net/dns/dns_protocol.h

// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef NET_DNS_DNS_PROTOCOL_H_
#define NET_DNS_DNS_PROTOCOL_H_

#include <stdint.h>

#include "net/base/net_export.h"

namespace net {

namespace dns_protocol {

static const uint16_t kDefaultPort = 53;
static const uint16_t kDefaultPortMulticast = 5353;

// DNS packet consists of a header followed by questions and/or answers.
// For the meaning of specific fields, please see RFC 1035 and 2535

// Header format.
//                                  1  1  1  1  1  1
//    0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5
//  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
//  |                      ID                       |
//  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
//  |QR|   Opcode  |AA|TC|RD|RA| Z|AD|CD|   RCODE   |
//  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
//  |                    QDCOUNT                    |
//  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
//  |                    ANCOUNT                    |
//  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
//  |                    NSCOUNT                    |
//  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
//  |                    ARCOUNT                    |
//  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

// Question format.
//                                  1  1  1  1  1  1
//    0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5
//  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
//  |                                               |
//  /                     QNAME                     /
//  /                                               /
//  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
//  |                     QTYPE                     |
//  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
//  |                     QCLASS                    |
//  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

// Answer format.
//                                  1  1  1  1  1  1
//    0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5
//  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
//  |                                               |
//  /                                               /
//  /                      NAME                     /
//  |                                               |
//  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
//  |                      TYPE                     |
//  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
//  |                     CLASS                     |
//  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
//  |                      TTL                      |
//  |                                               |
//  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
//  |                   RDLENGTH                    |
//  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--|
//  /                     RDATA                     /
//  /                                               /
//  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

#pragma pack(push)
#pragma pack(1)

// On-the-wire header. All uint16_t are in network order.
struct NET_EXPORT Header {
  uint16_t id;
  uint16_t flags;
  uint16_t qdcount;
  uint16_t ancount;
  uint16_t nscount;
  uint16_t arcount;
};

#pragma pack(pop)

static const uint8_t kLabelMask = 0xc0;
static const uint8_t kLabelPointer = 0xc0;
static const uint8_t kLabelDirect = 0x0;
static const uint16_t kOffsetMask = 0x3fff;

// In MDns the most significant bit of the rrclass is designated as the
// "cache-flush bit", as described in http://www.rfc-editor.org/rfc/rfc6762.txt
// section 10.2.
static const uint16_t kMDnsClassMask = 0x7FFF;

// RFC 1035, section 3.1: To simplify implementations, the total length of
// a domain name (i.e., label octets and label length octets) is restricted
// to 255 octets or less.
static const int kMaxNameLength = 255;

// RFC 1035, section 4.2.1: Messages carried by UDP are restricted to 512
// bytes (not counting the IP nor UDP headers).
static const int kMaxUDPSize = 512;

// RFC 6762, section 17: Messages over the local link are restricted by the
// medium's MTU, and must be under 9000 bytes
static const int kMaxMulticastSize = 9000;

// DNS class types.
//
// https://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml#dns-parameters-2
static const uint16_t kClassIN = 1;

// DNS resource record types.
//
// https://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml#dns-parameters-4
static const uint16_t kTypeA = 1;
static const uint16_t kTypeCNAME = 5;
static const uint16_t kTypeSOA = 6;
static const uint16_t kTypePTR = 12;
static const uint16_t kTypeTXT = 16;
static const uint16_t kTypeAAAA = 28;
static const uint16_t kTypeSRV = 33;
static const uint16_t kTypeOPT = 41;
static const uint16_t kTypeNSEC = 47;

// DNS reply codes (RCODEs).
//
// https://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml#dns-parameters-6
static const uint8_t kRcodeNOERROR = 0;
static const uint8_t kRcodeFORMERR = 1;
static const uint8_t kRcodeSERVFAIL = 2;
static const uint8_t kRcodeNXDOMAIN = 3;
static const uint8_t kRcodeNOTIMP = 4;
static const uint8_t kRcodeREFUSED = 5;

// DNS header flags.
//
// https://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml#dns-parameters-12
static const uint16_t kFlagResponse = 0x8000;
static const uint16_t kFlagRD = 0x100;  // Recursion Desired - query flag.
static const uint16_t kFlagTC = 0x200;  // Truncated - server flag.

}  // namespace dns_protocol

}  // namespace net

#endif  // NET_DNS_DNS_PROTOCOL_H_