docs/ares_getnameinfo.3

.\"
.\" Copyright 2005 by Dominick Meglio.
.\" SPDX-License-Identifier: MIT
.\"
.TH ARES_GETNAMEINFO 3 "1 May 2009"
.SH NAME
ares_getnameinfo \- Address-to-nodename translation in protocol-independent manner
.SH SYNOPSIS
.nf
#include <ares.h>

typedef void (*ares_nameinfo_callback)(void *\fIarg\fP, int \fIstatus\fP,
                                       int \fItimeouts\fP, char *\fInode\fP,
                                       char *\fIservice\fP)

void ares_getnameinfo(ares_channel_t *\fIchannel\fP, const struct sockaddr *\fIsa\fP,
                      ares_socklen_t \fIsalen\fP, int \fIflags\fP,
                      ares_nameinfo_callback \fIcallback\fP, void *\fIarg\fP)
.fi
.SH DESCRIPTION
The
.B ares_getnameinfo
function is defined for protocol-independent address translation. The function
is a combination of \fIares_gethostbyaddr(3)\fP and \fIgetservbyport(3)\fP. The function will
translate the address either by executing a host query on the name service channel
identified by
.IR channel 
or it will attempt to resolve it locally if possible.
The parameters
.I sa
and
.I len
give the address as a sockaddr structure, and
.I flags
gives the options that the function will use.  Valid flags are listed below:
.TP 19
.B ARES_NI_NOFQDN
Only the nodename portion of the FQDN is returned for local hosts.
.TP 19
.B ARES_NI_NUMERICHOST
The numeric form of the hostname is returned rather than the name.
.TP 19
.B ARES_NI_NAMEREQD
An error is returned if the hostname cannot be found in the DNS.
.TP 19
.B ARES_NI_NUMERICSERV
The numeric form of the service is returned rather than the name.
.TP 19
.B ARES_NI_TCP
The service name is to be looked up for the TCP protocol.
.TP 19
.B ARES_NI_UDP
The service name is to be looked up for the UDP protocol.
.TP 19
.B ARES_NI_SCTP
The service name is to be looked up for the SCTP protocol.
.TP 19
.B ARES_NI_DCCP
The service name is to be looked up for the DCCP protocol.
.TP 19
.B ARES_NI_NUMERICSCOPE
The numeric form of the scope ID is returned rather than the name.
.TP 19
.B ARES_NI_LOOKUPHOST
A hostname lookup is being requested.
.TP 19
.B ARES_NI_LOOKUPSERVICE
A service name lookup is being requested.
.PP
When the query
is complete or has 
failed, the ares library will invoke \fIcallback\fP.  Completion or failure of 
the query may happen immediately, or may happen during a later call to
\fIares_process(3)\fP, \fIares_destroy(3)\fP or \fIares_cancel(3)\fP.
.PP
When the associated callback is called, it is called with a channel lock so care
must be taken to ensure any processing is minimal to prevent DNS channel stalls.

The callback may be triggered from a different thread than the one which
called \fIares_getnameinfo(3)\fP.

For integrators running their own event loops and not using \fBARES_OPT_EVENT_THREAD\fP,
care needs to be taken to ensure any file descriptor lists are updated immediately
within the eventloop when notified.
.PP
The callback argument
.I arg
is copied from the
.B ares_getnameinfo
argument
.IR arg .
The callback argument
.I status
indicates whether the query succeeded and, if not, how it failed.  It
may have any of the following values:
.TP 19
.B ARES_SUCCESS
The host lookup completed successfully.
.TP 19
.B ARES_ENOTIMP
The ares library does not know how to look up addresses of type
.IR family .
.TP 19
.B ARES_ENOTFOUND
The address
.I addr
was not found.
.TP 19
.B ARES_ENOMEM
Memory was exhausted.
.TP 19
.B ARES_ECANCELLED
The query was cancelled.
.TP 19
.B ARES_EDESTRUCTION
The name service channel
.I channel
is being destroyed; the query will not be completed.
.TP 19
.B ARES_EBADFLAGS
The
.I flags
parameter contains an illegal value.
.PP
The callback argument
.I timeouts
reports how many times a query timed out during the execution of the
given request.
.PP
On successful completion of the query, the callback argument
.I node
contains a string representing the hostname (assuming 
.B ARES_NI_LOOKUPHOST
was specified). Additionally, 
.I service
contains a string representing the service name (assuming
.B ARES_NI_LOOKUPSERVICE
was specified).
If the query did not complete successfully, or one of the values
was not requested, 
.I node
or
.I service
will be 
.BR NULL .
.SH SEE ALSO
.BR ares_process (3),