ARES_QUERY
Section: C Library Functions (3)
Updated: 24 July 1998
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NAME
ares_query - Initiate a single-question DNS query
SYNOPSIS
#include <ares.h>
typedef void (*ares_callback)(void *arg, int status,
void ares_query(ares_channel channel, const char *name,
int dnsclass, int type, ares_callback callback,
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.