---
name: "ares_dns_mapping"
section: "3"
platform: "linux"
package: "c-ares"
version: "1.34.9-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/ares_dns_mapping"
---

# ares\_dns\_mapping(3)

Helper functions for converting dns record identifiers to and from their respective types, as well identifying datatypes for various records.

## NAME

ares\_dns\_class\_fromstr, ares\_dns\_class\_tostr, ares\_dns\_datatype\_t, ares\_dns\_opcode\_tostr, ares\_dns\_opt\_datatype\_t, ares\_dns\_opt\_get\_datatype, ares\_dns\_opt\_get\_name, ares\_dns\_rcode\_tostr, ares\_dns\_rec\_type\_fromstr, ares\_dns\_rr\_get\_keys, ares\_dns\_rr\_key\_datatype, ares\_dns\_rr\_key\_to\_rec\_type, ares\_dns\_rr\_key\_tostr, ares\_dns\_section\_tostr, ares\_opt\_param\_t, ares\_svcb\_param\_t - Helper functions for converting dns record identifiers to and from their respective types, as well identifying datatypes for various records.

## SYNOPSIS

```
#include <ares.h>
const char *ares_dns_rec_type_tostr(ares_dns_rec_type_t type);
const char *ares_dns_class_tostr(ares_dns_class_t qclass);
const char *ares_dns_opcode_tostr(ares_dns_opcode_t opcode);
const char *ares_dns_rr_key_tostr(ares_dns_rr_key_t key);
const char *ares_dns_section_tostr(ares_dns_section_t section);
const char *ares_dns_rcode_tostr(ares_dns_rcode_t rcode);
ares_bool_t ares_dns_class_fromstr(ares_dns_class_t *qclass, const char *str);
ares_bool_t ares_dns_rec_type_fromstr(ares_dns_rec_type_t *qtype,
                                      const char *str);
const ares_dns_rr_key_t *ares_dns_rr_get_keys(ares_dns_rec_type_t type,
                                              size_t *cnt);
ares_dns_datatype_t ares_dns_rr_key_datatype(ares_dns_rr_key_t key);
ares_dns_rec_type_t ares_dns_rr_key_to_rec_type(ares_dns_rr_key_t key);
ares_dns_opt_datatype_t ares_dns_opt_get_datatype(ares_dns_rr_key_t key,
                                                  unsigned short opt);
const char *ares_dns_opt_get_name(ares_dns_rr_key_t key, unsigned short opt);
```

## ENUMERATIONS

**ares\_dns\_datatype\_t -** Data types associated with *ares\_dns\_rr\_key\_t*:

**ARES\_DATATYPE\_INADDR** - IPv4 address as *struct in\_addr \**. Use *[ares\_dns\_rr\_set\_addr(3)](/ares_dns_rr_set_addr/3.md)* to set and *[ares\_dns\_rr\_get\_addr(3)](/ares_dns_rr_get_addr/3.md)* to get.\
 **ARES\_DATATYPE\_INADDR6** - IPv6 address as *struct ares\_in6\_addr \**. Use *[ares\_dns\_rr\_set\_addr6(3)](/ares_dns_rr_set_addr6/3.md)* to set and *[ares\_dns\_rr\_get\_addr6(3)](/ares_dns_rr_get_addr6/3.md)* to get.\
 **ARES\_DATATYPE\_U8** - 8bit unsigned integer. Use *[ares\_dns\_rr\_set\_u8(3)](/ares_dns_rr_set_u8/3.md)* to set and *[ares\_dns\_rr\_get\_u8(3)](/ares_dns_rr_get_u8/3.md)* to get.\
 **ARES\_DATATYPE\_U16** - 16bit unsigned integer. Use *[ares\_dns\_rr\_set\_u16(3)](/ares_dns_rr_set_u16/3.md)* to set and *[ares\_dns\_rr\_get\_u16(3)](/ares_dns_rr_get_u16/3.md)* to get.\
 **ARES\_DATATYPE\_U32** - 32bit unsigned integer. Use *[ares\_dns\_rr\_set\_u32(3)](/ares_dns_rr_set_u32/3.md)* to set and *[ares\_dns\_rr\_get\_u32(3)](/ares_dns_rr_get_u32/3.md)* to get.\
 **ARES\_DATATYPE\_NAME** - Null-terminated string of a domain name (series of labels). Use *[ares\_dns\_rr\_set\_str(3)](/ares_dns_rr_set_str/3.md)* to set and *[ares\_dns\_rr\_get\_str(3)](/ares_dns_rr_get_str/3.md)* to get.\
 **ARES\_DATATYPE\_STR** - Null-terminated string. Use *[ares\_dns\_rr\_set\_str(3)](/ares_dns_rr_set_str/3.md)* to set and *[ares\_dns\_rr\_get\_str(3)](/ares_dns_rr_get_str/3.md)* to get.\
 **ARES\_DATATYPE\_BIN** - Binary Data. Use *[ares\_dns\_rr\_set\_bin(3)](/ares_dns_rr_set_bin/3.md)* to set and *[ares\_dns\_rr\_get\_bin(3)](/ares_dns_rr_get_bin/3.md)* to get.\
 **ARES\_DATATYPE\_BINP** - Officially defined as binary data, but likely printable. Guaranteed to have a NULL terminator for convenience (not included in length). Use *[ares\_dns\_rr\_set\_bin(3)](/ares_dns_rr_set_bin/3.md)* to set and *[ares\_dns\_rr\_get\_bin(3)](/ares_dns_rr_get_bin/3.md)* to get.\
 **ARES\_DATATYPE\_OPT** - Array of options.  16bit identifier, Binary data. Use *[ares\_dns\_rr\_set\_opt(3)](/ares_dns_rr_set_opt/3.md)* to set and *[ares\_dns\_rr\_get\_opt(3)](/ares_dns_rr_get_opt/3.md)* to get.\
 **ARES\_DATATYPE\_ABINP** - Array of binary data, but likely printable. Guaranteed to have a NULL terminator for convenience (not included in length). Use *[ares\_dns\_rr\_add\_abin(3)](/ares_dns_rr_add_abin/3.md)* to set and *[ares\_dns\_rr\_get\_abin(3)](/ares_dns_rr_get_abin/3.md)* to get.  Can also use *[ares\_dns\_rr\_set\_bin(3)](/ares_dns_rr_set_bin/3.md)* and *[ares\_dns\_rr\_get\_bin(3)](/ares_dns_rr_get_bin/3.md)* if only concatenated strings are desired.\

**ares\_dns\_opt\_datatype\_t -** Data types associated with *ARES\_DATATYPE\_OPT* parameters if known as returned by *[ares\_dns\_opt\_get\_datatype(3)](/ares_dns_opt_get_datatype/3.md)*:

**ARES\_OPT\_DATATYPE\_NONE** - No value allowed for this parameter\
 **ARES\_OPT\_DATATYPE\_STR\_LIST** - List of strings, each prefixed with a single octet representing the length as defined by RFC 1035. Can use *[ares\_expand\_string(3)](/ares_expand_string/3.md)* until buffer is consumed.\
 **ARES\_OPT\_DATATYPE\_U8\_LIST** - List of 8bit unsigned integers, concatenated\
 **ARES\_OPT\_DATATYPE\_U16** - 16bit unsigned integer in network byte order\
 **ARES\_OPT\_DATATYPE\_U16\_LIST** - list of 16bit unsigned integers in network byte order, concatenated.\
 **ARES\_OPT\_DATATYPE\_U32** - 32bit unsigned integer in network byte order\
 **ARES\_OPT\_DATATYPE\_U32\_LIST** - list of 16bit unsigned integers in network byte order, concatenated.\
 **ARES\_OPT\_DATATYPE\_INADDR4\_LIST** - List of ipv4 addresses in network byte order, concatenated\
 **ARES\_OPT\_DATATYPE\_INADDR6\_LIST** - List of ipv6 addresses in network byte order, concatenated\
 **ARES\_OPT\_DATATYPE\_BIN** - Binary Data\
 **ARES\_OPT\_DATATYPE\_NAME** - DNS Domain Name binary format as defined in RFC1035, can use *[ares\_expand\_name(3)](/ares_expand_name/3.md)*\

**ares\_svcb\_param\_t -** SVCB (and HTTPS) RR known parameters as returned by *[ares\_dns\_opt\_get\_datatype(3)](/ares_dns_opt_get_datatype/3.md)* with *ARES\_RR\_SVCB\_PARAMS* or *ARES\_RR\_HTTPS\_PARAMS*:

**ARES\_SVCB\_PARAM\_MANDATORY** - Mandatory keys in this RR (RFC 9460 Section 8). Datatype: *ARES\_OPT\_DATATYPE\_U16\_LIST*\
 **ARES\_SVCB\_PARAM\_ALPN** - Additional supported protocols (RFC 9460 Section 7.1). Datatype: *ARES\_OPT\_DATATYPE\_STR\_LIST*\
 **ARES\_SVCB\_PARAM\_NO\_DEFAULT\_ALPN** - No support for default protocol (RFC 9460 Section 7.1). Datatype: *ARES\_OPT\_DATATYPE\_NONE*\
 **ARES\_SVCB\_PARAM\_PORT** - Port for alternative endpoint (RFC 9460 Section 7.2). Datatype: *ARES\_OPT\_DATATYPE\_U16*\
 **ARES\_SVCB\_PARAM\_IPV4HINT** - IPv4 address hints (RFC 9460 Section 7.3). Datatype: *ARES\_OPT\_DATATYPE\_INADDR4\_LIST*\
 **ARES\_SVCB\_PARAM\_ECH** - RESERVED (held for Encrypted ClientHello)\
 **ARES\_SVCB\_PARAM\_IPV6HINT** - IPv6 address hints (RFC 9460 Section 7.3). Datatype: *ARES\_OPT\_DATATYPE\_INADDR6\_LIST*\

**ares\_opt\_param\_t -** OPT RR known parameters as returned by *[ares\_dns\_opt\_get\_datatype(3)](/ares_dns_opt_get_datatype/3.md)* with *ARES\_RR\_OPT\_OPTIONS***:**

**ARES\_OPT\_PARAM\_LLQ** **- RFC 8764. Apple's DNS Long-Lived Queries Protocol. Datatype:** *ARES\_OPT\_DATATYPE\_BIN*\
 **ARES\_OPT\_PARAM\_UL** **- http://files.dns-sd.org/draft-sekar-dns-ul.txt: Update Lease. Datatype:** *ARES\_OPT\_DATATYPE\_U32*\
 **ARES\_OPT\_PARAM\_NSID** **- RFC 5001. Name Server Identification. Datatype:** *ARES\_OPT\_DATATYPE\_BIN*\
 **ARES\_OPT\_PARAM\_DAU** **- RFC 6975. DNSSEC Algorithm Understood. Datatype:** *ARES\_OPT\_DATATYPE\_U8\_LIST*\
 **ARES\_OPT\_PARAM\_DHU** **- RFC 6975. DS Hash Understood. Datatype:** *ARES\_OPT\_DATATYPE\_U8\_LIST*\
 **ARES\_OPT\_PARAM\_N3U** **- RFC 6975. NSEC3 Hash Understood. Datatype:** *ARES\_OPT\_DATATYPE\_U8\_LIST*\
 **ARES\_OPT\_PARAM\_EDNS\_CLIENT\_SUBNET** **- RFC 7871. Client Subnet. Datatype:** *ARES\_OPT\_DATATYPE\_BIN*\
 **ARES\_OPT\_PARAM\_EDNS\_EXPIRE** **- RFC 7314. Expire Timer. Datatype:** *ARES\_OPT\_DATATYPE\_U32*\
 **ARES\_OPT\_PARAM\_COOKIE** **- RFC 7873. Client and Server Cookies. Datatype:** *ARES\_OPT\_DATATYPE\_BIN*\
 **ARES\_OPT\_PARAM\_EDNS\_TCP\_KEEPALIVE** **- RFC 7828. TCP Keepalive timeout. Datatype:** *ARES\_OPT\_DATATYPE\_U16*\
 **ARES\_OPT\_PARAM\_PADDING** **- RFC 7830. Padding. Datatype:** *ARES\_OPT\_DATATYPE\_BIN*\
 **ARES\_OPT\_PARAM\_CHAIN** **- RFC 7901. Chain query requests. Datatype:** *ARES\_OPT\_DATATYPE\_NAME*\
 **ARES\_OPT\_PARAM\_EDNS\_KEY\_TAG** **- RFC 8145. Signaling Trust Anchor Knowledge in DNSSEC. Datatype:** *ARES\_OPT\_DATATYPE\_U16\_LIST*\
 **ARES\_OPT\_PARAM\_EXTENDED\_DNS\_ERROR** **- RFC 8914. Extended ERROR code and message. Datatype:** *ARES\_OPT\_DATATYPE\_BIN*\

## DESCRIPTION

**The** *[ares\_dns\_rec\_type\_tostr(3)](/ares_dns_rec_type_tostr/3.md)* **function outputs a human readable DNS record** **type from its numeric form passed in** *type*.

**The** *[ares\_dns\_class\_tostr(3)](/ares_dns_class_tostr/3.md)* **function outputs a human readable DNS class** **from its numeric form passed in** *qclass*.

**The** *[ares\_dns\_opcode\_tostr(3)](/ares_dns_opcode_tostr/3.md)* **function outputs a human readable DNS opcode** **from its numeric form in** *opcode*.

**The** *[ares\_dns\_rr\_key\_tostr(3)](/ares_dns_rr_key_tostr/3.md)* **function outputs a human readable DNS Resource** **Record parameter name from its numeric form in** *key*.

**The** *[ares\_dns\_section\_tostr(3)](/ares_dns_section_tostr/3.md)* **function outputs a human readable DNS** **message section from its numeric form in** *section*.

**The** *[ares\_dns\_rcode\_tostr(3)](/ares_dns_rcode_tostr/3.md)* **function outputs a human readable DNS** **response code from its numeric form in** *rcode*.

**The** *[ares\_dns\_class\_fromstr(3)](/ares_dns_class_fromstr/3.md)* **function outputs the DNS class in numeric** **from from its string representation in** *str*. **The result is stored into the variable pointed to by** *qclass*.

**The** *[ares\_dns\_rec\_type\_fromstr(3)](/ares_dns_rec_type_fromstr/3.md)* **function outputs the DNS record type in** **numeric from from its string representation in** *str*. **The result is stored into the variable pointed to by** *qtype*.

**The** *[ares\_dns\_rr\_get\_keys(3)](/ares_dns_rr_get_keys/3.md)* **function retrieves a list of parameters that** **may be set or retrieved for the provided** *type*. **The count of returned keys is stored into the variable pointed to by** *cnt*.

**The** *[ares\_dns\_rr\_key\_datatype(3)](/ares_dns_rr_key_datatype/3.md)* **function retrieves the associated datatype** **for an RR parameter specified by** *key*.

**The** *[ares\_dns\_rr\_key\_to\_rec\_type(3)](/ares_dns_rr_key_to_rec_type/3.md)* **function dereferences the provided RR** **parameter specified by** *key* **to the DNS Record Type it belongs.**

**The** *[ares\_dns\_opt\_get\_datatype(3)](/ares_dns_opt_get_datatype/3.md)* **function is used in association with** *[ares\_dns\_rr\_set\_opt(3)](/ares_dns_rr_set_opt/3.md)* **and** *[ares\_dns\_rr\_get\_opt(3)](/ares_dns_rr_get_opt/3.md)* **to retrieve the** **datatype of an option record contained within an RR as specified in** *key* **if it is known.  The raw option record identifier is provided by** *opt*.

**The** *[ares\_dns\_opt\_get\_name(3)](/ares_dns_opt_get_name/3.md)* **function is used in association with** *[ares\_dns\_rr\_set\_opt(3)](/ares_dns_rr_set_opt/3.md)* **and** *[ares\_dns\_rr\_get\_opt(3)](/ares_dns_rr_get_opt/3.md)* **to retrieve human** **readable parameter name of an option record contained within an RR as specified** **in** *key* **if it is known.  The raw option record identifier is provided by** *opt*.

## RETURN VALUES

*[ares\_dns\_rec\_type\_tostr(3)](/ares_dns_rec_type_tostr/3.md)***,** *[ares\_dns\_class\_tostr(3)](/ares_dns_class_tostr/3.md)***,** *[ares\_dns\_opcode\_tostr(3)](/ares_dns_opcode_tostr/3.md)***,** *[ares\_dns\_rr\_key\_tostr(3)](/ares_dns_rr_key_tostr/3.md)***,** *[ares\_dns\_section\_tostr(3)](/ares_dns_section_tostr/3.md)***,** *[ares\_dns\_rcode\_tostr(3)](/ares_dns_rcode_tostr/3.md)***, and** *[ares\_dns\_opt\_get\_name(3)](/ares_dns_opt_get_name/3.md)* **all return a human printable ASCII string, or** **NULL on error.**

*[ares\_dns\_class\_fromstr(3)](/ares_dns_class_fromstr/3.md)* **and** *[ares\_dns\_rec\_type\_fromstr(3)](/ares_dns_rec_type_fromstr/3.md)* **return** **ARES\_TRUE** **on successful conversion, otherwise** **ARES\_FALSE.**

*[ares\_dns\_rr\_get\_keys(3)](/ares_dns_rr_get_keys/3.md)* **returns an array of keys or NULL on failure.**

*[ares\_dns\_rr\_key\_datatype(3)](/ares_dns_rr_key_datatype/3.md)***,** *[ares\_dns\_rr\_key\_to\_rec\_type(3)](/ares_dns_rr_key_to_rec_type/3.md)***, and** *[ares\_dns\_opt\_get\_datatype(3)](/ares_dns_opt_get_datatype/3.md)* **return their respective integer values, or** **0 on failure.**

## AVAILABILITY

**These functions were first introduced in c-ares version 1.22.0.**

## SEE ALSO

[**ares\_dns\_record**(3)](/ares_dns_record/3.md), [**ares\_dns\_rr**(3)](/ares_dns_rr/3.md), [**ares\_init**(3)](/ares_init/3.md)