Encodings not latching onto STDIN

[japhy]

Someone on freenode #perl was asking about hooking STDIN, STDOUT, and STDERR to functions so that when things are read or written to those filehandles, they would be pre-processed. I suggested tie(), and then mentioned that an encoding could probably also do the trick.

So I wrote the following snarky little program:

#!/usr/bin/perl

use strict;
use warnings;

{
  package MyEnc;

  use base qw( Encode::Encoding );
  __PACKAGE__->Define(qw( japhy ));

  sub encode {
    my ($self, $str, $chk) = @_;
    $_[1] = '' if $chk;
    $str =~ s/^/> /mg;
    return $str;
  }

  sub decode {
    my ($self, $str, $chk) = @_;
    $_[1] = '' if $chk;
    $str =~ s/^< //mg;
    return $str;
  }
}

open my($in), "<:encoding(japhy)", "input" or die $!;
open my($out), ">:encoding(japhy)", "output" or die $!;
print $out $_ while <$in>;

If 'input' contains

< abc
< def

then 'output' ends up holding

> abc
> def

Proof-of-concept. Hooray. But then I tried using STDIN and STDOUT instead:

open my($in), "<&:encoding(japhy)", "STDIN" or die $!;
open my($out), ">&:encoding(japhy)", "STDOUT" or die $!;

I entered the same content as is in 'input', but it wasn't decoded, and I got this instead:

< > abc
< > def

I tried this, too:

open my($in), "<-:encoding(japhy)" or die $!;
open my($out), ">-:encoding(japhy)" or die $!;

That didn't decode OR encode! I had to call binmode() after opening the filehandles to get it to work.

So, what's the deal? Vitals:

Summary of my perl5 (revision 5 version 8 subversion 8) configuration:
  Platform:
    osname=linux, osvers=2.6.15, archname=i486-linux-gnu-thread-multi
    uname='linux ninsei 2.6.15 #1 smp preempt sat jan 7 12:47:52 pst 2
+006 i686 gnulinux '
    config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -Dccc
+dlflags=-fPIC -Darchname=i486-
linux-gnu -Dprefix=/usr -Dprivlib=/usr/share/perl/5.8 -Darchlib=/usr/l
+ib/perl/5.8 -Dvendorprefix=/us
r -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/perl5 -Dsiteprefi
+x=/usr/local -Dsitelib=/usr/lo
cal/share/perl/5.8.8 -Dsitearch=/usr/local/lib/perl/5.8.8 -Dman1dir=/u
+sr/share/man/man1 -Dman3dir=/u
sr/share/man/man3 -Dsiteman1dir=/usr/local/man/man1 -Dsiteman3dir=/usr
+/local/man/man3 -Dman1ext=1 -D
man3ext=3perl -Dpager=/usr/bin/sensible-pager -Uafs -Ud_csh -Uusesfio 
+-Uusenm -Duseshrplib -Dlibperl=
libperl.so.5.8.8 -Dd_dosuid -des'
    hint=recommended, useposix=true, d_sigaction=define
    usethreads=define use5005threads=undef useithreads=define usemulti
+plicity=define
    useperlio=define d_sfio=undef uselargefiles=define usesocks=undef
    use64bitint=undef use64bitall=undef uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS 
+-DDEBIAN -fno-strict-aliasing 
-pipe -Wdeclaration-after-statement -I/usr/local/include -D_LARGEFILE_
+SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-O2',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS -DDEBIAN 
+-fno-strict-aliasing -pipe
-Wdeclaration-after-statement -I/usr/local/include'
    ccversion='', gccversion='4.0.3 20060128 (prerelease) (Debian 4.0.
+2-8)', gccosandvers=''
    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=1
+2
    ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t',
+ lseeksize=8
    alignbytes=4, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib
    libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt
    perllibs=-ldl -lm -lpthread -lc -lcrypt
    libc=/lib/libc-2.3.5.so, so=so, useshrplib=true, libperl=libperl.s
+o.5.8.8
    gnulibc_version='2.3.5'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -L/usr/local/lib'


Characteristics of this binary (from libperl): 
  Compile-time options: MULTIPLICITY PERL_IMPLICIT_CONTEXT
                        PERL_MALLOC_WRAP THREADS_HAVE_PIDS USE_ITHREAD
+S
                        USE_LARGE_FILES USE_PERLIO USE_REENTRANT_API
  Built under linux
  Compiled at Feb  9 2006 22:12:59
  %ENV:
    PERL5LIB="/home/japhy/perllib/share/perl/5.8.7"
  @INC:
    /home/japhy/perllib/share/perl/5.8.7
    /etc/perl
    /usr/local/lib/perl/5.8.8
    /usr/local/share/perl/5.8.8
    /usr/lib/perl5
    /usr/share/perl5
    /usr/lib/perl/5.8
    /usr/share/perl/5.8
    /usr/local/lib/site_perl
    /usr/local/lib/perl/5.8.7
    /usr/local/share/perl/5.8.7

[alexz]

Not necessarily anything to do with STDIN/STDOUT, this goes through double encoding and no decoding as well:

open(INPUT, "<input");
open my($in), "<&:encoding(japhy)", "INPUT" or die $!;
open my($out), ">&:encoding(japhy)", "STDOUT" or die $!;
print $out $_ while <$in>;
close(INPUT);

The output is:

> < abc
> < def

Update: Confirmed that it works fine if you call binmode afterwards. It looks like this bug: http://rt.perl.org/rt3/Ticket/Display.html?id=34595

[converter]

This link should make authentication a little easier: http://guest:[e-mail]/rt3/Ticket/Display.html?id=34595

[ambrus]

In recent perls, you might be able to use PerlIO::via which is a core perl module to write your own perlio layers in perl.

However, in some situations, the simplest way to filter the input or output might just be to pipe it through another process (which may be perl or anything else). For example, the following code (from a script I wrote previously) compresses the output with gzip:

open STDOUT, "|gzip -c" or die "cannot open gzip";