Tribblix: manual page: ares_dns

ARES_DNS_RECORD(3) Introduction to Library Functions ARES_DNS_RECORD(3)

NAME

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, ares_dns_write - DNS Record parsing, writing,
creating and destroying functions.

SYNOPSIS

#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);

ENUMERATIONS

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_HESOID - 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

The ares_dns_record_destroy(3) function 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.

The ares_dns_parse(3) function 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).

The ares_dns_write(3) function 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).

The ares_dns_record_create(3) function 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.

The ares_dns_record_duplicate(3) function 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.

The ares_dns_record_get_id(3) function is used to retrieve the DNS
message id from the DNS record provided in the dnsrec parameter.

The ares_dns_record_set_id(3) function is used to set 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.

The ares_dns_record_get_flags(3) function is used to retrieve the DNS
message flags from the DNS record provided in the dnsrec parameter.

The ares_dns_record_get_opcode(3) function is used to retrieve the
DNS message flags from the DNS record provided in the dnsrec
parameter.

The ares_dns_record_get_rcode(3) function is used to retrieve the DNS
message response code from the DNS record provided in the dnsrec
parameter.

The ares_dns_record_query_add(3) function is used to add 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.

The ares_dns_record_query_set_name(3) function is used to modify 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.

The ares_dns_record_query_set_type(3) function is used to modify 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.

The ares_dns_record_query_cnt(3) function is used to retrieve the
number of DNS questions in the DNS record provided in the dnsrec
parameter.

The ares_dns_record_query_get(3) function is used to retrieve 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 invalided 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.

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_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.

AVAILABILITY