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 1.72 2000-08-01 17:35:05 itojun Exp $ (LBL)";
  25 #endif
  26
  27 #ifdef HAVE_CONFIG_H
  28 #include "config.h"
  29 #endif
  30
  31 #include <sys/param.h>
  32 #include <sys/time.h>
  33
  34 #include <rpc/rpc.h>
  35
  36 #include <netinet/in.h>
  37 #include <netinet/in_systm.h>
  38 #include <netinet/ip.h>
  39 #include <netinet/ip_var.h>
  40 #include <netinet/tcp.h>
  41
  42 #include <stdio.h>
  43 #include <stdlib.h>
  44 #include <string.h>
  45 #include <ctype.h>
  46 #include <unistd.h>
  47
  48 #ifdef INET6
  49 #include <netinet/ip6.h>
  50 #endif
  51
  52 #include "interface.h"
  53 #include "addrtoname.h"
  54 #include "extract.h"
  55
  56 static void print_tcp_rst_data(register const u_char *sp, u_int length);
  57
  58 #define MAX_RST_DATA_LEN        30
  59
  60 /* Compatibility */
  61 #ifndef TCPOPT_WSCALE
  62 #define TCPOPT_WSCALE           3       /* window scale factor (rfc1072) */
  63 #endif
  64 #ifndef TCPOPT_SACKOK
  65 #define TCPOPT_SACKOK           4       /* selective ack ok (rfc1072) */
  66 #endif
  67 #ifndef TCPOPT_SACK
  68 #define TCPOPT_SACK             5       /* selective ack (rfc1072) */
  69 #endif
  70 #ifndef TCPOPT_ECHO
  71 #define TCPOPT_ECHO             6       /* echo (rfc1072) */
  72 #endif
  73 #ifndef TCPOPT_ECHOREPLY
  74 #define TCPOPT_ECHOREPLY        7       /* echo (rfc1072) */
  75 #endif
  76 #ifndef TCPOPT_TIMESTAMP
  77 #define TCPOPT_TIMESTAMP        8       /* timestamps (rfc1323) */
  78 #endif
  79 #ifndef TCPOPT_CC
  80 #define TCPOPT_CC               11      /* T/TCP CC options (rfc1644) */
  81 #endif
  82 #ifndef TCPOPT_CCNEW
  83 #define TCPOPT_CCNEW            12      /* T/TCP CC options (rfc1644) */
  84 #endif
  85 #ifndef TCPOPT_CCECHO
  86 #define TCPOPT_CCECHO           13      /* T/TCP CC options (rfc1644) */
  87 #endif
  88
  89 /*
  90  * Definitions required for ECN
  91  * for use if the OS running tcpdump does not have ECN
  92  */
  93 #ifndef TH_ECNECHO
  94 #define TH_ECNECHO              0x40    /* ECN Echo in tcp header */
  95 #endif
  96 #ifndef TH_CWR
  97 #define TH_CWR                  0x80    /* ECN Cwnd Reduced in tcp header*/
  98 #endif
  99
 100 struct tha {
 101 #ifndef INET6
 102         struct in_addr src;
 103         struct in_addr dst;
 104 #else
 105         struct in6_addr src;
 106         struct in6_addr dst;
 107 #endif /*INET6*/
 108         u_int port;
 109 };
 110
 111 struct tcp_seq_hash {
 112         struct tcp_seq_hash *nxt;
 113         struct tha addr;
 114         tcp_seq seq;
 115         tcp_seq ack;
 116 };
 117
 118 #define TSEQ_HASHSIZE 919
 119
 120 /* These tcp optinos do not have the size octet */
 121 #define ZEROLENOPT(o) ((o) == TCPOPT_EOL || (o) == TCPOPT_NOP)
 122
 123 static struct tcp_seq_hash tcp_seq_hash[TSEQ_HASHSIZE];
 124
 125
 126 #ifndef TELNET_PORT
 127 #define TELNET_PORT     23
 128 #endif
 129 #ifndef BGP_PORT
 130 #define BGP_PORT        179
 131 #endif
 132 #define NETBIOS_SSN_PORT 139
 133 #ifndef NFS_PORT
 134 #define NFS_PORT        2049
 135 #endif
 136
 137 static int tcp_cksum(register const struct ip *ip,
 138                      register const struct tcphdr *tp,
 139                      register int len)
 140 {
 141         int i, tlen;
 142         union phu {
 143                 struct phdr {
 144                         u_int32_t src;
 145                         u_int32_t dst;
 146                         u_char mbz;
 147                         u_char proto;
 148                         u_int16_t len;
 149                 } ph;
 150                 u_int16_t pa[6];
 151         } phu;
 152         register const u_int16_t *sp;
 153         u_int32_t sum;
 154         tlen = ntohs(ip->ip_len) - ((const char *)tp-(const char*)ip);
 155
 156         /* pseudo-header.. */
 157         phu.ph.len = htons(tlen);
 158         phu.ph.mbz = 0;
 159         phu.ph.proto = IPPROTO_TCP;
 160         memcpy(&phu.ph.src, &ip->ip_src.s_addr, sizeof(u_int32_t));
 161         memcpy(&phu.ph.dst, &ip->ip_dst.s_addr, sizeof(u_int32_t));
 162
 163         sp = &phu.pa[0];
 164         sum = sp[0]+sp[1]+sp[2]+sp[3]+sp[4]+sp[5];
 165
 166         sp = (const u_int16_t *)tp;
 167
 168         for (i=0; i<(tlen&~1); i+= 2)
 169                 sum += *sp++;
 170
 171         if (tlen & 1) {
 172                 sum += htons( (*(const char *)sp) << 8);
 173         }
 174
 175         while (sum > 0xffff)
 176                 sum = (sum & 0xffff) + (sum >> 16);
 177         sum = ~sum & 0xffff;
 178
 179         return (sum);
 180 }
 181
 182 #ifdef INET6
 183 static int tcp6_cksum(const struct ip6_hdr *ip6, const struct tcphdr *tp,
 184         int len)
 185 {
 186         int i, tlen;
 187         register const u_int16_t *sp;
 188         u_int32_t sum;
 189         union {
 190                 struct {
 191                         struct in6_addr ph_src;
 192                         struct in6_addr ph_dst;
 193                         u_int32_t       ph_len;
 194                         u_int8_t        ph_zero[3];
 195                         u_int8_t        ph_nxt;
 196                 } ph;
 197                 u_int16_t pa[20];
 198         } phu;
 199
 200         tlen = ntohs(ip6->ip6_plen) + sizeof(struct ip6_hdr) -
 201             ((const char *)tp - (const char*)ip6);
 202
 203         /* pseudo-header */
 204         memset(&phu, 0, sizeof(phu));
 205         phu.ph.ph_src = ip6->ip6_src;
 206         phu.ph.ph_dst = ip6->ip6_dst;
 207         phu.ph.ph_len = htonl(tlen);
 208         phu.ph.ph_nxt = IPPROTO_TCP;
 209
 210         sum = 0;
 211         for (i = 0; i < sizeof(phu.pa) / sizeof(phu.pa[0]); i++)
 212                 sum += phu.pa[i];
 213
 214         sp = (const u_int16_t *)tp;
 215
 216         for (i = 0; i < (tlen & ~1); i += 2)
 217                 sum += *sp++;
 218
 219         if (tlen & 1)
 220                 sum += htons((*(const char *)sp) << 8);
 221
 222         while (sum > 0xffff)
 223                 sum = (sum & 0xffff) + (sum >> 16);
 224         sum = ~sum & 0xffff;
 225
 226         return (sum);
 227 }
 228 #endif
 229
 230 void
 231 tcp_print(register const u_char *bp, register u_int length,
 232           register const u_char *bp2)
 233 {
 234         register const struct tcphdr *tp;
 235         register const struct ip *ip;
 236         register u_char flags;
 237         register int hlen;
 238         register char ch;
 239         u_int16_t sport, dport, win, urp;
 240         u_int32_t seq, ack, thseq, thack;
 241         int threv;
 242 #ifdef INET6
 243         register const struct ip6_hdr *ip6;
 244 #endif
 245
 246         tp = (struct tcphdr *)bp;
 247         ip = (struct ip *)bp2;
 248 #ifdef INET6
 249         if (ip->ip_v == 6)
 250                 ip6 = (struct ip6_hdr *)bp2;
 251         else
 252                 ip6 = NULL;
 253 #endif /*INET6*/
 254         ch = '\0';
 255         if (!TTEST(tp->th_dport)) {
 256                 (void)printf("%s > %s: [|tcp]",
 257                         ipaddr_string(&ip->ip_src),
 258                         ipaddr_string(&ip->ip_dst));
 259                 return;
 260         }
 261
 262         sport = ntohs(tp->th_sport);
 263         dport = ntohs(tp->th_dport);
 264
 265
 266         hlen = tp->th_off * 4;
 267
 268         /*
 269          * If data present and NFS port used, assume NFS.
 270          * Pass offset of data plus 4 bytes for RPC TCP msg length
 271          * to NFS print routines.
 272          */
 273         if (!qflag) {
 274                 if ((u_char *)tp + 4 + sizeof(struct rpc_msg) <= snapend &&
 275                     dport == NFS_PORT) {
 276                         nfsreq_print((u_char *)tp + hlen + 4, length-hlen,
 277                                      (u_char *)ip);
 278                         return;
 279                 } else if ((u_char *)tp + 4 + sizeof(struct rpc_msg)
 280                            <= snapend &&
 281                            sport == NFS_PORT) {
 282                         nfsreply_print((u_char *)tp + hlen + 4,length-hlen,
 283                                        (u_char *)ip);
 284                         return;
 285                 }
 286         }
 287 #ifdef INET6
 288         if (ip6) {
 289                 if (ip6->ip6_nxt == IPPROTO_TCP) {
 290                         (void)printf("%s.%s > %s.%s: ",
 291                                 ip6addr_string(&ip6->ip6_src),
 292                                 tcpport_string(sport),
 293                                 ip6addr_string(&ip6->ip6_dst),
 294                                 tcpport_string(dport));
 295                 } else {
 296                         (void)printf("%s > %s: ",
 297                                 tcpport_string(sport), tcpport_string(dport));
 298                 }
 299         } else
 300 #endif /*INET6*/
 301         {
 302                 if (ip->ip_p == IPPROTO_TCP) {
 303                         (void)printf("%s.%s > %s.%s: ",
 304                                 ipaddr_string(&ip->ip_src),
 305                                 tcpport_string(sport),
 306                                 ipaddr_string(&ip->ip_dst),
 307                                 tcpport_string(dport));
 308                 } else {
 309                         (void)printf("%s > %s: ",
 310                                 tcpport_string(sport), tcpport_string(dport));
 311                 }
 312         }
 313
 314         TCHECK(*tp);
 315
 316         seq = (u_int32_t)ntohl(tp->th_seq);
 317         ack = (u_int32_t)ntohl(tp->th_ack);
 318         win = ntohs(tp->th_win);
 319         urp = ntohs(tp->th_urp);
 320
 321         if (qflag) {
 322                 (void)printf("tcp %d", length - tp->th_off * 4);
 323                 return;
 324         }
 325         if ((flags = tp->th_flags) & (TH_SYN|TH_FIN|TH_RST|TH_PUSH|
 326                                       TH_ECNECHO|TH_CWR)) {
 327                 if (flags & TH_SYN)
 328                         putchar('S');
 329                 if (flags & TH_FIN)
 330                         putchar('F');
 331                 if (flags & TH_RST)
 332                         putchar('R');
 333                 if (flags & TH_PUSH)
 334                         putchar('P');
 335                 if (flags & TH_CWR)
 336                         putchar('W');   /* congestion _W_indow reduced (ECN) */
 337                 if (flags & TH_ECNECHO)
 338                         putchar('E');   /* ecn _E_cho sent (ECN) */
 339         } else
 340                 putchar('.');
 341
 342         if (!Sflag && (flags & TH_ACK)) {
 343                 register struct tcp_seq_hash *th;
 344                 register int rev;
 345                 struct tha tha;
 346                 /*
 347                  * Find (or record) the initial sequence numbers for
 348                  * this conversation.  (we pick an arbitrary
 349                  * collating order so there's only one entry for
 350                  * both directions).
 351                  */
 352 #ifdef INET6
 353                 memset(&tha, 0, sizeof(tha));
 354                 rev = 0;
 355                 if (ip6) {
 356                         if (sport > dport) {
 357                                 rev = 1;
 358                         } else if (sport == dport) {
 359                             int i;
 360
 361                             for (i = 0; i < 4; i++) {
 362                                 if (((u_int32_t *)(&ip6->ip6_src))[i] >
 363                                     ((u_int32_t *)(&ip6->ip6_dst))[i]) {
 364                                         rev = 1;
 365                                         break;
 366                                 }
 367                             }
 368                         }
 369                         if (rev) {
 370                                 tha.src = ip6->ip6_dst;
 371                                 tha.dst = ip6->ip6_src;
 372                                 tha.port = dport << 16 | sport;
 373                         } else {
 374                                 tha.dst = ip6->ip6_dst;
 375                                 tha.src = ip6->ip6_src;
 376                                 tha.port = sport << 16 | dport;
 377                         }
 378                 } else {
 379                         if (sport > dport ||
 380                             (sport == dport &&
 381                              ip->ip_src.s_addr > ip->ip_dst.s_addr)) {
 382                                 rev = 1;
 383                         }
 384                         if (rev) {
 385                                 *(struct in_addr *)&tha.src = ip->ip_dst;
 386                                 *(struct in_addr *)&tha.dst = ip->ip_src;
 387                                 tha.port = dport << 16 | sport;
 388                         } else {
 389                                 *(struct in_addr *)&tha.dst = ip->ip_dst;
 390                                 *(struct in_addr *)&tha.src = ip->ip_src;
 391                                 tha.port = sport << 16 | dport;
 392                         }
 393                 }
 394 #else
 395                 if (sport < dport ||
 396                     (sport == dport &&
 397                      ip->ip_src.s_addr < ip->ip_dst.s_addr)) {
 398                         tha.src = ip->ip_src, tha.dst = ip->ip_dst;
 399                         tha.port = sport << 16 | dport;
 400                         rev = 0;
 401                 } else {
 402                         tha.src = ip->ip_dst, tha.dst = ip->ip_src;
 403                         tha.port = dport << 16 | sport;
 404                         rev = 1;
 405                 }
 406 #endif
 407
 408                 threv = rev;
 409                 for (th = &tcp_seq_hash[tha.port % TSEQ_HASHSIZE];
 410                      th->nxt; th = th->nxt)
 411                         if (!memcmp((char *)&tha, (char *)&th->addr,
 412                                   sizeof(th->addr)))
 413                                 break;
 414
 415                 if (!th->nxt || (flags & TH_SYN)) {
 416                         /* didn't find it or new conversation */
 417                         if (th->nxt == NULL) {
 418                                 th->nxt = (struct tcp_seq_hash *)
 419                                         calloc(1, sizeof(*th));
 420                                 if (th->nxt == NULL)
 421                                         error("tcp_print: calloc");
 422                         }
 423                         th->addr = tha;
 424                         if (rev)
 425                                 th->ack = seq, th->seq = ack - 1;
 426                         else
 427                                 th->seq = seq, th->ack = ack - 1;
 428
 429                 } else {
 430                         if (rev)
 431                                 seq -= th->ack, ack -= th->seq;
 432                         else
 433                                 seq -= th->seq, ack -= th->ack;
 434                 }
 435
 436                 thseq = th->seq;
 437                 thack = th->ack;
 438         } else {
 439                 /*fool gcc*/
 440                 thseq = thack = threv = 0;
 441         }
 442         if (hlen > length) {
 443                 (void)printf(" [bad hdr length]");
 444                 return;
 445         }
 446
 447         if (ip->ip_v == 4 && vflag) {
 448                 int sum;
 449                 if (TTEST2(tp->th_sport, length)) {
 450                         sum = tcp_cksum(ip, tp, length);
 451                         if (sum != 0)
 452                                 (void)printf(" [bad tcp cksum %x!]", sum);
 453                         else
 454                                 (void)printf(" [tcp sum ok]");
 455                 }
 456         }
 457 #ifdef INET6
 458         if (ip->ip_v == 6 && ip6->ip6_plen && vflag) {
 459                 int sum;
 460                 if (TTEST2(tp->th_sport, length)) {
 461                         sum = tcp6_cksum(ip6, tp, length);
 462                         if (sum != 0)
 463                                 (void)printf(" [bad tcp cksum %x!]", sum);
 464                         else
 465                                 (void)printf(" [tcp sum ok]");
 466                 }
 467         }
 468 #endif
 469
 470         length -= hlen;
 471         if (vflag > 1 || length > 0 || flags & (TH_SYN | TH_FIN | TH_RST))
 472                 (void)printf(" %u:%u(%d)", seq, seq + length, length);
 473         if (flags & TH_ACK)
 474                 (void)printf(" ack %u", ack);
 475
 476         (void)printf(" win %d", win);
 477
 478         if (flags & TH_URG)
 479                 (void)printf(" urg %d", urp);
 480         /*
 481          * Handle any options.
 482          */
 483         if ((hlen -= sizeof(*tp)) > 0) {
 484                 register const u_char *cp;
 485                 register int i, opt, len, datalen;
 486
 487                 cp = (const u_char *)tp + sizeof(*tp);
 488                 putchar(' ');
 489                 ch = '<';
 490                 while (hlen > 0) {
 491                         putchar(ch);
 492                         TCHECK(*cp);
 493                         opt = *cp++;
 494                         if (ZEROLENOPT(opt))
 495                                 len = 1;
 496                         else {
 497                                 TCHECK(*cp);
 498                                 len = *cp++;    /* total including type, len */
 499                                 if (len < 2 || len > hlen)
 500                                         goto bad;
 501                                 --hlen;         /* account for length byte */
 502                         }
 503                         --hlen;                 /* account for type byte */
 504                         datalen = 0;
 505
 506 /* Bail if "l" bytes of data are not left or were not captured  */
 507 #define LENCHECK(l) { if ((l) > hlen) goto bad; TCHECK2(*cp, l); }
 508
 509                         switch (opt) {
 510
 511                         case TCPOPT_MAXSEG:
 512                                 (void)printf("mss");
 513                                 datalen = 2;
 514                                 LENCHECK(datalen);
 515                                 (void)printf(" %u", EXTRACT_16BITS(cp));
 516
 517                                 break;
 518
 519                         case TCPOPT_EOL:
 520                                 (void)printf("eol");
 521                                 break;
 522
 523                         case TCPOPT_NOP:
 524                                 (void)printf("nop");
 525                                 break;
 526
 527                         case TCPOPT_WSCALE:
 528                                 (void)printf("wscale");
 529                                 datalen = 1;
 530                                 LENCHECK(datalen);
 531                                 (void)printf(" %u", *cp);
 532                                 break;
 533
 534                         case TCPOPT_SACKOK:
 535                                 (void)printf("sackOK");
 536                                 break;
 537
 538                         case TCPOPT_SACK:
 539                                 (void)printf("sack");
 540                                 datalen = len - 2;
 541                                 if (datalen % 8 != 0) {
 542                                         (void)printf(" malformed sack ");
 543                                 } else {
 544                                         u_int32_t s, e;
 545
 546                                         (void)printf(" sack %d ", datalen / 8);
 547                                         for (i = 0; i < datalen; i += 8) {
 548                                                 LENCHECK(i + 4);
 549                                                 s = EXTRACT_32BITS(cp + i);
 550                                                 LENCHECK(i + 8);
 551                                                 e = EXTRACT_32BITS(cp + i + 4);
 552                                                 if (threv) {
 553                                                         s -= thseq;
 554                                                         e -= thseq;
 555                                                 } else {
 556                                                         s -= thack;
 557                                                         e -= thack;
 558                                                 }
 559                                                 (void)printf("{%u:%u}", s, e);
 560                                         }
 561                                         (void)printf(" ");
 562                                 }
 563                                 break;
 564
 565                         case TCPOPT_ECHO:
 566                                 (void)printf("echo");
 567                                 datalen = 4;
 568                                 LENCHECK(datalen);
 569                                 (void)printf(" %u", EXTRACT_32BITS(cp));
 570                                 break;
 571
 572                         case TCPOPT_ECHOREPLY:
 573                                 (void)printf("echoreply");
 574                                 datalen = 4;
 575                                 LENCHECK(datalen);
 576                                 (void)printf(" %u", EXTRACT_32BITS(cp));
 577                                 break;
 578
 579                         case TCPOPT_TIMESTAMP:
 580                                 (void)printf("timestamp");
 581                                 datalen = 8;
 582                                 LENCHECK(4);
 583                                 (void)printf(" %u", EXTRACT_32BITS(cp));
 584                                 LENCHECK(datalen);
 585                                 (void)printf(" %u", EXTRACT_32BITS(cp + 4));
 586                                 break;
 587
 588                         case TCPOPT_CC:
 589                                 (void)printf("cc");
 590                                 datalen = 4;
 591                                 LENCHECK(datalen);
 592                                 (void)printf(" %u", EXTRACT_32BITS(cp));
 593                                 break;
 594
 595                         case TCPOPT_CCNEW:
 596                                 (void)printf("ccnew");
 597                                 datalen = 4;
 598                                 LENCHECK(datalen);
 599                                 (void)printf(" %u", EXTRACT_32BITS(cp));
 600                                 break;
 601
 602                         case TCPOPT_CCECHO:
 603                                 (void)printf("ccecho");
 604                                 datalen = 4;
 605                                 LENCHECK(datalen);
 606                                 (void)printf(" %u", EXTRACT_32BITS(cp));
 607                                 break;
 608
 609                         default:
 610                                 (void)printf("opt-%d:", opt);
 611                                 datalen = len - 2;
 612                                 for (i = 0; i < datalen; ++i) {
 613                                         LENCHECK(i);
 614                                         (void)printf("%02x", cp[i]);
 615                                 }
 616                                 break;
 617                         }
 618
 619                         /* Account for data printed */
 620                         cp += datalen;
 621                         hlen -= datalen;
 622
 623                         /* Check specification against observed length */
 624                         ++datalen;                      /* option octet */
 625                         if (!ZEROLENOPT(opt))
 626                                 ++datalen;              /* size octet */
 627                         if (datalen != len)
 628                                 (void)printf("[len %d]", len);
 629                         ch = ',';
 630                         if (opt == TCPOPT_EOL)
 631                                 break;
 632                 }
 633                 putchar('>');
 634         }
 635
 636         if (length <= 0)
 637                 return;
 638
 639         /*
 640          * Decode payload if necessary.
 641          */
 642         bp += (tp->th_off * 4);
 643         if (flags & TH_RST) {
 644                 if (vflag)
 645                         print_tcp_rst_data(bp, length);
 646         } else {
 647                 if (sport == TELNET_PORT || dport == TELNET_PORT) {
 648                         if (!qflag && vflag)
 649                                 telnet_print(bp, length);
 650                 } else if (sport == BGP_PORT || dport == BGP_PORT)
 651                         bgp_print(bp, length);
 652                 else if (sport == NETBIOS_SSN_PORT || dport == NETBIOS_SSN_PORT)
 653                         nbt_tcp_print(bp, length);
 654         }
 655         return;
 656 bad:
 657         fputs("[bad opt]", stdout);
 658         if (ch != '\0')
 659                 putchar('>');
 660         return;
 661 trunc:
 662         fputs("[|tcp]", stdout);
 663         if (ch != '\0')
 664                 putchar('>');
 665 }
 666
 667 /*
 668  * RFC1122 says the following on data in RST segments:
 669  *
 670  *         4.2.2.12  RST Segment: RFC-793 Section 3.4
 671  *
 672  *            A TCP SHOULD allow a received RST segment to include data.
 673  *
 674  *            DISCUSSION
 675  *                 It has been suggested that a RST segment could contain
 676  *                 ASCII text that encoded and explained the cause of the
 677  *                 RST.  No standard has yet been established for such
 678  *                 data.
 679  *
 680  */
 681
 682 static void
 683 print_tcp_rst_data(register const u_char *sp, u_int length)
 684 {
 685         int c;
 686
 687         if (TTEST2(*sp, length))
 688                 printf(" [RST");
 689         else
 690                 printf(" [!RST");
 691         if (length > MAX_RST_DATA_LEN) {
 692                 length = MAX_RST_DATA_LEN;      /* can use -X for longer */
 693                 putchar('+');                   /* indicate we truncate */
 694         }
 695         putchar(' ');
 696         while (length-- && sp <= snapend) {
 697                 c = *sp++;
 698                 if (isprint(c))
 699                         putchar(c);
 700                 else
 701                         putchar('.');
 702         }
 703         putchar(']');
 704 }