YAML::PP::Schema::Perl(3) User Contributed Perl Documentation YAML::PP::Schema::Perl(3)

YAML::PP::Schema::Perl - Schema for serializing perl objects and special types

    use YAML::PP;
    # This can be dangerous when loading untrusted YAML!
    my $yp = YAML::PP->new( schema => [qw/ + Perl /] );
    # or
    my $yp = YAML::PP->new( schema => [qw/ Core Perl /] );
    my $yaml = $yp->dump_string(sub { return 23 });
    # loading code references
    # This is very dangerous when loading untrusted YAML!!
    my $yp = YAML::PP->new( schema => [qw/ + Perl +loadcode /] );
    my $code = $yp->load_string(<<'EOM');
    --- !perl/code |
        {
            use 5.010;
            my ($name) = @_;
            say "Hello $name!";
        }
    EOM
    $code->("Ingy");

This schema allows you to load and dump perl objects and special types.

Please note that loading objects of arbitrary classes can be dangerous in Perl. You have to load the modules yourself, but if an exploitable module is loaded and an object is created, its "DESTROY" method will be called when the object falls out of scope. File::Temp is an example that can be exploitable and might remove arbitrary files.

Dumping code references is on by default, but not loading (because that is easily exploitable since it's using string "eval").

You can define the style of tags you want to support:

    my $yp_perl_two_one = YAML::PP->new(
        schema => [qw/ + Perl tags=!!perl+!perl /],
    );
"!perl" (default)
Only "!perl/type" tags are supported.
"!!perl"
Only "!!perl/type" tags are supported.
"!perl+!!perl"
Both "!perl/type" and "!!perl/tag" are supported when loading. When dumping, "!perl/type" is used.
"!!perl+!perl"
Both "!perl/type" and "!!perl/tag" are supported when loading. When dumping, "!!perl/type" is used.

YAML.pm, YAML::Syck and YAML::XS are using "!!perl/type" when dumping.

YAML.pm and YAML::Syck are supporting both "!perl/type" and "!!perl/type" when loading. YAML::XS currently only supports the latter.

Since v0.017

Blessing arbitrary objects can be dangerous. Maybe you want to allow blessing only specific classes and ignore others. For this you have to instantiate a Perl Schema object first and use the "classes" option.

Currently it only allows a list of strings:

    my $perl = YAML::PP::Schema::Perl->new(
        classes => ['Foo', 'Bar'],
    );
    my $yp = YAML::PP::Perl->new(
        schema => [qw/ + /, $perl],
    );

Allowed classes will be loaded and dumped as usual. The others will be ignored.

If you want to allow no objects at all, pass an empty array ref.

EXAMPLES

This is a list of the currently supported types and how they are dumped into YAML:

        # Code
        [
            qw/ one two three four /
        ]
        # YAML
        ---
        - one
        - two
        - three
        - four
    
        # Code
        bless [
            qw/ one two three four /
        ], "Just::An::Arrayref"
        # YAML
        --- !perl/array:Just::An::Arrayref
        - one
        - two
        - three
        - four
    
        # Code
        my $circle = bless [ 1, 2 ], 'Circle';
        push @$circle, $circle;
        $circle;
        # YAML
        --- &1 !perl/array:Circle
        - 1
        - 2
        - *1
    
        # Code
        sub {
            my (%args) = @_;
            return $args{x} + $args{y};
        }
        # YAML
        --- !perl/code |-
          {
              use warnings;
              use strict;
              (my(%args) = @_);
              (return ($args{'x'} + $args{'y'}));
          }
    
        # Code
        bless sub {
            my (%args) = @_;
            return $args{x} - $args{y};
        }, "I::Am::Code"
        # YAML
        --- !perl/code:I::Am::Code |-
          {
              use warnings;
              use strict;
              (my(%args) = @_);
              (return ($args{'x'} - $args{'y'}));
          }
    
        # Code
        {
            U => 2,
            B => 52,
        }
        # YAML
        ---
        B: 52
        U: 2
    
        # Code
        bless {
            U => 2,
            B => 52,
        }, 'A::Very::Exclusive::Class'
        # YAML
        --- !perl/hash:A::Very::Exclusive::Class
        B: 52
        U: 2
    
        # Code
        my $ref = { a => 'hash' };
        my $refref = \$ref;
        $refref;
        # YAML
        --- !perl/ref
        =:
          a: hash
    
        # Code
        my $ref = { a => 'hash' };
        my $refref = bless \$ref, 'Foo';
        $refref;
        # YAML
        --- !perl/ref:Foo
        =:
          a: hash
    
        # Code
        my $string = 'unblessed';
        qr{$string}
        # YAML
        --- !perl/regexp unblessed
    
        # Code
        my $string = 'blessed';
        bless qr{$string}, "Foo"
        # YAML
        --- !perl/regexp:Foo blessed
    
        # Code
        my $scalar = "some string";
        my $scalarref = \$scalar;
        $scalarref;
        # YAML
        --- !perl/scalar
        =: some string
    
        # Code
        my $scalar = "some other string";
        my $scalarref = bless \$scalar, 'Foo';
        $scalarref;
        # YAML
        --- !perl/scalar:Foo
        =: some other string

METHODS

    my $perl = YAML::PP::Schema::Perl->new(
        tags => "!perl",
        classes => ['MyClass'],
        loadcode => 1,
    );

The constructor recognizes the following options:

Default: '"!perl"'

See "Tag Styles"

Default: "undef"

Since: v0.017

Accepts an array ref of class names

Default: 0
A class method called by YAML::PP::Schema
Perl variables of the type "REF" are represented in yaml like this: 

    --- !perl/ref
    =:
      a: 1

"construct_ref" returns the perl data:

    my $data = YAML::PP::Schema::Perl->construct_ref([ '=', { some => 'data' } );
    my $data = \{ a => 1 };

"represent_ref" turns a "REF" variable into a YAML mapping:

    my $data = YAML::PP::Schema::Perl->represent_ref(\{ a => 1 });
    my $data = { '=' => { a => 1 } };
Perl variables of the type "SCALAR" are represented in yaml like this: 

    --- !perl/scalar
    =: string

"construct_scalar" returns the perl data:

    my $data = YAML::PP::Schema::Perl->construct_ref([ '=', 'string' );
    my $data = \'string';

"represent_scalar" turns a "SCALAR" variable into a YAML mapping:

    my $data = YAML::PP::Schema::Perl->represent_scalar(\'string');
    my $data = { '=' => 'string' };
"construct_regex" returns a "qr{}" object from the YAML string: 

    my $qr = YAML::PP::Schema::Perl->construct_regex('foo.*');

"represent_regex" returns a string representing the regex object:

    my $string = YAML::PP::Schema::Perl->represent_regex(qr{...});
"evaluate_code" returns a code reference from a string. The string must start with a "{" and end with a "}". 

    my $code = YAML::PP::Schema::Perl->evaluate_code('{ return 23 }');

"represent_code" returns a string representation of the code reference with the help of B::Deparse:

    my $string = YAML::PP::Schema::Perl->represent_code(sub { return 23 });
"construct_glob" returns a glob from a hash. 

    my $glob = YAML::PP::Schema::Perl->construct_glob($hash);

"represent_glob" returns a hash representation of the glob.

    my $hash = YAML::PP::Schema::Perl->represent_glob($glob);
Does the same as "bless": 

    my $object = YAML::PP::Schema::Perl->object($data, $class);
2020-09-10 perl v5.34.0