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)

AUTHOR

       Greg Hudson, MIT Information Systems
       Copyright 1998 by the Massachusetts Institute of Technology.

                                           24 July 1998                     ARES_GETHOSTBYADDR(3)