.\"

.\" Copyright 1998 by the Massachusetts Institute of Technology.

.\"

.\" Permission to use, copy, modify, and distribute this

.\" software and its documentation for any purpose and without

.\" fee is hereby granted, provided that the above copyright

.\" notice appear in all copies and that both that copyright

.\" notice and this permission notice appear in supporting

.\" documentation, and that the name of M.I.T. not be used in

.\" advertising or publicity pertaining to distribution of the

.\" software without specific, written prior permission.

.\" M.I.T. makes no representations about the suitability of

.\" this software for any purpose.  It is provided "as is"

.\" without express or implied warranty.

.\"

.TH ARES_QUERY 3 "24 July 1998"

.SH NAME

ares_query \- Initiate a single-question DNS query

.SH SYNOPSIS

.nf

.B #include <ares.h>

.PP

.B typedef void (*ares_callback)(void *\fIarg\fP, int \fIstatus\fP,

.B	int \fItimeouts\fP, unsigned char *\fIabuf\fP, int \fIalen\fP)

.PP

.B void ares_query(ares_channel \fIchannel\fP, const char *\fIname\fP,

.B 	int \fIdnsclass\fP, int \fItype\fP, ares_callback \fIcallback\fP,

.B	void *\fIarg\fP)

.fi

.SH DESCRIPTION

The

.B ares_query

function initiates a single-question DNS query on the name service

channel identified by

.IR channel .

The parameter

.I 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

.I dnsclass

and

.I type

give the class and type of the query using the values defined in

.BR <arpa/nameser.h> .

When the query is complete or has failed, the ares library will invoke

.IR callback .

Completion or failure of the query may happen immediately, or may

happen during a later call to

.BR ares_process (3)

or

.BR ares_destroy (3).

.PP

The callback argument

.I arg

is copied from the

.B ares_query

argument

.IR arg .

The callback argument

.I status

indicates whether the query succeeded and, if not, how it failed.  It

may have any of the following values:

.TP 19

.B ARES_SUCCESS

The query completed successfully.

.TP 19

.B ARES_ENODATA

The query completed but contains no answers.

.TP 19

.B ARES_EFORMERR

The query completed but the server claims that the query was

malformatted.

.TP 19

.B ARES_ESERVFAIL

The query completed but the server claims to have experienced a

failure.  (This code can only occur if the

.B ARES_FLAG_NOCHECKRESP

flag was specified at channel initialization time; otherwise, such

responses are ignored at the

.BR ares_send (3)

level.)

.TP 19

.B ARES_ENOTFOUND

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

.TP 19

.B ARES_ENOTIMP

The query completed but the server does not implement the operation

requested by the query.  (This code can only occur if the

.B ARES_FLAG_NOCHECKRESP

flag was specified at channel initialization time; otherwise, such

responses are ignored at the

.BR ares_send (3)

level.)

.TP 19

.B ARES_EREFUSED

The query completed but the server refused the query.  (This code can

only occur if the

.B ARES_FLAG_NOCHECKRESP

flag was specified at channel initialization time; otherwise, such

responses are ignored at the

.BR ares_send (3)

level.)

.TP 19

.B ARES_EBADNAME

The query name

.I 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.

.TP 19

.B ARES_ETIMEOUT

No name servers responded within the timeout period.

.TP 19

.B ARES_ECONNREFUSED

No name servers could be contacted.

.TP 19

.B ARES_ENOMEM

Memory was exhausted.

.TP 19

.B ARES_ECANCELLED

The query was cancelled.

.TP 19

.B ARES_EDESTRUCTION

The name service channel

.I channel

is being destroyed; the query will not be completed.

.PP

The callback argument

.I timeouts

reports how many times a query timed out during the execution of the

given request.

.PP

If the query completed (even if there was something wrong with it, as

indicated by some of the above error codes), the callback argument

.I abuf

points to a result buffer of length

.IR alen .

If the query did not complete,

.I abuf

will be NULL and

.I alen

will be 0.

.SH SEE ALSO

.BR ares_process (3)

.SH AUTHOR

Greg Hudson, MIT Information Systems

.br

Copyright 1998 by the Massachusetts Institute of Technology.