NAME
ares_query - Initiate a single-question DNS query
SYNOPSIS
#include <ares.h>
typedef void (*ares_callback)(void *arg, int status,
unsigned char *abuf, int alen)
void ares_query(ares_channel channel, const char *name,
int dnsclass, int type, ares_callback callback,
void *arg)
DESCRIPTION
The ares_query function initiates a single-question DNS query on the
name service channel identified by channel. The parameter name gives
the query name as a NUL-terminated C string of period-separated labels
optionally ending with a period; periods and backslashes within a label
must be escaped with a backslash. The parameters dnsclass and type
give the class and type of the query using the values defined in
<arpa/nameser.h>. 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_query 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 successfully.
ARES_ENODATA The query completed but contains no answers.
ARES_EFORMERR The query completed but the server claims that the
query was malformatted.
ARES_ESERVFAIL The query completed but the server claims to have
experienced a failure. (This code can only occur if
the ARES_FLAG_NOCHECKRESP flag was specified at
channel initialization time; otherwise, such
responses are ignored at the ares_send(3) level.)
ARES_ENOTFOUND The query completed but the queried-for domain name
was not found.
ARES_ENOTIMP The query completed but the server does not
implement the operation requested by the query.
(This code can only occur if the
ARES_FLAG_NOCHECKRESP flag was specified at channel
initialization time; otherwise, such responses are
ignored at the ares_send(3) level.)
ARES_EREFUSED The query completed but the server refused the
query. (This code can only occur if the
ARES_FLAG_NOCHECKRESP flag was specified at channel
initialization time; otherwise, such responses are
ignored at the ares_send(3) level.)
ARES_EBADNAME The query name name could not be encoded as a domain
name, either because it contained a zero-length
label or because it contained a label of more than
63 characters.
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 (even if there was something wrong with it, as
indicated by some of the above error codes), 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.
SEE ALSO
ares_process(3)
AUTHOR
Greg Hudson, MIT Information Systems
Copyright 1998 by the Massachusetts Institute of Technology.
24 July 1998