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
 149 /*
 150  * ns_name_pton(src, dst, dstsiz)
 151  *      Convert a ascii string into an encoded domain name as per RFC1035.
 152  * return:
 153  *      -1 if it fails
 154  *      1 if string was fully qualified
 155  *      0 is string was not fully qualified
 156  * notes:
 157  *      Enforces label and domain length limits.
 158  */
 159
 160 int
 161 ns_name_pton(const char *src, u_char *dst, size_t dstsiz) {
 162         u_char *label, *bp, *eom;
 163         int c, n, escaped;
 164         char *cp;
 165
 166         escaped = 0;
 167         bp = dst;
 168         eom = dst + dstsiz;
 169         label = bp++;
 170
 171         while ((c = *src++) != 0) {
 172                 if (escaped) {
 173                         if ((cp = strchr(digits, c)) != NULL) {
 174                                 n = (cp - digits) * 100;
 175                                 if ((c = *src++) == 0 ||
 176                                     (cp = strchr(digits, c)) == NULL) {
 177                                         __set_errno (EMSGSIZE);
 178                                         return (-1);
 179                                 }
 180                                 n += (cp - digits) * 10;
 181                                 if ((c = *src++) == 0 ||
 182                                     (cp = strchr(digits, c)) == NULL) {
 183                                         __set_errno (EMSGSIZE);
 184                                         return (-1);
 185                                 }
 186                                 n += (cp - digits);
 187                                 if (n > 255) {
 188                                         __set_errno (EMSGSIZE);
 189                                         return (-1);
 190                                 }
 191                                 c = n;
 192                         } else if (c == '[' && label == bp - 1 && *src == 'x') {
 193                                 /* Theoretically we would have to handle \[o
 194                                    as well but we do not since we do not need
 195                                    it internally.  */
 196                                 *label = 0x41;
 197                                 label = bp++;
 198                                 ++src;
 199                                 while (isxdigit (*src)) {
 200                                         n = *src > '9' ? *src - 'a' + 10 : *src - '0';
 201                                         ++src;
 202                                         if (! isxdigit(*src)) {
 203                                                 __set_errno (EMSGSIZE);
 204                                                 return (-1);
 205                                         }
 206                                         n <<= 4;
 207                                         n += *src > '9' ? *src - 'a' + 10 : *src - '0';
 208                                         if (bp + 1 >= eom) {
 209                                                 __set_errno (EMSGSIZE);
 210                                                 return (-1);
 211                                         }
 212                                         *bp++ = n;
 213                                         ++src;
 214                                 }
 215                                 *label = (bp - label - 1) * 8;
 216                                 if (*src++ != ']' || *src++ != '.') {
 217                                         __set_errno (EMSGSIZE);
 218                                         return (-1);
 219                                 }
 220                                 escaped = 0;
 221                                 label = bp++;
 222                                 if (bp >= eom) {
 223                                         __set_errno (EMSGSIZE);
 224                                         return (-1);
 225                                 }
 226                                 continue;
 227                         }
 228                         escaped = 0;
 229                 } else if (c == '\\') {
 230                         escaped = 1;
 231                         continue;
 232                 } else if (c == '.') {
 233                         c = (bp - label - 1);
 234                         if ((c & NS_CMPRSFLGS) != 0) {  /* Label too big. */
 235                                 __set_errno (EMSGSIZE);
 236                                 return (-1);
 237                         }
 238                         if (label >= eom) {
 239                                 __set_errno (EMSGSIZE);
 240                                 return (-1);
 241                         }
 242                         *label = c;
 243                         /* Fully qualified ? */
 244                         if (*src == '\0') {
 245                                 if (c != 0) {
 246                                         if (bp >= eom) {
 247                                                 __set_errno (EMSGSIZE);
 248                                                 return (-1);
 249                                         }
 250                                         *bp++ = '\0';
 251                                 }
 252                                 if ((bp - dst) > MAXCDNAME) {
 253                                         __set_errno (EMSGSIZE);
 254                                         return (-1);
 255                                 }
 256                                 return (1);
 257                         }
 258                         if (c == 0 || *src == '.') {
 259                                 __set_errno (EMSGSIZE);
 260                                 return (-1);
 261                         }
 262                         label = bp++;
 263                         continue;
 264                 }
 265                 if (bp >= eom) {
 266                         __set_errno (EMSGSIZE);
 267                         return (-1);
 268                 }
 269                 *bp++ = (u_char)c;
 270         }
 271         c = (bp - label - 1);
 272         if ((c & NS_CMPRSFLGS) != 0) {          /* Label too big. */
 273                 __set_errno (EMSGSIZE);
 274                 return (-1);
 275         }
 276         if (label >= eom) {
 277                 __set_errno (EMSGSIZE);
 278                 return (-1);
 279         }
 280         *label = c;
 281         if (c != 0) {
 282                 if (bp >= eom) {
 283                         __set_errno (EMSGSIZE);
 284                         return (-1);
 285                 }
 286                 *bp++ = 0;
 287         }
 288         if ((bp - dst) > MAXCDNAME) {   /* src too big */
 289                 __set_errno (EMSGSIZE);
 290                 return (-1);
 291         }
 292         return (0);
 293 }
 294
 295 /*
 296  * ns_name_ntol(src, dst, dstsiz)
 297  *      Convert a network strings labels into all lowercase.
 298  * return:
 299  *      Number of bytes written to buffer, or -1 (with errno set)
 300  * notes:
 301  *      Enforces label and domain length limits.
 302  */
 303
 304 int
 305 ns_name_ntol(const u_char *src, u_char *dst, size_t dstsiz) {
 306         const u_char *cp;
 307         u_char *dn, *eom;
 308         u_char c;
 309         u_int n;
 310
 311         cp = src;
 312         dn = dst;
 313         eom = dst + dstsiz;
 314
 315         while ((n = *cp++) != 0) {
 316                 if ((n & NS_CMPRSFLGS) != 0) {
 317                         /* Some kind of compression pointer. */
 318                         __set_errno (EMSGSIZE);
 319                         return (-1);
 320                 }
 321                 *dn++ = n;
 322                 if (dn + n >= eom) {
 323                         __set_errno (EMSGSIZE);
 324                         return (-1);
 325                 }
 326                 for ((void)NULL; n > 0; n--) {
 327                         c = *cp++;
 328                         if (isupper(c))
 329                                 *dn++ = tolower(c);
 330                         else
 331                                 *dn++ = c;
 332                 }
 333         }
 334         *dn++ = '\0';
 335         return (dn - dst);
 336 }
 337
 338 /*
 339  * ns_name_unpack(msg, eom, src, dst, dstsiz)
 340  *      Unpack a domain name from a message, source may be compressed.
 341  * return:
 342  *      -1 if it fails, or consumed octets if it succeeds.
 343  */
 344 int
 345 ns_name_unpack(const u_char *msg, const u_char *eom, const u_char *src,
 346                u_char *dst, size_t dstsiz)
 347 {
 348         const u_char *srcp, *dstlim;
 349         u_char *dstp;
 350         int n, len, checked;
 351
 352         len = -1;
 353         checked = 0;
 354         dstp = dst;
 355         srcp = src;
 356         dstlim = dst + dstsiz;
 357         if (srcp < msg || srcp >= eom) {
 358                 __set_errno (EMSGSIZE);
 359                 return (-1);
 360         }
 361         /* Fetch next label in domain name. */
 362         while ((n = *srcp++) != 0) {
 363                 /* Check for indirection. */
 364                 switch (n & NS_CMPRSFLGS) {
 365                 case 0x40:
 366                         if (n == 0x41) {
 367                                 if (dstp + 1 >= dstlim) {
 368                                         __set_errno (EMSGSIZE);
 369                                         return (-1);
 370                                 }
 371                                 *dstp++ = 0x41;
 372                                 n = *srcp++ / 8;
 373                                 ++checked;
 374                         } else {
 375                                 __set_errno (EMSGSIZE);
 376                                 return (-1);            /* flag error */
 377                         }
 378                         /* FALLTHROUGH */
 379                 case 0:
 380                         /* Limit checks. */
 381                         if (dstp + n + 1 >= dstlim || srcp + n >= eom) {
 382                                 __set_errno (EMSGSIZE);
 383                                 return (-1);
 384                         }
 385                         checked += n + 1;
 386                         dstp = mempcpy(dstp, srcp - 1, n + 1);
 387                         srcp += n;
 388                         break;
 389
 390                 case NS_CMPRSFLGS:
 391                         if (srcp >= eom) {
 392                                 __set_errno (EMSGSIZE);
 393                                 return (-1);
 394                         }
 395                         if (len < 0)
 396                                 len = srcp - src + 1;
 397                         srcp = msg + (((n & 0x3f) << 8) | (*srcp & 0xff));
 398                         if (srcp < msg || srcp >= eom) {  /* Out of range. */
 399                                 __set_errno (EMSGSIZE);
 400                                 return (-1);
 401                         }
 402                         checked += 2;
 403                         /*
 404                          * Check for loops in the compressed name;
 405                          * if we've looked at the whole message,
 406                          * there must be a loop.
 407                          */
 408                         if (checked >= eom - msg) {
 409                                 __set_errno (EMSGSIZE);
 410                                 return (-1);
 411                         }
 412                         break;
 413
 414                 default:
 415                         __set_errno (EMSGSIZE);
 416                         return (-1);                    /* flag error */
 417                 }
 418         }
 419         *dstp = '\0';
 420         if (len < 0)
 421                 len = srcp - src;
 422         return (len);
 423 }
 424
 425 /*
 426  * ns_name_pack(src, dst, dstsiz, dnptrs, lastdnptr)
 427  *      Pack domain name 'domain' into 'comp_dn'.
 428  * return:
 429  *      Size of the compressed name, or -1.
 430  * notes:
 431  *      'dnptrs' is an array of pointers to previous compressed names.
 432  *      dnptrs[0] is a pointer to the beginning of the message. The array
 433  *      ends with NULL.
 434  *      'lastdnptr' is a pointer to the end of the array pointed to
 435  *      by 'dnptrs'.
 436  * Side effects:
 437  *      The list of pointers in dnptrs is updated for labels inserted into
 438  *      the message as we compress the name.  If 'dnptr' is NULL, we don't
 439  *      try to compress names. If 'lastdnptr' is NULL, we don't update the
 440  *      list.
 441  */
 442 int
 443 ns_name_pack(const u_char *src, u_char *dst, int dstsiz,
 444              const u_char **dnptrs, const u_char **lastdnptr)
 445 {
 446         u_char *dstp;
 447         const u_char **cpp, **lpp, *eob, *msg;
 448         const u_char *srcp;
 449         int n, l, first = 1;
 450
 451         srcp = src;
 452         dstp = dst;
 453         eob = dstp + dstsiz;
 454         lpp = cpp = NULL;
 455         if (dnptrs != NULL) {
 456                 if ((msg = *dnptrs++) != NULL) {
 457                         for (cpp = dnptrs; *cpp != NULL; cpp++)
 458                                 (void)NULL;
 459                         lpp = cpp;      /* end of list to search */
 460                 }
 461         } else
 462                 msg = NULL;
 463
 464         /* make sure the domain we are about to add is legal */
 465         l = 0;
 466         do {
 467                 n = *srcp;
 468                 if ((n & NS_CMPRSFLGS) != 0 && n != 0x41) {
 469                         __set_errno (EMSGSIZE);
 470                         return (-1);
 471                 }
 472                 if (n == 0x41)
 473                         n = *++srcp / 8;
 474                 l += n + 1;
 475                 if (l > MAXCDNAME) {
 476                         __set_errno (EMSGSIZE);
 477                         return (-1);
 478                 }
 479                 srcp += n + 1;
 480         } while (n != 0);
 481
 482         /* from here on we need to reset compression pointer array on error */
 483         srcp = src;
 484         do {
 485                 /* Look to see if we can use pointers. */
 486                 n = *srcp;
 487                 if (n != 0 && n != 0x41 && msg != NULL) {
 488                         l = dn_find(srcp, msg, (const u_char * const *)dnptrs,
 489                                     (const u_char * const *)lpp);
 490                         if (l >= 0) {
 491                                 if (dstp + 1 >= eob) {
 492                                         goto cleanup;
 493                                 }
 494                                 *dstp++ = (l >> 8) | NS_CMPRSFLGS;
 495                                 *dstp++ = l % 256;
 496                                 return (dstp - dst);
 497                         }
 498                         /* Not found, save it. */
 499                         if (lastdnptr != NULL && cpp < lastdnptr - 1 &&
 500                             (dstp - msg) < 0x4000 && first) {
 501                                 *cpp++ = dstp;
 502                                 *cpp = NULL;
 503                                 first = 0;
 504                         }
 505                 }
 506                 /* copy label to buffer */
 507                 if ((n & NS_CMPRSFLGS) != 0 && n != 0x41) {             /* Should not happen. */
 508                         goto cleanup;
 509                 }
 510                 if (n == 0x41) {
 511                         n = *++srcp / 8;
 512                         if (dstp + 1 >= eob)
 513                                 goto cleanup;
 514                         *dstp++ = 0x41;
 515                 }
 516                 if (dstp + 1 + n >= eob) {
 517                         goto cleanup;
 518                 }
 519                 memcpy(dstp, srcp, n + 1);
 520                 srcp += n + 1;
 521                 dstp += n + 1;
 522         } while (n != 0);
 523
 524         if (dstp > eob) {
 525 cleanup:
 526                 if (msg != NULL)
 527                         *lpp = NULL;
 528                 __set_errno (EMSGSIZE);
 529                 return (-1);
 530         }
 531         return (dstp - dst);
 532 }
 533
 534 /*
 535  * ns_name_uncompress(msg, eom, src, dst, dstsiz)
 536  *      Expand compressed domain name to presentation format.
 537  * return:
 538  *      Number of bytes read out of `src', or -1 (with errno set).
 539  * note:
 540  *      Root domain returns as "." not "".
 541  */
 542 int
 543 ns_name_uncompress(const u_char *msg, const u_char *eom, const u_char *src,
 544                    char *dst, size_t dstsiz)
 545 {
 546         u_char tmp[NS_MAXCDNAME];
 547         int n;
 548
 549         if ((n = ns_name_unpack(msg, eom, src, tmp, sizeof tmp)) == -1)
 550                 return (-1);
 551         if (ns_name_ntop(tmp, dst, dstsiz) == -1)
 552                 return (-1);
 553         return (n);
 554 }
 555
 556 /*
 557  * ns_name_compress(src, dst, dstsiz, dnptrs, lastdnptr)
 558  *      Compress a domain name into wire format, using compression pointers.
 559  * return:
 560  *      Number of bytes consumed in `dst' or -1 (with errno set).
 561  * notes:
 562  *      'dnptrs' is an array of pointers to previous compressed names.
 563  *      dnptrs[0] is a pointer to the beginning of the message.
 564  *      The list ends with NULL.  'lastdnptr' is a pointer to the end of the
 565  *      array pointed to by 'dnptrs'. Side effect is to update the list of
 566  *      pointers for labels inserted into the message as we compress the name.
 567  *      If 'dnptr' is NULL, we don't try to compress names. If 'lastdnptr'
 568  *      is NULL, we don't update the list.
 569  */
 570 int
 571 ns_name_compress(const char *src, u_char *dst, size_t dstsiz,
 572                  const u_char **dnptrs, const u_char **lastdnptr)
 573 {
 574         u_char tmp[NS_MAXCDNAME];
 575
 576         if (ns_name_pton(src, tmp, sizeof tmp) == -1)
 577                 return (-1);
 578         return (ns_name_pack(tmp, dst, dstsiz, dnptrs, lastdnptr));
 579 }
 580
 581 /*
 582  * Reset dnptrs so that there are no active references to pointers at or
 583  * after src.
 584  */
 585 void
 586 ns_name_rollback(const u_char *src, const u_char **dnptrs,
 587                  const u_char **lastdnptr)
 588 {
 589         while (dnptrs < lastdnptr && *dnptrs != NULL) {
 590                 if (*dnptrs >= src) {
 591                         *dnptrs = NULL;
 592                         break;
 593                 }
 594                 dnptrs++;
 595         }
 596 }
 597
 598 /*
 599  * ns_name_skip(ptrptr, eom)
 600  *      Advance *ptrptr to skip over the compressed name it points at.
 601  * return:
 602  *      0 on success, -1 (with errno set) on failure.
 603  */
 604 int
 605 ns_name_skip(const u_char **ptrptr, const u_char *eom) {
 606         const u_char *cp;
 607         u_int n;
 608
 609         cp = *ptrptr;
 610         while (cp < eom && (n = *cp++) != 0) {
 611                 /* Check for indirection. */
 612                 switch (n & NS_CMPRSFLGS) {
 613                 case 0:                 /* normal case, n == len */
 614                         cp += n;
 615                         continue;
 616                 case NS_CMPRSFLGS:      /* indirection */
 617                         cp++;
 618                         break;
 619                 default:                /* illegal type */
 620                         __set_errno (EMSGSIZE);
 621                         return (-1);
 622                 }
 623                 break;
 624         }
 625         if (cp > eom) {
 626                 __set_errno (EMSGSIZE);
 627                 return (-1);
 628         }
 629         *ptrptr = cp;
 630         return (0);
 631 }
 632
 633 /* Private. */
 634
 635 /*
 636  * special(ch)
 637  *      Thinking in noninternationalized USASCII (per the DNS spec),
 638  *      is this characted special ("in need of quoting") ?
 639  * return:
 640  *      boolean.
 641  */
 642 static int
 643 special(int ch) {
 644         switch (ch) {
 645         case 0x22: /* '"' */
 646         case 0x2E: /* '.' */
 647         case 0x3B: /* ';' */
 648         case 0x5C: /* '\\' */
 649         /* Special modifiers in zone files. */
 650         case 0x40: /* '@' */
 651         case 0x24: /* '$' */
 652                 return (1);
 653         default:
 654                 return (0);
 655         }
 656 }
 657
 658 /*
 659  * printable(ch)
 660  *      Thinking in noninternationalized USASCII (per the DNS spec),
 661  *      is this character visible and not a space when printed ?
 662  * return:
 663  *      boolean.
 664  */
 665 static int
 666 printable(int ch) {
 667         return (ch > 0x20 && ch < 0x7f);
 668 }
 669
 670 /*
 671  *      Thinking in noninternationalized USASCII (per the DNS spec),
 672  *      convert this character to lower case if it's upper case.
 673  */
 674 static int
 675 mklower(int ch) {
 676         if (ch >= 0x41 && ch <= 0x5A)
 677                 return (ch + 0x20);
 678         return (ch);
 679 }
 680
 681 /*
 682  * dn_find(domain, msg, dnptrs, lastdnptr)
 683  *      Search for the counted-label name in an array of compressed names.
 684  * return:
 685  *      offset from msg if found, or -1.
 686  * notes:
 687  *      dnptrs is the pointer to the first name on the list,
 688  *      not the pointer to the start of the message.
 689  */
 690 static int
 691 dn_find(const u_char *domain, const u_char *msg,
 692         const u_char * const *dnptrs,
 693         const u_char * const *lastdnptr)
 694 {
 695         const u_char *dn, *cp, *sp;
 696         const u_char * const *cpp;
 697         u_int n;
 698
 699         for (cpp = dnptrs; cpp < lastdnptr; cpp++) {
 700                 sp = *cpp;
 701                 /*
 702                  * terminate search on:
 703                  * root label
 704                  * compression pointer
 705                  * unusable offset
 706                  */
 707                 while (*sp != 0 && (*sp & NS_CMPRSFLGS) == 0 &&
 708                        (sp - msg) < 0x4000) {
 709                         dn = domain;
 710                         cp = sp;
 711                         while ((n = *cp++) != 0) {
 712                                 /*
 713                                  * check for indirection
 714                                  */
 715                                 switch (n & NS_CMPRSFLGS) {
 716                                 case 0:         /* normal case, n == len */
 717                                         if (n != *dn++)
 718                                                 goto next;
 719                                         for ((void)NULL; n > 0; n--)
 720                                                 if (mklower(*dn++) !=
 721                                                     mklower(*cp++))
 722                                                         goto next;
 723                                         /* Is next root for both ? */
 724                                         if (*dn == '\0' && *cp == '\0')
 725                                                 return (sp - msg);
 726                                         if (*dn)
 727                                                 continue;
 728                                         goto next;
 729
 730                                 case NS_CMPRSFLGS:      /* indirection */
 731                                         cp = msg + (((n & 0x3f) << 8) | *cp);
 732                                         break;
 733
 734                                 default:        /* illegal type */
 735                                         __set_errno (EMSGSIZE);
 736                                         return (-1);
 737                                 }
 738                         }
 739  next:
 740                         sp += *sp + 1;
 741                 }
 742         }
 743         __set_errno (ENOENT);
 744         return (-1);
 745 }