c-ares/docs/ares_search.3

.\"
.\" Copyright 1998 by the Massachusetts Institute of Technology.
.\"
.\" Permission to use, copy, modify, and distribute this
.\" software and its documentation for any purpose and without
.\" fee is hereby granted, provided that the above copyright
.\" notice appear in all copies and that both that copyright
.\" notice and this permission notice appear in supporting
.\" documentation, and that the name of M.I.T. not be used in
.\" advertising or publicity pertaining to distribution of the
.\" software without specific, written prior permission.
.\" M.I.T. makes no representations about the suitability of
.\" this software for any purpose.  It is provided "as is"
.\" without express or implied warranty.
.\"
.\" SPDX-License-Identifier: MIT
.\"
.TH ARES_SEARCH 3 "24 July 1998"
.SH NAME
ares_search \- Initiate a DNS query with domain search
.SH SYNOPSIS
.nf
#include <ares.h>

typedef void (*ares_callback)(void *\fIarg\fP, int \fIstatus\fP,
                              int \fItimeouts\fP, unsigned char *\fIabuf\fP,
                              int \fIalen\fP)

void ares_search(ares_channel_t *\fIchannel\fP, const char *\fIname\fP,
                 int \fIdnsclass\fP, int \fItype\fP,
                 ares_callback \fIcallback\fP, void *\fIarg\fP)
.fi
.SH DESCRIPTION
The
.B ares_search
function initiates a series of single-question DNS queries on the name
service channel identified by
.IR channel ,
using the channel's search domains as well as a host alias file given
by the HOSTALIAS environment variable.  The parameter
.I name
gives the alias name or the base of the query name as a NUL-terminated
C string of period-separated labels; if it ends with a period, the
channel's search domains will not be used.  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 using the values defined in
.BR <arpa/nameser.h> .
When the query sequence is complete or has failed, the ares library
will invoke
.IR callback .
Completion or failure of the query sequence may happen immediately, or
may happen during a later call to
.BR ares_process (3)
or
.BR ares_destroy (3).
.PP
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.
.PP
The callback argument
.I arg
is copied from the
.B ares_search
argument
.IR arg .
The callback argument
.I status
indicates whether the query sequence ended with a successful query
and, if not, how the query sequence failed.  It may have any of the
following values:
.TP 19
.B ARES_SUCCESS
A query completed successfully.
.TP 19
.B ARES_ENODATA
No query completed successfully; when the query was tried without a
search domain appended, a response was returned with no answers.
.TP 19
.B ARES_EFORMERR
A query completed but the server claimed that the query was
malformatted.
.TP 19
.B ARES_ESERVFAIL
No query completed successfully; when the query was tried without a
search domain appended, the server claimed 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
.BR ares_send (3)
level.)
.TP 19
.B ARES_ENOTFOUND
No query completed successfully; when the query was tried without a
search domain appended, the server reported that the queried-for
domain name was not found.
.TP 19
.B ARES_ENOTIMP
A 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
.BR ares_send (3)
level.)
.TP 19
.B ARES_EREFUSED
A query completed but the server refused the query.  (This code can
only occur returned if the
.B ARES_FLAG_NOCHECKRESP
flag was specified at channel initialization time; otherwise, such
responses are ignored at the
.BR ares_send (3)
level.)
.TP 19
.B ARES_TIMEOUT
No name servers responded to a query 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.
.PP
The callback argument
.I timeouts
reports how many times a query timed out during the execution of the
given request.
.PP
If a query completed successfully, the callback argument
.I abuf
points to a result buffer of length
.IR alen .
If the query did not complete successfully,
.I abuf
will usually be NULL and
.I alen
will usually be 0, but in some cases an unsuccessful query result may
be placed in
.IR abuf .
.SH SEE ALSO
.BR ares_process (3),
.BR ares_dns_record (3)
.SH AUTHOR
Greg Hudson, MIT Information Systems
.br
Copyright 1998 by the Massachusetts Institute of Technology.