rangetosubnet.3

This a good VPN source

.TH IPSEC_RANGETOSUBNET 3 "8 Sept 2000"
.\" RCSID $Id: rangetosubnet.3,v 1.5 2004/04/09 18:00:36 mcr Exp $
.SH NAME
ipsec rangetosubnet \- convert address range to subnet
.SH SYNOPSIS
.B "#include <freeswan.h>"
.sp
.B "const char *rangetosubnet(const ip_address *start,"
.ti +1c
.B "const ip_address *stop, ip_subnet *dst);"
.SH DESCRIPTION
.I Rangetosubnet
accepts two IP addresses which define an address range,
from
.I start
to
.I stop
inclusive,
and converts this to a subnet if possible.
The addresses must both be IPv4 or both be IPv6,
and the address family of the resulting subnet is the same.
.PP
.I Rangetosubnet
returns NULL for success and
a pointer to a string-literal error message for failure;
see DIAGNOSTICS.
.SH SEE ALSO
ipsec_initsubnet(3), ipsec_ttosubnet(3)
.SH DIAGNOSTICS
Fatal errors in
.I rangetosubnet
are:
mixed address families;
unknown address family;
.I start
and
.I stop
do not define a subnet.
.SH HISTORY
Written for the FreeS/WAN project by Henry Spencer.
.SH BUGS
The restriction of error reports to literal strings
(so that callers don't need to worry about freeing them or copying them)
does limit the precision of error reporting.
.PP
The error-reporting convention lends itself
to slightly obscure code,
because many readers will not think of NULL as signifying success.
A good way to make it clearer is to write something like:
.PP
.RS
.nf
.B "const char *error;"
.sp
.B "error = rangetosubnet( /* ... */ );"
.B "if (error != NULL) {"
.B "        /* something went wrong */"
.fi
.RE