dns_txt.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2020, Sean Bright
 *
 * Sean Bright <sean.bright@gmail.com>
 *
 * 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 <sean.bright@gmail.com>
 */
 
/*** 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);
}