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Author image Curtis "Ovid" Poe
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NAME

CodeGen::Protection::Format::Perl - Safely rewrite parts of Perl documents

VERSION

version 0.06

SYNOPSIS

    my $rewrite = CodeGen::Protection::Format::Perl->new(
        protected_code => $text,
    );
    say $rewrite->rewritten;

    my $rewrite = CodeGen::Protection::Format::Perl->new(
        existing_code => $existing_code,
        protected_code => $protected_code,
    );
    say $rewrite->rewritten;

DESCRIPTION

This module allows you to do a safe partial rewrite of documents. If you're familiar with DBIx::Class::Schema::Loader, you probably know the basic concept.

Note that this code is designed for Perl documents and is not very configurable.

In short, we wrap your "protected" (protected_code) Perl code in start and end comments, with checksums for the code:

    #<<< CodeGen::Protection::Format::Perl 0.01. Do not touch any code between this and the end comment. Checksum: fa97a021bd70bf3b9fa3e52f203f2660
    
    # protected code goes here

    #>>> CodeGen::Protection::Format::Perl 0.01. Do not touch any code between this and the start comment. Checksum: fa97a021bd70bf3b9fa3e52f203f2660

If existing_code is provided, this module removes the code between the old code's start and end markers and replaces it with the protected_code. If the code between the start and end markers has been altered, it will no longer match the checksums and rewriting the code will fail.

CONSTRUCTOR

    my $rewrite = CodeGen::Protection::Format::Perl->new(
        protected_code => $protected_code,    # required
        existing_code => $existing_code,    # optional
        perltidy      => 1,                 # optional
        name          => $name,             # optional
        overwrite     => 0,                 # optional
    );

The constructor only requires that protected_code be passed in.

  • protected_code

    This is a required string containing any new Perl code to be built with this tool. If protected_code is passed in an existing_code is not, we're in "Creation mode" (see #Modes) and the new Perl code must not have start and end markers generated by this tool.

  • existing_code

    This is an optional string containing Perl code already built with this tool. If provided, this code must have the start and end markers generated by this tool so that the rewriter knows the section of code to replace with the injected code.

  • name

    Optional name for the code. This is only used in error messages if you're generating a lot of code and an error occurs and you'd like to see the name in the error.

  • perltidy

    If true, will attempt to run Perl::Tidy on the code between the start and end markers. If the value of perltidy is the number 1 (one), then a generic pass of Perl::Tidy will be done on the code. If the value is true and anything other than one, this is assumed to be the path to a .perltidyrc file and that will be used to tidy the code (or croak() if the .perltidyrc file cannot be found).

  • overwrite

    Optional boolean, default false. In "Rewrite mode", if the checksum in the start and end markers doesn't match the code within them, someone has manually altered that code and we do not automatically overwrite it (in fact, we croak()). Setting overwrite to true will cause it to be overwritten.

MODES

There are two modes: "Creation" and "Rewrite."

Creation Mode

    my $rewrite = CodeGen::Protection::Format::Perl->new(
        protected_code => $text,
    );
    say $rewrite->rewritten;

If you create an instance with protected_code but not old text, this will wrap the new text in start and end tags that "protect" the document if you rewrite it:

    my $perl = <<'END';
    sub sum {
        my $total = 0;
        $total += $_ foreach @_;
        return $total;
    }
    END
    my $rewrite = CodeGen::Protection::Format::Perl->new( protected_code => $perl );
    say $rewrite->rewritten;

Output:

    #<<< CodeGen::Protection::Format::Perl 0.01. Do not touch any code between this and the end comment. Checksum: fa97a021bd70bf3b9fa3e52f203f2660

    sub sum {
        my $total = 0;
        $total += $_ foreach @_;
        return $total;
    }

    #>>> CodeGen::Protection::Format::Perl 0.01. Do not touch any code between this and the start comment. Checksum: fa97a021bd70bf3b9fa3e52f203f2660

You can then take the marked up document and insert it into another Perl document and use the rewrite mode to safely rewrite the code between the start and end markers. The rest of the document will be ignored.

Note that leading and trailing comments start with #<<< and #>>> respectively. Those are special comments which tell Perl::Tidy to ignore what ever is between them. Thus, you can safely tidy code written with this.

The start and end checksums are the same and are the checksum of the text between the comments. Leading and trailing lines which are all whitespace are removed and one leading and one trailing newline will be added.

Rewrite Mode

Given a document created with the "Creating" mode, you can then take the marked up document and insert it into another Perl document and use the rewrite mode to safely rewrite the code between the start and end markers. The rest of the document will be ignored.

    my $rewrite = CodeGen::Protection::Format::Perl->new(
        existing_code => $existing_code,
        protected_code => $protected_code,
    );
    say $rewrite->rewritten;

In the above, assuming that $existing_code is a rewritable document, the $protected_code will replace the rewritable section of the $existing_code, leaving the rest unchanged.

However, if $protected_code is also a rewritable document, then the rewritable portion of the $protected_code will be extract and used to replace the rewritable portion of the $existing_code.

So for the code shown in the "Creation mode" section, you could add more code like this:

    package My::Package;

    use strict;
    use warnings;

    sub average {
        return sum(@_)/@_;
    }

    #<<< CodeGen::Protection::Format::Perl 0.01. Do not touch any code between this and the end comment. Checksum: fa97a021bd70bf3b9fa3e52f203f2660

    sub sum {
        my $total = 0;
        $total += $_ foreach @_;
        return $total;
    }

    #>>> CodeGen::Protection::Format::Perl 0.01. Do not touch any code between this and the start comment. Checksum: fa97a021bd70bf3b9fa3e52f203f2660
    
    1;

However, later on I might realize that the sum function will happily try to sum things which are not numbers, so I want to fix that. I'll slurp the My::Package code into the $existing_code variable and then:

    my $perl = <<'END';
    use Scalar::Util 'looks_like_number';

    sub sum {
        my $total = 0;
        foreach my $number (@_) {
            unless (looks_like_number($number)) {
                die "'$number' doesn't look like a numbeer!";
            }
            $total += $number;
        }
        return $total;
    }
    END
    my $rewrite = CodeGen::Protection::Format::Perl->new( existing_code => $existing_code, protected_code => $perl );
    say $rewrite->rewritten;

And that will print out:

    package My::Package;
    
    use strict;
    use warnings;
    
    sub average {
        return sum(@_)/@_;
    }
    
    #<<< CodeGen::Protection::Format::Perl 0.01. Do not touch any code between this and the end comment. Checksum: d135a051f158ee19fbd68af5466fb1ae
    
    use Scalar::Util 'looks_like_number';
    
    sub sum {
        my $total = 0;
        foreach my $number (@_) {
            unless (looks_like_number($number)) {
                die "'$number' doesn't look like a numbeer!";
            }
            $total += $number;
        }
        return $total;
    }
    
    #>>> CodeGen::Protection::Format::Perl 0.01. Do not touch any code between this and the start comment. Checksum: d135a051f158ee19fbd68af5466fb1ae
    
    1;

You can see that the code between the start and end checksum comments and been rewritten, while the rest of the code remains unchanged.

AUTHOR

Curtis "Ovid" Poe <ovid@allaroundtheworld.fr>

COPYRIGHT AND LICENSE

This software is copyright (c) 2021 by Curtis "Ovid" Poe.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.