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151 lines
4.5 KiB
151 lines
4.5 KiB
.\" |
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.\" Copyright 1998 by the Massachusetts Institute of Technology. |
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.\" SPDX-License-Identifier: MIT |
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.\" |
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.TH ARES_SEARCH 3 "24 July 1998" |
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.SH NAME |
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ares_search \- Initiate a DNS query with domain search |
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.SH SYNOPSIS |
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.nf |
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#include <ares.h> |
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typedef void (*ares_callback)(void *\fIarg\fP, int \fIstatus\fP, |
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int \fItimeouts\fP, unsigned char *\fIabuf\fP, |
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int \fIalen\fP) |
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void ares_search(ares_channel_t *\fIchannel\fP, const char *\fIname\fP, |
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int \fIdnsclass\fP, int \fItype\fP, |
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ares_callback \fIcallback\fP, 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_search |
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function initiates a series of single-question DNS queries on the name |
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service channel identified by |
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.IR channel , |
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using the channel's search domains as well as a host alias file given |
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by the HOSTALIAS environment variable. The parameter |
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.I name |
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gives the alias name or the base of the query name as a NUL-terminated |
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C string of period-separated labels; if it ends with a period, the |
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channel's search domains will not be used. Periods and backslashes |
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within 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 sequence is complete or has failed, the ares library |
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will invoke |
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.IR callback . |
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Completion or failure of the query sequence may happen immediately, or |
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may 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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If this is called from a thread other than which the main program event loop is |
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running, care needs to be taken to ensure any file descriptor lists are updated |
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immediately within the eventloop. When the associated callback is called, |
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it is called with a channel lock so care must be taken to ensure any processing |
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is minimal to prevent DNS channel stalls. |
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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_search |
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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 sequence ended with a successful query |
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and, if not, how the query sequence failed. It may have any of the |
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following values: |
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.TP 19 |
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.B ARES_SUCCESS |
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A query completed successfully. |
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.TP 19 |
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.B ARES_ENODATA |
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No query completed successfully; when the query was tried without a |
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search domain appended, a response was returned with no answers. |
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.TP 19 |
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.B ARES_EFORMERR |
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A query completed but the server claimed 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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No query completed successfully; when the query was tried without a |
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search domain appended, the server claimed 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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No query completed successfully; when the query was tried without a |
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search domain appended, the server reported that the queried-for |
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domain name was not found. |
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.TP 19 |
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.B ARES_ENOTIMP |
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A 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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A query completed but the server refused the query. (This code can |
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only occur returned 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_TIMEOUT |
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No name servers responded to a query 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_ECANCELLED |
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The query was cancelled. |
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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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.TP 19 |
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.B ARES_ENOSERVER |
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No query completed successfully; no DNS servers were configured on the channel. |
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.PP |
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The callback argument |
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.I timeouts |
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reports how many times a query timed out during the execution of the |
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given request. |
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.PP |
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If a query completed successfully, 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 successfully, |
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.I abuf |
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will usually be NULL and |
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.I alen |
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will usually be 0, but in some cases an unsuccessful query result may |
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be placed in |
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.IR abuf . |
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.SH SEE ALSO |
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.BR ares_process (3), |
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.BR ares_dns_record (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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