Insane_DNS/include/insane_dns/constants.h

/*
 *  Global constants file.
 *  Copyright (C) 2023  Brett Terpstra, Et al
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program 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 General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

#ifndef INSANE_DNS_CONSTANTS_H
#define INSANE_DNS_CONSTANTS_H

/*
 * --------------------------------------------
 *          | Magic Number Constants |
 * --------------------------------------------
 */

static constexpr size_t PACKET_BUFFER_SIZE = 65535;

/*
 * These structs are used in combination with templates to create polymorphism between the UDP and TCP implementation.
 * this design decision has significantly reduced the code reuse while not introducing any runtime overhead.
 * The data set within these structures are specific to the protocol they implement. UDP is exactly as specified in the RFC spec
 * TCP is what I observed from wireshark (+2 byte offset)
 */
struct DNS_UDP_INFO_t
{
    /** DNS header data offset. This is the first byte that isn't a header value (should be question label length octet) */
    size_t HEADER_END = 12;
    /** DNS questions count data offset. In the standard header this is 4 bytes in */
    size_t QUESTIONS_BEGIN = 4;
    /** DNS answer count data offset. */
    size_t ANSWERS_BEGIN = 6;
};

/*
 * The TCP version appears to use a 2 byte unsigned short to represent length. This struct accounts for that.
 */
struct DNS_TCP_INFO_t
{
    size_t HEADER_END = 14;
    size_t QUESTIONS_BEGIN = 6;
    size_t ANSWERS_BEGIN = 8;
};

static constexpr DNS_UDP_INFO_t DNS_UDP_INFO;
static constexpr DNS_TCP_INFO_t DNS_TCP_INFO;

#endif //INSANE_DNS_CONSTANTS_H