ARES_DNS_RECORD(3)

💖 NAME 💖

okay bestie, gather round — this is the manual page for ARES_DNS_RECORD(3), and it's giving “the whole DNS record lifecycle, but make it c-ares.” 💅 It covers ares_dns_class_t, ares_dns_flags_t, ares_dns_opcode_t, ares_dns_parse, ares_dns_rcode_t, ares_dns_record_create, ares_dns_record_destroy, ares_dns_record_get_flags, ares_dns_record_get_id, ares_dns_record_get_opcode, ares_dns_record_get_rcode, ares_dns_record_query_add, ares_dns_record_query_cnt, ares_dns_record_query_get, ares_dns_rec_type_t, and ares_dns_write — aka the DNS Record parsing, writing, creating and destroying functions. No cap. 🫶

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✨ SYNOPSIS ✨

bestie, here's the whole function lineup, copied exactly because we do not mess with signatures. Not even a little. 😭

#include <ares.h>

void ares_dns_record_destroy(ares_dns_record_t *dnsrec);

ares_status_t ares_dns_parse(const unsigned char *buf,
                             size_t buf_len, unsigned int flags,
                             ares_dns_record_t **dnsrec);

ares_status_t ares_dns_write(const ares_dns_record_t *dnsrec,
                             unsigned char **buf, size_t *buf_len);

ares_status_t ares_dns_record_create(ares_dns_record_t **dnsrec,
                                     unsigned short      id,
                                     unsigned short      flags,
                                     ares_dns_opcode_t   opcode,
                                     ares_dns_rcode_t    rcode);

ares_dns_record_t *ares_dns_record_duplicate(const ares_dns_record_t *dnsrec);

unsigned short ares_dns_record_get_id(const ares_dns_record_t *dnsrec);

ares_bool_t ares_dns_record_set_id(ares_dns_record_t *dnsrec,
                                   unsigned short id);

unsigned short ares_dns_record_get_flags(const ares_dns_record_t *dnsrec);

ares_dns_opcode_t ares_dns_record_get_opcode(const ares_dns_record_t *dnsrec);

ares_dns_rcode_t ares_dns_record_get_rcode(const ares_dns_record_t *dnsrec);

ares_status_t ares_dns_record_query_add(ares_dns_record_t  *dnsrec,
                                        const char         *name,
                                        ares_dns_rec_type_t qtype,
                                        ares_dns_class_t    qclass);

ares_status_t ares_dns_record_query_set_name(ares_dns_record_t  *dnsrec,
                                             size_t              idx,
                                             const char         *name);

ares_status_t ares_dns_record_query_set_type(ares_dns_record_t  *dnsrec,
                                             size_t              idx,
                                             ares_dns_rec_type_t qtype);

size_t ares_dns_record_query_cnt(const ares_dns_record_t *dnsrec);

ares_status_t ares_dns_record_query_get(const ares_dns_record_t *dnsrec,
                                        size_t idx, const char **name,
                                        ares_dns_rec_type_t *qtype,
                                        ares_dns_class_t *qclass);

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💅 ENUMERATIONS 💅

these are the enums that make the DNS world go round. every identifier is literal, so keep the spelling. 🎀

🦋 ares_dns_rec_type_t 🦋

DNS Record types handled by c-ares. Some record types may only be valid on requests, and some may only be valid on responses:

• ARES_REC_TYPE_A — Host address
• ARES_REC_TYPE_NS — Authoritative server
• ARES_REC_TYPE_CNAME — Canonical name
• ARES_REC_TYPE_SOA — Start of authority zone
• ARES_REC_TYPE_PTR — Domain name pointer
• ARES_REC_TYPE_HINFO — Host information
• ARES_REC_TYPE_MX — Mail routing information
• ARES_REC_TYPE_TXT — Text strings
• ARES_REC_TYPE_SIG — RFC 2535. RFC 2931. SIG Record
• ARES_REC_TYPE_AAAA — RFC 3596. Ip6 Address
• ARES_REC_TYPE_SRV — RFC 2782. Server Selection
• ARES_REC_TYPE_NAPTR — RFC 3403. Naming Authority Pointer
• ARES_REC_TYPE_OPT — RFC 6891. EDNS0 option (meta-RR). Pseudo Record.
• ARES_REC_TYPE_TLSA — RFC 6698. DNS-Based Authentication of Named Entities (DANE) Transport Layer Security (TLS) Protocol: TLSA
• ARES_REC_TYPE_SVCB — RFC 9460. General Purpose Service Binding
• ARES_REC_TYPE_HTTPS — RFC 9460. Service Binding type for use with HTTPS
• ARES_REC_TYPE_ANY — Wildcard match. Not response RR
• ARES_REC_TYPE_URI — RFC 7553. Uniform Resource Identifier
• ARES_REC_TYPE_CAA — RFC 6844. Certification Authority Authorization
• ARES_REC_TYPE_RAW_RR — Used as an indicator that the RR record is not parsed, but provided in wire format

🌸 ares_dns_class_t 🌸

DNS Classes for requests and responses:

• ARES_CLASS_IN — Internet
• ARES_CLASS_CHAOS — CHAOS
• ARES_CLASS_HESIOD — Hesoid [Dyer 87]
• ARES_CLASS_NONE — RFC 2136
• ARES_CLASS_ANY — Any class (requests only)

🧚 ares_dns_opcode_t 🧚

DNS Header Opcodes:

• ARES_OPCODE_QUERY — Standard query
• ARES_OPCODE_IQUERY — Inverse query. Obsolete
• ARES_OPCODE_STATUS — Name server status query
• ARES_OPCODE_NOTIFY — Zone change notification (RFC 1996)
• ARES_OPCODE_UPDATE — Zone update message (RFC 2136)

🔥 ares_dns_flags_t 🔥

DNS Header Flags:

• ARES_FLAG_QR — QR. If set, is a response
• ARES_FLAG_AA — Authoritative Answer. If set, is authoritative
• ARES_FLAG_TC — Truncation. If set, is truncated response
• ARES_FLAG_RD — Recursion Desired. If set, recursion is desired
• ARES_FLAG_RA — Recursion Available. If set, server supports recursion
• ARES_FLAG_AD — RFC 2065. Authentic Data bit indicates in a response that the data included has been verified by the server providing it
• ARES_FLAG_CD — RFC 2065. Checking Disabled bit indicates in a query that non-verified data is acceptable to the resolver sending the query

💜 ares_dns_rcode_t 💜

DNS Response codes from server:

• ARES_RCODE_NOERROR — Success
• ARES_RCODE_FORMERR — Format error. The name server was unable to interpret the query
• ARES_RCODE_SERVFAIL — Server Failure. The name server was unable to process this query due to a problem with the nameserver
• ARES_RCODE_NXDOMAIN — Name Error. Meaningful only for responses from an authoritative name server, this code signifies that the domain name referenced in the query does not exist.
• ARES_RCODE_NOTIMP — Not implemented. The name server does not support the requested kind of query
• ARES_RCODE_REFUSED — Refused. The name server refuses to perform the specified operation for policy reasons.
• ARES_RCODE_YXDOMAIN — RFC 2136. Some name that ought not to exist, does exist
• ARES_RCODE_YXRRSET — RFC 2136. Some RRset that ought to not exist, does exist
• ARES_RCODE_NXRRSET — RFC 2136. Some RRset that ought to exist, does not exist
• ARES_RCODE_NOTAUTH — RFC 2136. The server is not authoritative for the zone named in the Zone section.
• ARES_RCODE_NOTZONE — RFC 2136. A name used in the Prerequisite or Update Section is not within the zone denoted by the Zone Section.
• ARES_RCODE_DSOTYPEI — RFC 8409. DSO-TYPE Not implemented
• ARES_RCODE_BADSIG — RFC 8945. TSIG Signature Failure
• ARES_RCODE_BADKEY — RFC 8945. Key not recognized
• ARES_RCODE_BADTIME — RFC 8945. Signature out of time window
• ARES_RCODE_BADMODE — RFC 2930. Bad TKEY Mode
• ARES_RCODE_BADNAME — RFC 2930. Duplicate Key Name
• ARES_RCODE_BADALG — RFC 2930. Algorithm not supported
• ARES_RCODE_BADTRUNC — RFC 8945. Bad Truncation
• ARES_RCODE_BADCOOKIE — RFC 7973. Bad/missing Server Cookie

🍓 ares_dns_parse_flags_t 🍓

Flags for altering ares_dns_parse(3) behaviour:

• ARES_DNS_PARSE_AN_BASE_RAW — Parse Answer Section from RFC 1035 that allow name compression as RAW RR type
• ARES_DNS_PARSE_NS_BASE_RAW — Parse Authority Section from RFC 1035 that allow name compression as RAW RR type
• ARES_DNS_PARSE_AR_BASE_RAW — Parse Additional Section from RFC 1035 that allow name compression as RAW RR type
• ARES_DNS_PARSE_AN_EXT_RAW — Parse Answer Section from later RFCs (no name compression) as RAW RR type
• ARES_DNS_PARSE_NS_EXT_RAW — Parse Authority Section from later RFCs (no name compression) as RAW RR type
• ARES_DNS_PARSE_AR_EXT_RAW — Parse Additional Section from later RFCs (no name compression) as RAW RR type

💅 DESCRIPTION 💅

okay so bestie, this is the part where all the actual DNS-record actions live. buckle up, because these functions are the main characters 💖

• ares_dns_record_destroy(3) — destroys the memory associated with the DNS record created by either ares_dns_record_create(3) or ares_dns_parse(3), passed in via dnsrec. bye-bye, record 👋
• ares_dns_parse(3) — parses the buffer provided in buf with length provided in buf_len. The flags parameter can be one or more ares_dns_parse_flags_t, or zero if no flags are needed. The resulting DNS record data structure is stored into the variable pointed to by dnsrec and must be destroyed using ares_dns_record_destroy(3). no leaving it lying around, bestie ✨
• ares_dns_write(3) — takes a populated DNS record structure in dnsrec and writes a wire-format DNS message into the variable pointed to by buf, and writes the length of the buffer into the variable pointed to by buf_len. The buffer must be destroyed using ares_free_string(3). slay the wire format 💅
• ares_dns_record_create(3) — creates an empty DNS record structure in the variable pointed to by dnsrec. The id parameter is the DNS message id, however if passing to ares_send(3) this identifier will be overwritten, so should typically be 0. The flags parameter is one or more ares_dns_flags_t. The opcode is passed in the opcode parameter and should typically be ARES_OPCODE_QUERY. The response code is meant mostly for responses and is passed in the rcode parameter and is typically ARES_RCODE_NOERROR. blank canvas energy 🎀
• ares_dns_record_duplicate(3) — duplicates an existing DNS record structure. This may be useful if needing to save a result as retrieved from ares_send_dnsrec(3) or ares_search_dnsrec(3). The structure to be duplicated is passed in the dnsrec parameter, and the duplicated copy is returned, or NULL on error such as out of memory. twin flame, but make it memory-safe 🫶
• ares_dns_record_get_id(3) — retrieves the DNS message id from the DNS record provided in the dnsrec parameter. got that id 🔍
• ares_dns_record_set_id(3) — sets the DNS message id in the id parameter from the DNS record provided in the dnsrec parameter. This id will be overwritten when passing the record to c-ares, so mostly exists for external purposes. noted, bestie 📝
• ares_dns_record_get_flags(3) — retrieves the DNS message flags from the DNS record provided in the dnsrec parameter. flags secured 🚩
• ares_dns_record_get_opcode(3) — retrieves the DNS message flags from the DNS record provided in the dnsrec parameter. yes, that's what the page says, and we keep every detail around here 😌
• ares_dns_record_get_rcode(3) — retrieves the DNS message response code from the DNS record provided in the dnsrec parameter. rcode check ✅
• ares_dns_record_query_add(3) — adds a question to the DNS record provided in the dnsrec parameter. The domain name specified for the question is provided in the name parameter, along with the question type in the qtype parameter and the question class (typically ARES_CLASS_IN) in the qclass parameter. adding the question like it's going out of style 🙋‍♀️
• ares_dns_record_query_set_name(3) — modifies the question name in the DNS record provided in the dnsrec parameter. The index of the query, which must be less than ares_dns_record_query_cnt(3), is provided in the idx parameter. The new domain name is provided in the name parameter. Care should be taken as this will cause invalidation of any name pointer retrieved from ares_dns_Record_query_get(3). This function is useful if sending multiple similar queries without re-creating the entire DNS query. glow-up the name, but watch those pointers ⚠️
• ares_dns_record_query_set_type(3) — modifies the question type in the DNS record provided in the dnsrec parameter. The index of the query, which must be less than ares_dns_record_query_cnt(3), is provided in the idx parameter. The new query type is provided in the qtype parameter. switch the type, keep it cute 🔁
• ares_dns_record_query_cnt(3) — retrieves the number of DNS questions in the DNS record provided in the dnsrec parameter. counting questions like counting blessings ✨
• ares_dns_record_query_get(3) — retrieves the details of a single DNS question in the provided dnsrec parameter. The index provided in the idx parameter must be less than the value returned from ares_dns_record_query_cnt(3). The DNS question name will be returned in the variable pointed to by the name parameter, this may be provided as NULL if the name is not needed. This pointer will be invalidated by any call to ares_dns_record_query_set_name(3). The DNS question type will be returned in the variable pointed to by the qtype parameter, this may be provided as NULL if the type is not needed. The DNS question class will be returned in the variable pointed to by the qclass parameter, this may be provided as NULL if the class is not needed. get the question details, bestie 🔎

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💖 RETURN VALUES 💖

ares_dns_parse(3), ares_dns_write(3), ares_dns_record_create(3), ares_dns_record_query_add(3), and ares_dns_record_query_get(3) all return an ares_status_t error code.

• ARES_SUCCESS is returned on success ✅
• ARES_ENOMEM is returned on out of memory 😭
• ARES_EFORMERR is returned on misuse 🙈

ares_dns_write(3) also returns ARES_EBADQUERY if the message is too large to encode. too big, too much 💀

ares_dns_record_get_id(3), ares_dns_record_set_id(3), ares_dns_record_get_flags(3), ares_dns_record_get_opcode(3), ares_dns_record_get_rcode(3), and ares_dns_record_query_cnt(3) all returned their prescribed datatype values and in general can't fail except for misuse cases, in which a 0 may be returned, however 0 can also be a valid return value for most of these functions. so like, 0 is giving both "error-ish" and "valid," iykyk 😌

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✨ AVAILABILITY ✨

These functions were first introduced in c-ares version 1.22.0. vintage-ish but make it new 🦋

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🦋 SEE ALSO 🦋

• ares_dns_mapping(3)
• ares_dns_rr(3)
• ares_free_string(3)

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mwah 💋 — that's the whole glow-up, bestie. source/version: ARES_DNS_RECORD(3); date: 12 November 2023. periodt 💅