/* -*- Mode: C++; tab-width: 4; c-basic-offset: 4; indent-tabs-mode: nil -*- */ /* * Copyright 2020-2021 Couchbase, Inc. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ #pragma once #include #include #include namespace couchbase::core::io::dns { /** * 3.2.2. TYPE values * ================== * * TYPE fields are used in resource records. Note that these types are a subset of QTYPEs. */ enum class resource_type : std::uint16_t { /** * a host address */ a = 1, /** * an authoritative name server */ ns = 2, /** * a mail destination (Obsolete - use MX) */ md = 3, /** * a mail forwarder (Obsolete - use MX) */ mf = 4, /** * the canonical name for an alias */ cname = 5, /** * marks the start of a zone of authority */ soa = 6, /** * a mailbox domain name (EXPERIMENTAL) */ mb = 7, /** * a mail group member (EXPERIMENTAL) */ mg = 8, /** * a mail rename domain name (EXPERIMENTAL) */ mr = 9, /** * a null RR (EXPERIMENTAL) */ null = 10, /** * a well known service description */ wks = 11, /** * a domain name pointer */ ptr = 12, /** * host information */ hinfo = 13, /** * mailbox or mail list information */ minfo = 14, /** * mail exchange */ mx = 15, /** * text strings */ txt = 16, /** * location services (RFC2782) */ srv = 33, }; /** * 3.2.4. CLASS values * =================== * * CLASS fields appear in resource records. The following CLASS mnemonics and values are defined: * * * 3.2.5. QCLASS values * ==================== * * QCLASS fields appear in the question section of a query. QCLASS values are a superset of CLASS values; every CLASS is a valid QCLASS. In * addition to CLASS values, the following QCLASSes are defined: */ enum class resource_class : std::uint16_t { /** * the Internet */ in = 1, /** * the CSNET class (Obsolete - used only for examples in some obsolete RFCs) */ cs = 2, /** * the CHAOS class */ ch = 3, /** * Hesiod [Dyer 87] */ hs = 4, /** * any class */ any = 255, }; /** * [OPCODE] * * A four bit field that specifies kind of query in this message. This value is set by the originator of a query and copied into the * response. The values are: * * 3-15 reserved for future use */ enum class opcode : std::uint8_t { /** * a standard query (QUERY) */ standard_query = 0, /** * an inverse query (IQUERY) */ inverse_query = 1, /** * a server status request (STATUS) */ status = 2, }; /** * [QR] * * A one bit field that specifies whether this message is a query (0), or a response (1). */ enum class message_type : std::uint8_t { query = 0, response = 1, }; /** * [AA] * * Authoritative Answer - this bit is valid in responses, and specifies that the responding name server is an authority for the domain name * in question section. * * Note that the contents of the answer section may have multiple owner names because of aliases. The AA bit corresponds to the name which * matches the query name, or the first owner name in the answer section. */ enum class authoritative_answer : std::uint8_t { no = 0, yes = 1, }; /** * [TC] * * TrunCation - specifies that this message was truncated due to length greater than that permitted on the transmission channel. */ enum class truncation : std::uint8_t { no = 0, yes = 1, }; /** * [RD] * * Recursion Desired - this bit may be set in a query and is copied into the response. If RD is set, it directs the name server to pursue * the query recursively. Recursive query support is optional. */ enum class recursion_desired : std::uint8_t { no = 0, yes = 1, }; /** * [RA] * * Recursion Available - this be is set or cleared in a response, and denotes whether recursive query support is available in the name * server. */ enum class recursion_available : std::uint8_t { no = 0, yes = 1, }; /** * [RCODE] * * Response code - this 4 bit field is set as part of responses. The values have the following interpretation: * * 6-15 Reserved for future use. */ enum class response_code : std::uint8_t { /** * No error condition */ no_error = 0, /** * The name server was unable to interpret the query. */ format_error = 1, /** * The name server was unable to process this query due to a problem with the name server. */ server_failure = 2, /** * Meaningful only for responses from an authoritative name server, this code signifies that the domain name referenced in the query * does not exist. */ name_error = 3, /** * The name server does not support the requested kind of query. */ not_implemented = 4, /** * The name server refuses to perform the specified operation for policy reasons. For example, a name server may not wish to provide * the information to the particular requester, or a name server may not wish to perform a particular operation (e.g., zone transfer) * for particular data. */ refused = 5, }; /** * 4.1.1. Header section format * ============================ * * The header contains the following fields: * * 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| | RCODE | * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ * | QDCOUNT | * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ * | ANCOUNT | * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ * | NSCOUNT | * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ * | ARCOUNT | * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ */ struct dns_header { struct dns_flags { message_type qr{ message_type::query }; dns::opcode opcode{ dns::opcode::standard_query }; authoritative_answer aa{ authoritative_answer::no }; truncation tc{ truncation::no }; recursion_desired rd{ recursion_desired::yes }; recursion_available ra{ recursion_available::no }; response_code rcode{ response_code::no_error }; [[nodiscard]] std::uint16_t encode() const { return std::uint16_t((static_cast(qr) & 1U) << 15U | (static_cast(opcode) & 15U) << 11U | (static_cast(aa) & 1U) << 10U | (static_cast(tc) & 1U) << 9U | (static_cast(rd) & 1U) << 8U | (static_cast(ra) & 1U) << 7U | (static_cast(rcode) & 15U)); } void decode(std::uint16_t blob) { qr = message_type((static_cast(blob) >> 15U) & 1U); opcode = dns::opcode((static_cast(blob) >> 11U) & 15U); aa = ((static_cast(blob) >> 10U) & 1U) != 0U ? authoritative_answer::yes : authoritative_answer::no; tc = ((static_cast(blob) >> 9U) & 1U) != 0U ? truncation::yes : truncation::no; rd = ((static_cast(blob) >> 8U) & 1U) != 0U ? recursion_desired::yes : recursion_desired::no; ra = ((static_cast(blob) >> 7U) & 1U) != 0U ? recursion_available::yes : recursion_available::no; rcode = response_code(blob & 15U); } }; /** * [ID] * * A 16 bit identifier assigned by the program that generates any kind of query. This identifier is copied the corresponding reply and * can be used by the requester to match up replies to outstanding queries. */ std::uint16_t id; dns_flags flags; /** * [QDCOUNT] * * an unsigned 16 bit integer specifying the number of entries in the question section. */ std::uint16_t question_records; /** * [ANCOUNT] * * an unsigned 16 bit integer specifying the number of resource records in the answer section. */ std::uint16_t answer_records; /** * [NSCOUNT] * * an unsigned 16 bit integer specifying the number of name server resource records in the authority records section. */ std::uint16_t authority_records; /** * [ARCOUNT] * * an unsigned 16 bit integer specifying the number of resource records in the additional records section. */ std::uint16_t additional_records; }; struct resource_name { std::vector labels{}; }; /** * 4.1.2. Question section format * ============================== * * The question section is used to carry the "question" in most queries, i.e., the parameters that define what is being asked. The section * contains QDCOUNT (usually 1) entries, each of the following 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 | * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ */ struct question_record { /** * [QNAME] * * a domain name represented as a sequence of labels, where each label consists of a length octet followed by that number of octets. The * domain name terminates with the zero length octet for the null label of the root. Note that this field may be an odd number of * octets; no padding is used. */ resource_name name{}; /** * [QTYPE] * * a two octet code which specifies the type of the query. The values for this field include all codes valid for a TYPE field, together * with some more general codes which can match more than one type of RR. */ resource_type type{}; /** * [QCLASS] * * a two octet code that specifies the class of the query. For example, the QCLASS field is IN for the Internet. */ resource_class klass{}; [[nodiscard]] std::size_t size() const { std::size_t res = 2 * sizeof(std::uint16_t); // type + class for (const auto& label : name.labels) { res += sizeof(std::uint8_t) + label.size(); } ++res; // '\0' return res; } }; /** * 4.1.3. Resource record format * ============================= * * The answer, authority, and additional sections all share the same format: a variable number of resource records, where * the number of records is specified in the corresponding count field in the header. Each resource record has the * following 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 / * / / * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ * * [RDLENGTH] * * an unsigned 16 bit integer that specifies the length in octets of the RDATA field. * * [RDATA] * * a variable length string of octets that describes the resource. The format of this information varies according to the TYPE and CLASS * of the resource record. For example, the if the TYPE is A and the CLASS is IN, the RDATA field is a 4 octet ARPA Internet address. */ struct resource_record { /** * [NAME] * * a domain name to which this resource record pertains. */ resource_name name{}; /** * [TYPE] * * two octets containing one of the RR type codes. This field specifies the meaning of the data in the RDATA field. */ resource_type type{}; /** * [CLASS] * * two octets which specify the class of the data in the RDATA field. */ resource_class klass{}; /** * * [TTL] * * a 32 bit unsigned integer that specifies the time interval (in seconds) that the resource record may be cached before it should be * discarded. Zero values are interpreted to mean that the RR can only be used for the transaction in progress, and should not be * cached. */ std::uint32_t ttl{}; }; struct srv_record : resource_record { std::uint16_t priority{}; std::uint16_t weight{}; std::uint16_t port{}; resource_name target{}; }; /** * 4.1. Format * =========== * * All communications inside of the domain protocol are carried in a single format called a message. The top level format of message is * divided into 5 sections (some of which are empty in certain cases) shown below: * * +---------------------+ * | Header | * +---------------------+ * | Question | the question for the name server * +---------------------+ * | Answer | RRs answering the question * +---------------------+ * | Authority | RRs pointing toward an authority * +---------------------+ * | Additional | RRs holding additional information * +---------------------+ * * The header section is always present. The header includes fields that specify which of the remaining sections are present, and also * specify whether the message is a query or a response, a standard query or some other opcode, etc. * * The names of the sections after the header are derived from their use in standard queries. The question section contains fields that * describe a question to a name server. These fields are a query type (QTYPE), a query class (QCLASS), and a query domain name (QNAME). * The last three sections have the same format: a possibly empty list of concatenated resource records (RRs). The answer section contains * RRs that answer the question; the authority section contains RRs that point toward an authoritative name server; the additional records * section contains RRs which relate to the query, but are not strictly answers for the question. */ struct dns_message { dns_header header{}; std::vector questions{}; std::vector answers{}; // the implementation only cares about SRV answers, so ignore everything else [[nodiscard]] std::size_t request_size() const { std::size_t res = 6 * sizeof(std::uint16_t); // header for (const auto& question : questions) { res += question.size(); } return res; } }; } // namespace couchbase::core::io::dns