bionic (3) ares_query.3.gz

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 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).

       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.

       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)