.\"

.\" Copyright 1998 by the Massachusetts Institute of Technology.

.\"

.\" Permission to use, copy, modify, and distribute this

.\" software and its documentation for any purpose and without

.\" fee is hereby granted, provided that the above copyright

.\" notice appear in all copies and that both that copyright

.\" notice and this permission notice appear in supporting

.\" documentation, and that the name of M.I.T. not be used in

.\" advertising or publicity pertaining to distribution of the

.\" software without specific, written prior permission.

.\" M.I.T. makes no representations about the suitability of

.\" this software for any purpose.  It is provided "as is"

.\" without express or implied warranty.

.\"

.TH ARES_GETHOSTBYADDR 3 "24 July 1998"

.SH NAME

ares_gethostbyaddr \- Initiate a host query by address

.SH SYNOPSIS

.nf

.B #include <ares.h>

.PP

.B typedef void (*ares_host_callback)(void *\fIarg\fP, int \fIstatus\fP,

.B	int \fItimeouts\fP, struct hostent *\fIhostent\fP)

.PP

.B void ares_gethostbyaddr(ares_channel \fIchannel\fP, const void *\fIaddr\fP,

.B 	int \fIaddrlen\fP, int \fIfamily\fP, ares_host_callback \fIcallback\fP,

.B 	void *\fIarg\fP)

.fi

.SH DESCRIPTION

The

.B ares_gethostbyaddr

function initiates a host query by address on the name service channel

identified by

.IR channel .

The parameters

.I addr

and

.I addrlen

give the address as a series of bytes, and

.I family

gives the type of address.  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

The callback argument

.I arg

is copied from the

.B ares_gethostbyaddr

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.

.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 hostent

points to a

.B struct hostent

containing the name of the host returned by the query.  The callback

need not and should not attempt to free the memory pointed to by

.IR hostent ;

the ares library will free it when the callback returns.  If the query

did not complete successfully,

.I hostent

will be

.BR NULL .

.SH SEE ALSO

.BR ares_process (3),

.BR ares_gethostbyname (3)

.SH AUTHOR

Greg Hudson, MIT Information Systems

.br

Copyright 1998 by the Massachusetts Institute of Technology.