155 lines
4.9 KiB
Groff
155 lines
4.9 KiB
Groff
.\"
|
|
.\" Copyright 1998 by the Massachusetts Institute of Technology.
|
|
.\" SPDX-License-Identifier: MIT
|
|
.\"
|
|
.TH ARES_QUERY 3 "24 July 1998"
|
|
.SH NAME
|
|
ares_query \- Initiate a single-question DNS query
|
|
.SH SYNOPSIS
|
|
.nf
|
|
#include <ares.h>
|
|
|
|
typedef void (*ares_callback_dnsrec)(void *arg, ares_status_t status,
|
|
size_t timeouts,
|
|
const ares_dns_record_t *dnsrec);
|
|
|
|
ares_status_t ares_query_dnsrec(ares_channel_t *channel,
|
|
const char *name,
|
|
ares_dns_class_t dnsclass,
|
|
ares_dns_rec_type_t type,
|
|
ares_callback_dnsrec callback,
|
|
void *arg,
|
|
unsigned short *qid);
|
|
|
|
typedef void (*ares_callback)(void *arg, int status,
|
|
int timeouts, unsigned char *abuf,
|
|
int alen);
|
|
|
|
void ares_query(ares_channel_t *channel, const char *name,
|
|
int dnsclass, int type,
|
|
ares_callback callback, void *arg);
|
|
|
|
.fi
|
|
|
|
.SH DESCRIPTION
|
|
|
|
The \fBares_query_dnsrec(3)\fP and \fBares_query(3)\fP functions initiate a
|
|
single-question DNS query on the name service channel identified by
|
|
.IR channel .
|
|
The parameter
|
|
.I 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
|
|
.I dnsclass
|
|
and
|
|
.I type
|
|
give the class and type of the query.
|
|
|
|
\fBares_query_dnsrec(3)\fP uses the ares \fBares_dns_class_t\fP and
|
|
\fBares_dns_rec_type_t\fP defined types. However, \fBares_query(3)\fP uses
|
|
the values defined in \fB<arpa/nameser.h>\fP.
|
|
|
|
When the query is complete or has failed, the ares library will invoke
|
|
.IR callback .
|
|
Completion or failure of the query may happen immediately (even before the
|
|
return of the function call), or may happen during a later call to
|
|
\fBares_process(3)\fP or \fBares_destroy(3)\fP.
|
|
|
|
If this is called from a thread other than which the main program event loop is
|
|
running, care needs to be taken to ensure any file descriptor lists are updated
|
|
immediately within the eventloop. When the associated callback is called,
|
|
it is called with a channel lock so care must be taken to ensure any processing
|
|
is minimal to prevent DNS channel stalls.
|
|
|
|
The callback argument
|
|
.I arg
|
|
is copied from the \fBares_query_dnsrec(3)\fP or \fBares_query(3)\fP argument
|
|
.IR arg .
|
|
The callback argument
|
|
.I status
|
|
indicates whether the query succeeded and, if not, how it failed. It
|
|
may have any of the following values:
|
|
.TP 19
|
|
.B ARES_SUCCESS
|
|
The query completed successfully.
|
|
.TP 19
|
|
.B ARES_ENODATA
|
|
The query completed but contains no answers.
|
|
.TP 19
|
|
.B ARES_EFORMERR
|
|
The query completed but the server claims that the query was
|
|
malformatted.
|
|
.TP 19
|
|
.B ARES_ESERVFAIL
|
|
The query completed but the server claims to have experienced a
|
|
failure. (This code can only occur if the
|
|
.B ARES_FLAG_NOCHECKRESP
|
|
flag was specified at channel initialization time; otherwise, such
|
|
responses are ignored at the \fBares_send_dnsrec(3)\fP level.)
|
|
.TP 19
|
|
.B ARES_ENOTFOUND
|
|
The query completed but the queried-for domain name was not found.
|
|
.TP 19
|
|
.B ARES_ENOTIMP
|
|
The query completed but the server does not implement the operation
|
|
requested by the query. (This code can only occur if the
|
|
.B ARES_FLAG_NOCHECKRESP
|
|
flag was specified at channel initialization time; otherwise, such
|
|
responses are ignored at the \fBares_send_dnsrec(3)\fP level.)
|
|
.TP 19
|
|
.B ARES_EREFUSED
|
|
The query completed but the server refused the query. (This code can
|
|
only occur if the
|
|
.B ARES_FLAG_NOCHECKRESP
|
|
flag was specified at channel initialization time; otherwise, such
|
|
responses are ignored at the \fBares_send_dnsrec(3)\fP level.)
|
|
.TP 19
|
|
.B ARES_EBADNAME
|
|
The query name
|
|
.I 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.
|
|
.TP 19
|
|
.B ARES_ETIMEOUT
|
|
No name servers responded within the timeout period.
|
|
.TP 19
|
|
.B ARES_ECONNREFUSED
|
|
No name servers could be contacted.
|
|
.TP 19
|
|
.B ARES_ENOMEM
|
|
Memory was exhausted.
|
|
.TP 19
|
|
.B ARES_ECANCELLED
|
|
The query was cancelled.
|
|
.TP 19
|
|
.B ARES_EDESTRUCTION
|
|
The name service channel
|
|
.I channel
|
|
is being destroyed; the query will not be completed.
|
|
.TP 19
|
|
.B ARES_ENOSERVER
|
|
The query will not be completed because no DNS servers were configured on the
|
|
channel.
|
|
.PP
|
|
|
|
The callback argument
|
|
.I timeouts
|
|
reports how many times a query timed out during the execution of the
|
|
given request.
|
|
|
|
If the query completed (even if there was something wrong with it, as
|
|
indicated by some of the above error codes), the callback argument
|
|
.I dnsrec
|
|
or
|
|
.I abuf
|
|
will be non-NULL, otherwise they will be NULL.
|
|
|
|
.SH AVAILABILITY
|
|
\fBares_query_dnsrec(3)\fP was introduced in c-ares 1.28.0.
|
|
|
|
.SH SEE ALSO
|
|
.BR ares_process (3),
|
|
.BR ares_dns_record (3)
|