ARES_GETHOSTBYADDR(3) Introduction to Library Functions
NAME
ares_gethostbyaddr - Initiate a host query by address
SYNOPSIS
#include <ares.h>
typedef void (*ares_host_callback)(void *
arg, int
status,
int
timeouts,
struct hostent *
hostent)
void ares_gethostbyaddr(ares_channel_t *
channel, const void *
addr,
int
addrlen, int
family,
ares_host_callback
callback, void *
arg)
DESCRIPTION
The
ares_gethostbyaddr function initiates a host query by address on
the name service channel identified by
channel. The parameters
addr and
addrlen give the address as a series of bytes, and
family gives
the type of address. 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_gethostbyaddr 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 look up
addresses of type
family.
ARES_ENOTFOUND The address
addr 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_gethostbyaddr(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_gethostbyname(3) 24 July 1998 ARES_GETHOSTBYADDR(3)
