--- name: "ares_getaddrinfo" 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_getaddrinfo" --- # ares\_getaddrinfo(3) Initiate a host query by name and service ## NAME ares\_getaddrinfo - Initiate a host query by name and service ## SYNOPSIS ``` #include typedef void (*ares_addrinfo_callback)(void *arg, int status, int timeouts, struct ares_addrinfo *result) void ares_getaddrinfo(ares_channel_t *channel, const char *name, const char* service, const struct ares_addrinfo_hints *hints, ares_addrinfo_callback callback, void *arg) ``` ## DESCRIPTION The **[ares\_getaddrinfo(3)](/ares_getaddrinfo/3.md)** function initiates a host query by name on the name service channel identified by *channel*. The *name* and *service* parameters give the hostname and service as NULL-terminated C strings. Either *name* or *service* may be NULL, but not both. If *name* is NULL, the returned addresses are synthesized from *service*: the wildcard address (0.0.0.0 or ::) is returned when **ARES\_AI\_PASSIVE** is set in *ai\_flags*, otherwise the loopback address (127.0.0.1 or ::1) is returned. The *hints* parameter is an **ares\_addrinfo\_hints** structure: ``` struct ares_addrinfo_hints { int ai_flags; int ai_family; int ai_socktype; int ai_protocol; }; ``` - *ai\_family* Specifies desired address family. AF\_UNSPEC means return both AF\_INET and AF\_INET6. - *ai\_socktype* Specifies desired socket type, for example SOCK\_STREAM or SOCK\_DGRAM. Setting this to 0 means any type. - *ai\_protocol* Setting this to 0 means any protocol. - *ai\_flags* Specifies additional options, see below. - **ARES\_AI\_NUMERICSERV** If this option is set *service* field will be treated as a numeric value. - **ARES\_AI\_PASSIVE** If this option is set and *name* is NULL, the returned addresses will use the wildcard address (0.0.0.0 or ::), suitable for [**bind**(2)](/bind/2.md)ing a socket that will accept connections. If not set and *name* is NULL, the loopback address (127.0.0.1 or ::1) is returned instead. - **ARES\_AI\_CANONNAME** The ares\_addrinfo structure will return a canonical names list. - **ARES\_AI\_NOSORT** Result addresses will not be sorted and no connections to resolved addresses will be attempted. - **ARES\_AI\_ENVHOSTS** Read hosts file path from the environment variable *CARES\_HOSTS .* When the query is complete or has failed, the ares library will invoke *callback*. Completion or failure of the query may happen immediately, or may happen during a later call to *[ares\_process(3)](/ares_process/3.md)*, *[ares\_destroy(3)](/ares_destroy/3.md)* or *[ares\_cancel(3)](/ares_cancel/3.md)*. When the associated callback is called, it is called with a channel lock so care must be taken to ensure any processing is minimal to prevent DNS channel stalls. The callback may be triggered from a different thread than the one which called *[ares\_getaddrinfo(3)](/ares_getaddrinfo/3.md)*. For integrators running their own event loops and not using **ARES\_OPT\_EVENT\_THREAD**, care needs to be taken to ensure any file descriptor lists are updated immediately within the eventloop when notified. The callback argument *arg* is copied from the **[ares\_getaddrinfo(3)](/ares_getaddrinfo/3.md)** argument *arg*. The callback argument *status* indicates whether the query succeeded and, if not, how it failed. It may have any of the following values: - **ARES\_SUCCESS** The host lookup completed successfully. - **ARES\_ENOTIMP** The ares library does not know how to find addresses of type *family*. - **ARES\_ENOTFOUND** The *name* was not found. - **ARES\_ENOMEM** Memory was exhausted. - **ARES\_ESERVICE** The textual service name provided could not be dereferenced into a port. - **ARES\_ECANCELLED** The query was cancelled. - **ARES\_EDESTRUCTION** The name service channel *channel* is being destroyed; the query will not be completed. On successful completion of the query, the callback argument *result* points to a **struct ares\_addrinfo** which contains two linked lists, one with resolved addresses and another with canonical names. Also included is the official name of the host (analogous to gethostbyname() h\_name). ``` struct ares_addrinfo { struct ares_addrinfo_cname *cnames; struct ares_addrinfo_node *nodes; char *name; }; ``` *ares\_addrinfo\_node* structure is similar to RFC3493 addrinfo, but without canonname and with extra ttl field. ``` struct ares_addrinfo_node { int ai_ttl; int ai_flags; int ai_family; int ai_socktype; int ai_protocol; ares_socklen_t ai_addrlen; struct sockaddr *ai_addr; struct ares_addrinfo_node *ai_next; }; ``` *ares\_addrinfo\_cname* structure is a linked list of CNAME records where *ttl* is a time to live *alias* is a label of the resource record and *name* is a value (canonical name) of the resource record. See RFC2181 10.1.1. CNAME terminology. ``` struct ares_addrinfo_cname { int ttl; char *alias; char *name; struct ares_addrinfo_cname *next; }; ``` The reserved memory has to be deleted by **[ares\_freeaddrinfo(3)](/ares_freeaddrinfo/3.md)**. The result is sorted according to RFC6724 except:\ \- Rule 3 (Avoid deprecated addresses)\ \- Rule 4 (Prefer home addresses)\ \- Rule 7 (Prefer native transport) Please note that the function will attempt a connection on each of the resolved addresses as per RFC6724. ## AVAILABILITY This function was added in c-ares 1.16.0, released in March 2020. ## SEE ALSO [**ares\_freeaddrinfo**(3)](/ares_freeaddrinfo/3.md)