Perl select returning undef on sysread when using Windows, IPC::Open3, and IO::Socket->socketpair()

Question

I found this example (posted by @ikegami) of a way to use IPC::Open3 on windows using sockets. The problem is that, when I run it, I get an error An existing connection was forcibly closed by the remote host on the sysread. The command runs, the select works correctly, but the sysread is getting an undef instead of the expected 0 for end of file. This behavior is not the same for all commands. If I change the command to echo Hello World! it does not cause the error. Any idea what is going on here?

Here is the code from the example:

use strict;
use warnings;

use IO::Select qw( );
use IPC::Open3 qw( open3 );
use Socket     qw( AF_UNIX SOCK_STREAM PF_UNSPEC );

print( "REMOVE ME: getting started\n" );

sub _pipe {
    socketpair($_[0], $_[1], AF_UNIX, SOCK_STREAM, PF_UNSPEC)
        or return undef;
    shutdown($_[0], 1);  # No more writing for reader
    shutdown($_[1], 0);  # No more reading for writer
    return 1;
}

sub _open3 {
    local (*TO_CHLD_R,     *TO_CHLD_W);
    local (*FR_CHLD_R,     *FR_CHLD_W);
    local (*FR_CHLD_ERR_R, *FR_CHLD_ERR_W);

    if ($^O =~ /Win32/) {
        _pipe(*TO_CHLD_R,     *TO_CHLD_W    ) or die $^E;
        _pipe(*FR_CHLD_R,     *FR_CHLD_W    ) or die $^E;
        _pipe(*FR_CHLD_ERR_R, *FR_CHLD_ERR_W) or die $^E;
    } else {
        pipe(*TO_CHLD_R,     *TO_CHLD_W    ) or die $!;
        pipe(*FR_CHLD_R,     *FR_CHLD_W    ) or die $!;
        pipe(*FR_CHLD_ERR_R, *FR_CHLD_ERR_W) or die $!;
    }

    my $pid = open3('>&TO_CHLD_R', '<&FR_CHLD_W', '<&FR_CHLD_ERR_W', @_);

    return ( $pid, *TO_CHLD_W, *FR_CHLD_R, *FR_CHLD_ERR_R );
}

# when i change the command to 'echo Hello World' it works...
my ($pid, $to_chld, $fr_chld, $fr_chld_err) =
    _open3('cmd /c "dir /s/b"');

my %objs;

my $in_sel  = IO::Select->new();
my $out_sel = IO::Select->new();

for my $fh ($fr_chld, $fr_chld_err) {
    my $obj = {
        buf => '',
    };
    $objs{ fileno($fh) } = $obj;
    $in_sel->add($fh);
}

close($to_chld);

while ($in_sel->count() + $out_sel->count()) {
    my ($ins, $outs) = IO::Select::select($in_sel, $out_sel, undef);

    for my $fh (@$ins) {
        my $obj = $objs{ fileno($fh) };
        our $buf; local *buf = \( $obj->{buf} );
        my $bytes_read = sysread($fh, $buf, 64*1024, length($buf));
        if (!$bytes_read) {
            warn("Error reading from child: $!\n")
                if !defined($bytes_read);
            $in_sel->remove($fh);
        }
    }

    for my $fh (@$outs) {
    }
}

waitpid($pid, 0);

print("STDOUT:\n$objs{ fileno( $fr_chld     ) }{buf}");
print("\n" );
print("STDERR:\n$objs{ fileno( $fr_chld_err ) }{buf}");

Answer 1

I think it's because something like shutdown was used instead of something like close. Sounds safe to ignore.

grep $!{$_}, keys %! shows ECONNRESET, so just change

warn("Error reading from child: $!\n")
    if !defined($bytes_read);

to

warn("Error reading from child: $!\n")
    if !defined($bytes_read) && !$!{ECONNRESET};