// Copyright 2012 The Chromium Authors // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. #ifndef NET_DNS_PUBLIC_DNS_PROTOCOL_H_ #define NET_DNS_PUBLIC_DNS_PROTOCOL_H_ #include #include "net/base/net_export.h" namespace net { // General constants and structs defined by the DNS and MDNS protocols. // // Direct interaction with DNS and MDNS, as well as parsing DNS and MDNS // messages, should generally only be done within network stack code. // Network-stack-external code should interact indirectly through network // service APIs, e.g. NetworkContext::ResolveHost(). But these constants may // still be useful for other minor purposes. namespace dns_protocol { static const uint16_t kDefaultPort = 53; // RFC 5353. static const uint16_t kDefaultPortMulticast = 5353; // https://www.iana.org/assignments/multicast-addresses/multicast-addresses.xhtml#multicast-addresses-1 static const char kMdnsMulticastGroupIPv4[] = "224.0.0.251"; // https://www.iana.org/assignments/ipv6-multicast-addresses/ipv6-multicast-addresses.xhtml#link-local static const char kMdnsMulticastGroupIPv6[] = "FF02::FB"; // 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 = 0; uint16_t flags = 0; uint16_t qdcount = 0; uint16_t ancount = 0; uint16_t nscount = 0; uint16_t arcount = 0; }; #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 in wire form (i.e., label octets and label length octets) is // restricted to 255 octets or less. // // Note that RFC 1035 is ambiguous over whether or not this limit includes the // final zero-length terminating label, but RFC 6762 unambiguously uses the // more permissive interpretation of not including the terminating label against // the limit for mDNS and argues in RFC 6762 Appendix C that that is the correct // interpretation for unicast DNS. To avoid overcomplicating logic, Chrome // universally uses the more permissive RFC 6762 interpretation for all parsing. static const int kMaxNameLength = 255; // The maximum number of ASCII characters allowed in a domain in dotted form, // derived from `kMaxNameLength` above by subtracting one from the count to // correspond to the first byte, which is not available to encode characters and // does not correspond to a dot after conversion. static const uint16_t kMaxCharNameLength = 254; // RFC 1035, section 2.3.4: labels 63 octets or less. // Section 3.1: Each label is represented as a one octet length field followed // by that number of octets. const int kMaxLabelLength = 63; // 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; // RFC 1035, Section 4.1.3. // TYPE (2 bytes) + CLASS (2 bytes) + TTL (4 bytes) + RDLENGTH (2 bytes) static const int kResourceRecordSizeInBytesWithoutNameAndRData = 10; // DNS class types. // // https://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml#dns-parameters-2 static const uint16_t kClassIN = 1; // RFC 6762, Section 10.2. // // For resource records sent through mDNS, the top bit of the class field in a // resource record is repurposed to the cache-flush bit. This bit should only be // used in mDNS transactions. static const uint16_t kFlagCacheFlush = 0x8000; // 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; static const uint16_t kTypeHttps = 65; static const uint16_t kTypeANY = 255; // 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 EDNS(0) option codes (OPT) // // https://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml#dns-parameters-11 static constexpr uint16_t kEdnsPadding = 12; static constexpr uint16_t kEdnsExtendedDnsError = 15; // 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 kFlagAA = 0x400; // Authoritative Answer - response flag. static const uint16_t kFlagRD = 0x100; // Recursion Desired - query flag. static const uint16_t kFlagTC = 0x200; // Truncated - server flag. // SVCB/HTTPS ServiceParamKey // // IANA registration pending. Values from draft-ietf-dnsop-svcb-https-08. static constexpr uint16_t kHttpsServiceParamKeyMandatory = 0; static constexpr uint16_t kHttpsServiceParamKeyAlpn = 1; static constexpr uint16_t kHttpsServiceParamKeyNoDefaultAlpn = 2; static constexpr uint16_t kHttpsServiceParamKeyPort = 3; static constexpr uint16_t kHttpsServiceParamKeyIpv4Hint = 4; static constexpr uint16_t kHttpsServiceParamKeyEchConfig = 5; static constexpr uint16_t kHttpsServiceParamKeyIpv6Hint = 6; // draft-ietf-dnsop-svcb-https-08#section-9 inline constexpr char kHttpsServiceDefaultAlpn[] = "http/1.1"; } // namespace dns_protocol } // namespace net #endif // NET_DNS_PUBLIC_DNS_PROTOCOL_H_