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/* Initialize a simple DNS packet parser.
Copyright (C) 2022-2023 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <arpa/nameser.h>
#include <errno.h>
#include <stdbool.h>
#include <string.h>
bool
__ns_rr_cursor_init (struct ns_rr_cursor *c,
const unsigned char *buf, size_t len)
{
c->begin = buf;
c->end = buf + len;
/* Check for header size and 16-bit question count value (it must be 1). */
if (len < 12 || buf[4] != 0 || buf[5] != 1)
{
__set_errno (EMSGSIZE);
c->current = c->end;
return false;
}
c->current = buf + 12;
int consumed = __ns_name_length_uncompressed (c->current, c->end);
if (consumed < 0)
{
__set_errno (EMSGSIZE);
c->current = c->end;
c->first_rr = NULL;
return false;
}
c->current += consumed;
/* Ensure there is room for question type and class. */
if (c->end - c->current < 4)
{
__set_errno (EMSGSIZE);
c->current = c->end;
c->first_rr = NULL;
return false;
}
c->current += 4;
c->first_rr = c->current;
return true;
}
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