dns_txt.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2020, Sean Bright
 *
 * Sean Bright <[email protected]>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */

/*! \file
 * \brief DNS TXT Record Parsing API
 * \author Sean Bright <[email protected]>
 */

/*** MODULEINFO
   <support_level>core</support_level>
 ***/

#include "asterisk.h"

#include <netinet/in.h>
#include <resolv.h>

#include "asterisk/dns_core.h"
#include "asterisk/dns_txt.h"
#include "asterisk/dns_internal.h"
#include "asterisk/utils.h"

struct ast_dns_record *dns_txt_alloc(struct ast_dns_query *query, const char *data, const size_t size)
{
   struct ast_dns_txt_record *txt;
   const char *end_of_record = data + size;
   size_t count = 0;

   /* Because we can't allocate additional memory, the best we can do here is just
    * validate that this conforms to a TXT record. */
   while (data < end_of_record) {
      uint8_t byte_count = (uint8_t) *data;
      count++;
      data += byte_count + 1;
   }

   if (data != end_of_record) {
      /* This is not a valid TXT record, so we can bail out */
      return NULL;
   }

   txt = ast_calloc(1, sizeof(*txt) + size);
   if (!txt) {
      return NULL;
   }

   txt->count = count;
   txt->generic.data_ptr = txt->data;

   return (struct ast_dns_record *) txt;
}

size_t ast_dns_txt_get_count(const struct ast_dns_record *record)
{
   struct ast_dns_txt_record *txt = (struct ast_dns_txt_record *) record;
   ast_assert(ast_dns_record_get_rr_type(record) == T_TXT);
   return txt->count;
}

struct ast_vector_string *ast_dns_txt_get_strings(const struct ast_dns_record *record)
{
   struct ast_vector_string *strings;

   const size_t size = ast_dns_record_get_data_size(record);
   const char *data = ast_dns_record_get_data(record);
   const char *end_of_record = data + size;

   ast_assert(ast_dns_record_get_rr_type(record) == T_TXT);

   strings = ast_malloc(sizeof(struct ast_vector_const_string));
   if (!strings) {
      return NULL;
   }

   if (AST_VECTOR_INIT(strings, ast_dns_txt_get_count(record))) {
      ast_free(strings);
      return NULL;
   }

   while (data < end_of_record) {
      char *s;
      uint8_t bytes = (uint8_t) *data;

      s = ast_malloc(bytes + 1);
      if (!s) {
         ast_dns_txt_free_strings(strings);
         return NULL;
      }

      memcpy(s, &data[1], bytes);
      s[bytes] = 0;

      /* We know the size in advance so this can't fail */
      AST_VECTOR_APPEND(strings, s);

      data += bytes + 1;
   }

   /* Sanity check */
   if (data != end_of_record) {
      ast_dns_txt_free_strings(strings);
      return NULL;
   }

   return strings;
}

void ast_dns_txt_free_strings(struct ast_vector_string *strings)
{
   AST_VECTOR_CALLBACK_VOID(strings, ast_free);
   AST_VECTOR_PTR_FREE(strings);
}