.\"	$OpenBSD: getnetent.3,v 1.17 2017/11/28 18:10:59 schwarze Exp $
.\"
.\" Copyright (c) 1983, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.Dd $Mdocdate: November 28 2017 $
.Dt GETNETENT 3
.Os
.Sh NAME
.Nm getnetent ,
.Nm getnetbyaddr ,
.Nm getnetbyname ,
.Nm setnetent ,
.Nm endnetent
.Nd get network entry
.Sh SYNOPSIS
.In netdb.h
.Ft struct netent *
.Fn getnetent "void"
.Ft struct netent *
.Fn getnetbyname "const char *name"
.Ft struct netent *
.Fn getnetbyaddr "in_addr_t net" "int type"
.Ft void
.Fn setnetent "int stayopen"
.Ft void
.Fn endnetent "void"
.Sh DESCRIPTION
The
.Fn getnetent ,
.Fn getnetbyname ,
and
.Fn getnetbyaddr
functions each return a pointer to an object with the following structure
containing the broken-out fields of a line in the network database,
.Pa /etc/networks .
.Bd -literal -offset indent
struct	netent {
	char		*n_name;	/* official name of net */
	char		**n_aliases;	/* alias list */
	int		n_addrtype;	/* net number type */
	in_addr_t	n_net;		/* net number */
};
.Ed
.Pp
The members of this structure are:
.Bl -tag -width n_addrtype
.It Fa n_name
The official name of the network.
.It Fa n_aliases
A null-terminated list of alternate names for the network.
.It Fa n_addrtype
The type of the network number returned; currently only
.Dv AF_INET .
.It Fa n_net
The network number.
Network numbers are returned in machine byte order.
.El
.Pp
The
.Fn getnetent
function reads the next line of the file, opening the file if necessary.
.Pp
The
.Fn setnetent
function opens and rewinds the file.
If the
.Fa stayopen
flag is non-zero,
the net database will not be closed after each call to
.Fn getnetbyname
or
.Fn getnetbyaddr .
.Pp
The
.Fn endnetent
function closes the file.
.Pp
The
.Fn getnetbyname
and
.Fn getnetbyaddr
functions search the domain name server if the system is configured to use one.
If the search fails, or no name server is configured, they sequentially
search from the beginning of the file until a matching net name or
net address and type is found, or until
.Dv EOF
is encountered.
Network numbers are supplied in host order.
.Sh RETURN VALUES
The
.Fn getnetent ,
.Fn getnetbyaddr ,
and
.Fn getnetbyname
functions return
.Dv NULL
if the requested entry is not found.
.Sh FILES
.Bl -tag -width /etc/networks -compact
.It Pa /etc/networks
.El
.Sh SEE ALSO
.Xr resolver 3 ,
.Xr networks 5
.Sh STANDARDS
These functions conform to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn getnetent ,
.Fn getnetbyaddr ,
.Fn getnetbyname ,
.Fn setnetent ,
and
.Fn endnetent
functions appeared in
.Bx 4.2 .
.Sh BUGS
The data space used by these functions is static; if future use
requires the data, it should be copied before any subsequent calls
to these functions overwrite it.
Only Internet network numbers are currently understood.
Expecting network numbers to fit in no more than 32 bits is naive.