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PK �["f�8] 8] Simple.pmnu �[��� package Filter::Simple;
use Text::Balanced ':ALL';
use vars qw{ $VERSION @EXPORT };
$VERSION = '0.94';
use Filter::Util::Call;
use Carp;
@EXPORT = qw( FILTER FILTER_ONLY );
sub import {
if (@_>1) { shift; goto &FILTER }
else { *{caller()."::$_"} = \&$_ foreach @EXPORT }
}
sub fail {
croak "FILTER_ONLY: ", @_;
}
my $exql = sub {
my @bits = extract_quotelike $_[0], qr//;
return unless $bits[0];
return \@bits;
};
my $ncws = qr/\s+/;
my $comment = qr/(?<![\$\@%])#.*/;
my $ws = qr/(?:$ncws|$comment)+/;
my $id = qr/\b(?!([ysm]|q[rqxw]?|tr)\b)\w+/;
my $EOP = qr/\n\n|\Z/;
my $CUT = qr/\n=cut.*$EOP/;
my $pod_or_DATA = qr/
^=(?:head[1-4]|item) .*? $CUT
| ^=pod .*? $CUT
| ^=for .*? $CUT
| ^=begin .*? $CUT
| ^__(DATA|END)__\r?\n.*
/smx;
my $variable = qr{
[\$*\@%]\s*
\{\s*(?!::)(?:\d+|[][&`'#+*./|,";%=~:?!\@<>()-]|\^[A-Z]?)\}
| (?:\$#?|[*\@\%]|\\&)\$*\s*
(?: \{\s*(?:\^(?=[A-Z_]))?(?:\w|::|'\w)*\s*\}
| (?:\^(?=[A-Z_]))?(?:\w|::|'\w)*
| (?=\{) # ${ block }
)
)
| \$\s*(?!::)(?:\d+|[][&`'#+*./|,";%=~:?!\@<>()-]|\^[A-Z]?)
}x;
my %extractor_for = (
quotelike => [ $ws, $variable, $id, { MATCH => \&extract_quotelike } ],
regex => [ $ws, $pod_or_DATA, $id, $exql ],
string => [ $ws, $pod_or_DATA, $id, $exql ],
code => [ $ws, { DONT_MATCH => $pod_or_DATA }, $variable,
$id, { DONT_MATCH => \&extract_quotelike } ],
code_no_comments
=> [ { DONT_MATCH => $comment },
$ncws, { DONT_MATCH => $pod_or_DATA }, $variable,
$id, { DONT_MATCH => \&extract_quotelike } ],
executable => [ $ws, { DONT_MATCH => $pod_or_DATA } ],
executable_no_comments
=> [ { DONT_MATCH => $comment },
$ncws, { DONT_MATCH => $pod_or_DATA } ],
all => [ { MATCH => qr/(?s:.*)/ } ],
);
my %selector_for = (
all => sub { my ($t)=@_; sub{ $_=$$_; $t->(@_); $_} },
executable=> sub { my ($t)=@_; sub{ref() ? $_=$$_ : $t->(@_); $_} },
quotelike => sub { my ($t)=@_; sub{ref() && do{$_=$$_; $t->(@_)}; $_} },
regex => sub { my ($t)=@_;
sub{ref() or return $_;
my ($ql,undef,$pre,$op,$ld,$pat) = @$_;
return $_->[0] unless $op =~ /^(qr|m|s)/
|| !$op && ($ld eq '/' || $ld eq '?');
$_ = $pat;
$t->(@_);
$ql =~ s/^(\s*\Q$op\E\s*\Q$ld\E)\Q$pat\E/$1$_/;
return "$pre$ql";
};
},
string => sub { my ($t)=@_;
sub{ref() or return $_;
local *args = \@_;
my ($pre,$op,$ld1,$str1,$rd1,$ld2,$str2,$rd2,$flg) = @{$_}[2..10];
return $_->[0] if $op =~ /^(qr|m)/
|| !$op && ($ld1 eq '/' || $ld1 eq '?');
if (!$op || $op eq 'tr' || $op eq 'y') {
local *_ = \$str1;
$t->(@args);
}
if ($op =~ /^(tr|y|s)/) {
local *_ = \$str2;
$t->(@args);
}
my $result = "$pre$op$ld1$str1$rd1";
$result .= $ld2 if $ld1 =~ m/[[({<]/; #])}>
$result .= "$str2$rd2$flg";
return $result;
};
},
);
sub gen_std_filter_for {
my ($type, $transform) = @_;
return sub {
my $instr;
local @components;
for (extract_multiple($_,$extractor_for{$type})) {
if (ref()) { push @components, $_; $instr=0 }
elsif ($instr) { $components[-1] .= $_ }
else { push @components, $_; $instr=1 }
}
if ($type =~ /^code/) {
my $count = 0;
local $placeholder = qr/\Q$;\E(.{4})\Q$;\E/s;
my $extractor = qr/\Q$;\E(.{4})\Q$;\E/s;
$_ = join "",
map { ref $_ ? $;.pack('N',$count++).$; : $_ }
@components;
@components = grep { ref $_ } @components;
$transform->(@_);
s/$extractor/${$components[unpack('N',$1)]}/g;
}
else {
my $selector = $selector_for{$type}->($transform);
$_ = join "", map $selector->(@_), @components;
}
}
};
sub FILTER (&;$) {
my $caller = caller;
my ($filter, $terminator) = @_;
no warnings 'redefine';
*{"${caller}::import"} = gen_filter_import($caller,$filter,$terminator);
*{"${caller}::unimport"} = gen_filter_unimport($caller);
}
sub FILTER_ONLY {
my $caller = caller;
while (@_ > 1) {
my ($what, $how) = splice(@_, 0, 2);
fail "Unknown selector: $what"
unless exists $extractor_for{$what};
fail "Filter for $what is not a subroutine reference"
unless ref $how eq 'CODE';
push @transforms, gen_std_filter_for($what,$how);
}
my $terminator = shift;
my $multitransform = sub {
foreach my $transform ( @transforms ) {
$transform->(@_);
}
};
no warnings 'redefine';
*{"${caller}::import"} =
gen_filter_import($caller,$multitransform,$terminator);
*{"${caller}::unimport"} = gen_filter_unimport($caller);
}
my $ows = qr/(?:[ \t]+|#[^\n]*)*/;
sub gen_filter_import {
my ($class, $filter, $terminator) = @_;
my %terminator;
my $prev_import = *{$class."::import"}{CODE};
return sub {
my ($imported_class, @args) = @_;
my $def_terminator =
qr/^(?:\s*no\s+$imported_class\s*;$ows|__(?:END|DATA)__)\r?$/;
if (!defined $terminator) {
$terminator{terminator} = $def_terminator;
}
elsif (!ref $terminator || ref $terminator eq 'Regexp') {
$terminator{terminator} = $terminator;
}
elsif (ref $terminator ne 'HASH') {
croak "Terminator must be specified as scalar or hash ref"
}
elsif (!exists $terminator->{terminator}) {
$terminator{terminator} = $def_terminator;
}
filter_add(
sub {
my ($status, $lastline);
my $count = 0;
my $data = "";
while ($status = filter_read()) {
return $status if $status < 0;
if ($terminator{terminator} &&
m/$terminator{terminator}/) {
$lastline = $_;
$count++;
last;
}
$data .= $_;
$count++;
$_ = "";
}
return $count if not $count;
$_ = $data;
$filter->($imported_class, @args) unless $status < 0;
if (defined $lastline) {
if (defined $terminator{becomes}) {
$_ .= $terminator{becomes};
}
elsif ($lastline =~ $def_terminator) {
$_ .= $lastline;
}
}
return $count;
}
);
if ($prev_import) {
goto &$prev_import;
}
elsif ($class->isa('Exporter')) {
$class->export_to_level(1,@_);
}
}
}
sub gen_filter_unimport {
my ($class) = @_;
return sub {
filter_del();
goto &$prev_unimport if $prev_unimport;
}
}
1;
__END__
=head1 NAME
Filter::Simple - Simplified source filtering
=head1 SYNOPSIS
# in MyFilter.pm:
package MyFilter;
use Filter::Simple;
FILTER { ... };
# or just:
#
# use Filter::Simple sub { ... };
# in user's code:
use MyFilter;
# this code is filtered
no MyFilter;
# this code is not
=head1 DESCRIPTION
=head2 The Problem
Source filtering is an immensely powerful feature of recent versions of Perl.
It allows one to extend the language itself (e.g. the Switch module), to
simplify the language (e.g. Language::Pythonesque), or to completely recast the
language (e.g. Lingua::Romana::Perligata). Effectively, it allows one to use
the full power of Perl as its own, recursively applied, macro language.
The excellent Filter::Util::Call module (by Paul Marquess) provides a
usable Perl interface to source filtering, but it is often too powerful
and not nearly as simple as it could be.
To use the module it is necessary to do the following:
=over 4
=item 1.
Download, build, and install the Filter::Util::Call module.
(If you have Perl 5.7.1 or later, this is already done for you.)
=item 2.
Set up a module that does a C<use Filter::Util::Call>.
=item 3.
Within that module, create an C<import> subroutine.
=item 4.
Within the C<import> subroutine do a call to C<filter_add>, passing
it either a subroutine reference.
=item 5.
Within the subroutine reference, call C<filter_read> or C<filter_read_exact>
to "prime" $_ with source code data from the source file that will
C<use> your module. Check the status value returned to see if any
source code was actually read in.
=item 6.
Process the contents of $_ to change the source code in the desired manner.
=item 7.
Return the status value.
=item 8.
If the act of unimporting your module (via a C<no>) should cause source
code filtering to cease, create an C<unimport> subroutine, and have it call
C<filter_del>. Make sure that the call to C<filter_read> or
C<filter_read_exact> in step 5 will not accidentally read past the
C<no>. Effectively this limits source code filters to line-by-line
operation, unless the C<import> subroutine does some fancy
pre-pre-parsing of the source code it's filtering.
=back
For example, here is a minimal source code filter in a module named
BANG.pm. It simply converts every occurrence of the sequence C<BANG\s+BANG>
to the sequence C<die 'BANG' if $BANG> in any piece of code following a
C<use BANG;> statement (until the next C<no BANG;> statement, if any):
package BANG;
use Filter::Util::Call ;
sub import {
filter_add( sub {
my $caller = caller;
my ($status, $no_seen, $data);
while ($status = filter_read()) {
if (/^\s*no\s+$caller\s*;\s*?$/) {
$no_seen=1;
last;
}
$data .= $_;
$_ = "";
}
$_ = $data;
s/BANG\s+BANG/die 'BANG' if \$BANG/g
unless $status < 0;
$_ .= "no $class;\n" if $no_seen;
return 1;
})
}
sub unimport {
filter_del();
}
1 ;
This level of sophistication puts filtering out of the reach of
many programmers.
=head2 A Solution
The Filter::Simple module provides a simplified interface to
Filter::Util::Call; one that is sufficient for most common cases.
Instead of the above process, with Filter::Simple the task of setting up
a source code filter is reduced to:
=over 4
=item 1.
Download and install the Filter::Simple module.
(If you have Perl 5.7.1 or later, this is already done for you.)
=item 2.
Set up a module that does a C<use Filter::Simple> and then
calls C<FILTER { ... }>.
=item 3.
Within the anonymous subroutine or block that is passed to
C<FILTER>, process the contents of $_ to change the source code in
the desired manner.
=back
In other words, the previous example, would become:
package BANG;
use Filter::Simple;
FILTER {
s/BANG\s+BANG/die 'BANG' if \$BANG/g;
};
1 ;
Note that the source code is passed as a single string, so any regex that
uses C<^> or C<$> to detect line boundaries will need the C</m> flag.
=head2 Disabling or changing <no> behaviour
By default, the installed filter only filters up to a line consisting of one of
the three standard source "terminators":
no ModuleName; # optional comment
or:
__END__
or:
__DATA__
but this can be altered by passing a second argument to C<use Filter::Simple>
or C<FILTER> (just remember: there's I<no> comma after the initial block when
you use C<FILTER>).
That second argument may be either a C<qr>'d regular expression (which is then
used to match the terminator line), or a defined false value (which indicates
that no terminator line should be looked for), or a reference to a hash
(in which case the terminator is the value associated with the key
C<'terminator'>.
For example, to cause the previous filter to filter only up to a line of the
form:
GNAB esu;
you would write:
package BANG;
use Filter::Simple;
FILTER {
s/BANG\s+BANG/die 'BANG' if \$BANG/g;
}
qr/^\s*GNAB\s+esu\s*;\s*?$/;
or:
FILTER {
s/BANG\s+BANG/die 'BANG' if \$BANG/g;
}
{ terminator => qr/^\s*GNAB\s+esu\s*;\s*?$/ };
and to prevent the filter's being turned off in any way:
package BANG;
use Filter::Simple;
FILTER {
s/BANG\s+BANG/die 'BANG' if \$BANG/g;
}
""; # or: 0
or:
FILTER {
s/BANG\s+BANG/die 'BANG' if \$BANG/g;
}
{ terminator => "" };
B<Note that, no matter what you set the terminator pattern to,
the actual terminator itself I<must> be contained on a single source line.>
=head2 All-in-one interface
Separating the loading of Filter::Simple:
use Filter::Simple;
from the setting up of the filtering:
FILTER { ... };
is useful because it allows other code (typically parser support code
or caching variables) to be defined before the filter is invoked.
However, there is often no need for such a separation.
In those cases, it is easier to just append the filtering subroutine and
any terminator specification directly to the C<use> statement that loads
Filter::Simple, like so:
use Filter::Simple sub {
s/BANG\s+BANG/die 'BANG' if \$BANG/g;
};
This is exactly the same as:
use Filter::Simple;
BEGIN {
Filter::Simple::FILTER {
s/BANG\s+BANG/die 'BANG' if \$BANG/g;
};
}
except that the C<FILTER> subroutine is not exported by Filter::Simple.
=head2 Filtering only specific components of source code
One of the problems with a filter like:
use Filter::Simple;
FILTER { s/BANG\s+BANG/die 'BANG' if \$BANG/g };
is that it indiscriminately applies the specified transformation to
the entire text of your source program. So something like:
warn 'BANG BANG, YOU'RE DEAD';
BANG BANG;
will become:
warn 'die 'BANG' if $BANG, YOU'RE DEAD';
die 'BANG' if $BANG;
It is very common when filtering source to only want to apply the filter
to the non-character-string parts of the code, or alternatively to I<only>
the character strings.
Filter::Simple supports this type of filtering by automatically
exporting the C<FILTER_ONLY> subroutine.
C<FILTER_ONLY> takes a sequence of specifiers that install separate
(and possibly multiple) filters that act on only parts of the source code.
For example:
use Filter::Simple;
FILTER_ONLY
code => sub { s/BANG\s+BANG/die 'BANG' if \$BANG/g },
quotelike => sub { s/BANG\s+BANG/CHITTY CHITTY/g };
The C<"code"> subroutine will only be used to filter parts of the source
code that are not quotelikes, POD, or C<__DATA__>. The C<quotelike>
subroutine only filters Perl quotelikes (including here documents).
The full list of alternatives is:
=over
=item C<"code">
Filters only those sections of the source code that are not quotelikes, POD, or
C<__DATA__>.
=item C<"code_no_comments">
Filters only those sections of the source code that are not quotelikes, POD,
comments, or C<__DATA__>.
=item C<"executable">
Filters only those sections of the source code that are not POD or C<__DATA__>.
=item C<"executable_no_comments">
Filters only those sections of the source code that are not POD, comments, or C<__DATA__>.
=item C<"quotelike">
Filters only Perl quotelikes (as interpreted by
C<&Text::Balanced::extract_quotelike>).
=item C<"string">
Filters only the string literal parts of a Perl quotelike (i.e. the
contents of a string literal, either half of a C<tr///>, the second
half of an C<s///>).
=item C<"regex">
Filters only the pattern literal parts of a Perl quotelike (i.e. the
contents of a C<qr//> or an C<m//>, the first half of an C<s///>).
=item C<"all">
Filters everything. Identical in effect to C<FILTER>.
=back
Except for C<< FILTER_ONLY code => sub {...} >>, each of
the component filters is called repeatedly, once for each component
found in the source code.
Note that you can also apply two or more of the same type of filter in
a single C<FILTER_ONLY>. For example, here's a simple
macro-preprocessor that is only applied within regexes,
with a final debugging pass that prints the resulting source code:
use Regexp::Common;
FILTER_ONLY
regex => sub { s/!\[/[^/g },
regex => sub { s/%d/$RE{num}{int}/g },
regex => sub { s/%f/$RE{num}{real}/g },
all => sub { print if $::DEBUG };
=head2 Filtering only the code parts of source code
Most source code ceases to be grammatically correct when it is broken up
into the pieces between string literals and regexes. So the C<'code'>
and C<'code_no_comments'> component filter behave slightly differently
from the other partial filters described in the previous section.
Rather than calling the specified processor on each individual piece of
code (i.e. on the bits between quotelikes), the C<'code...'> partial
filters operate on the entire source code, but with the quotelike bits
(and, in the case of C<'code_no_comments'>, the comments) "blanked out".
That is, a C<'code...'> filter I<replaces> each quoted string, quotelike,
regex, POD, and __DATA__ section with a placeholder. The
delimiters of this placeholder are the contents of the C<$;> variable
at the time the filter is applied (normally C<"\034">). The remaining
four bytes are a unique identifier for the component being replaced.
This approach makes it comparatively easy to write code preprocessors
without worrying about the form or contents of strings, regexes, etc.
For convenience, during a C<'code...'> filtering operation, Filter::Simple
provides a package variable (C<$Filter::Simple::placeholder>) that
contains a pre-compiled regex that matches any placeholder...and
captures the identifier within the placeholder. Placeholders can be
moved and re-ordered within the source code as needed.
In addition, a second package variable (C<@Filter::Simple::components>)
contains a list of the various pieces of C<$_>, as they were originally split
up to allow placeholders to be inserted.
Once the filtering has been applied, the original strings, regexes, POD,
etc. are re-inserted into the code, by replacing each placeholder with
the corresponding original component (from C<@components>). Note that
this means that the C<@components> variable must be treated with extreme
care within the filter. The C<@components> array stores the "back-
translations" of each placeholder inserted into C<$_>, as well as the
interstitial source code between placeholders. If the placeholder
backtranslations are altered in C<@components>, they will be similarly
changed when the placeholders are removed from C<$_> after the filter
is complete.
For example, the following filter detects concatenated pairs of
strings/quotelikes and reverses the order in which they are
concatenated:
package DemoRevCat;
use Filter::Simple;
FILTER_ONLY code => sub {
my $ph = $Filter::Simple::placeholder;
s{ ($ph) \s* [.] \s* ($ph) }{ $2.$1 }gx
};
Thus, the following code:
use DemoRevCat;
my $str = "abc" . q(def);
print "$str\n";
would become:
my $str = q(def)."abc";
print "$str\n";
and hence print:
defabc
=head2 Using Filter::Simple with an explicit C<import> subroutine
Filter::Simple generates a special C<import> subroutine for
your module (see L<"How it works">) which would normally replace any
C<import> subroutine you might have explicitly declared.
However, Filter::Simple is smart enough to notice your existing
C<import> and Do The Right Thing with it.
That is, if you explicitly define an C<import> subroutine in a package
that's using Filter::Simple, that C<import> subroutine will still
be invoked immediately after any filter you install.
The only thing you have to remember is that the C<import> subroutine
I<must> be declared I<before> the filter is installed. If you use C<FILTER>
to install the filter:
package Filter::TurnItUpTo11;
use Filter::Simple;
FILTER { s/(\w+)/\U$1/ };
that will almost never be a problem, but if you install a filtering
subroutine by passing it directly to the C<use Filter::Simple>
statement:
package Filter::TurnItUpTo11;
use Filter::Simple sub{ s/(\w+)/\U$1/ };
then you must make sure that your C<import> subroutine appears before
that C<use> statement.
=head2 Using Filter::Simple and Exporter together
Likewise, Filter::Simple is also smart enough
to Do The Right Thing if you use Exporter:
package Switch;
use base Exporter;
use Filter::Simple;
@EXPORT = qw(switch case);
@EXPORT_OK = qw(given when);
FILTER { $_ = magic_Perl_filter($_) }
Immediately after the filter has been applied to the source,
Filter::Simple will pass control to Exporter, so it can do its magic too.
Of course, here too, Filter::Simple has to know you're using Exporter
before it applies the filter. That's almost never a problem, but if you're
nervous about it, you can guarantee that things will work correctly by
ensuring that your C<use base Exporter> always precedes your
C<use Filter::Simple>.
=head2 How it works
The Filter::Simple module exports into the package that calls C<FILTER>
(or C<use>s it directly) -- such as package "BANG" in the above example --
two automagically constructed
subroutines -- C<import> and C<unimport> -- which take care of all the
nasty details.
In addition, the generated C<import> subroutine passes its own argument
list to the filtering subroutine, so the BANG.pm filter could easily
be made parametric:
package BANG;
use Filter::Simple;
FILTER {
my ($die_msg, $var_name) = @_;
s/BANG\s+BANG/die '$die_msg' if \${$var_name}/g;
};
# and in some user code:
use BANG "BOOM", "BAM"; # "BANG BANG" becomes: die 'BOOM' if $BAM
The specified filtering subroutine is called every time a C<use BANG> is
encountered, and passed all the source code following that call, up to
either the next C<no BANG;> (or whatever terminator you've set) or the
end of the source file, whichever occurs first. By default, any C<no
BANG;> call must appear by itself on a separate line, or it is ignored.
=head1 AUTHOR
Damian Conway
=head1 CONTACT
Filter::Simple is now maintained by the Perl5-Porters.
Please submit bug via the C<perlbug> tool that comes with your perl.
For usage instructions, read C<perldoc perlbug> or possibly C<man perlbug>.
For mostly anything else, please contact E<lt>perl5-porters@perl.orgE<gt>.
Maintainer of the CPAN release is Steffen Mueller E<lt>smueller@cpan.orgE<gt>.
Contact him with technical difficulties with respect to the packaging of the
CPAN module.
Praise of the module, flowers, and presents still go to the author,
Damian Conway E<lt>damian@conway.orgE<gt>.
=head1 COPYRIGHT AND LICENSE
Copyright (c) 2000-2014, Damian Conway. All Rights Reserved.
This module is free software. It may be used, redistributed
and/or modified under the same terms as Perl itself.
PK �`[�iz�q q sh.pmnu �[��� package Filter::sh;
use Filter::Util::Exec ;
use strict ;
use warnings ;
our $VERSION = "1.58" ;
sub import
{
my($self, @args) = @_ ;
unless (@args) {
require Carp;
Carp::croak("Usage: use Filter::sh 'command'");
}
if ($^O eq 'MSWin32') {
Filter::Util::Exec::filter_add ($self, 'cmd', '/c', "@args") ;
}
else {
Filter::Util::Exec::filter_add ($self, 'sh', '-c', "@args") ;
}
}
1 ;
__END__
=head1 NAME
Filter::sh - sh source filter
=head1 SYNOPSIS
use Filter::sh 'command' ;
=head1 DESCRIPTION
This filter pipes the current source file through the program which
corresponds to the C<command> parameter using the Bourne shell.
As with all source filters its scope is limited to the current source
file only. Every file you want to be processed by the filter must have a
use Filter::sh 'command' ;
near the top.
Here is an example script which uses the filter:
use Filter::sh 'tr XYZ PQR' ;
$a = 1 ;
print "XYZ a = $a\n" ;
And here is what it will output:
PQR = 1
=head1 WARNING
You should be I<very> careful when using this filter. Because of the
way the filter is implemented it is possible to end up with deadlock.
Be especially careful when stacking multiple instances of the filter in
a single source file.
=head1 AUTHOR
Paul Marquess
=head1 DATE
11th December 1995.
=cut
PK �`[D�0η �
decrypt.pmnu �[��� package Filter::decrypt ;
require 5.006 ;
require XSLoader;
our $VERSION = "1.58" ;
XSLoader::load('Filter::decrypt');
1;
__END__
=head1 NAME
Filter::decrypt - template for a decrypt source filter
=head1 SYNOPSIS
use Filter::decrypt ;
=head1 DESCRIPTION
This is a sample decrypting source filter.
Although this is a fully functional source filter and it does implement
a I<very> simple decrypt algorithm, it is I<not> intended to be used as
it is supplied. Consider it to be a template which you can combine with
a proper decryption algorithm to develop your own decryption filter.
=head1 WARNING
It is important to note that a decryption filter can I<never> provide
complete security against attack. At some point the parser within Perl
needs to be able to scan the original decrypted source. That means that
at some stage fragments of the source will exist in a memory buffer.
Also, with the introduction of the Perl Compiler backend modules, and
the B::Deparse module in particular, using a Source Filter to hide source
code is becoming an increasingly futile exercise.
The best you can hope to achieve by decrypting your Perl source using a
source filter is to make it unavailable to the casual user.
Given that proviso, there are a number of things you can do to make
life more difficult for the prospective cracker.
=over 5
=item 1.
Strip the Perl binary to remove all symbols.
=item 2.
Build the decrypt extension using static linking. If the extension is
provided as a dynamic module, there is nothing to stop someone from
linking it at run time with a modified Perl binary.
=item 3.
Do not build Perl with C<-DDEBUGGING>. If you do then your source can
be retrieved with the C<-DP> command line option.
The sample filter contains logic to detect the C<DEBUGGING> option.
=item 4.
Do not build Perl with C debugging support enabled.
=item 5.
Do not implement the decryption filter as a sub-process (like the cpp
source filter). It is possible to peek into the pipe that connects to
the sub-process.
=item 6.
Check that the Perl Compiler isn't being used.
There is code in the BOOT: section of decrypt.xs that shows how to detect
the presence of the Compiler. Make sure you include it in your module.
Assuming you haven't taken any steps to spot when the compiler is in
use and you have an encrypted Perl script called "myscript.pl", you can
get access the source code inside it using the perl Compiler backend,
like this
perl -MO=Deparse myscript.pl
Note that even if you have included the BOOT: test, it is still
possible to use the Deparse module to get the source code for individual
subroutines.
=item 7.
Do not use the decrypt filter as-is. The algorithm used in this filter
has been purposefully left simple.
=back
If you feel that the source filtering mechanism is not secure enough
you could try using the unexec/undump method. See the Perl FAQ for
further details.
=head1 AUTHOR
Paul Marquess
=head1 DATE
19th December 1995
=cut
PK �`[��l� � cpp.pmnu �[��� package Filter::cpp;
use Filter::Util::Exec ;
use Config ;
use strict;
use warnings;
our $VERSION = '1.58' ;
my $cpp;
my $sep;
if ($^O eq 'MSWin32') {
$cpp = 'cpp.exe' ;
$sep = ';';
}
else {
($cpp) = $Config{cppstdin} =~ /^(\S+)/;
$sep = ':';
}
if (! $cpp) {
require Carp;
Carp::croak ("Cannot find cpp\n");
}
# Check if cpp is installed
if ( ! -x $cpp) {
my $foundCPP = 0 ;
foreach my $dir (split($sep, $ENV{PATH}), '')
{
if (-x "$dir/$cpp")
{
$foundCPP = 1;
last ;
}
}
if (! $foundCPP) {
require Carp;
Carp::croak("Cannot find cpp\n");
}
}
sub import
{
my($self, @args) = @_ ;
if ($^O eq 'MSWin32') {
Filter::Util::Exec::filter_add ($self, 'cmd', '/c',
"cpp.exe 2>nul") ;
}
else {
Filter::Util::Exec::filter_add ($self, 'sh', '-c',
"$Config{'cppstdin'} $Config{'cppminus'} 2>/dev/null") ;
}
}
1 ;
__END__
=head1 NAME
Filter::cpp - cpp source filter
=head1 SYNOPSIS
use Filter::cpp ;
=head1 DESCRIPTION
This source filter pipes the current source file through the C
pre-processor (cpp) if it is available.
As with all source filters its scope is limited to the current source
file only. Every file you want to be processed by the filter must have a
use Filter::cpp ;
near the top.
Here is an example script which uses the filter:
use Filter::cpp ;
#define FRED 1
$a = 2 + FRED ;
print "a = $a\n" ;
#ifdef FRED
print "Hello FRED\n" ;
#else
print "Where is FRED\n" ;
#endif
And here is what it will output:
a = 3
Hello FRED
This example below, provided by Michael G Schwern, shows a clever way
to get Perl to use a C pre-processor macro when the Filter::cpp module
is available, or to use a Perl sub when it is not.
# use Filter::cpp if we can.
BEGIN { eval 'use Filter::cpp' }
sub PRINT {
my($string) = shift;
#define PRINT($string) \
(print $string."\n")
}
PRINT("Mu");
Look at Michael's Tie::VecArray module for a practical use.
=head1 AUTHOR
Paul Marquess
=head1 DATE
11th December 1995.
=cut
PK �`[#��� � Util/Exec.pmnu �[��� package Filter::Util::Exec ;
require 5.006 ;
require XSLoader;
our $VERSION = "1.58" ;
XSLoader::load('Filter::Util::Exec');
1 ;
__END__
=head1 NAME
Filter::Util::Exec - exec source filter
=head1 SYNOPSIS
use Filter::Util::Exec;
=head1 DESCRIPTION
This module is provides the interface to allow the creation of I<Source
Filters> which use a Unix coprocess.
See L<Filter::exec>, L<Filter::cpp> and L<Filter::sh> for examples of
the use of this module.
Note that the size of the buffers is limited to 32-bit.
=head2 B<filter_add()>
The function, C<filter_add> installs a filter. It takes one
parameter which should be a reference. The kind of reference used will
dictate which of the two filter types will be used.
If a CODE reference is used then a I<closure filter> will be assumed.
If a CODE reference is not used, a I<method filter> will be assumed.
In a I<method filter>, the reference can be used to store context
information. The reference will be I<blessed> into the package by
C<filter_add>.
See L<Filter::Util::Call> for examples of using context information
using both I<method filters> and I<closure filters>.
=head1 AUTHOR
Paul Marquess
=head1 DATE
11th December 1995.
=cut
PK �`[U���6 �6 Util/Call.pmnu �[��� # Call.pm
#
# Copyright (c) 1995-2011 Paul Marquess. All rights reserved.
# Copyright (c) 2011-2014 Reini Urban. All rights reserved.
# Copyright (c) 2014-2017 cPanel Inc. All rights reserved.
#
# This program is free software; you can redistribute it and/or
# modify it under the same terms as Perl itself.
package Filter::Util::Call ;
require 5.006 ; # our
require Exporter;
use XSLoader ();
use strict;
use warnings;
our @ISA = qw(Exporter);
our @EXPORT = qw( filter_add filter_del filter_read filter_read_exact) ;
our $VERSION = "1.58" ;
our $XS_VERSION = $VERSION;
$VERSION = eval $VERSION;
sub filter_read_exact($)
{
my ($size) = @_ ;
my ($left) = $size ;
my ($status) ;
unless ( $size > 0 ) {
require Carp;
Carp::croak("filter_read_exact: size parameter must be > 0");
}
# try to read a block which is exactly $size bytes long
while ($left and ($status = filter_read($left)) > 0) {
$left = $size - length $_ ;
}
# EOF with pending data is a special case
return 1 if $status == 0 and length $_ ;
return $status ;
}
sub filter_add($)
{
my($obj) = @_ ;
# Did we get a code reference?
my $coderef = (ref $obj eq 'CODE');
# If the parameter isn't already a reference, make it one.
if (!$coderef and (!ref($obj) or ref($obj) =~ /^ARRAY|HASH$/)) {
$obj = bless (\$obj, (caller)[0]);
}
# finish off the installation of the filter in C.
Filter::Util::Call::real_import($obj, (caller)[0], $coderef) ;
}
XSLoader::load('Filter::Util::Call');
1;
__END__
=head1 NAME
Filter::Util::Call - Perl Source Filter Utility Module
=head1 SYNOPSIS
use Filter::Util::Call ;
=head1 DESCRIPTION
This module provides you with the framework to write I<Source Filters>
in Perl.
An alternate interface to Filter::Util::Call is now available. See
L<Filter::Simple> for more details.
A I<Perl Source Filter> is implemented as a Perl module. The structure
of the module can take one of two broadly similar formats. To
distinguish between them, the first will be referred to as I<method
filter> and the second as I<closure filter>.
Here is a skeleton for the I<method filter>:
package MyFilter ;
use Filter::Util::Call ;
sub import
{
my($type, @arguments) = @_ ;
filter_add([]) ;
}
sub filter
{
my($self) = @_ ;
my($status) ;
$status = filter_read() ;
$status ;
}
1 ;
and this is the equivalent skeleton for the I<closure filter>:
package MyFilter ;
use Filter::Util::Call ;
sub import
{
my($type, @arguments) = @_ ;
filter_add(
sub
{
my($status) ;
$status = filter_read() ;
$status ;
} )
}
1 ;
To make use of either of the two filter modules above, place the line
below in a Perl source file.
use MyFilter;
In fact, the skeleton modules shown above are fully functional I<Source
Filters>, albeit fairly useless ones. All they does is filter the
source stream without modifying it at all.
As you can see both modules have a broadly similar structure. They both
make use of the C<Filter::Util::Call> module and both have an C<import>
method. The difference between them is that the I<method filter>
requires a I<filter> method, whereas the I<closure filter> gets the
equivalent of a I<filter> method with the anonymous sub passed to
I<filter_add>.
To make proper use of the I<closure filter> shown above you need to
have a good understanding of the concept of a I<closure>. See
L<perlref> for more details on the mechanics of I<closures>.
=head2 B<use Filter::Util::Call>
The following functions are exported by C<Filter::Util::Call>:
filter_add()
filter_read()
filter_read_exact()
filter_del()
=head2 B<import()>
The C<import> method is used to create an instance of the filter. It is
called indirectly by Perl when it encounters the C<use MyFilter> line
in a source file (See L<perlfunc/import> for more details on
C<import>).
It will always have at least one parameter automatically passed by Perl
- this corresponds to the name of the package. In the example above it
will be C<"MyFilter">.
Apart from the first parameter, import can accept an optional list of
parameters. These can be used to pass parameters to the filter. For
example:
use MyFilter qw(a b c) ;
will result in the C<@_> array having the following values:
@_ [0] => "MyFilter"
@_ [1] => "a"
@_ [2] => "b"
@_ [3] => "c"
Before terminating, the C<import> function must explicitly install the
filter by calling C<filter_add>.
=head2 B<filter_add()>
The function, C<filter_add>, actually installs the filter. It takes one
parameter which should be a reference. The kind of reference used will
dictate which of the two filter types will be used.
If a CODE reference is used then a I<closure filter> will be assumed.
If a CODE reference is not used, a I<method filter> will be assumed.
In a I<method filter>, the reference can be used to store context
information. The reference will be I<blessed> into the package by
C<filter_add>, unless the reference was already blessed.
See the filters at the end of this documents for examples of using
context information using both I<method filters> and I<closure
filters>.
=head2 B<filter() and anonymous sub>
Both the C<filter> method used with a I<method filter> and the
anonymous sub used with a I<closure filter> is where the main
processing for the filter is done.
The big difference between the two types of filter is that the I<method
filter> uses the object passed to the method to store any context data,
whereas the I<closure filter> uses the lexical variables that are
maintained by the closure.
Note that the single parameter passed to the I<method filter>,
C<$self>, is the same reference that was passed to C<filter_add>
blessed into the filter's package. See the example filters later on for
details of using C<$self>.
Here is a list of the common features of the anonymous sub and the
C<filter()> method.
=over 5
=item B<$_>
Although C<$_> doesn't actually appear explicitly in the sample filters
above, it is implicitly used in a number of places.
Firstly, when either C<filter> or the anonymous sub are called, a local
copy of C<$_> will automatically be created. It will always contain the
empty string at this point.
Next, both C<filter_read> and C<filter_read_exact> will append any
source data that is read to the end of C<$_>.
Finally, when C<filter> or the anonymous sub are finished processing,
they are expected to return the filtered source using C<$_>.
This implicit use of C<$_> greatly simplifies the filter.
=item B<$status>
The status value that is returned by the user's C<filter> method or
anonymous sub and the C<filter_read> and C<read_exact> functions take
the same set of values, namely:
< 0 Error
= 0 EOF
> 0 OK
=item B<filter_read> and B<filter_read_exact>
These functions are used by the filter to obtain either a line or block
from the next filter in the chain or the actual source file if there
aren't any other filters.
The function C<filter_read> takes two forms:
$status = filter_read() ;
$status = filter_read($size) ;
The first form is used to request a I<line>, the second requests a
I<block>.
In line mode, C<filter_read> will append the next source line to the
end of the C<$_> scalar.
In block mode, C<filter_read> will append a block of data which is <=
C<$size> to the end of the C<$_> scalar. It is important to emphasise
the that C<filter_read> will not necessarily read a block which is
I<precisely> C<$size> bytes.
If you need to be able to read a block which has an exact size, you can
use the function C<filter_read_exact>. It works identically to
C<filter_read> in block mode, except it will try to read a block which
is exactly C<$size> bytes in length. The only circumstances when it
will not return a block which is C<$size> bytes long is on EOF or
error.
It is I<very> important to check the value of C<$status> after I<every>
call to C<filter_read> or C<filter_read_exact>.
=item B<filter_del>
The function, C<filter_del>, is used to disable the current filter. It
does not affect the running of the filter. All it does is tell Perl not
to call filter any more.
See L<Example 4: Using filter_del> for details.
=item I<real_import>
Internal function which adds the filter, based on the L<filter_add>
argument type.
=item I<unimport()>
May be used to disable a filter, but is rarely needed. See L<filter_del>.
=back
=head1 LIMITATIONS
See L<perlfilter/LIMITATIONS> for an overview of the general problems
filtering code in a textual line-level only.
=over
=item __DATA__ is ignored
The content from the __DATA__ block is not filtered.
This is a serious limitation, e.g. for the L<Switch> module.
See L<http://search.cpan.org/perldoc?Switch#LIMITATIONS> for more.
=item Max. codesize limited to 32-bit
Currently internal buffer lengths are limited to 32-bit only.
=back
=head1 EXAMPLES
Here are a few examples which illustrate the key concepts - as such
most of them are of little practical use.
The C<examples> sub-directory has copies of all these filters
implemented both as I<method filters> and as I<closure filters>.
=head2 Example 1: A simple filter.
Below is a I<method filter> which is hard-wired to replace all
occurrences of the string C<"Joe"> to C<"Jim">. Not particularly
Useful, but it is the first example and I wanted to keep it simple.
package Joe2Jim ;
use Filter::Util::Call ;
sub import
{
my($type) = @_ ;
filter_add(bless []) ;
}
sub filter
{
my($self) = @_ ;
my($status) ;
s/Joe/Jim/g
if ($status = filter_read()) > 0 ;
$status ;
}
1 ;
Here is an example of using the filter:
use Joe2Jim ;
print "Where is Joe?\n" ;
And this is what the script above will print:
Where is Jim?
=head2 Example 2: Using the context
The previous example was not particularly useful. To make it more
general purpose we will make use of the context data and allow any
arbitrary I<from> and I<to> strings to be used. This time we will use a
I<closure filter>. To reflect its enhanced role, the filter is called
C<Subst>.
package Subst ;
use Filter::Util::Call ;
use Carp ;
sub import
{
croak("usage: use Subst qw(from to)")
unless @_ == 3 ;
my ($self, $from, $to) = @_ ;
filter_add(
sub
{
my ($status) ;
s/$from/$to/
if ($status = filter_read()) > 0 ;
$status ;
})
}
1 ;
and is used like this:
use Subst qw(Joe Jim) ;
print "Where is Joe?\n" ;
=head2 Example 3: Using the context within the filter
Here is a filter which a variation of the C<Joe2Jim> filter. As well as
substituting all occurrences of C<"Joe"> to C<"Jim"> it keeps a count
of the number of substitutions made in the context object.
Once EOF is detected (C<$status> is zero) the filter will insert an
extra line into the source stream. When this extra line is executed it
will print a count of the number of substitutions actually made.
Note that C<$status> is set to C<1> in this case.
package Count ;
use Filter::Util::Call ;
sub filter
{
my ($self) = @_ ;
my ($status) ;
if (($status = filter_read()) > 0 ) {
s/Joe/Jim/g ;
++ $$self ;
}
elsif ($$self >= 0) { # EOF
$_ = "print q[Made ${$self} substitutions\n]" ;
$status = 1 ;
$$self = -1 ;
}
$status ;
}
sub import
{
my ($self) = @_ ;
my ($count) = 0 ;
filter_add(\$count) ;
}
1 ;
Here is a script which uses it:
use Count ;
print "Hello Joe\n" ;
print "Where is Joe\n" ;
Outputs:
Hello Jim
Where is Jim
Made 2 substitutions
=head2 Example 4: Using filter_del
Another variation on a theme. This time we will modify the C<Subst>
filter to allow a starting and stopping pattern to be specified as well
as the I<from> and I<to> patterns. If you know the I<vi> editor, it is
the equivalent of this command:
:/start/,/stop/s/from/to/
When used as a filter we want to invoke it like this:
use NewSubst qw(start stop from to) ;
Here is the module.
package NewSubst ;
use Filter::Util::Call ;
use Carp ;
sub import
{
my ($self, $start, $stop, $from, $to) = @_ ;
my ($found) = 0 ;
croak("usage: use Subst qw(start stop from to)")
unless @_ == 5 ;
filter_add(
sub
{
my ($status) ;
if (($status = filter_read()) > 0) {
$found = 1
if $found == 0 and /$start/ ;
if ($found) {
s/$from/$to/ ;
filter_del() if /$stop/ ;
}
}
$status ;
} )
}
1 ;
=head1 Filter::Simple
If you intend using the Filter::Call functionality, I would strongly
recommend that you check out Damian Conway's excellent Filter::Simple
module. Damian's module provides a much cleaner interface than
Filter::Util::Call. Although it doesn't allow the fine control that
Filter::Util::Call does, it should be adequate for the majority of
applications. It's available at
http://search.cpan.org/dist/Filter-Simple/
=head1 AUTHOR
Paul Marquess
=head1 DATE
26th January 1996
=head1 LICENSE
Copyright (c) 1995-2011 Paul Marquess. All rights reserved.
Copyright (c) 2011-2014 Reini Urban. All rights reserved.
Copyright (c) 2014-2017 cPanel Inc. All rights reserved.
This program is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.
=cut
PK �`[R���W W Util/perlfilter.podnu �[��� =head1 NAME
perlfilter - Source Filters
=head1 DESCRIPTION
This article is about a little-known feature of Perl called
I<source filters>. Source filters alter the program text of a module
before Perl sees it, much as a C preprocessor alters the source text of
a C program before the compiler sees it. This article tells you more
about what source filters are, how they work, and how to write your
own.
The original purpose of source filters was to let you encrypt your
program source to prevent casual piracy. This isn't all they can do, as
you'll soon learn. But first, the basics.
=head1 CONCEPTS
Before the Perl interpreter can execute a Perl script, it must first
read it from a file into memory for parsing and compilation. If that
script itself includes other scripts with a C<use> or C<require>
statement, then each of those scripts will have to be read from their
respective files as well.
Now think of each logical connection between the Perl parser and an
individual file as a I<source stream>. A source stream is created when
the Perl parser opens a file, it continues to exist as the source code
is read into memory, and it is destroyed when Perl is finished parsing
the file. If the parser encounters a C<require> or C<use> statement in
a source stream, a new and distinct stream is created just for that
file.
The diagram below represents a single source stream, with the flow of
source from a Perl script file on the left into the Perl parser on the
right. This is how Perl normally operates.
file -------> parser
There are two important points to remember:
=over 5
=item 1.
Although there can be any number of source streams in existence at any
given time, only one will be active.
=item 2.
Every source stream is associated with only one file.
=back
A source filter is a special kind of Perl module that intercepts and
modifies a source stream before it reaches the parser. A source filter
changes our diagram like this:
file ----> filter ----> parser
If that doesn't make much sense, consider the analogy of a command
pipeline. Say you have a shell script stored in the compressed file
I<trial.gz>. The simple pipeline command below runs the script without
needing to create a temporary file to hold the uncompressed file.
gunzip -c trial.gz | sh
In this case, the data flow from the pipeline can be represented as follows:
trial.gz ----> gunzip ----> sh
With source filters, you can store the text of your script compressed and use a source filter to uncompress it for Perl's parser:
compressed gunzip
Perl program ---> source filter ---> parser
=head1 USING FILTERS
So how do you use a source filter in a Perl script? Above, I said that
a source filter is just a special kind of module. Like all Perl
modules, a source filter is invoked with a use statement.
Say you want to pass your Perl source through the C preprocessor before
execution. As it happens, the source filters distribution comes with a C
preprocessor filter module called Filter::cpp.
Below is an example program, C<cpp_test>, which makes use of this filter.
Line numbers have been added to allow specific lines to be referenced
easily.
1: use Filter::cpp;
2: #define TRUE 1
3: $a = TRUE;
4: print "a = $a\n";
When you execute this script, Perl creates a source stream for the
file. Before the parser processes any of the lines from the file, the
source stream looks like this:
cpp_test ---------> parser
Line 1, C<use Filter::cpp>, includes and installs the C<cpp> filter
module. All source filters work this way. The use statement is compiled
and executed at compile time, before any more of the file is read, and
it attaches the cpp filter to the source stream behind the scenes. Now
the data flow looks like this:
cpp_test ----> cpp filter ----> parser
As the parser reads the second and subsequent lines from the source
stream, it feeds those lines through the C<cpp> source filter before
processing them. The C<cpp> filter simply passes each line through the
real C preprocessor. The output from the C preprocessor is then
inserted back into the source stream by the filter.
.-> cpp --.
| |
| |
| <-'
cpp_test ----> cpp filter ----> parser
The parser then sees the following code:
use Filter::cpp;
$a = 1;
print "a = $a\n";
Let's consider what happens when the filtered code includes another
module with use:
1: use Filter::cpp;
2: #define TRUE 1
3: use Fred;
4: $a = TRUE;
5: print "a = $a\n";
The C<cpp> filter does not apply to the text of the Fred module, only
to the text of the file that used it (C<cpp_test>). Although the use
statement on line 3 will pass through the cpp filter, the module that
gets included (C<Fred>) will not. The source streams look like this
after line 3 has been parsed and before line 4 is parsed:
cpp_test ---> cpp filter ---> parser (INACTIVE)
Fred.pm ----> parser
As you can see, a new stream has been created for reading the source
from C<Fred.pm>. This stream will remain active until all of C<Fred.pm>
has been parsed. The source stream for C<cpp_test> will still exist,
but is inactive. Once the parser has finished reading Fred.pm, the
source stream associated with it will be destroyed. The source stream
for C<cpp_test> then becomes active again and the parser reads line 4
and subsequent lines from C<cpp_test>.
You can use more than one source filter on a single file. Similarly,
you can reuse the same filter in as many files as you like.
For example, if you have a uuencoded and compressed source file, it is
possible to stack a uudecode filter and an uncompression filter like
this:
use Filter::uudecode; use Filter::uncompress;
M'XL(".H<US4''V9I;F%L')Q;>7/;1I;_>_I3=&E=%:F*I"T?22Q/
M6]9*<IQCO*XFT"0[PL%%'Y+IG?WN^ZYN-$'J.[.JE$,20/?K=_[>
...
Once the first line has been processed, the flow will look like this:
file ---> uudecode ---> uncompress ---> parser
filter filter
Data flows through filters in the same order they appear in the source
file. The uudecode filter appeared before the uncompress filter, so the
source file will be uudecoded before it's uncompressed.
=head1 WRITING A SOURCE FILTER
There are three ways to write your own source filter. You can write it
in C, use an external program as a filter, or write the filter in Perl.
I won't cover the first two in any great detail, so I'll get them out
of the way first. Writing the filter in Perl is most convenient, so
I'll devote the most space to it.
=head1 WRITING A SOURCE FILTER IN C
The first of the three available techniques is to write the filter
completely in C. The external module you create interfaces directly
with the source filter hooks provided by Perl.
The advantage of this technique is that you have complete control over
the implementation of your filter. The big disadvantage is the
increased complexity required to write the filter - not only do you
need to understand the source filter hooks, but you also need a
reasonable knowledge of Perl guts. One of the few times it is worth
going to this trouble is when writing a source scrambler. The
C<decrypt> filter (which unscrambles the source before Perl parses it)
included with the source filter distribution is an example of a C
source filter (see Decryption Filters, below).
=over 5
=item B<Decryption Filters>
All decryption filters work on the principle of "security through
obscurity." Regardless of how well you write a decryption filter and
how strong your encryption algorithm is, anyone determined enough can
retrieve the original source code. The reason is quite simple - once
the decryption filter has decrypted the source back to its original
form, fragments of it will be stored in the computer's memory as Perl
parses it. The source might only be in memory for a short period of
time, but anyone possessing a debugger, skill, and lots of patience can
eventually reconstruct your program.
That said, there are a number of steps that can be taken to make life
difficult for the potential cracker. The most important: Write your
decryption filter in C and statically link the decryption module into
the Perl binary. For further tips to make life difficult for the
potential cracker, see the file I<decrypt.pm> in the source filters
distribution.
=back
=head1 CREATING A SOURCE FILTER AS A SEPARATE EXECUTABLE
An alternative to writing the filter in C is to create a separate
executable in the language of your choice. The separate executable
reads from standard input, does whatever processing is necessary, and
writes the filtered data to standard output. C<Filter::cpp> is an
example of a source filter implemented as a separate executable - the
executable is the C preprocessor bundled with your C compiler.
The source filter distribution includes two modules that simplify this
task: C<Filter::exec> and C<Filter::sh>. Both allow you to run any
external executable. Both use a coprocess to control the flow of data
into and out of the external executable. (For details on coprocesses,
see Stephens, W.R., "Advanced Programming in the UNIX Environment."
Addison-Wesley, ISBN 0-210-56317-7, pages 441-445.) The difference
between them is that C<Filter::exec> spawns the external command
directly, while C<Filter::sh> spawns a shell to execute the external
command. (Unix uses the Bourne shell; NT uses the cmd shell.) Spawning
a shell allows you to make use of the shell metacharacters and
redirection facilities.
Here is an example script that uses C<Filter::sh>:
use Filter::sh 'tr XYZ PQR';
$a = 1;
print "XYZ a = $a\n";
The output you'll get when the script is executed:
PQR a = 1
Writing a source filter as a separate executable works fine, but a
small performance penalty is incurred. For example, if you execute the
small example above, a separate subprocess will be created to run the
Unix C<tr> command. Each use of the filter requires its own subprocess.
If creating subprocesses is expensive on your system, you might want to
consider one of the other options for creating source filters.
=head1 WRITING A SOURCE FILTER IN PERL
The easiest and most portable option available for creating your own
source filter is to write it completely in Perl. To distinguish this
from the previous two techniques, I'll call it a Perl source filter.
To help understand how to write a Perl source filter we need an example
to study. Here is a complete source filter that performs rot13
decoding. (Rot13 is a very simple encryption scheme used in Usenet
postings to hide the contents of offensive posts. It moves every letter
forward thirteen places, so that A becomes N, B becomes O, and Z
becomes M.)
package Rot13;
use Filter::Util::Call;
sub import {
my ($type) = @_;
my ($ref) = [];
filter_add(bless $ref);
}
sub filter {
my ($self) = @_;
my ($status);
tr/n-za-mN-ZA-M/a-zA-Z/
if ($status = filter_read()) > 0;
$status;
}
1;
All Perl source filters are implemented as Perl classes and have the
same basic structure as the example above.
First, we include the C<Filter::Util::Call> module, which exports a
number of functions into your filter's namespace. The filter shown
above uses two of these functions, C<filter_add()> and
C<filter_read()>.
Next, we create the filter object and associate it with the source
stream by defining the C<import> function. If you know Perl well
enough, you know that C<import> is called automatically every time a
module is included with a use statement. This makes C<import> the ideal
place to both create and install a filter object.
In the example filter, the object (C<$ref>) is blessed just like any
other Perl object. Our example uses an anonymous array, but this isn't
a requirement. Because this example doesn't need to store any context
information, we could have used a scalar or hash reference just as
well. The next section demonstrates context data.
The association between the filter object and the source stream is made
with the C<filter_add()> function. This takes a filter object as a
parameter (C<$ref> in this case) and installs it in the source stream.
Finally, there is the code that actually does the filtering. For this
type of Perl source filter, all the filtering is done in a method
called C<filter()>. (It is also possible to write a Perl source filter
using a closure. See the C<Filter::Util::Call> manual page for more
details.) It's called every time the Perl parser needs another line of
source to process. The C<filter()> method, in turn, reads lines from
the source stream using the C<filter_read()> function.
If a line was available from the source stream, C<filter_read()>
returns a status value greater than zero and appends the line to C<$_>.
A status value of zero indicates end-of-file, less than zero means an
error. The filter function itself is expected to return its status in
the same way, and put the filtered line it wants written to the source
stream in C<$_>. The use of C<$_> accounts for the brevity of most Perl
source filters.
In order to make use of the rot13 filter we need some way of encoding
the source file in rot13 format. The script below, C<mkrot13>, does
just that.
die "usage mkrot13 filename\n" unless @ARGV;
my $in = $ARGV[0];
my $out = "$in.tmp";
open(IN, "<$in") or die "Cannot open file $in: $!\n";
open(OUT, ">$out") or die "Cannot open file $out: $!\n";
print OUT "use Rot13;\n";
while (<IN>) {
tr/a-zA-Z/n-za-mN-ZA-M/;
print OUT;
}
close IN;
close OUT;
unlink $in;
rename $out, $in;
If we encrypt this with C<mkrot13>:
print " hello fred \n";
the result will be this:
use Rot13;
cevag "uryyb serq\a";
Running it produces this output:
hello fred
=head1 USING CONTEXT: THE DEBUG FILTER
The rot13 example was a trivial example. Here's another demonstration
that shows off a few more features.
Say you wanted to include a lot of debugging code in your Perl script
during development, but you didn't want it available in the released
product. Source filters offer a solution. In order to keep the example
simple, let's say you wanted the debugging output to be controlled by
an environment variable, C<DEBUG>. Debugging code is enabled if the
variable exists, otherwise it is disabled.
Two special marker lines will bracket debugging code, like this:
## DEBUG_BEGIN
if ($year > 1999) {
warn "Debug: millennium bug in year $year\n";
}
## DEBUG_END
The filter ensures that Perl parses the code between the <DEBUG_BEGIN>
and C<DEBUG_END> markers only when the C<DEBUG> environment variable
exists. That means that when C<DEBUG> does exist, the code above
should be passed through the filter unchanged. The marker lines can
also be passed through as-is, because the Perl parser will see them as
comment lines. When C<DEBUG> isn't set, we need a way to disable the
debug code. A simple way to achieve that is to convert the lines
between the two markers into comments:
## DEBUG_BEGIN
#if ($year > 1999) {
# warn "Debug: millennium bug in year $year\n";
#}
## DEBUG_END
Here is the complete Debug filter:
package Debug;
use strict;
use warnings;
use Filter::Util::Call;
use constant TRUE => 1;
use constant FALSE => 0;
sub import {
my ($type) = @_;
my (%context) = (
Enabled => defined $ENV{DEBUG},
InTraceBlock => FALSE,
Filename => (caller)[1],
LineNo => 0,
LastBegin => 0,
);
filter_add(bless \%context);
}
sub Die {
my ($self) = shift;
my ($message) = shift;
my ($line_no) = shift || $self->{LastBegin};
die "$message at $self->{Filename} line $line_no.\n"
}
sub filter {
my ($self) = @_;
my ($status);
$status = filter_read();
++ $self->{LineNo};
# deal with EOF/error first
if ($status <= 0) {
$self->Die("DEBUG_BEGIN has no DEBUG_END")
if $self->{InTraceBlock};
return $status;
}
if ($self->{InTraceBlock}) {
if (/^\s*##\s*DEBUG_BEGIN/ ) {
$self->Die("Nested DEBUG_BEGIN", $self->{LineNo})
} elsif (/^\s*##\s*DEBUG_END/) {
$self->{InTraceBlock} = FALSE;
}
# comment out the debug lines when the filter is disabled
s/^/#/ if ! $self->{Enabled};
} elsif ( /^\s*##\s*DEBUG_BEGIN/ ) {
$self->{InTraceBlock} = TRUE;
$self->{LastBegin} = $self->{LineNo};
} elsif ( /^\s*##\s*DEBUG_END/ ) {
$self->Die("DEBUG_END has no DEBUG_BEGIN", $self->{LineNo});
}
return $status;
}
1;
The big difference between this filter and the previous example is the
use of context data in the filter object. The filter object is based on
a hash reference, and is used to keep various pieces of context
information between calls to the filter function. All but two of the
hash fields are used for error reporting. The first of those two,
Enabled, is used by the filter to determine whether the debugging code
should be given to the Perl parser. The second, InTraceBlock, is true
when the filter has encountered a C<DEBUG_BEGIN> line, but has not yet
encountered the following C<DEBUG_END> line.
If you ignore all the error checking that most of the code does, the
essence of the filter is as follows:
sub filter {
my ($self) = @_;
my ($status);
$status = filter_read();
# deal with EOF/error first
return $status if $status <= 0;
if ($self->{InTraceBlock}) {
if (/^\s*##\s*DEBUG_END/) {
$self->{InTraceBlock} = FALSE
}
# comment out debug lines when the filter is disabled
s/^/#/ if ! $self->{Enabled};
} elsif ( /^\s*##\s*DEBUG_BEGIN/ ) {
$self->{InTraceBlock} = TRUE;
}
return $status;
}
Be warned: just as the C-preprocessor doesn't know C, the Debug filter
doesn't know Perl. It can be fooled quite easily:
print <<EOM;
##DEBUG_BEGIN
EOM
Such things aside, you can see that a lot can be achieved with a modest
amount of code.
=head1 CONCLUSION
You now have better understanding of what a source filter is, and you
might even have a possible use for them. If you feel like playing with
source filters but need a bit of inspiration, here are some extra
features you could add to the Debug filter.
First, an easy one. Rather than having debugging code that is
all-or-nothing, it would be much more useful to be able to control
which specific blocks of debugging code get included. Try extending the
syntax for debug blocks to allow each to be identified. The contents of
the C<DEBUG> environment variable can then be used to control which
blocks get included.
Once you can identify individual blocks, try allowing them to be
nested. That isn't difficult either.
Here is an interesting idea that doesn't involve the Debug filter.
Currently Perl subroutines have fairly limited support for formal
parameter lists. You can specify the number of parameters and their
type, but you still have to manually take them out of the C<@_> array
yourself. Write a source filter that allows you to have a named
parameter list. Such a filter would turn this:
sub MySub ($first, $second, @rest) { ... }
into this:
sub MySub($$@) {
my ($first) = shift;
my ($second) = shift;
my (@rest) = @_;
...
}
Finally, if you feel like a real challenge, have a go at writing a
full-blown Perl macro preprocessor as a source filter. Borrow the
useful features from the C preprocessor and any other macro processors
you know. The tricky bit will be choosing how much knowledge of Perl's
syntax you want your filter to have.
=head1 LIMITATIONS
Source filters only work on the string level, thus are highly limited
in its ability to change source code on the fly. It cannot detect
comments, quoted strings, heredocs, it is no replacement for a real
parser.
The only stable usage for source filters are encryption, compression,
or the byteloader, to translate binary code back to source code.
See for example the limitations in L<Switch>, which uses source filters,
and thus is does not work inside a string eval, the presence of
regexes with embedded newlines that are specified with raw C</.../>
delimiters and don't have a modifier C<//x> are indistinguishable from
code chunks beginning with the division operator C</>. As a workaround
you must use C<m/.../> or C<m?...?> for such patterns. Also, the presence of
regexes specified with raw C<?...?> delimiters may cause mysterious
errors. The workaround is to use C<m?...?> instead. See
L<http://search.cpan.org/perldoc?Switch#LIMITATIONS>
Currently the content of the C<__DATA__> block is not filtered.
Currently internal buffer lengths are limited to 32-bit only.
=head1 THINGS TO LOOK OUT FOR
=over 5
=item Some Filters Clobber the C<DATA> Handle
Some source filters use the C<DATA> handle to read the calling program.
When using these source filters you cannot rely on this handle, nor expect
any particular kind of behavior when operating on it. Filters based on
Filter::Util::Call (and therefore Filter::Simple) do not alter the C<DATA>
filehandle, but on the other hand totally ignore the text after C<__DATA__>.
=back
=head1 REQUIREMENTS
The Source Filters distribution is available on CPAN, in
CPAN/modules/by-module/Filter
Starting from Perl 5.8 Filter::Util::Call (the core part of the
Source Filters distribution) is part of the standard Perl distribution.
Also included is a friendlier interface called Filter::Simple, by
Damian Conway.
=head1 AUTHOR
Paul Marquess E<lt>Paul.Marquess@btinternet.comE<gt>
Reini Urban E<lt>rurban@cpan.orgE<gt>
=head1 Copyrights
The first version of this article originally appeared in The Perl
Journal #11, and is copyright 1998 The Perl Journal. It appears
courtesy of Jon Orwant and The Perl Journal. This document may be
distributed under the same terms as Perl itself.
PK �`[د[� � exec.pmnu �[��� package Filter::exec ;
use Filter::Util::Exec ;
use strict ;
use warnings ;
our $VERSION = "1.58" ;
sub import
{
my($self, @args) = @_ ;
unless (@args) {
require Carp;
Carp::croak("Usage: use Filter::exec 'command'");
}
Filter::Util::Exec::filter_add($self, @args) ;
}
1 ;
__END__
=head1 NAME
Filter::exec - exec source filter
=head1 SYNOPSIS
use Filter::exec qw(command parameters) ;
=head1 DESCRIPTION
This filter pipes the current source file through the program which
corresponds to the C<command> parameter.
As with all source filters its scope is limited to the current source
file only. Every file you want to be processed by the filter must have a
use Filter::exec qw(command ) ;
near the top.
Here is an example script which uses the filter:
use Filter::exec qw(tr XYZ PQR) ;
$a = 1 ;
print "XYZ a = $a\n" ;
And here is what it will output:
PQR = 1
=head1 WARNING
You should be I<very> careful when using this filter. Because of the
way the filter is implemented it is possible to end up with deadlock.
Be especially careful when stacking multiple instances of the filter in
a single source file.
=head1 AUTHOR
Paul Marquess
=head1 DATE
11th December 1995.
=cut
PK �`[��I tee.pmnu �[��� package Filter::tee ;
require 5.006 ;
require XSLoader;
our $VERSION = "1.58" ;
XSLoader::load('Filter::tee');
1;
__END__
=head1 NAME
Filter::tee - tee source filter
=head1 SYNOPSIS
use Filter::tee 'filename' ;
use Filter::tee '>filename' ;
use Filter::tee '>>filename' ;
=head1 DESCRIPTION
This filter copies all text from the line after the C<use> in the
current source file to the file specified by the parameter
C<filename>.
By default and when the filename is prefixed with a '>' the output file
will be emptied first if it already exists.
If the output filename is prefixed with '>>' it will be opened for
appending.
This filter is useful as a debugging aid when developing other source
filters.
=head1 AUTHOR
Paul Marquess
=head1 DATE
20th June 1995.
=cut
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