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142 lines
4.0 KiB
142 lines
4.0 KiB
.\" $Id$ |
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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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