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121 lines
3.2 KiB
121 lines
3.2 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_SEND 3 "25 July 1998" |
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.SH NAME |
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ares_send \- Initiate a DNS query |
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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_send(ares_channel_t *\fIchannel\fP, const unsigned char *\fIqbuf\fP, |
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int \fIqlen\fP, 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_send |
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function initiates a DNS query on the name service channel identified |
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by |
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.IR channel . |
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The parameters |
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.I qbuf |
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and |
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.I qlen |
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give the DNS query, which should already have been formatted according |
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to the DNS protocol. When the query is complete or has failed, the |
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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 later as network events are processed. |
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.PP |
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When the associated callback is called, it is called with a channel lock so care |
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must be taken to ensure any processing is minimal to prevent DNS channel stalls. |
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The callback may be triggered from a different thread than the one which |
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called \fIares_send(3)\fP. |
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For integrators running their own event loops and not using \fBARES_OPT_EVENT_THREAD\fP, |
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care needs to be taken to ensure any file descriptor lists are updated immediately |
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within the eventloop when notified. |
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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_send |
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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. |
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.TP 19 |
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.B ARES_EBADQUERY |
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The query buffer was poorly formed (was not long enough for a DNS |
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header or was too long for TCP transmission). |
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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_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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.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 the query completed, 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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.PP |
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Unless the flag |
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.B ARES_FLAG_NOCHECKRESP |
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was set at channel initialization time, |
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.B ares_send |
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will normally ignore responses whose questions do not match the |
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questions in |
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.IR qbuf , |
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as well as responses with reply codes of |
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.BR SERVFAIL , |
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.BR NOTIMP , |
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and |
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.BR REFUSED . |
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Unlike other query functions in the ares library, however, |
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.B ares_send |
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does not inspect the header of the reply packet to determine the error |
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status, so a callback status of |
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.B ARES_SUCCESS |
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does not reflect as much about the response as for other query |
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functions. |
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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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