NAME

       ares_query - Initiate a single-question DNS query

SYNOPSIS

       #include <ares.h>

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

       void ares_query(ares_channel_t *channel, const char *name,
                       int dnsclass, int type,
                       ares_callback callback, void *arg)

DESCRIPTION

       The  ares_query function initiates a single-question DNS query on the name service channel
       identified by channel.  The parameter name gives the query  name  as  a  NUL-terminated  C
       string of period-separated labels optionally ending with a period; periods and backslashes
       within a label must be escaped with a backslash.  The parameters dnsclass  and  type  give
       the  class  and  type of the query using the values defined in <arpa/nameser.h>.  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).

       If this is called from a thread other than which the main program event loop  is  running,
       care  needs to be taken to ensure any file descriptor lists are updated immediately within
       the eventloop.  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  argument  arg  is  copied  from  the ares_query 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 successfully.

       ARES_ENODATA       The query completed but contains no answers.

       ARES_EFORMERR      The   query  completed  but  the  server  claims  that  the  query  was
                          malformatted.

       ARES_ESERVFAIL     The query completed  but  the  server  claims  to  have  experienced  a
                          failure.   (This  code can only occur if the ARES_FLAG_NOCHECKRESP flag
                          was specified at channel initialization time; otherwise, such responses
                          are ignored at the ares_send(3) level.)

       ARES_ENOTFOUND     The query completed but the queried-for domain name was not found.

       ARES_ENOTIMP       The  query  completed  but  the server does not implement the operation
                          requested  by  the  query.   (This  code  can   only   occur   if   the
                          ARES_FLAG_NOCHECKRESP  flag  was  specified  at  channel initialization
                          time; otherwise, such responses are ignored at the ares_send(3) level.)

       ARES_EREFUSED      The query completed but the server refused the query.  (This  code  can
                          only  occur  if the ARES_FLAG_NOCHECKRESP flag was specified at channel
                          initialization time; otherwise,  such  responses  are  ignored  at  the
                          ares_send(3) level.)

       ARES_EBADNAME      The  query  name  name  could  not  be encoded as a domain name, either
                          because it contained a zero-length label  or  because  it  contained  a
                          label of more than 63 characters.

       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 (even if there was something wrong with it, as indicated by some of
       the  above  error  codes),  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.

SEE ALSO

       ares_process(3)

AUTHOR

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

                                           24 July 1998                             ARES_QUERY(3)