ARES_GETHOSTBYNAME(3) Introduction to Library Functions

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. 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)

25 July 1998 ARES_GETHOSTBYNAME(3)