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143 lines
4.0 KiB
Groff
143 lines
4.0 KiB
Groff
.\" $Id$
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.\"
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.\" Copyright 1998 by the Massachusetts Institute of Technology.
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.\"
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.\" Permission to use, copy, modify, and distribute this
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.\" software and its documentation for any purpose and without
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.\" fee is hereby granted, provided that the above copyright
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.\" notice appear in all copies and that both that copyright
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.\" notice and this permission notice appear in supporting
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.\" documentation, and that the name of M.I.T. not be used in
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.\" advertising or publicity pertaining to distribution of the
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.\" software without specific, written prior permission.
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.\" M.I.T. makes no representations about the suitability of
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.\" this software for any purpose. It is provided "as is"
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.\" without express or implied warranty.
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.\"
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.TH ARES_QUERY 3 "24 July 1998"
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.SH NAME
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ares_query \- Initiate a single-question DNS query
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.SH SYNOPSIS
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.nf
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.B #include <ares.h>
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.PP
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.B typedef void (*ares_callback)(void *\fIarg\fP, int \fIstatus\fP,
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.B unsigned char *\fIabuf\fP, int \fIalen\fP)
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.PP
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.B void ares_query(ares_channel \fIchannel\fP, const char *\fIname\fP,
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.B int \fIdnsclass\fP, int \fItype\fP, ares_callback \fIcallback\fP,
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.B void *\fIarg\fP)
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.fi
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.SH DESCRIPTION
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The
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.B ares_query
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function initiates a single-question DNS query on the name service
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channel identified by
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.IR channel .
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The parameter
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.I name
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gives the query name as a NUL-terminated C string of period-separated
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labels optionally ending with a period; periods and backslashes within
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a label must be escaped with a backslash. The parameters
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.I dnsclass
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and
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.I type
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give the class and type of the query using the values defined in
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.BR <arpa/nameser.h> .
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When the query is complete or has failed, the ares library will invoke
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.IR callback .
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Completion or failure of the query may happen immediately, or may
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happen during a later call to
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.BR ares_process (3)
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or
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.BR ares_destroy (3).
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.PP
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The callback argument
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.I arg
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is copied from the
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.B ares_query
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argument
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.IR arg .
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The callback argument
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.I status
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indicates whether the query succeeded and, if not, how it failed. It
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may have any of the following values:
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.TP 19
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.B ARES_SUCCESS
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The query completed successfully.
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.TP 19
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.B ARES_ENODATA
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The query completed but contains no answers.
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.TP 19
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.B ARES_EFORMERR
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The query completed but the server claims that the query was
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malformatted.
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.TP 19
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.B ARES_ESERVFAIL
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The query completed but the server claims to have experienced a
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failure. (This code can only occur if the
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.B ARES_FLAG_NOCHECKRESP
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flag was specified at channel initialization time; otherwise, such
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responses are ignored at the
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.BR ares_send (3)
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level.)
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.TP 19
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.B ARES_ENOTFOUND
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The query completed but the queried-for domain name was not found.
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.TP 19
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.B ARES_ENOTIMP
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The query completed but the server does not implement the operation
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requested by the query. (This code can only occur if the
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.B ARES_FLAG_NOCHECKRESP
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flag was specified at channel initialization time; otherwise, such
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responses are ignored at the
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.BR ares_send (3)
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level.)
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.TP 19
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.B ARES_EREFUSED
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The query completed but the server refused the query. (This code can
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only occur if the
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.B ARES_FLAG_NOCHECKRESP
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flag was specified at channel initialization time; otherwise, such
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responses are ignored at the
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.BR ares_send (3)
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level.)
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.TP 19
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.B ARES_EBADNAME
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The query name
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.I name
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could not be encoded as a domain name, either because it contained a
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zero-length label or because it contained a label of more than 63
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characters.
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.TP 19
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.B ARES_ETIMEOUT
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No name servers responded within the timeout period.
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.TP 19
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.B ARES_ECONNREFUSED
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No name servers could be contacted.
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.TP 19
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.B ARES_ENOMEM
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Memory was exhausted.
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.TP 19
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.B ARES_EDESTRUCTION
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The name service channel
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.I channel
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is being destroyed; the query will not be completed.
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.PP
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If the query completed (even if there was something wrong with it, as
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indicated by some of the above error codes), the callback argument
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.I abuf
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points to a result buffer of length
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.IR alen .
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If the query did not complete,
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.I abuf
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will be NULL and
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.I alen
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will be 0.
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.SH SEE ALSO
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.BR ares_process (3)
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.SH AUTHOR
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Greg Hudson, MIT Information Systems
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.br
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Copyright 1998 by the Massachusetts Institute of Technology.
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