mirror of https://github.com/nodejs/node.git
157 lines
4.8 KiB
Groff
157 lines
4.8 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_dnsrec)(void *arg, ares_status_t status,
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size_t timeouts,
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const ares_dns_record_t *dnsrec);
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ares_status_t ares_send_dnsrec(ares_channel_t *channel,
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const ares_dns_record_t *dnsrec,
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ares_callback_dnsrec callback,
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void *arg, unsigned short *qid);
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typedef void (*ares_callback)(void *arg, int status,
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int timeouts, unsigned char *abuf,
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int alen);
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void ares_send(ares_channel_t *channel, const unsigned char *qbuf,
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int qlen, ares_callback callback, void *arg);
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.fi
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.SH DESCRIPTION
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The \fIares_send_dnsrec(3)\fP function initiates a DNS query formatted using the
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\fIares_dns_record_t *\fP data structure created via
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\fIares_dns_record_create(3)\fP in the
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.IR dnsrec
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parameter. The supplied callback in the
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.IR callback
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parameter also returns the response using a
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\fIares_dns_record_t *\fP data structure.
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The \fIares_send(3)\fP function similarly initiates a DNS query, but instead uses
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raw binary buffers with fully formatted DNS messages passed in the request via the
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.IR qbuf
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and
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.IR qlen
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parameters. The supplied callback in the
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.IR callback
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parameter also returns the raw binary DNS response in the
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.IR abuf
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and
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.IR alen
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parameters. This method should be considered deprecated in favor of
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\fIares_send_dnsrec(3)\fP.
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Both functions take an initialized ares channel identified by
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.IR channel .
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The \fIares_send_dnsrec(3)\fP also can be supplied an optional output parameter of
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.IR qid
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to populate the query id as it was placed on the wire.
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The \fIares_send_dnsrec(3)\fP function returns an \fIares_status_t\fP response
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code. This may be useful to know that the query was enqueued properly. The
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response code does not reflect the result of the query, just the result of the
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enqueuing of the query.
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Completion or failure of the query may happen immediately (even before the
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function returning), or may happen later as network events are processed.
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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_dnsrec(3)\fP or \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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The callback argument
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.IR arg
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is copied from the \fIares_send_dnsrec(3)\fP or \fIares_send(3)\fP
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.IR arg
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parameter.
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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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.TP 19
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.B ARES_EBADQUERY
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Misformatted DNS query.
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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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If the query completed, the callback argument
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.IR dnsrec
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for \fIares_send_dnsrec(3)\fP or
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.IR abuf
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and
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.IR alen
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for \fIares_send(3)\fP will be non-NULL.
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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, \fIares_send_dnsrec(3)\fP and
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\fIares_send(3)\fP will normally ignore responses whose questions do not match
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the supplied questions, 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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\fIares_send_dnsrec(3)\fP and \fIares_send(3)\fP do not inspect the header of
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the reply packet to determine the error 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 functions.
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.SH AVAILABILITY
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\fBares_send_dnsrec(3)\fP was introduced in c-ares 1.28.0.
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.SH SEE ALSO
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.BR ares_dns_record_create (3),
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.BR ares_process (3),
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.BR ares_search (3),
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.BR ares_dns_record (3)
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