resolv/ns_name.c

   1 /*
   2  * Copyright (c) 1996,1999 by Internet Software Consortium.
   3  *
   4  * Permission to use, copy, modify, and distribute this software for any
   5  * purpose with or without fee is hereby granted, provided that the above
   6  * copyright notice and this permission notice appear in all copies.
   7  *
   8  * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
   9  * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
  10  * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
  11  * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
  12  * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
  13  * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
  14  * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
  15  * SOFTWARE.
  16  */
  17
  18 #if !defined(_LIBC) && !defined(lint)
  19 static const char rcsid[] = "$BINDId: ns_name.c,v 8.15 2000/03/30 22:53:46 vixie Exp $";
  20 #endif
  21
  22 #include <sys/types.h>
  23
  24 #include <netinet/in.h>
  25 #include <arpa/nameser.h>
  26
  27 #include <ctype.h>
  28 #include <errno.h>
  29 #include <resolv.h>
  30 #include <string.h>
  31 #include <ctype.h>
  32
  33 /* Data. */
  34
  35 static const char       digits[] = "0123456789";
  36
  37 /* Forward. */
  38
  39 static int              special(int);
  40 static int              printable(int);
  41 static int              dn_find(const u_char *, const u_char *,
  42                                 const u_char * const *,
  43                                 const u_char * const *);
  44
  45 /* Public. */
  46
  47 /*
  48  * ns_name_ntop(src, dst, dstsiz)
  49  *      Convert an encoded domain name to printable ascii as per RFC1035.
  50  * return:
  51  *      Number of bytes written to buffer, or -1 (with errno set)
  52  * notes:
  53  *      The root is returned as "."
  54  *      All other domains are returned in non absolute form
  55  */
  56 int
  57 ns_name_ntop(const u_char *src, char *dst, size_t dstsiz) {
  58         const u_char *cp;
  59         char *dn, *eom;
  60         u_char c;
  61         u_int n;
  62
  63         cp = src;
  64         dn = dst;
  65         eom = dst + dstsiz;
  66
  67         while ((n = *cp++) != 0) {
  68                 if ((n & NS_CMPRSFLGS) != 0 && n != 0x41) {
  69                         /* Some kind of compression pointer. */
  70                         __set_errno (EMSGSIZE);
  71                         return (-1);
  72                 }
  73                 if (dn != dst) {
  74                         if (dn >= eom) {
  75                                 __set_errno (EMSGSIZE);
  76                                 return (-1);
  77                         }
  78                         *dn++ = '.';
  79                 }
  80
  81                 if (n == 0x41) {
  82                         n = *cp++ / 8;
  83                         if (dn + n * 2 + 4 >= eom) {
  84                                 __set_errno (EMSGSIZE);
  85                                 return (-1);
  86                         }
  87                         *dn++ = '\\';
  88                         *dn++ = '[';
  89                         *dn++ = 'x';
  90
  91                         while (n-- > 0) {
  92                                 c = *cp++;
  93                                 unsigned u = c >> 4;
  94                                 *dn++ = u > 9 ? 'a' + u - 10 : '0' + u;
  95                                 u = c & 0xf;
  96                                 *dn++ = u > 9 ? 'a' + u - 10 : '0' + u;
  97                         }
  98
  99                         *dn++ = ']';
 100                         continue;
 101                 }
 102
 103                 if (dn + n >= eom) {
 104                         __set_errno (EMSGSIZE);
 105                         return (-1);
 106                 }
 107                 for ((void)NULL; n > 0; n--) {
 108                         c = *cp++;
 109                         if (special(c)) {
 110                                 if (dn + 1 >= eom) {
 111                                         __set_errno (EMSGSIZE);
 112                                         return (-1);
 113                                 }
 114                                 *dn++ = '\\';
 115                                 *dn++ = (char)c;
 116                         } else if (!printable(c)) {
 117                                 if (dn + 3 >= eom) {
 118                                         __set_errno (EMSGSIZE);
 119                                         return (-1);
 120                                 }
 121                                 *dn++ = '\\';
 122                                 *dn++ = digits[c / 100];
 123                                 *dn++ = digits[(c % 100) / 10];
 124                                 *dn++ = digits[c % 10];
 125                         } else {
 126                                 if (dn >= eom) {
 127                                         __set_errno (EMSGSIZE);
 128                                         return (-1);
 129                                 }
 130                                 *dn++ = (char)c;
 131                         }
 132                 }
 133         }
 134         if (dn == dst) {
 135                 if (dn >= eom) {
 136                         __set_errno (EMSGSIZE);
 137                         return (-1);
 138                 }
 139                 *dn++ = '.';
 140         }
 141         if (dn >= eom) {
 142                 __set_errno (EMSGSIZE);
 143                 return (-1);
 144         }
 145         *dn++ = '\0';
 146         return (dn - dst);
 147 }
 148 libresolv_hidden_def (ns_name_ntop)
 149
 150 /*
 151  * ns_name_pton(src, dst, dstsiz)
 152  *      Convert a ascii string into an encoded domain name as per RFC1035.
 153  * return:
 154  *      -1 if it fails
 155  *      1 if string was fully qualified
 156  *      0 is string was not fully qualified
 157  * notes:
 158  *      Enforces label and domain length limits.
 159  */
 160
 161 int
 162 ns_name_pton(const char *src, u_char *dst, size_t dstsiz) {
 163         u_char *label, *bp, *eom;
 164         int c, n, escaped;
 165         char *cp;
 166
 167         escaped = 0;
 168         bp = dst;
 169         eom = dst + dstsiz;
 170         label = bp++;
 171
 172         while ((c = *src++) != 0) {
 173                 if (escaped) {
 174                         if ((cp = strchr(digits, c)) != NULL) {
 175                                 n = (cp - digits) * 100;
 176                                 if ((c = *src++) == 0 ||
 177                                     (cp = strchr(digits, c)) == NULL) {
 178                                         __set_errno (EMSGSIZE);
 179                                         return (-1);
 180                                 }
 181                                 n += (cp - digits) * 10;
 182                                 if ((c = *src++) == 0 ||
 183                                     (cp = strchr(digits, c)) == NULL) {
 184                                         __set_errno (EMSGSIZE);
 185                                         return (-1);
 186                                 }
 187                                 n += (cp - digits);
 188                                 if (n > 255) {
 189                                         __set_errno (EMSGSIZE);
 190                                         return (-1);
 191                                 }
 192                                 c = n;
 193                         } else if (c == '[' && label == bp - 1 && *src == 'x') {
 194                                 /* Theoretically we would have to handle \[o
 195                                    as well but we do not since we do not need
 196                                    it internally.  */
 197                                 *label = 0x41;
 198                                 label = bp++;
 199                                 ++src;
 200                                 while (isxdigit (*src)) {
 201                                         n = *src > '9' ? *src - 'a' + 10 : *src - '0';
 202                                         ++src;
 203                                         if (! isxdigit(*src)) {
 204                                                 __set_errno (EMSGSIZE);
 205                                                 return (-1);
 206                                         }
 207                                         n <<= 4;
 208                                         n += *src > '9' ? *src - 'a' + 10 : *src - '0';
 209                                         if (bp + 1 >= eom) {
 210                                                 __set_errno (EMSGSIZE);
 211                                                 return (-1);
 212                                         }
 213                                         *bp++ = n;
 214                                         ++src;
 215                                 }
 216                                 *label = (bp - label - 1) * 8;
 217                                 if (*src++ != ']' || *src++ != '.') {
 218                                         __set_errno (EMSGSIZE);
 219                                         return (-1);
 220                                 }
 221                                 escaped = 0;
 222                                 label = bp++;
 223                                 if (bp >= eom) {
 224                                         __set_errno (EMSGSIZE);
 225                                         return (-1);
 226                                 }
 227                                 continue;
 228                         }
 229                         escaped = 0;
 230                 } else if (c == '\\') {
 231                         escaped = 1;
 232                         continue;
 233                 } else if (c == '.') {
 234                         c = (bp - label - 1);
 235                         if ((c & NS_CMPRSFLGS) != 0) {  /* Label too big. */
 236                                 __set_errno (EMSGSIZE);
 237                                 return (-1);
 238                         }
 239                         if (label >= eom) {
 240                                 __set_errno (EMSGSIZE);
 241                                 return (-1);
 242                         }
 243                         *label = c;
 244                         /* Fully qualified ? */
 245                         if (*src == '\0') {
 246                                 if (c != 0) {
 247                                         if (bp >= eom) {
 248                                                 __set_errno (EMSGSIZE);
 249                                                 return (-1);
 250                                         }
 251                                         *bp++ = '\0';
 252                                 }
 253                                 if ((bp - dst) > MAXCDNAME) {
 254                                         __set_errno (EMSGSIZE);
 255                                         return (-1);
 256                                 }
 257                                 return (1);
 258                         }
 259                         if (c == 0 || *src == '.') {
 260                                 __set_errno (EMSGSIZE);
 261                                 return (-1);
 262                         }
 263                         label = bp++;
 264                         continue;
 265                 }
 266                 if (bp >= eom) {
 267                         __set_errno (EMSGSIZE);
 268                         return (-1);
 269                 }
 270                 *bp++ = (u_char)c;
 271         }
 272         c = (bp - label - 1);
 273         if ((c & NS_CMPRSFLGS) != 0) {          /* Label too big. */
 274                 __set_errno (EMSGSIZE);
 275                 return (-1);
 276         }
 277         if (label >= eom) {
 278                 __set_errno (EMSGSIZE);
 279                 return (-1);
 280         }
 281         *label = c;
 282         if (c != 0) {
 283                 if (bp >= eom) {
 284                         __set_errno (EMSGSIZE);
 285                         return (-1);
 286                 }
 287                 *bp++ = 0;
 288         }
 289         if ((bp - dst) > MAXCDNAME) {   /* src too big */
 290                 __set_errno (EMSGSIZE);
 291                 return (-1);
 292         }
 293         return (0);
 294 }
 295
 296 /*
 297  * ns_name_ntol(src, dst, dstsiz)
 298  *      Convert a network strings labels into all lowercase.
 299  * return:
 300  *      Number of bytes written to buffer, or -1 (with errno set)
 301  * notes:
 302  *      Enforces label and domain length limits.
 303  */
 304
 305 int
 306 ns_name_ntol(const u_char *src, u_char *dst, size_t dstsiz) {
 307         const u_char *cp;
 308         u_char *dn, *eom;
 309         u_char c;
 310         u_int n;
 311
 312         cp = src;
 313         dn = dst;
 314         eom = dst + dstsiz;
 315
 316         while ((n = *cp++) != 0) {
 317                 if ((n & NS_CMPRSFLGS) != 0) {
 318                         /* Some kind of compression pointer. */
 319                         __set_errno (EMSGSIZE);
 320                         return (-1);
 321                 }
 322                 *dn++ = n;
 323                 if (dn + n >= eom) {
 324                         __set_errno (EMSGSIZE);
 325                         return (-1);
 326                 }
 327                 for ((void)NULL; n > 0; n--) {
 328                         c = *cp++;
 329                         if (isupper(c))
 330                                 *dn++ = tolower(c);
 331                         else
 332                                 *dn++ = c;
 333                 }
 334         }
 335         *dn++ = '\0';
 336         return (dn - dst);
 337 }
 338
 339 /*
 340  * ns_name_unpack(msg, eom, src, dst, dstsiz)
 341  *      Unpack a domain name from a message, source may be compressed.
 342  * return:
 343  *      -1 if it fails, or consumed octets if it succeeds.
 344  */
 345 int
 346 ns_name_unpack(const u_char *msg, const u_char *eom, const u_char *src,
 347                u_char *dst, size_t dstsiz)
 348 {
 349         const u_char *srcp, *dstlim;
 350         u_char *dstp;
 351         int n, len, checked;
 352
 353         len = -1;
 354         checked = 0;
 355         dstp = dst;
 356         srcp = src;
 357         dstlim = dst + dstsiz;
 358         if (srcp < msg || srcp >= eom) {
 359                 __set_errno (EMSGSIZE);
 360                 return (-1);
 361         }
 362         /* Fetch next label in domain name. */
 363         while ((n = *srcp++) != 0) {
 364                 /* Check for indirection. */
 365                 switch (n & NS_CMPRSFLGS) {
 366                 case 0x40:
 367                         if (n == 0x41) {
 368                                 if (dstp + 1 >= dstlim) {
 369                                         __set_errno (EMSGSIZE);
 370                                         return (-1);
 371                                 }
 372                                 *dstp++ = 0x41;
 373                                 n = *srcp++ / 8;
 374                                 ++checked;
 375                         } else {
 376                                 __set_errno (EMSGSIZE);
 377                                 return (-1);            /* flag error */
 378                         }
 379                         /* FALLTHROUGH */
 380                 case 0:
 381                         /* Limit checks. */
 382                         if (dstp + n + 1 >= dstlim || srcp + n >= eom) {
 383                                 __set_errno (EMSGSIZE);
 384                                 return (-1);
 385                         }
 386                         checked += n + 1;
 387                         dstp = mempcpy(dstp, srcp - 1, n + 1);
 388                         srcp += n;
 389                         break;
 390
 391                 case NS_CMPRSFLGS:
 392                         if (srcp >= eom) {
 393                                 __set_errno (EMSGSIZE);
 394                                 return (-1);
 395                         }
 396                         if (len < 0)
 397                                 len = srcp - src + 1;
 398                         srcp = msg + (((n & 0x3f) << 8) | (*srcp & 0xff));
 399                         if (srcp < msg || srcp >= eom) {  /* Out of range. */
 400                                 __set_errno (EMSGSIZE);
 401                                 return (-1);
 402                         }
 403                         checked += 2;
 404                         /*
 405                          * Check for loops in the compressed name;
 406                          * if we've looked at the whole message,
 407                          * there must be a loop.
 408                          */
 409                         if (checked >= eom - msg) {
 410                                 __set_errno (EMSGSIZE);
 411                                 return (-1);
 412                         }
 413                         break;
 414
 415                 default:
 416                         __set_errno (EMSGSIZE);
 417                         return (-1);                    /* flag error */
 418                 }
 419         }
 420         *dstp = '\0';
 421         if (len < 0)
 422                 len = srcp - src;
 423         return (len);
 424 }
 425 libresolv_hidden_def (ns_name_unpack)
 426
 427 /*
 428  * ns_name_pack(src, dst, dstsiz, dnptrs, lastdnptr)
 429  *      Pack domain name 'domain' into 'comp_dn'.
 430  * return:
 431  *      Size of the compressed name, or -1.
 432  * notes:
 433  *      'dnptrs' is an array of pointers to previous compressed names.
 434  *      dnptrs[0] is a pointer to the beginning of the message. The array
 435  *      ends with NULL.
 436  *      'lastdnptr' is a pointer to the end of the array pointed to
 437  *      by 'dnptrs'.
 438  * Side effects:
 439  *      The list of pointers in dnptrs is updated for labels inserted into
 440  *      the message as we compress the name.  If 'dnptr' is NULL, we don't
 441  *      try to compress names. If 'lastdnptr' is NULL, we don't update the
 442  *      list.
 443  */
 444 int
 445 ns_name_pack(const u_char *src, u_char *dst, int dstsiz,
 446              const u_char **dnptrs, const u_char **lastdnptr)
 447 {
 448         u_char *dstp;
 449         const u_char **cpp, **lpp, *eob, *msg;
 450         const u_char *srcp;
 451         int n, l, first = 1;
 452
 453         srcp = src;
 454         dstp = dst;
 455         eob = dstp + dstsiz;
 456         lpp = cpp = NULL;
 457         if (dnptrs != NULL) {
 458                 if ((msg = *dnptrs++) != NULL) {
 459                         for (cpp = dnptrs; *cpp != NULL; cpp++)
 460                                 (void)NULL;
 461                         lpp = cpp;      /* end of list to search */
 462                 }
 463         } else
 464                 msg = NULL;
 465
 466         /* make sure the domain we are about to add is legal */
 467         l = 0;
 468         do {
 469                 n = *srcp;
 470                 if ((n & NS_CMPRSFLGS) != 0 && n != 0x41) {
 471                         __set_errno (EMSGSIZE);
 472                         return (-1);
 473                 }
 474                 if (n == 0x41)
 475                         n = *++srcp / 8;
 476                 l += n + 1;
 477                 if (l > MAXCDNAME) {
 478                         __set_errno (EMSGSIZE);
 479                         return (-1);
 480                 }
 481                 srcp += n + 1;
 482         } while (n != 0);
 483
 484         /* from here on we need to reset compression pointer array on error */
 485         srcp = src;
 486         do {
 487                 /* Look to see if we can use pointers. */
 488                 n = *srcp;
 489                 if (n != 0 && n != 0x41 && msg != NULL) {
 490                         l = dn_find(srcp, msg, (const u_char * const *)dnptrs,
 491                                     (const u_char * const *)lpp);
 492                         if (l >= 0) {
 493                                 if (dstp + 1 >= eob) {
 494                                         goto cleanup;
 495                                 }
 496                                 *dstp++ = (l >> 8) | NS_CMPRSFLGS;
 497                                 *dstp++ = l % 256;
 498                                 return (dstp - dst);
 499                         }
 500                         /* Not found, save it. */
 501                         if (lastdnptr != NULL && cpp < lastdnptr - 1 &&
 502                             (dstp - msg) < 0x4000 && first) {
 503                                 *cpp++ = dstp;
 504                                 *cpp = NULL;
 505                                 first = 0;
 506                         }
 507                 }
 508                 /* copy label to buffer */
 509                 if ((n & NS_CMPRSFLGS) != 0 && n != 0x41) {             /* Should not happen. */
 510                         goto cleanup;
 511                 }
 512                 if (n == 0x41) {
 513                         n = *++srcp / 8;
 514                         if (dstp + 1 >= eob)
 515                                 goto cleanup;
 516                         *dstp++ = 0x41;
 517                 }
 518                 if (dstp + 1 + n >= eob) {
 519                         goto cleanup;
 520                 }
 521                 memcpy(dstp, srcp, n + 1);
 522                 srcp += n + 1;
 523                 dstp += n + 1;
 524         } while (n != 0);
 525
 526         if (dstp > eob) {
 527 cleanup:
 528                 if (msg != NULL)
 529                         *lpp = NULL;
 530                 __set_errno (EMSGSIZE);
 531                 return (-1);
 532         }
 533         return (dstp - dst);
 534 }
 535
 536 /*
 537  * ns_name_uncompress(msg, eom, src, dst, dstsiz)
 538  *      Expand compressed domain name to presentation format.
 539  * return:
 540  *      Number of bytes read out of `src', or -1 (with errno set).
 541  * note:
 542  *      Root domain returns as "." not "".
 543  */
 544 int
 545 ns_name_uncompress(const u_char *msg, const u_char *eom, const u_char *src,
 546                    char *dst, size_t dstsiz)
 547 {
 548         u_char tmp[NS_MAXCDNAME];
 549         int n;
 550
 551         if ((n = ns_name_unpack(msg, eom, src, tmp, sizeof tmp)) == -1)
 552                 return (-1);
 553         if (ns_name_ntop(tmp, dst, dstsiz) == -1)
 554                 return (-1);
 555         return (n);
 556 }
 557
 558 /*
 559  * ns_name_compress(src, dst, dstsiz, dnptrs, lastdnptr)
 560  *      Compress a domain name into wire format, using compression pointers.
 561  * return:
 562  *      Number of bytes consumed in `dst' or -1 (with errno set).
 563  * notes:
 564  *      'dnptrs' is an array of pointers to previous compressed names.
 565  *      dnptrs[0] is a pointer to the beginning of the message.
 566  *      The list ends with NULL.  'lastdnptr' is a pointer to the end of the
 567  *      array pointed to by 'dnptrs'. Side effect is to update the list of
 568  *      pointers for labels inserted into the message as we compress the name.
 569  *      If 'dnptr' is NULL, we don't try to compress names. If 'lastdnptr'
 570  *      is NULL, we don't update the list.
 571  */
 572 int
 573 ns_name_compress(const char *src, u_char *dst, size_t dstsiz,
 574                  const u_char **dnptrs, const u_char **lastdnptr)
 575 {
 576         u_char tmp[NS_MAXCDNAME];
 577
 578         if (ns_name_pton(src, tmp, sizeof tmp) == -1)
 579                 return (-1);
 580         return (ns_name_pack(tmp, dst, dstsiz, dnptrs, lastdnptr));
 581 }
 582
 583 /*
 584  * Reset dnptrs so that there are no active references to pointers at or
 585  * after src.
 586  */
 587 void
 588 ns_name_rollback(const u_char *src, const u_char **dnptrs,
 589                  const u_char **lastdnptr)
 590 {
 591         while (dnptrs < lastdnptr && *dnptrs != NULL) {
 592                 if (*dnptrs >= src) {
 593                         *dnptrs = NULL;
 594                         break;
 595                 }
 596                 dnptrs++;
 597         }
 598 }
 599
 600 /*
 601  * ns_name_skip(ptrptr, eom)
 602  *      Advance *ptrptr to skip over the compressed name it points at.
 603  * return:
 604  *      0 on success, -1 (with errno set) on failure.
 605  */
 606 int
 607 ns_name_skip(const u_char **ptrptr, const u_char *eom) {
 608         const u_char *cp;
 609         u_int n;
 610
 611         cp = *ptrptr;
 612         while (cp < eom && (n = *cp++) != 0) {
 613                 /* Check for indirection. */
 614                 switch (n & NS_CMPRSFLGS) {
 615                 case 0:                 /* normal case, n == len */
 616                         cp += n;
 617                         continue;
 618                 case NS_CMPRSFLGS:      /* indirection */
 619                         cp++;
 620                         break;
 621                 default:                /* illegal type */
 622                         __set_errno (EMSGSIZE);
 623                         return (-1);
 624                 }
 625                 break;
 626         }
 627         if (cp > eom) {
 628                 __set_errno (EMSGSIZE);
 629                 return (-1);
 630         }
 631         *ptrptr = cp;
 632         return (0);
 633 }
 634
 635 /* Private. */
 636
 637 /*
 638  * special(ch)
 639  *      Thinking in noninternationalized USASCII (per the DNS spec),
 640  *      is this characted special ("in need of quoting") ?
 641  * return:
 642  *      boolean.
 643  */
 644 static int
 645 special(int ch) {
 646         switch (ch) {
 647         case 0x22: /* '"' */
 648         case 0x2E: /* '.' */
 649         case 0x3B: /* ';' */
 650         case 0x5C: /* '\\' */
 651         /* Special modifiers in zone files. */
 652         case 0x40: /* '@' */
 653         case 0x24: /* '$' */
 654                 return (1);
 655         default:
 656                 return (0);
 657         }
 658 }
 659
 660 /*
 661  * printable(ch)
 662  *      Thinking in noninternationalized USASCII (per the DNS spec),
 663  *      is this character visible and not a space when printed ?
 664  * return:
 665  *      boolean.
 666  */
 667 static int
 668 printable(int ch) {
 669         return (ch > 0x20 && ch < 0x7f);
 670 }
 671
 672 /*
 673  *      Thinking in noninternationalized USASCII (per the DNS spec),
 674  *      convert this character to lower case if it's upper case.
 675  */
 676 static int
 677 mklower(int ch) {
 678         if (ch >= 0x41 && ch <= 0x5A)
 679                 return (ch + 0x20);
 680         return (ch);
 681 }
 682
 683 /*
 684  * dn_find(domain, msg, dnptrs, lastdnptr)
 685  *      Search for the counted-label name in an array of compressed names.
 686  * return:
 687  *      offset from msg if found, or -1.
 688  * notes:
 689  *      dnptrs is the pointer to the first name on the list,
 690  *      not the pointer to the start of the message.
 691  */
 692 static int
 693 dn_find(const u_char *domain, const u_char *msg,
 694         const u_char * const *dnptrs,
 695         const u_char * const *lastdnptr)
 696 {
 697         const u_char *dn, *cp, *sp;
 698         const u_char * const *cpp;
 699         u_int n;
 700
 701         for (cpp = dnptrs; cpp < lastdnptr; cpp++) {
 702                 sp = *cpp;
 703                 /*
 704                  * terminate search on:
 705                  * root label
 706                  * compression pointer
 707                  * unusable offset
 708                  */
 709                 while (*sp != 0 && (*sp & NS_CMPRSFLGS) == 0 &&
 710                        (sp - msg) < 0x4000) {
 711                         dn = domain;
 712                         cp = sp;
 713                         while ((n = *cp++) != 0) {
 714                                 /*
 715                                  * check for indirection
 716                                  */
 717                                 switch (n & NS_CMPRSFLGS) {
 718                                 case 0:         /* normal case, n == len */
 719                                         if (n != *dn++)
 720                                                 goto next;
 721                                         for ((void)NULL; n > 0; n--)
 722                                                 if (mklower(*dn++) !=
 723                                                     mklower(*cp++))
 724                                                         goto next;
 725                                         /* Is next root for both ? */
 726                                         if (*dn == '\0' && *cp == '\0')
 727                                                 return (sp - msg);
 728                                         if (*dn)
 729                                                 continue;
 730                                         goto next;
 731
 732                                 case NS_CMPRSFLGS:      /* indirection */
 733                                         cp = msg + (((n & 0x3f) << 8) | *cp);
 734                                         break;
 735
 736                                 default:        /* illegal type */
 737                                         __set_errno (EMSGSIZE);
 738                                         return (-1);
 739                                 }
 740                         }
 741  next:
 742                         sp += *sp + 1;
 743                 }
 744         }
 745         __set_errno (ENOENT);
 746         return (-1);
 747 }