resolv/res_query.c

   1 /*
   2  * Copyright (c) 1988, 1993
   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 the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 4. Neither the name of the University nor the names of its contributors
  14  *    may be used to endorse or promote products derived from this software
  15  *    without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27  * SUCH DAMAGE.
  28  */
  29
  30 /*
  31  * Portions Copyright (c) 1993 by Digital Equipment Corporation.
  32  *
  33  * Permission to use, copy, modify, and distribute this software for any
  34  * purpose with or without fee is hereby granted, provided that the above
  35  * copyright notice and this permission notice appear in all copies, and that
  36  * the name of Digital Equipment Corporation not be used in advertising or
  37  * publicity pertaining to distribution of the document or software without
  38  * specific, written prior permission.
  39  *
  40  * THE SOFTWARE IS PROVIDED "AS IS" AND DIGITAL EQUIPMENT CORP. DISCLAIMS ALL
  41  * WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES
  42  * OF MERCHANTABILITY AND FITNESS.   IN NO EVENT SHALL DIGITAL EQUIPMENT
  43  * CORPORATION BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
  44  * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
  45  * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
  46  * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
  47  * SOFTWARE.
  48  */
  49
  50 /*
  51  * Portions Copyright (c) 1996-1999 by Internet Software Consortium.
  52  *
  53  * Permission to use, copy, modify, and distribute this software for any
  54  * purpose with or without fee is hereby granted, provided that the above
  55  * copyright notice and this permission notice appear in all copies.
  56  *
  57  * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
  58  * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
  59  * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
  60  * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
  61  * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
  62  * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
  63  * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
  64  * SOFTWARE.
  65  */
  66
  67 #if defined(LIBC_SCCS) && !defined(lint)
  68 static const char sccsid[] = "@(#)res_query.c   8.1 (Berkeley) 6/4/93";
  69 static const char rcsid[] = "$BINDId: res_query.c,v 8.20 2000/02/29 05:39:12 vixie Exp $";
  70 #endif /* LIBC_SCCS and not lint */
  71
  72 #include <assert.h>
  73 #include <sys/types.h>
  74 #include <sys/param.h>
  75 #include <netinet/in.h>
  76 #include <arpa/inet.h>
  77 #include <arpa/nameser.h>
  78 #include <ctype.h>
  79 #include <errno.h>
  80 #include <netdb.h>
  81 #include <resolv.h>
  82 #include <stdio.h>
  83 #include <stdlib.h>
  84 #include <string.h>
  85
  86 /* Options.  Leave them on. */
  87 /* #undef DEBUG */
  88
  89 #if PACKETSZ > 65536
  90 #define MAXPACKET       PACKETSZ
  91 #else
  92 #define MAXPACKET       65536
  93 #endif
  94
  95 #define QUERYSIZE       (HFIXEDSZ + QFIXEDSZ + MAXCDNAME + 1)
  96
  97 static int
  98 __libc_res_nquerydomain(res_state statp, const char *name, const char *domain,
  99                         int class, int type, u_char *answer, int anslen,
 100                         u_char **answerp, u_char **answerp2, int *nanswerp2);
 101
 102 /*
 103  * Formulate a normal query, send, and await answer.
 104  * Returned answer is placed in supplied buffer "answer".
 105  * Perform preliminary check of answer, returning success only
 106  * if no error is indicated and the answer count is nonzero.
 107  * Return the size of the response on success, -1 on error.
 108  * Error number is left in H_ERRNO.
 109  *
 110  * Caller must parse answer and determine whether it answers the question.
 111  */
 112 int
 113 __libc_res_nquery(res_state statp,
 114                   const char *name,     /* domain name */
 115                   int class, int type,  /* class and type of query */
 116                   u_char *answer,       /* buffer to put answer */
 117                   int anslen,           /* size of answer buffer */
 118                   u_char **answerp,     /* if buffer needs to be enlarged */
 119                   u_char **answerp2,
 120                   int *nanswerp2)
 121 {
 122         HEADER *hp = (HEADER *) answer;
 123         int n, use_malloc = 0;
 124         u_int oflags = statp->_flags;
 125
 126         size_t bufsize = (type == T_UNSPEC ? 2 : 1) * QUERYSIZE;
 127         u_char *buf = alloca (bufsize);
 128         u_char *query1 = buf;
 129         int nquery1 = -1;
 130         u_char *query2 = NULL;
 131         int nquery2 = 0;
 132
 133  again:
 134         hp->rcode = NOERROR;    /* default */
 135
 136 #ifdef DEBUG
 137         if (statp->options & RES_DEBUG)
 138                 printf(";; res_query(%s, %d, %d)\n", name, class, type);
 139 #endif
 140
 141         if (type == T_UNSPEC)
 142           {
 143             n = res_nmkquery(statp, QUERY, name, class, T_A, NULL, 0, NULL,
 144                              query1, bufsize);
 145             if (n > 0)
 146               {
 147                 if ((oflags & RES_F_EDNS0ERR) == 0
 148                     && (statp->options & RES_USE_EDNS0) != 0)
 149                   {
 150                     n = __res_nopt(statp, n, query1, bufsize, anslen / 2);
 151                     if (n < 0)
 152                       goto unspec_nomem;
 153                   }
 154
 155                 nquery1 = n;
 156                 /* Align the buffer.  */
 157                 int npad = ((nquery1 + __alignof__ (HEADER) - 1)
 158                             & ~(__alignof__ (HEADER) - 1)) - nquery1;
 159                 if (n > bufsize - npad)
 160                   {
 161                     n = -1;
 162                     goto unspec_nomem;
 163                   }
 164                 int nused = n + npad;
 165                 query2 = buf + nused;
 166                 n = res_nmkquery(statp, QUERY, name, class, T_AAAA, NULL, 0,
 167                                  NULL, query2, bufsize - nused);
 168                 if (n > 0
 169                     && (oflags & RES_F_EDNS0ERR) == 0
 170                     && (statp->options & RES_USE_EDNS0) != 0)
 171                   n = __res_nopt(statp, n, query2, bufsize - nused - n,
 172                                  anslen / 2);
 173                 nquery2 = n;
 174               }
 175
 176           unspec_nomem:;
 177           }
 178         else
 179           {
 180             n = res_nmkquery(statp, QUERY, name, class, type, NULL, 0, NULL,
 181                              query1, bufsize);
 182
 183             if (n > 0
 184                 && (oflags & RES_F_EDNS0ERR) == 0
 185                 && (statp->options & RES_USE_EDNS0) != 0)
 186               n = __res_nopt(statp, n, query1, bufsize, anslen);
 187
 188             nquery1 = n;
 189           }
 190
 191         if (__builtin_expect (n <= 0, 0) && !use_malloc) {
 192                 /* Retry just in case res_nmkquery failed because of too
 193                    short buffer.  Shouldn't happen.  */
 194                 bufsize = (type == T_UNSPEC ? 2 : 1) * MAXPACKET;
 195                 buf = malloc (bufsize);
 196                 if (buf != NULL) {
 197                         query1 = buf;
 198                         use_malloc = 1;
 199                         goto again;
 200                 }
 201         }
 202         if (__builtin_expect (n <= 0, 0)) {
 203                 /* If the query choked with EDNS0, retry without EDNS0.  */
 204                 if ((statp->options & RES_USE_EDNS0) != 0
 205                     && ((oflags ^ statp->_flags) & RES_F_EDNS0ERR) != 0) {
 206                         statp->_flags |= RES_F_EDNS0ERR;
 207 #ifdef DEBUG
 208                         if (statp->options & RES_DEBUG)
 209                                 printf(";; res_nquery: retry without EDNS0\n");
 210 #endif
 211                         goto again;
 212                 }
 213 #ifdef DEBUG
 214                 if (statp->options & RES_DEBUG)
 215                         printf(";; res_query: mkquery failed\n");
 216 #endif
 217                 RES_SET_H_ERRNO(statp, NO_RECOVERY);
 218                 if (use_malloc)
 219                         free (buf);
 220                 return (n);
 221         }
 222         assert (answerp == NULL || (void *) *answerp == (void *) answer);
 223         n = __libc_res_nsend(statp, query1, nquery1, query2, nquery2, answer,
 224                              anslen, answerp, answerp2, nanswerp2);
 225         if (use_malloc)
 226                 free (buf);
 227         if (n < 0) {
 228 #ifdef DEBUG
 229                 if (statp->options & RES_DEBUG)
 230                         printf(";; res_query: send error\n");
 231 #endif
 232                 RES_SET_H_ERRNO(statp, TRY_AGAIN);
 233                 return (n);
 234         }
 235
 236         if (answerp != NULL)
 237           /* __libc_res_nsend might have reallocated the buffer.  */
 238           hp = (HEADER *) *answerp;
 239
 240         /* We simplify the following tests by assigning HP to HP2.  It
 241            is easy to verify that this is the same as ignoring all
 242            tests of HP2.  */
 243         HEADER *hp2 = answerp2 ? (HEADER *) *answerp2 : hp;
 244
 245         if (n < sizeof (HEADER) && nanswerp2 != NULL
 246             && *nanswerp2 > sizeof (HEADER))
 247           {
 248             /* Special case of partial answer.  */
 249             assert (hp != hp2);
 250             hp = hp2;
 251           }
 252         else if (nanswerp2 != NULL
 253                  && *nanswerp2 < sizeof (HEADER) && n > sizeof (HEADER))
 254           {
 255             /* Special case of partial answer.  */
 256             assert (hp != hp2);
 257             hp2 = hp;
 258           }
 259
 260         if ((hp->rcode != NOERROR || ntohs(hp->ancount) == 0)
 261             && (hp2->rcode != NOERROR || ntohs(hp2->ancount) == 0)) {
 262 #ifdef DEBUG
 263                 if (statp->options & RES_DEBUG) {
 264                         printf(";; rcode = %d, ancount=%d\n", hp->rcode,
 265                             ntohs(hp->ancount));
 266                         if (hp != hp2)
 267                           printf(";; rcode2 = %d, ancount2=%d\n", hp2->rcode,
 268                                  ntohs(hp2->ancount));
 269                 }
 270 #endif
 271                 switch (hp->rcode == NOERROR ? hp2->rcode : hp->rcode) {
 272                 case NXDOMAIN:
 273                         if ((hp->rcode == NOERROR && ntohs (hp->ancount) != 0)
 274                             || (hp2->rcode == NOERROR
 275                                 && ntohs (hp2->ancount) != 0))
 276                                 goto success;
 277                         RES_SET_H_ERRNO(statp, HOST_NOT_FOUND);
 278                         break;
 279                 case SERVFAIL:
 280                         RES_SET_H_ERRNO(statp, TRY_AGAIN);
 281                         break;
 282                 case NOERROR:
 283                         if (ntohs (hp->ancount) != 0
 284                             || ntohs (hp2->ancount) != 0)
 285                                 goto success;
 286                         RES_SET_H_ERRNO(statp, NO_DATA);
 287                         break;
 288                 case FORMERR:
 289                 case NOTIMP:
 290                 case REFUSED:
 291                 default:
 292                         RES_SET_H_ERRNO(statp, NO_RECOVERY);
 293                         break;
 294                 }
 295                 return (-1);
 296         }
 297  success:
 298         return (n);
 299 }
 300 libresolv_hidden_def (__libc_res_nquery)
 301
 302 int
 303 res_nquery(res_state statp,
 304            const char *name,    /* domain name */
 305            int class, int type, /* class and type of query */
 306            u_char *answer,      /* buffer to put answer */
 307            int anslen)          /* size of answer buffer */
 308 {
 309         return __libc_res_nquery(statp, name, class, type, answer, anslen,
 310                                  NULL, NULL, NULL);
 311 }
 312 libresolv_hidden_def (res_nquery)
 313
 314 /*
 315  * Formulate a normal query, send, and retrieve answer in supplied buffer.
 316  * Return the size of the response on success, -1 on error.
 317  * If enabled, implement search rules until answer or unrecoverable failure
 318  * is detected.  Error code, if any, is left in H_ERRNO.
 319  */
 320 int
 321 __libc_res_nsearch(res_state statp,
 322                    const char *name,    /* domain name */
 323                    int class, int type, /* class and type of query */
 324                    u_char *answer,      /* buffer to put answer */
 325                    int anslen,          /* size of answer */
 326                    u_char **answerp,
 327                    u_char **answerp2,
 328                    int *nanswerp2)
 329 {
 330         const char *cp, * const *domain;
 331         HEADER *hp = (HEADER *) answer;
 332         char tmp[NS_MAXDNAME];
 333         u_int dots;
 334         int trailing_dot, ret, saved_herrno;
 335         int got_nodata = 0, got_servfail = 0, root_on_list = 0;
 336         int tried_as_is = 0;
 337
 338         __set_errno (0);
 339         RES_SET_H_ERRNO(statp, HOST_NOT_FOUND);  /* True if we never query. */
 340
 341         dots = 0;
 342         for (cp = name; *cp != '\0'; cp++)
 343                 dots += (*cp == '.');
 344         trailing_dot = 0;
 345         if (cp > name && *--cp == '.')
 346                 trailing_dot++;
 347
 348         /* If there aren't any dots, it could be a user-level alias. */
 349         if (!dots && (cp = res_hostalias(statp, name, tmp, sizeof tmp))!= NULL)
 350                 return (__libc_res_nquery(statp, cp, class, type, answer,
 351                                           anslen, answerp, answerp2,
 352                                           nanswerp2));
 353
 354 #ifdef DEBUG
 355         if (statp->options & RES_DEBUG)
 356                 printf("dots=%d, statp->ndots=%d, trailing_dot=%d, name=%s\n",
 357                        (int)dots,(int)statp->ndots,(int)trailing_dot,name);
 358 #endif
 359
 360         /*
 361          * If there are enough dots in the name, let's just give it a
 362          * try 'as is'. The threshold can be set with the "ndots" option.
 363          * Also, query 'as is', if there is a trailing dot in the name.
 364          */
 365         saved_herrno = -1;
 366         if (dots >= statp->ndots || trailing_dot) {
 367                 ret = __libc_res_nquerydomain(statp, name, NULL, class, type,
 368                                               answer, anslen, answerp,
 369                                               answerp2, nanswerp2);
 370                 if (ret > 0 || trailing_dot)
 371                         return (ret);
 372                 saved_herrno = h_errno;
 373                 tried_as_is++;
 374                 if (answerp && *answerp != answer) {
 375                         answer = *answerp;
 376                         anslen = MAXPACKET;
 377                 }
 378                 if (answerp2
 379                     && (*answerp2 < answer || *answerp2 >= answer + anslen))
 380                   {
 381                     free (*answerp2);
 382                     *answerp2 = NULL;
 383                   }
 384         }
 385
 386         /*
 387          * We do at least one level of search if
 388          *      - there is no dot and RES_DEFNAME is set, or
 389          *      - there is at least one dot, there is no trailing dot,
 390          *        and RES_DNSRCH is set.
 391          */
 392         if ((!dots && (statp->options & RES_DEFNAMES) != 0) ||
 393             (dots && !trailing_dot && (statp->options & RES_DNSRCH) != 0)) {
 394                 int done = 0;
 395
 396                 for (domain = (const char * const *)statp->dnsrch;
 397                      *domain && !done;
 398                      domain++) {
 399
 400                         if (domain[0][0] == '\0' ||
 401                             (domain[0][0] == '.' && domain[0][1] == '\0'))
 402                                 root_on_list++;
 403
 404                         ret = __libc_res_nquerydomain(statp, name, *domain,
 405                                                       class, type,
 406                                                       answer, anslen, answerp,
 407                                                       answerp2, nanswerp2);
 408                         if (ret > 0)
 409                                 return (ret);
 410
 411                         if (answerp && *answerp != answer) {
 412                                 answer = *answerp;
 413                                 anslen = MAXPACKET;
 414                         }
 415                         if (answerp2
 416                             && (*answerp2 < answer
 417                                 || *answerp2 >= answer + anslen))
 418                           {
 419                             free (*answerp2);
 420                             *answerp2 = NULL;
 421                           }
 422
 423                         /*
 424                          * If no server present, give up.
 425                          * If name isn't found in this domain,
 426                          * keep trying higher domains in the search list
 427                          * (if that's enabled).
 428                          * On a NO_DATA error, keep trying, otherwise
 429                          * a wildcard entry of another type could keep us
 430                          * from finding this entry higher in the domain.
 431                          * If we get some other error (negative answer or
 432                          * server failure), then stop searching up,
 433                          * but try the input name below in case it's
 434                          * fully-qualified.
 435                          */
 436                         if (errno == ECONNREFUSED) {
 437                                 RES_SET_H_ERRNO(statp, TRY_AGAIN);
 438                                 return (-1);
 439                         }
 440
 441                         switch (statp->res_h_errno) {
 442                         case NO_DATA:
 443                                 got_nodata++;
 444                                 /* FALLTHROUGH */
 445                         case HOST_NOT_FOUND:
 446                                 /* keep trying */
 447                                 break;
 448                         case TRY_AGAIN:
 449                                 if (hp->rcode == SERVFAIL) {
 450                                         /* try next search element, if any */
 451                                         got_servfail++;
 452                                         break;
 453                                 }
 454                                 /* FALLTHROUGH */
 455                         default:
 456                                 /* anything else implies that we're done */
 457                                 done++;
 458                         }
 459
 460                         /* if we got here for some reason other than DNSRCH,
 461                          * we only wanted one iteration of the loop, so stop.
 462                          */
 463                         if ((statp->options & RES_DNSRCH) == 0)
 464                                 done++;
 465                 }
 466         }
 467
 468         /*
 469          * If the name has any dots at all, and no earlier 'as-is' query
 470          * for the name, and "." is not on the search list, then try an as-is
 471          * query now.
 472          */
 473         if (dots && !(tried_as_is || root_on_list)) {
 474                 ret = __libc_res_nquerydomain(statp, name, NULL, class, type,
 475                                               answer, anslen, answerp,
 476                                               answerp2, nanswerp2);
 477                 if (ret > 0)
 478                         return (ret);
 479         }
 480
 481         /* if we got here, we didn't satisfy the search.
 482          * if we did an initial full query, return that query's H_ERRNO
 483          * (note that we wouldn't be here if that query had succeeded).
 484          * else if we ever got a nodata, send that back as the reason.
 485          * else send back meaningless H_ERRNO, that being the one from
 486          * the last DNSRCH we did.
 487          */
 488         if (answerp2 && (*answerp2 < answer || *answerp2 >= answer + anslen))
 489           {
 490             free (*answerp2);
 491             *answerp2 = NULL;
 492           }
 493         if (saved_herrno != -1)
 494                 RES_SET_H_ERRNO(statp, saved_herrno);
 495         else if (got_nodata)
 496                 RES_SET_H_ERRNO(statp, NO_DATA);
 497         else if (got_servfail)
 498                 RES_SET_H_ERRNO(statp, TRY_AGAIN);
 499         return (-1);
 500 }
 501 libresolv_hidden_def (__libc_res_nsearch)
 502
 503 int
 504 res_nsearch(res_state statp,
 505             const char *name,   /* domain name */
 506             int class, int type,        /* class and type of query */
 507             u_char *answer,     /* buffer to put answer */
 508             int anslen)         /* size of answer */
 509 {
 510         return __libc_res_nsearch(statp, name, class, type, answer,
 511                                   anslen, NULL, NULL, NULL);
 512 }
 513 libresolv_hidden_def (res_nsearch)
 514
 515 /*
 516  * Perform a call on res_query on the concatenation of name and domain,
 517  * removing a trailing dot from name if domain is NULL.
 518  */
 519 static int
 520 __libc_res_nquerydomain(res_state statp,
 521                         const char *name,
 522                         const char *domain,
 523                         int class, int type,    /* class and type of query */
 524                         u_char *answer,         /* buffer to put answer */
 525                         int anslen,                     /* size of answer */
 526                         u_char **answerp,
 527                         u_char **answerp2,
 528                         int *nanswerp2)
 529 {
 530         char nbuf[MAXDNAME];
 531         const char *longname = nbuf;
 532         int n, d;
 533
 534 #ifdef DEBUG
 535         if (statp->options & RES_DEBUG)
 536                 printf(";; res_nquerydomain(%s, %s, %d, %d)\n",
 537                        name, domain?domain:"<Nil>", class, type);
 538 #endif
 539         if (domain == NULL) {
 540                 /*
 541                  * Check for trailing '.';
 542                  * copy without '.' if present.
 543                  */
 544                 n = strlen(name);
 545                 if (n >= MAXDNAME) {
 546                         RES_SET_H_ERRNO(statp, NO_RECOVERY);
 547                         return (-1);
 548                 }
 549                 n--;
 550                 if (n >= 0 && name[n] == '.') {
 551                         strncpy(nbuf, name, n);
 552                         nbuf[n] = '\0';
 553                 } else
 554                         longname = name;
 555         } else {
 556                 n = strlen(name);
 557                 d = strlen(domain);
 558                 if (n + d + 1 >= MAXDNAME) {
 559                         RES_SET_H_ERRNO(statp, NO_RECOVERY);
 560                         return (-1);
 561                 }
 562                 sprintf(nbuf, "%s.%s", name, domain);
 563         }
 564         return (__libc_res_nquery(statp, longname, class, type, answer,
 565                                   anslen, answerp, answerp2, nanswerp2));
 566 }
 567
 568 int
 569 res_nquerydomain(res_state statp,
 570             const char *name,
 571             const char *domain,
 572             int class, int type,        /* class and type of query */
 573             u_char *answer,             /* buffer to put answer */
 574             int anslen)         /* size of answer */
 575 {
 576         return __libc_res_nquerydomain(statp, name, domain, class, type,
 577                                        answer, anslen, NULL, NULL, NULL);
 578 }
 579 libresolv_hidden_def (res_nquerydomain)
 580
 581 const char *
 582 res_hostalias(const res_state statp, const char *name, char *dst, size_t siz) {
 583         char *file, *cp1, *cp2;
 584         char buf[BUFSIZ];
 585         FILE *fp;
 586
 587         if (statp->options & RES_NOALIASES)
 588                 return (NULL);
 589         file = getenv("HOSTALIASES");
 590         if (file == NULL || (fp = fopen(file, "r")) == NULL)
 591                 return (NULL);
 592         setbuf(fp, NULL);
 593         buf[sizeof(buf) - 1] = '\0';
 594         while (fgets(buf, sizeof(buf), fp)) {
 595                 for (cp1 = buf; *cp1 && !isspace(*cp1); ++cp1)
 596                         ;
 597                 if (!*cp1)
 598                         break;
 599                 *cp1 = '\0';
 600                 if (ns_samename(buf, name) == 1) {
 601                         while (isspace(*++cp1))
 602                                 ;
 603                         if (!*cp1)
 604                                 break;
 605                         for (cp2 = cp1 + 1; *cp2 && !isspace(*cp2); ++cp2)
 606                                 ;
 607                         *cp2 = '\0';
 608                         strncpy(dst, cp1, siz - 1);
 609                         dst[siz - 1] = '\0';
 610                         fclose(fp);
 611                         return (dst);
 612                 }
 613         }
 614         fclose(fp);
 615         return (NULL);
 616 }
 617 libresolv_hidden_def (res_hostalias)