optionsfrom.3

This a good VPN source

.TH IPSEC_OPTIONSFROM 3 "16 Oct 1998"
.\" RCSID $Id: optionsfrom.3,v 1.9 2004/04/09 18:00:40 mcr Exp $
.SH NAME
ipsec optionsfrom \- read additional ``command-line'' options from file
.SH SYNOPSIS
.B "#include <freeswan.h>
.sp
.B "const char *optionsfrom(char *filename, int *argcp,"
.ti +1c
.B "char ***argvp, int optind, FILE *errsto);"
.SH DESCRIPTION
.I Optionsfrom
is called from within a
.IR getopt_long (3)
scan,
as the result of the appearance of an option (preferably
.BR \-\-optionsfrom )
to insert additional ``command-line'' arguments
into the scan immediately after
the option.
Typically this would be done to pick up options which are
security-sensitive and should not be visible to
.IR ps (1)
and similar commands,
and hence cannot be supplied as part
of the actual command line or the environment.
.PP
.I Optionsfrom
reads the additional arguments from the specified
.IR filename ,
allocates a new argument vector to hold pointers to the existing
arguments plus the new ones,
and amends
.I argc
and
.I argv
(via the pointers
.I argcp
and
.IR argvp ,
which must point to the
.I argc
and
.I argv
being supplied to
.IR getopt_long (3))
accordingly.
.I Optind
must be the index, in the original argument vector,
of the next argument.
.PP
If
.I errsto
is NULL,
.I optionsfrom
returns NULL for success and
a pointer to a string-literal error message for failure;
see DIAGNOSTICS.
If
.I errsto
is non-NULL and an error occurs,
.I optionsfrom
prints a suitable complaint onto the
.I errsto
descriptor and invokes
.I exit
with an exit status of 2;
this is a convenience for cases where more sophisticated
responses are not required.
.PP
The text of existing arguments is not disturbed by
.IR optionsfrom ,
so pointers to them and into them remain valid.
.PP
The file of additional arguments is an ASCII text file.
Lines consisting solely of white space,
and lines beginning with
.BR # ,
are comments and are ignored.
Otherwise, a line which does not begin with
.BR \-
is taken to be a single argument;
if it both begins and ends with double-quote ("),
those quotes are stripped off (note, no other processing is done within
the line!).
A line beginning with
.B \-
is considered to contain multiple arguments separated by white space.
.PP
Because
.I optionsfrom
reads its entire file before the
.IR getopt_long (3)
scan is resumed, an
.I optionsfrom
file can contain another
.B \-\-optionsfrom
option.
Obviously, infinite loops are possible here.
If
.I errsto
is non-NULL,
.I optionsfrom
considers it an error to be called more than 100 times.
If
.I errsto
is NULL,
loop detection is up to the caller
(and the internal loop counter is zeroed out).
.SH EXAMPLE
A reasonable way to invoke
.I optionsfrom
would be like so:
.PP
.nf
.ft B
#include <getopt.h>

struct option opts[] = {
	/* ... */
	"optionsfrom",	1,	NULL,	'+',
	/* ... */
};

int
main(argc, argv)
int argc;
char *argv[];
{
	int opt;
	extern char *optarg;
	extern int optind;

	while ((opt = getopt_long(argc, argv, "", opts, NULL)) != EOF)
		switch (opt) {
		/* ... */
		case '+':	/* optionsfrom */
			optionsfrom(optarg, &argc, &argv, optind, stderr);
			/* does not return on error */
			break;
		/* ... */
		}
	/* ... */
.ft
.fi
.SH SEE ALSO
getopt_long(3)
.SH DIAGNOSTICS
Errors in
.I optionsfrom
are:
unable to open file;
attempt to allocate temporary storage for argument or
argument vector failed;
read error in file;
line too long.
.SH HISTORY
Written for the FreeS/WAN project by Henry Spencer.
.SH BUGS
The double-quote convention is rather simplistic.
.PP
Line length is currently limited to 1023 bytes,
and there is no continuation convention.
.PP
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.
.PP
There is a certain element of unwarranted chumminess with
the insides of
.IR getopt_long (3)
here.
No non-public interfaces are actually used, but
.IR optionsfrom
does rely on
.IR getopt_long (3)
being well-behaved in certain ways that are not actually
promised by the specs.