# DNS utility functions

libuv provides asynchronous variants of getaddrinfo and getnameinfo.

## Data types

type uv_getaddrinfo_t

  getaddrinfo request type.

typedef void (*uv_getaddrinfo_cb)(uv_getaddrinfo_t *req, int status, struct addrinfo *res)

  Callback which will be called with the getaddrinfo request result once complete. In case it was cancelled, status will have a value of `UV_ECANCELED`.

type uv_getnameinfo_t

  getnameinfo request type.

typedef void (*uv_getnameinfo_cb)(uv_getnameinfo_t *req, int status, const char *hostname, const char *service)

  Callback which will be called with the getnameinfo request result once complete. In case it was cancelled, status will have a value of `UV_ECANCELED`.

### Public members

uv_loop_t *uv_getaddrinfo_t.loop

  Loop that started this getaddrinfo request and where completion will be reported. Readonly.

struct addrinfo *uv_getaddrinfo_t.addrinfo

  Pointer to a struct addrinfo containing the result. Must be freed by the user with `uv_freeaddrinfo()`.

  Changed in version 1.3.0: the field is declared as public.

uv_loop_t *uv_getnameinfo_t.loop

  Loop that started this getnameinfo request and where completion will be reported. Readonly.

char[NI_MAXHOST] uv_getnameinfo_t.host

  Char array containing the resulting host. It’s null terminated.

  Changed in version 1.3.0: the field is declared as public.

char[NI_MAXSERV] uv_getnameinfo_t.service

  Char array containing the resulting service. It’s null terminated.

  Changed in version 1.3.0: the field is declared as public.

See also

The `uv_req_t` members also apply.

## API

int uv_getaddrinfo(uv_loop_t *loop, uv_getaddrinfo_t *req, uv_getaddrinfo_cb getaddrinfo_cb, const char *node, const char *service, const struct addrinfo *hints)

  Asynchronous getaddrinfo(3).

  Either node or service may be NULL but not both.

  hints is a pointer to a struct addrinfo with additional address type constraints, or NULL. Consult man -s 3 getaddrinfo for more details.

  Returns 0 on success or an error code < 0 on failure. If successful, the callback will get called sometime in the future with the lookup result, which is either:

  - status == 0, the res argument points to a valid struct addrinfo, or

  - status < 0, the res argument is NULL. See the UV_EAI_* constants.

  Call `uv_freeaddrinfo()` to free the addrinfo structure.

  Changed in version 1.3.0: the callback parameter is now allowed to be NULL, in which case the request will run synchronously.

void uv_freeaddrinfo(struct addrinfo *ai)

  Free the struct addrinfo. Passing NULL is allowed and is a no-op.

int uv_getnameinfo(uv_loop_t *loop, uv_getnameinfo_t *req, uv_getnameinfo_cb getnameinfo_cb, const struct sockaddr *addr, int flags)

  Asynchronous getnameinfo(3).

  Returns 0 on success or an error code < 0 on failure. If successful, the callback will get called sometime in the future with the lookup result. Consult man -s 3 getnameinfo for more details.

  Changed in version 1.3.0: the callback parameter is now allowed to be NULL, in which case the request will run synchronously.

See also

The `uv_req_t` API functions also apply.