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)