ARES_GETHOSTBYNAME(3)

NAME
ares_gethostbyname - Initiate a host query by name

SYNOPSIS
#include <ares.h>
typedef void (*ares_host_callback)(void *arg, int status,
                                   int timeouts,
                                   struct hostent *hostent)
void ares_gethostbyname(ares_channel_t *channel, const char *name,
                        int family, ares_host_callback callback,
                        void *arg)

DESCRIPTION
The ares_gethostbyname function initiates a host query by name on the name service channel identified by channel. The parameter name gives the hostname as a NUL-terminated C string, and family gives the desired type of address for the resulting host entry. 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_destroy(3) or ares_cancel(3).

The callback argument arg is copied from the ares_gethostbyname 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_EBADNAME
    The hostname name is composed entirely of numbers and periods, but is not a valid representation of an Internet address.

ARES_ENODATA
    There was no data returned to extract a result from.

ARES_ENOTFOUND
    The name name was not found.

ARES_ENOMEM
    Memory was exhausted.

ARES_ECANCELLED
    The query was cancelled.

ARES_EDESTRUCTION
    The name service channel channel is being destroyed; the query will not be completed.

The callback argument timeouts reports how many times a query timed out during the execution of the given request.

On successful completion of the query, the callback argument hostent points to a struct hostent containing the name of the host returned by the query. The callback need not and should not attempt to free the memory pointed to by hostent; the ares library will free it when the callback returns. The callback must not modify the struct hostent or retain a reference to it after returning; it is owned by c-ares and is only valid for the duration of the callback. The parameter is intentionally not declared const solely to preserve API/ABI compatibility with existing applications. If the query did not complete successfully, hostent will be NULL.

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_gethostbyname(3). 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.

SEE ALSO
ares_process(3), ares_gethostbyaddr(3)