 128                         sp[0]+sp[1]+sp[2]+sp[3]+sp[4]+sp[5]);
 129 }
 130
 131 #ifdef INET6
 132 static int tcp6_cksum(const struct ip6_hdr *ip6, const struct tcphdr *tp,
 133         int len)
 134 {
 135         int i, tlen;
 136         register const u_int16_t *sp;
 137         u_int32_t sum;
 138         union {
 139                 struct {
 140                         struct in6_addr ph_src;
 141                         struct in6_addr ph_dst;
 142                         u_int32_t       ph_len;
 143                         u_int8_t        ph_zero[3];
 144                         u_int8_t        ph_nxt;
 145                 } ph;
 146                 u_int16_t pa[20];
 147         } phu;
 148
 149         tlen = EXTRACT_16BITS(&ip6->ip6_plen) + sizeof(struct ip6_hdr) -
 150             ((const char *)tp - (const char*)ip6);
 151
 152         /* pseudo-header */
 153         memset(&phu, 0, sizeof(phu));
 154         phu.ph.ph_src = ip6->ip6_src;
 155         phu.ph.ph_dst = ip6->ip6_dst;
 156         phu.ph.ph_len = htonl(tlen);
 157         phu.ph.ph_nxt = IPPROTO_TCP;
 158
 159         sum = 0;
 160         for (i = 0; i < sizeof(phu.pa) / sizeof(phu.pa[0]); i++)
 161                 sum += phu.pa[i];
 162
 163         sp = (const u_int16_t *)tp;
 164
 165         for (i = 0; i < (tlen & ~1); i += 2)
 166                 sum += *sp++;
 167
 168         if (tlen & 1)
 169                 sum += htons((*(const u_int8_t *)sp) << 8);
 170
 171         while (sum > 0xffff)
 172                 sum = (sum & 0xffff) + (sum >> 16);
 173         sum = ~sum & 0xffff;
 174
 175         return (sum);
 176 }
 177 #endif
 178
 179 void
 180 tcp_print(register const u_char *bp, register u_int length,
 181           register const u_char *bp2, int fragmented)
 182 {
 183         register const struct tcphdr *tp;
 184         register const struct ip *ip;
 185         register u_char flags;
 186         register u_int hlen;
 187         register char ch;
 188         u_int16_t sport, dport, win, urp;
 189         u_int32_t seq, ack, thseq, thack;
 190         int threv;
 191 #ifdef INET6
 192         register const struct ip6_hdr *ip6;
 193 #endif
 194
 195         tp = (struct tcphdr *)bp;
 196         ip = (struct ip *)bp2;
 197 #ifdef INET6
 198         if (IP_V(ip) == 6)
 199                 ip6 = (struct ip6_hdr *)bp2;
 200         else
 201                 ip6 = NULL;
 202 #endif /*INET6*/
 203         ch = '\0';
 204         if (!TTEST(tp->th_dport)) {
 205                 (void)printf("%s > %s: [|tcp]",
 206                         ipaddr_string(&ip->ip_src),
 207                         ipaddr_string(&ip->ip_dst));
 208                 return;
 209         }
 210
 211         sport = EXTRACT_16BITS(&tp->th_sport);
 212         dport = EXTRACT_16BITS(&tp->th_dport);
 213
 214         hlen = TH_OFF(tp) * 4;
 215
 216         /*
 217          * If data present and NFS port used, assume NFS.
 218          * Pass offset of data plus 4 bytes for RPC TCP msg length
 219          * to NFS print routines.
 220          */
 221         if (!qflag) {
 222                 if ((u_char *)tp + 4 + sizeof(struct rpc_msg) <= snapend &&
 223                     dport == NFS_PORT) {
 224                         nfsreq_print((u_char *)tp + hlen + 4, length - hlen,
 225                                      (u_char *)ip);
 226                         return;
 227                 } else if ((u_char *)tp + 4 + sizeof(struct rpc_msg)
 228                            <= snapend &&
 229                            sport == NFS_PORT) {
 230                         nfsreply_print((u_char *)tp + hlen + 4, length - hlen,
 231                                        (u_char *)ip);
 232                         return;
 233                 }
 234         }
 235 #ifdef INET6
 236         if (ip6) {
 237                 if (ip6->ip6_nxt == IPPROTO_TCP) {
 238                         (void)printf("%s.%s > %s.%s: ",
 239                                 ip6addr_string(&ip6->ip6_src),
 240                                 tcpport_string(sport),
 241                                 ip6addr_string(&ip6->ip6_dst),
 242                                 tcpport_string(dport));
 243                 } else {
 244                         (void)printf("%s > %s: ",
 245                                 tcpport_string(sport), tcpport_string(dport));
 246                 }
 247         } else
 248 #endif /*INET6*/
 249         {
 250                 if (ip->ip_p == IPPROTO_TCP) {
 251                         (void)printf("%s.%s > %s.%s: ",
 252                                 ipaddr_string(&ip->ip_src),
 253                                 tcpport_string(sport),
 254                                 ipaddr_string(&ip->ip_dst),
 255                                 tcpport_string(dport));
 256                 } else {
 257                         (void)printf("%s > %s: ",
 258                                 tcpport_string(sport), tcpport_string(dport));
 259                 }
 260         }
 261
 262         TCHECK(*tp);
 263
 264         seq = EXTRACT_32BITS(&tp->th_seq);
 265         ack = EXTRACT_32BITS(&tp->th_ack);
 266         win = EXTRACT_16BITS(&tp->th_win);
 267         urp = EXTRACT_16BITS(&tp->th_urp);
 268
 269         if (qflag) {
 270                 (void)printf("tcp %d", length - TH_OFF(tp) * 4);
 271                 return;
 272         }
 273         if ((flags = tp->th_flags) & (TH_SYN|TH_FIN|TH_RST|TH_PUSH|
 274                                       TH_ECNECHO|TH_CWR)) {
 275                 if (flags & TH_SYN)
 276                         putchar('S');
 277                 if (flags & TH_FIN)
 278                         putchar('F');
 279                 if (flags & TH_RST)
 280                         putchar('R');
 281                 if (flags & TH_PUSH)
 282                         putchar('P');
 283                 if (flags & TH_CWR)
 284                         putchar('W');   /* congestion _W_indow reduced (ECN) */
 285                 if (flags & TH_ECNECHO)
 286                         putchar('E');   /* ecn _E_cho sent (ECN) */
 287         } else
 288                 putchar('.');
 289
 290         if (!Sflag && (flags & TH_ACK)) {
 291                 register struct tcp_seq_hash *th;
 292                 const void *src, *dst;
 293                 register int rev;
 294                 struct tha tha;
 295                 /*
 296                  * Find (or record) the initial sequence numbers for
 297                  * this conversation.  (we pick an arbitrary
 298                  * collating order so there's only one entry for
 299                  * both directions).
 300                  */
 301 #ifdef INET6
 302                 memset(&tha, 0, sizeof(tha));
 303                 rev = 0;
 304                 if (ip6) {
 305                         src = &ip6->ip6_src;
 306                         dst = &ip6->ip6_dst;
 307                         if (sport > dport)
 308                                 rev = 1;
 309                         else if (sport == dport) {
 310                                 if (memcmp(src, dst, sizeof ip6->ip6_dst) > 0)
 311                                         rev = 1;
 312                         }
 313                         if (rev) {
 314                                 memcpy(&tha.src, dst, sizeof ip6->ip6_dst);
 315                                 memcpy(&tha.dst, src, sizeof ip6->ip6_src);
 316                                 tha.port = dport << 16 | sport;
 317                         } else {
 318                                 memcpy(&tha.dst, dst, sizeof ip6->ip6_dst);
 319                                 memcpy(&tha.src, src, sizeof ip6->ip6_src);
 320                                 tha.port = sport << 16 | dport;
 321                         }
 322                 } else {
 323                         src = &ip->ip_src;
 324                         dst = &ip->ip_dst;
 325                         if (sport > dport)
 326                                 rev = 1;
 327                         else if (sport == dport) {
 328                                 if (memcmp(src, dst, sizeof ip->ip_dst) > 0)
 329                                         rev = 1;
 330                         }
 331                         if (rev) {
 332                                 memcpy(&tha.src, dst, sizeof ip->ip_dst);
 333                                 memcpy(&tha.dst, src, sizeof ip->ip_src);
 334                                 tha.port = dport << 16 | sport;
 335                         } else {
 336                                 memcpy(&tha.dst, dst, sizeof ip->ip_dst);
 337                                 memcpy(&tha.src, src, sizeof ip->ip_src);
 338                                 tha.port = sport << 16 | dport;
 339                         }
 340                 }
 341 #else
 342                 rev = 0;
 343                 src = &ip->ip_src;
 344                 dst = &ip->ip_dst;
 345                 if (sport > dport)
 346                         rev = 1;
 347                 else if (sport == dport) {
 348                         if (memcmp(src, dst, sizeof ip->ip_dst) > 0)
 349                                 rev = 1;
 350                 }
 351                 if (rev) {
 352                         memcpy(&tha.src, dst, sizeof ip->ip_dst);
 353                         memcpy(&tha.dst, src, sizeof ip->ip_src);
 354                         tha.port = dport << 16 | sport;
 355                 } else {
 356                         memcpy(&tha.dst, dst, sizeof ip->ip_dst);
 357                         memcpy(&tha.src, src, sizeof ip->ip_src);
 358                         tha.port = sport << 16 | dport;
 359                 }
 360 #endif
 361
 362                 threv = rev;
 363                 for (th = &tcp_seq_hash[tha.port % TSEQ_HASHSIZE];
 364                      th->nxt; th = th->nxt)
 365                         if (memcmp((char *)&tha, (char *)&th->addr,
 366                                   sizeof(th->addr)) == 0)
 367                                 break;
 368
 369                 if (!th->nxt || (flags & TH_SYN)) {
 370                         /* didn't find it or new conversation */
 371                         if (th->nxt == NULL) {
 372                                 th->nxt = (struct tcp_seq_hash *)
 373                                         calloc(1, sizeof(*th));
 374                                 if (th->nxt == NULL)
 375                                         error("tcp_print: calloc");
 376                         }
 377                         th->addr = tha;
 378                         if (rev)
 379                                 th->ack = seq, th->seq = ack - 1;
 380                         else
 381                                 th->seq = seq, th->ack = ack - 1;
 382                 } else {
 383                         if (rev)
 384                                 seq -= th->ack, ack -= th->seq;
 385                         else
 386                                 seq -= th->seq, ack -= th->ack;
 387                 }
 388
 389                 thseq = th->seq;
 390                 thack = th->ack;
 391         } else {
 392                 /*fool gcc*/
 393                 thseq = thack = threv = 0;
 394         }
 395         if (hlen > length) {
 396                 (void)printf(" [bad hdr length]");
 397                 return;
 398         }
 399
 400         if (IP_V(ip) == 4 && vflag && !fragmented) {
 401                 u_int16_t sum, tcp_sum;
 402                 if (TTEST2(tp->th_sport, length)) {
 403                         sum = tcp_cksum(ip, tp, length);
 404                         if (sum != 0) {
 405                                 tcp_sum = EXTRACT_16BITS(&tp->th_sum);
 406                                 (void)printf(" [bad tcp cksum %x (->%x)!]",
 407                                     tcp_sum, in_cksum_shouldbe(tcp_sum, sum));
 408                         } else
 409                                 (void)printf(" [tcp sum ok]");
 410                 }
 411         }
 412 #ifdef INET6
 413         if (IP_V(ip) == 6 && ip6->ip6_plen && vflag && !fragmented) {
 414                 int sum;
 415                 if (TTEST2(tp->th_sport, length)) {
 416                         sum = tcp6_cksum(ip6, tp, length);
 417                         if (sum != 0)
 418                                 (void)printf(" [bad tcp cksum %x!]", sum);
 419                         else
 420                                 (void)printf(" [tcp sum ok]");
 421                 }
 422         }
 423 #endif
 424
 425         length -= hlen;
 426         if (vflag > 1 || length > 0 || flags & (TH_SYN | TH_FIN | TH_RST))
 427                 (void)printf(" %u:%u(%u)", seq, seq + length, length);
 428         if (flags & TH_ACK)
 429                 (void)printf(" ack %u", ack);
 430
 431         (void)printf(" win %d", win);
 432
 433         if (flags & TH_URG)
 434                 (void)printf(" urg %d", urp);
 435         /*
 436          * Handle any options.
 437          */
 438         if (hlen > sizeof(*tp)) {
 439                 register const u_char *cp;
 440                 register u_int i, opt, datalen;
 441                 register u_int len;
 442
 443                 hlen -= sizeof(*tp);
 444                 cp = (const u_char *)tp + sizeof(*tp);
 445                 putchar(' ');
 446                 ch = '<';
 447                 while (hlen > 0) {
 448                         putchar(ch);
 449                         TCHECK(*cp);
 450                         opt = *cp++;
 451                         if (ZEROLENOPT(opt))
 452                                 len = 1;
 453                         else {
 454                                 TCHECK(*cp);
 455                                 len = *cp++;    /* total including type, len */
 456                                 if (len < 2 || len > hlen)
 457                                         goto bad;
 458                                 --hlen;         /* account for length byte */
 459                         }
 460                         --hlen;                 /* account for type byte */
 461                         datalen = 0;
 462
 463 /* Bail if "l" bytes of data are not left or were not captured  */
 464 #define LENCHECK(l) { if ((l) > hlen) goto bad; TCHECK2(*cp, l); }
 465
 466                         switch (opt) {
 467
 468                         case TCPOPT_MAXSEG:
 469                                 (void)printf("mss");
 470                                 datalen = 2;
 471                                 LENCHECK(datalen);
 472                                 (void)printf(" %u", EXTRACT_16BITS(cp));
 473
 474                                 break;
 475
 476                         case TCPOPT_EOL:
 477                                 (void)printf("eol");
 478                                 break;
 479
 480                         case TCPOPT_NOP:
 481                                 (void)printf("nop");
 482                                 break;
 483
 484                         case TCPOPT_WSCALE:
 485                                 (void)printf("wscale");
 486                                 datalen = 1;
 487                                 LENCHECK(datalen);
 488                                 (void)printf(" %u", *cp);
 489                                 break;
 490
 491                         case TCPOPT_SACKOK:
 492                                 (void)printf("sackOK");
 493                                 break;
 494
 495                         case TCPOPT_SACK:
 496                                 (void)printf("sack");
 497                                 datalen = len - 2;
 498                                 if (datalen % 8 != 0) {
 499                                         (void)printf(" malformed sack ");
 500                                 } else {
 501                                         u_int32_t s, e;
 502
 503                                         (void)printf(" sack %d ", datalen / 8);
 504                                         for (i = 0; i < datalen; i += 8) {
 505                                                 LENCHECK(i + 4);
 506                                                 s = EXTRACT_32BITS(cp + i);
 507                                                 LENCHECK(i + 8);
 508                                                 e = EXTRACT_32BITS(cp + i + 4);
 509                                                 if (threv) {
 510                                                         s -= thseq;
 511                                                         e -= thseq;
 512                                                 } else {
 513                                                         s -= thack;
 514                                                         e -= thack;
 515                                                 }
 516                                                 (void)printf("{%u:%u}", s, e);
 517                                         }
 518                                         (void)printf(" ");
 519                                 }
 520                                 break;
 521
 522                         case TCPOPT_ECHO:
 523                                 (void)printf("echo");
 524                                 datalen = 4;
 525                                 LENCHECK(datalen);
 526                                 (void)printf(" %u", EXTRACT_32BITS(cp));
 527                                 break;
 528
 529                         case TCPOPT_ECHOREPLY:
 530                                 (void)printf("echoreply");
 531                                 datalen = 4;
 532                                 LENCHECK(datalen);
 533                                 (void)printf(" %u", EXTRACT_32BITS(cp));
 534                                 break;
 535
 536                         case TCPOPT_TIMESTAMP:
 537                                 (void)printf("timestamp");
 538                                 datalen = 8;
 539                                 LENCHECK(4);
 540                                 (void)printf(" %u", EXTRACT_32BITS(cp));
 541                                 LENCHECK(datalen);
 542                                 (void)printf(" %u", EXTRACT_32BITS(cp + 4));
 543                                 break;
 544
 545                         case TCPOPT_CC:
 546                                 (void)printf("cc");
 547                                 datalen = 4;
 548                                 LENCHECK(datalen);
 549                                 (void)printf(" %u", EXTRACT_32BITS(cp));
 550                                 break;
 551
 552                         case TCPOPT_CCNEW:
 553                                 (void)printf("ccnew");
 554                                 datalen = 4;
 555                                 LENCHECK(datalen);
 556                                 (void)printf(" %u", EXTRACT_32BITS(cp));
 557                                 break;
 558
 559                         case TCPOPT_CCECHO:
 560                                 (void)printf("ccecho");
 561                                 datalen = 4;
 562                                 LENCHECK(datalen);
 563                                 (void)printf(" %u", EXTRACT_32BITS(cp));
 564                                 break;
 565
 566                         default:
 567                                 (void)printf("opt-%u:", opt);
 568                                 datalen = len - 2;
 569                                 for (i = 0; i < datalen; ++i) {
 570                                         LENCHECK(i);
 571                                         (void)printf("%02x", cp[i]);
 572                                 }
 573                                 break;
 574                         }
 575
 576                         /* Account for data printed */
 577                         cp += datalen;
 578                         hlen -= datalen;
 579
 580                         /* Check specification against observed length */
 581                         ++datalen;                      /* option octet */
 582                         if (!ZEROLENOPT(opt))
 583                                 ++datalen;              /* size octet */
 584                         if (datalen != len)
 585                                 (void)printf("[len %d]", len);
 586                         ch = ',';
 587                         if (opt == TCPOPT_EOL)
 588                                 break;
 589                 }
 590                 putchar('>');
 591         }
 592
 593         if (length <= 0)
 594                 return;
 595
 596         /*
 597          * Decode payload if necessary.
 598          */
 599         bp += TH_OFF(tp) * 4;
 600         if (flags & TH_RST) {
 601                 if (vflag)
 602                         print_tcp_rst_data(bp, length);
 603         } else {
 604                 if (sport == TELNET_PORT || dport == TELNET_PORT) {
 605                         if (!qflag && vflag)
 606                                 telnet_print(bp, length);
 607                 } else if (sport == BGP_PORT || dport == BGP_PORT)
 608                         bgp_print(bp, length);
 609                 else if (sport == PPTP_PORT || dport == PPTP_PORT)
 610                         pptp_print(bp);
 611 #ifdef TCPDUMP_DO_SMB
 612                 else if (sport == NETBIOS_SSN_PORT || dport == NETBIOS_SSN_PORT)
 613                         nbt_tcp_print(bp, length);
 614 #endif
 615                 else if (sport == BEEP_PORT || dport == BEEP_PORT)
 616                         beep_print(bp, length);
 617                 else if (length > 2 &&
 618                     (sport == NAMESERVER_PORT || dport == NAMESERVER_PORT ||
 619                      sport == MULTICASTDNS_PORT || dport == MULTICASTDNS_PORT)) {
 620                         /*
 621                          * TCP DNS query has 2byte length at the head.
 622                          * XXX packet could be unaligned, it can go strange
 623                          */
 624                         ns_print(bp + 2, length - 2);
 625                 } else if (sport == MSDP_PORT || dport == MSDP_PORT) {
 626                         msdp_print(bp, length);
 627                 }
 628                 else if (sport == LDP_PORT || dport == LDP_PORT)
 629                         printf(": LDP, length: %u", length);
 630         }
 631         return;
 632 bad:
 633         fputs("[bad opt]", stdout);
 634         if (ch != '\0')
 635                 putchar('>');
 636         return;
 637 trunc:
 638         fputs("[|tcp]", stdout);
 639         if (ch != '\0')
 640                 putchar('>');
 641 }
 642
 643 /*
 644  * RFC1122 says the following on data in RST segments:
 645  *
 646  *         4.2.2.12  RST Segment: RFC-793 Section 3.4
 647  *
 648  *            A TCP SHOULD allow a received RST segment to include data.
 649  *
 650  *            DISCUSSION
 651  *                 It has been suggested that a RST segment could contain
 652  *                 ASCII text that encoded and explained the cause of the
 653  *                 RST.  No standard has yet been established for such
 654  *                 data.
 655  *
 656  */
 657
 658 static void
 659 print_tcp_rst_data(register const u_char *sp, u_int length)
 660 {
 661         int c;
 662
 663         if (TTEST2(*sp, length))
 664                 printf(" [RST");
 665         else
 666                 printf(" [!RST");
 667         if (length > MAX_RST_DATA_LEN) {
 668                 length = MAX_RST_DATA_LEN;      /* can use -X for longer */
 669                 putchar('+');                   /* indicate we truncate */
 670         }
 671         putchar(' ');
 672         while (length-- && sp <= snapend) {
 673                 c = *sp++;
 674                 safeputchar(c);
 675         }
 676         putchar(']');
 677 }