ares_send - Initiate a DNS query
typedef void (*ares_callback)(void *arg, int status,
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 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
ARES_ETIMEOUT No name servers responded within the timeout period.
ARES_ECONNREFUSED No name servers could be contacted.
ARES_ENOMEM Memory was exhausted.
ARES_EDESTRUCTION The name service channel channel is being destroyed;
the query will not be completed.
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
Greg Hudson, MIT Information Systems
Copyright 1998 by the Massachusetts Institute of Technology.
25 July 1998