ares_send - Initiate a DNS query
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)
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 immedi-
ately, 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 argu-
ment 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
The callback argument timeouts reports how many times a query timed out during the execu-
tion 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 func-
tions 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.
Greg Hudson, MIT Information Systems
Copyright 1998 by the Massachusetts Institute of Technology.
25 July 1998 ARES_SEND(3)