.\"

.\" 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

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.\" 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_SEND 3 "25 July 1998"

.SH NAME

ares_send \- Initiate a 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_send(ares_channel \fIchannel\fP, const unsigned char *\fIqbuf\fP,

.B 	int \fIqlen\fP, ares_callback \fIcallback\fP, void *\fIarg\fP)

.fi

.SH DESCRIPTION

The

.B ares_send

function initiates a DNS query on the name service channel identified

by

.IR channel .

The parameters

.I qbuf

and

.I qlen

give the DNS query, which should already have been formatted according

to the DNS protocol.  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_send

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.

.TP 19

.B ARES_EBADQUERY

The query buffer was poorly formed (was not long enough for a DNS

header or was too long for TCP transmission).

.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, 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.

.PP

Unless the flag

.B ARES_FLAG_NOCHECKRESP

was set at channel initialization time,

.B ares_send

will normally ignore responses whose questions do not match the

questions in

.IR qbuf ,

as well as responses with reply codes of

.BR SERVFAIL ,

.BR NOTIMP ,

and

.BR REFUSED .

Unlike other query functions in the ares library, however,

.B ares_send

does not inspect the header of the reply packet to determine the error

status, so a callback status of

.B ARES_SUCCESS

does not reflect as much about the response as for other query

functions.

.SH SEE ALSO

.BR ares_process (3)

.SH AUTHOR

Greg Hudson, MIT Information Systems

.br

Copyright 1998 by the Massachusetts Institute of Technology.