package IPC::Open3;

use strict;
no strict 'refs'; # because users pass me bareword filehandles
use vars qw($VERSION @ISA @EXPORT $Fh $Me);

require 5.001;
require Exporter;

use Carp;
use Symbol 'qualify';

$VERSION	= 1.01;
@ISA		= qw(Exporter);
@EXPORT		= qw(open3);

=head1 NAME

IPC::Open3, open3 - open a process for reading, writing, and error handling

=head1 SYNOPSIS

    $pid = open3(\*WTRFH, \*RDRFH, \*ERRFH
		    'some cmd and args', 'optarg', ...);

=head1 DESCRIPTION

Extremely similar to open2(), open3() spawns the given $cmd and
connects RDRFH for reading, WTRFH for writing, and ERRFH for errors.  If
ERRFH is '', or the same as RDRFH, then STDOUT and STDERR of the child are
on the same file handle.

If WTRFH begins with "E<lt>&", then WTRFH will be closed in the parent, and
the child will read from it directly.  If RDRFH or ERRFH begins with
"E<gt>&", then the child will send output directly to that file handle.  In both
cases, there will be a dup(2) instead of a pipe(2) made.

If you try to read from the child's stdout writer and their stderr
writer, you'll have problems with blocking, which means you'll
want to use select(), which means you'll have to use sysread() instead
of normal stuff.

open3() returns the process ID of the child process.  It doesn't return on
failure: it just raises an exception matching C</^open3:/>.

=head1 WARNING

It will not create these file handles for you.  You have to do this
yourself.  So don't pass it empty variables expecting them to get filled
in for you.

Additionally, this is very dangerous as you may block forever.  It
assumes it's going to talk to something like B<bc>, both writing to it
and reading from it.  This is presumably safe because you "know" that
commands like B<bc> will read a line at a time and output a line at a
time.  Programs like B<sort> that read their entire input stream first,
however, are quite apt to cause deadlock.

The big problem with this approach is that if you don't have control
over source code being run in the the child process, you can't control
what it does with pipe buffering.  Thus you can't just open a pipe to
C<cat -v> and continually read and write a line from it.

=cut

# &open3: Marc Horowitz <marc@mit.edu>
# derived mostly from &open2 by tom christiansen, <tchrist@convex.com>
# fixed for 5.001 by Ulrich Kunitz <kunitz@mai-koeln.com>
#
# $Id: open3.pl,v 1.1 1993/11/23 06:26:15 marc Exp $
#
# usage: $pid = open3('wtr', 'rdr', 'err' 'some cmd and args', 'optarg', ...);
#
# spawn the given $cmd and connect rdr for
# reading, wtr for writing, and err for errors.
# if err is '', or the same as rdr, then stdout and
# stderr of the child are on the same fh.  returns pid
# of child (or dies on failure).


# if wtr begins with '<&', then wtr will be closed in the parent, and
# the child will read from it directly.  if rdr or err begins with
# '>&', then the child will send output directly to that fd.  In both
# cases, there will be a dup() instead of a pipe() made.


# WARNING: this is dangerous, as you may block forever
# unless you are very careful.
#
# $wtr is left unbuffered.
#
# abort program if
#   rdr or wtr are null
#   a system call fails

$Fh = 'FHOPEN000';	# package static in case called more than once
$Me = 'open3 (bug)';	# you should never see this, it's always localized

# Fatal.pm needs to be fixed WRT prototypes.

sub xfork {
    my $pid = fork;
    defined $pid or croak "$Me: fork failed: $!";
    return $pid;
}

sub xpipe {
    pipe $_[0], $_[1] or croak "$Me: pipe($_[0], $_[1]) failed: $!";
}

# I tried using a * prototype character for the filehandle but it still
# disallows a bearword while compiling under strict subs.

sub xopen {
    open $_[0], $_[1] or croak "$Me: open($_[0], $_[1]) failed: $!";
}

sub xclose {
    close $_[0] or croak "$Me: close($_[0]) failed: $!";
}

sub _open3 {
    local $Me = shift;
    my($package, $dad_wtr, $dad_rdr, $dad_err, @cmd) = @_;
    my($dup_wtr, $dup_rdr, $dup_err, $kidpid);

    $dad_wtr			or croak "$Me: wtr should not be null";
    $dad_rdr			or croak "$Me: rdr should not be null";
    $dad_err = $dad_rdr if ($dad_err eq '');

    $dup_wtr = ($dad_wtr =~ s/^[<>]&//);
    $dup_rdr = ($dad_rdr =~ s/^[<>]&//);
    $dup_err = ($dad_err =~ s/^[<>]&//);

    # force unqualified filehandles into callers' package
    $dad_wtr = qualify $dad_wtr, $package;
    $dad_rdr = qualify $dad_rdr, $package;
    $dad_err = qualify $dad_err, $package;

    my $kid_rdr = ++$Fh;
    my $kid_wtr = ++$Fh;
    my $kid_err = ++$Fh;

    xpipe $kid_rdr, $dad_wtr if !$dup_wtr;
    xpipe $dad_rdr, $kid_wtr if !$dup_rdr;
    xpipe $dad_err, $kid_err if !$dup_err && $dad_err ne $dad_rdr;

    $kidpid = xfork;
    if ($kidpid == 0) {
	# If she wants to dup the kid's stderr onto her stdout I need to
	# save a copy of her stdout before I put something else there.
	if ($dad_rdr ne $dad_err && $dup_err
		&& fileno($dad_err) == fileno(STDOUT)) {
	    my $tmp = ++$Fh;
	    xopen($tmp, ">&$dad_err");
	    $dad_err = $tmp;
	}

	if ($dup_wtr) {
	    xopen \*STDIN,  "<&$dad_wtr" if fileno(STDIN) != fileno($dad_wtr);
	} else {
	    xclose $dad_wtr;
	    xopen \*STDIN,  "<&$kid_rdr";
	    xclose $kid_rdr;
	}
	if ($dup_rdr) {
	    xopen \*STDOUT, ">&$dad_rdr" if fileno(STDOUT) != fileno($dad_rdr);
	} else {
	    xclose $dad_rdr;
	    xopen \*STDOUT, ">&$kid_wtr";
	    xclose $kid_wtr;
	}
	if ($dad_rdr ne $dad_err) {
	    if ($dup_err) {
		xopen \*STDERR, ">&$dad_err"
		    if fileno(STDERR) != fileno($dad_err);
	    } else {
		xclose $dad_err;
		xopen \*STDERR, ">&$kid_err";
		xclose $kid_err;
	    }
	} else {
	    xopen \*STDERR, ">&STDOUT" if fileno(STDERR) != fileno(STDOUT);
	}
	local($")=(" ");
	exec @cmd
	    or croak "open3: exec of @cmd failed";
    }

    xclose $kid_rdr if !$dup_wtr;
    xclose $kid_wtr if !$dup_rdr;
    xclose $kid_err if !$dup_err && $dad_rdr ne $dad_err;
    # If the write handle is a dup give it away entirely, close my copy
    # of it.
    xclose $dad_wtr if $dup_wtr;

    select((select($dad_wtr), $| = 1)[0]); # unbuffer pipe
    $kidpid;
}

sub open3 {
    return _open3 'open3', scalar caller, @_
}
1; # so require is happy

