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       ares_send - Initiate a DNS query


       #include <ares.h>

       typedef void (*ares_callback)(void *arg, int status,
       unsigned char *abuf, int alen)

       void ares_send(ares_channel channel, const unsigned char *qbuf,
            int qlen, ares_callback callback, void *arg)


       The  ares_send  function  initiates  a  DNS  query  on the name service
       channel identified by channel.  The parameters qbuf and qlen  give  the
       DNS  query,  which  should already have been formatted according to the
       DNS protocol.  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) or ares_destroy(3).

       The  callback  argument  arg is copied from the ares_send 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 query completed.

       ARES_EBADQUERY     The  query  buffer  was  poorly formed (was not long
                          enough for a DNS header or  was  too  long  for  TCP

       ARES_ETIMEOUT      No name servers responded within the timeout period.

       ARES_ECONNREFUSED  No name servers could be contacted.

       ARES_ENOMEM        Memory was exhausted.

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

       If  the  query completed, the callback argument abuf points to a result
       buffer of length alen.  If the query did not  complete,  abuf  will  be
       NULL and alen will be 0.

       Unless the flag ARES_FLAG_NOCHECKRESP was set at channel initialization
       time, ares_send will normally ignore responses whose questions  do  not
       match  the  questions in qbuf, as well as responses with reply codes of
       SERVFAIL, NOTIMP, and REFUSED.  Unlike other  query  functions  in  the
       ares  library,  however,  ares_send  does not inspect the header of the
       reply packet to determine the error status, so  a  callback  status  of
       ARES_SUCCESS  does  not reflect as much about the response as for other
       query functions.




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

                                 25 July 1998