c-ares/docs/ares_send.3

.\"
.\" Copyright 1998 by the Massachusetts Institute of Technology.
.\" SPDX-License-Identifier: MIT
.\"
.TH ARES_SEND 3 "25 July 1998"
.SH NAME
ares_send \- Initiate a DNS query
.SH SYNOPSIS
.nf
#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_send_dnsrec(ares_channel_t *channel,
                               const ares_dns_record_t *dnsrec,
                               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_send(ares_channel_t *channel, const unsigned char *qbuf,
               int qlen, ares_callback callback, void *arg);

.fi
.SH DESCRIPTION
The \fIares_send_dnsrec(3)\fP function initiates a DNS query formatted using the
\fIares_dns_record_t *\fP data structure created via
\fIares_dns_record_create(3)\fP in the
.IR dnsrec
parameter.  The supplied callback in the
.IR callback
parameter also returns the response using a
\fIares_dns_record_t *\fP data structure.

The \fIares_send(3)\fP function similarly initiates a DNS query, but instead uses
raw binary buffers with fully formatted DNS messages passed in the request via the
.IR qbuf
and
.IR qlen
parameters. The supplied callback in the
.IR callback
parameter also returns the raw binary DNS response in the
.IR abuf
and
.IR alen
parameters. This method should be considered deprecated in favor of
\fIares_send_dnsrec(3)\fP.

Both functions take an initialized ares channel identified by
.IR channel .

The \fIares_send_dnsrec(3)\fP also can be supplied an optional output parameter of
.IR qid
to populate the query id as it was placed on the wire.

The \fIares_send_dnsrec(3)\fP function returns an \fIares_status_t\fP response
code.  This may be useful to know that the query was enqueued properly.  The
response code does not reflect the result of the query, just the result of the
enqueuing of the query.

Completion or failure of the query may happen immediately (even before the
function returning), or may happen later as network events are processed.

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 may be triggered from a different thread than the one which
called \fIares_send_dnsrec(3)\fP or \fIares_send(3)\fP.

For integrators running their own event loops and not using \fBARES_OPT_EVENT_THREAD\fP,
care needs to be taken to ensure any file descriptor lists are updated immediately
within the eventloop when notified.

The callback argument
.IR arg
is copied from the \fIares_send_dnsrec(3)\fP or \fIares_send(3)\fP
.IR arg
parameter.

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.
.TP 19
.B ARES_ENOSERVER
The query will not be completed because no DNS servers were configured on the
channel.
.PP

The callback argument
.I timeouts
reports how many times a query timed out during the execution of the
given request.

If the query completed, the callback argument
.IR dnsrec
for \fIares_send_dnsrec(3)\fP or
.IR abuf
and
.IR alen
for \fIares_send(3)\fP will be non-NULL.

Unless the flag
.B ARES_FLAG_NOCHECKRESP
was set at channel initialization time, \fIares_send_dnsrec(3)\fP and
\fIares_send(3)\fP will normally ignore responses whose questions do not match
the supplied questions, as well as responses with reply codes of
.BR SERVFAIL ,
.BR NOTIMP ,
and
.BR REFUSED .
Unlike other query functions in the ares library, however,
\fIares_send_dnsrec(3)\fP and \fIares_send(3)\fP do 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 AVAILABILITY
\fBares_send_dnsrec(3)\fP was introduced in c-ares 1.28.0.

.SH SEE ALSO
.BR ares_dns_record_create (3),
.BR ares_process (3),
.BR ares_search (3),
.BR ares_dns_record (3)