Ikegami, I tried subs again. It's pretty close to what I had tried before, but I was trying explicitly to be as close as possible to what you suggest. The script hangs on the print/read statement without the custom "open" function running.

#!perl -w
use strict;
use warnings;
use subs qw(open);
use Errno qw(EPIPE);

sub open {
    $! = EPIPE;
    warn "open faked";
    return 0;
}

Test::subs();
exit(0);

package Test;

sub subs {
    my $string = "hello world";
    local *STDIN;
    open(STDIN, '<', \$string) or die "open failed: $!";
    binmode STDIN;

    while(<>) {
        print;
    }
}

1
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bluescreen I arrived at this situation by trying to follow best practices. 1.) opening a file should be error checked. 2.) I should use Devel::Cover to make sure that my tests provide 100% test coverage. It does seem likely that this particular call can never fail, but I still thinking the problem would be hard in some other circumstances. Also may be there could be a security hole in the perl core, which would allow hackers to generate such a situation and I want to defend my code against such known unknowns.

Actually I have had two more ideas on how to approach this. One is experimenting with

local *IO::File::open = sub {.....}
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Edit: Looking at the code for subs I can see why it won't work for me. It only deals with the calling package not where as I want to change how "open" works inside a package from outside.

Edit 2: My experimentation with typeglobs is failing. It does no better than the subs code above.

#!perl -w
use warnings;
use Errno qw(EPIPE);
use lib qw(.);
eval "use Test;";

BEGIN {
*{main::open} = sub {
    $! = EPIPE;
    warn "open faked";
    return 0;
};
}

Test::subs();
exit(0);
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package Test;

sub subs {
    my $string = "hello world";
    local *STDIN;
    open(STDIN, '<', \$string) or die "open failed: $!";
    binmode STDIN;

    while(<>) {
        print;
    }
}

1
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