NAME

       ares_send - Initiate a DNS query

SYNOPSIS

       #include <ares.h>

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

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

DESCRIPTION

       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  later  as  network  events  are
       processed.

       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_send(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.

       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 transmission).

       ARES_ETIMEOUT      No name servers responded within the timeout period.

       ARES_ECONNREFUSED  No name servers could be contacted.

       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.

       ARES_ENOSERVER     The query will not be completed because no DNS servers were configured on the channel.

       The callback argument timeouts reports how many times a query timed out during the execution of the given
       request.

       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.

SEE ALSO

       ares_process(3), ares_dns_record(3)

AUTHOR

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

                                                  25 July 1998                                      ARES_SEND(3)