resolv/ns_rr_cursor_next.c

   1 /* Simple DNS record parser without textual name decoding.
   2    Copyright (C) 2022-2023 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <arpa/nameser.h>
  20 #include <errno.h>
  21 #include <stdbool.h>
  22 #include <string.h>
  23
  24 bool
  25 __ns_rr_cursor_next (struct ns_rr_cursor *c, struct ns_rr_wire *rr)
  26 {
  27   rr->rdata = NULL;
  28
  29   /* Extract the record owner name.  */
  30   int consumed = __ns_name_unpack (c->begin, c->end, c->current,
  31                                    rr->rname, sizeof (rr->rname));
  32   if (consumed < 0)
  33     {
  34       memset (rr, 0, sizeof (*rr));
  35       __set_errno (EMSGSIZE);
  36       return false;
  37     }
  38   c->current += consumed;
  39
  40   /* Extract the metadata.  */
  41   struct
  42   {
  43     uint16_t rtype;
  44     uint16_t rclass;
  45     uint32_t ttl;
  46     uint16_t rdlength;
  47   } __attribute__ ((packed)) metadata;
  48   _Static_assert (sizeof (metadata) == 10, "sizeof metadata");
  49   if (c->end - c->current < sizeof (metadata))
  50     {
  51       memset (rr, 0, sizeof (*rr));
  52       __set_errno (EMSGSIZE);
  53       return false;
  54     }
  55   memcpy (&metadata, c->current, sizeof (metadata));
  56   c->current += sizeof (metadata);
  57   /* Endianess conversion.  */
  58   rr->rtype = ntohs (metadata.rtype);
  59   rr->rclass = ntohs (metadata.rclass);
  60   rr->ttl = ntohl (metadata.ttl);
  61   rr->rdlength = ntohs (metadata.rdlength);
  62
  63   /* Extract record data.  */
  64   if (c->end - c->current < rr->rdlength)
  65     {
  66       memset (rr, 0, sizeof (*rr));
  67       __set_errno (EMSGSIZE);
  68       return false;
  69     }
  70   rr->rdata = c->current;
  71   c->current += rr->rdlength;
  72
  73   return true;
  74 }