plucky (3) ares_query.3.gz

NAME

       ares_query - Initiate a single-question DNS query

SYNOPSIS

       #include <ares.h>

       typedef void (*ares_callback_dnsrec)(void *arg, ares_status_t status,
                                            size_t timeouts,
                                            const ares_dns_record_t *dnsrec);

       ares_status_t ares_query_dnsrec(ares_channel_t      *channel,
                                       const char          *name,
                                       ares_dns_class_t     dnsclass,
                                       ares_dns_rec_type_t  type,
                                       ares_callback_dnsrec callback,
                                       void                *arg,
                                       unsigned short      *qid);

       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_dnsrec(3)  and  ares_query(3)  functions initiate 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.

       ares_query_dnsrec(3) uses the ares ares_dns_class_t  and  ares_dns_rec_type_t  defined  types.   However,
       ares_query(3) uses 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 (even before the return of the function call), 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_dnsrec(3) or  ares_query(3)  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_dnsrec(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_dnsrec(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_dnsrec(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 dnsrec or abuf will be non-NULL, otherwise they will be NULL.

AVAILABILITY

       ares_query_dnsrec(3) was introduced in c-ares 1.28.0.

SEE ALSO

       ares_process(3), ares_dns_record(3)

                                                  24 July 1998                                     ARES_QUERY(3)