NAME¶
ares_send - Initiate a DNS query
SYNOPSIS¶
#include <ares.h>
typedef void (*ares_callback)(void *arg, int status,
int timeouts, unsigned char *abuf, int alen)
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.