mpv/TOOLS/lib/Parse/Matroska/Element.pm

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Perl
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use 5.008;
use strict;
use warnings;
# ABSTRACT: a mid-level representation of an EBML element
package Parse::Matroska::Element;
use Carp;
use List::Util qw{first};
=head1 SYNOPSIS
use Parse::Matroska::Reader;
my $reader = Parse::Matroska::Reader->new($path);
my $elem = $reader->read_element;
print "ID: $elem->{elid}\n";
print "Name: $elem->{name}\n";
print "Length: $elem->{content_len}\n";
print "Type: $elem->{type}\n";
print "Child count: ", scalar(@{$elem->all_children}), "\n";
if ($elem->{type} eq 'sub') {
while (my $chld = $elem->next_child) {
print "Child Name: $chld->{name}\n";
}
} else {
print "Value: ", $elem->get_value, "\n";
}
=head1 DESCRIPTION
Represents a single Matroska element as decoded by
L<Parse::Matroska::Reader>. This is essentially a hash
augmented with functions for delay-loading of binary
values and children elements.
=head1 NOTE
The API of this module is not yet considered stable.
=attr elid
The EBML Element ID, suitable for passing to
L<Parse::Matroska::Definitions/elem_by_hexid>.
=attr name
The EBML Element's name.
=attr type
The EBML Element's type. Can be C<uint>, C<sint>,
C<float>, C<ebml_id>, C<str> or C<binary>. See L</value>
for details.
Equivalent to
C<elem_by_hexid($elem-E<gt>{value})-E<gt>{valtype}>.
=attr value
The EBML Element's value. Should be obtained through
L</get_value>.
Is an unicode string if the L</type> is C<str>, that is,
the string has already been decoded by L<Encode/decode>.
Is C<undef> if the L</type> is C<binary> and the contents
were delay-loaded and not yet read. L</get_value> will
do the delayed load if needed.
Is an arrayref if the L</type> is C<sub>, containing
the children nodes that were already loaded.
Is a hashref if the L</type> is C<ebml_id>, containing
the referred element's information as defined in
L<Parse::Matroska::Definitions>. Calling
C<elem_by_hexid($elem-E<gt>{value}-E<gt>{elid})> will
return the same object as $elem->{value}.
=attr full_len
The entire length of this EBML Element, including
the header's.
=attr size_len
The length of the size marker. Used when calculating
L</full_len> from L</content_len>
=attr content_len
The length of the contents of this EBML Element,
which excludes the header.
=attr reader
A weakened reference to the associated
L<Parse::Matroska::Reader>.
=method new(%hash)
Creates a new Element initialized with the hash
given as argument.
=cut
sub new {
my $class = shift;
my $self = {};
bless $self, $class;
$self->initialize(@_);
return $self;
}
=method initialize(%hash)
Called by L</new> on initialization.
=cut
sub initialize {
my ($self, %args) = @_;
for (keys %args) {
$self->{$_} = $args{$_};
}
$self->{depth} = 0 unless $self->{depth};
}
=method skip
Called by the user to ignore the contents of this EBML node.
Needed when ignoring the children of a node.
=cut
sub skip {
my ($self) = @_;
my $reader = $self->{reader};
return unless $reader; # we don't have to skip if there's no reader
my $pos = $reader->getpos;
croak "Too late to skip, reads were already done"
if $pos ne $self->{data_pos};
$reader->skip($self->{content_len});
}
=method get_value($keep_bin)
Returns the value contained by this EBML element.
If the element has children, returns an arrayref to
the children elements that were already encountered.
If the element's type is C<binary> and the value was
delay-loaded, does the reading now.
If $keep_bin is true, the delay-loaded data is kept
as the L</value>, otherwise, further calls to
C<get_value> will reread the data from the L</reader>.
=cut
sub get_value {
my ($self, $keep_bin) = @_;
return undef if $self->{type} eq 'skip';
return $self->{value} if $self->{value};
my $reader = $self->{reader} or
croak "The associated Reader has been deleted";
# delay-loaded 'binary'
if ($self->{type} eq 'binary') {
croak "Cannot seek in the current Reader" unless $self->{data_pos};
# seek to the data position...
$reader->setpos($self->{data_pos});
# read the data, keeping it in value if requested
if ($keep_bin) {
$self->{value} = $reader->readlen($self->{content_len});
return $self->{value};
} else {
return $reader->readlen($self->{content_len});
}
}
}
=method next_child($read_bin)
Builtin iterator; reads and returns the next child element.
Always returns undef if the type isn't C<sub>.
Returns undef at the end of the iterator and resets itself to
point to the first element; so calling L</next_child($read_bin)>
after the iterator returned C<undef> will return the first child.
The optional C<$read_bin> parameter has the children elements
not delay-load their value if their type is C<binary>.
If all children elements have already been read, return
each element in-order as would be given by
L</all_children($recurse,$read_bin)>.
=cut
sub next_child {
my ($self, $read_bin) = @_;
return unless $self->{type} eq 'sub';
if ($self->{_all_children_read}) {
my $idx = $self->{_last_child} ||= 0;
if ($idx == @{$self->{value}}) {
# reset the iterator, returning undef once
$self->{_last_child} = 0;
return;
}
my $ret = $self->{value}->[$idx];
++$idx;
$self->{_last_child} = $idx;
return $ret;
}
my $len = defined $self->{remaining_len}
? $self->{remaining_len}
: $self->{content_len};
if ($len == 0) {
# we've read all children; switch into $self->{value} iteration mode
$self->{_all_children_read} = 1;
# return undef since the iterator will reset
return;
}
$self->{pos_offset} ||= 0;
my $pos = $self->{data_pos};
my $reader = $self->{reader} or croak "The associated reader has been deleted";
$reader->setpos($pos);
$reader->{fh}->seek($self->{pos_offset}, 1) if $pos;
my $chld = $reader->read_element($read_bin);
return undef unless defined $chld;
$self->{pos_offset} += $chld->{full_len};
$self->{remaining_len} = $len - $chld->{full_len};
if ($self->{remaining_len} < 0) {
croak "Child elements consumed $self->{remaining_len} more bytes than parent $self->{name} contained";
}
$chld->{depth} = $self->{depth} + 1;
$self->{value} ||= [];
push @{$self->{value}}, $chld;
return $chld;
}
=method all_children($recurse,$read_bin)
Calls L</populate_children($recurse,$read_bin)> on self
and returns an arrayref with the children nodes.
Both C<$recurse> and C<$read_bin> are optional and default
to false.
=cut
sub all_children {
my ($self, $recurse, $read_bin) = @_;
$self->populate_children($recurse, $read_bin);
return $self->{value};
}
=method children_by_name($name)
Searches in the already read children elements for all
elements with the EBML name C<$name>. Returns an array
containing all found elements. On scalar context,
returns only the first element found.
Croaks if the element's C<type> isn't C<sub>.
=cut
sub children_by_name {
my ($self, $name) = @_;
return unless defined wantarray; # don't do work if work isn't wanted
croak "Element can't have children" unless $self->{type} eq 'sub';
my @found = grep { $_->{name} eq $name } @{$self->{value}};
return @found if wantarray; # list
return shift @found if defined wantarray; # scalar
}
=method populate_children($recurse,$read_bin)
Populates the internal array of children elements, that is,
requests that the associated L<Matroska::Parser::Reader> reads
all children elements. Returns itself.
Returns false if the element's C<type> isn't C<sub>.
If C<$recurse> is provided and is true, the method will call
itself in the children elements with the same parameters it
received; this will build a full EBML tree.
If C<$read_bin> is provided and is true, disables delay-loading
of the contents of C<binary>-type nodes, reading the contents
to memory.
If both C<$recurse> and C<$read_bin> are true, entire EBML trees
can be loaded without requiring seeks, thus behaving correctly
on unseekable streams. If C<$read_bin> is false, the entire EBML
tree is still loaded, but calling L</get_value> on C<binary>-type
nodes will produce an error on unseekable streams.
=cut
sub populate_children {
my ($self, $recurse, $read_bin) = @_;
return unless $self->{type} eq 'sub';
if (@{$self->{value}} && $recurse) {
# only recurse
foreach (@{$self->{value}}) {
$_->populate_children($recurse, $read_bin);
}
return $self;
}
while (my $chld = $self->next_child($read_bin)) {
$chld->populate_children($recurse, $read_bin) if $recurse;
}
return $self;
}
1;