c7083720cc
PR-URL: https://github.com/nodejs/node/pull/51846 Reviewed-By: Michaël Zasso <targos@protonmail.com> Reviewed-By: Mohammed Keyvanzadeh <mohammadkeyvanzade94@gmail.com> Reviewed-By: Marco Ippolito <marcoippolito54@gmail.com> Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
125 lines
3.3 KiB
Groff
125 lines
3.3 KiB
Groff
.\"
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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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.TP 19
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.B ARES_ENOSERVER
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The query will not be completed because no DNS servers were configured on the
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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 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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