ARES_SEND
Section: C Library Functions (3)
Updated: 25 July 1998
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NAME
ares_send - Initiate a DNS query
SYNOPSIS
#include <ares.h>
typedef void (*ares_callback)(void *arg, int status,
void ares_send(ares_channel channel, const unsigned char *qbuf,
int qlen, ares_callback callback, void *arg)
DESCRIPTION
The
ares_send
function initiates a DNS query on the name service channel identified
by
channel.
The parameters
qbuf
and
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
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_send
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.
- ARES_EBADQUERY
-
The query buffer was poorly formed (was not long enough for a DNS
header or was too long for TCP transmission).
- 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, 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.
Unless the flag
ARES_FLAG_NOCHECKRESP
was set at channel initialization time,
ares_send
will normally ignore responses whose questions do not match the
questions in
qbuf,
as well as responses with reply codes of
SERVFAIL,
NOTIMP,
and
REFUSED.
Unlike other query functions in the ares library, however,
ares_send
does not inspect the header of the reply packet to determine the error
status, so a callback status of
ARES_SUCCESS
does not reflect as much about the response as for other query
functions.
SEE ALSO
ares_process(3)
AUTHOR
Greg Hudson, MIT Information Systems
Copyright 1998 by the Massachusetts Institute of Technology.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- SEE ALSO
-
- AUTHOR
-