UTF-8-encoded string: Perl parsing library

UTF-8 is a popular character encoding scheme that allows to represent strings as sequence of code points defined in Unicode standard. Its features are:

  • variable width (i.e. one code point might be represented by 1 to 4 bytes)
  • backward compatiblity with ASCII
  • basic validity checking (and thus distinguishing from other legacy 8-bit encodings)
  • maintaining sort order of codepoints if sorted as a byte array

WARNING: For the vast majority of practical purposes of format definitions in Kaitai Struct, you'd likely NOT want to use this and rather just use type: str with encoding: utf-8. That will use native string implementations, which are most likely more efficient and will give you native language strings, rather than an array of individual codepoints. This format definition is provided mostly for educational / research purposes.

File extension

txt

KS implementation details

License: CC0-1.0

References

This page hosts a formal specification of UTF-8-encoded string using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.

Perl source code to parse UTF-8-encoded string

Utf8String.pm

Download 

# This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild

use strict;
use warnings;
use IO::KaitaiStruct 0.009_000;

########################################################################
package Utf8String;

our @ISA = 'IO::KaitaiStruct::Struct';

sub from_file {
    my ($class, $filename) = @_;
    my $fd;

    open($fd, '<', $filename) or return undef;
    binmode($fd);
    return new($class, IO::KaitaiStruct::Stream->new($fd));
}

sub new {
    my ($class, $_io, $_parent, $_root) = @_;
    my $self = IO::KaitaiStruct::Struct->new($_io);

    bless $self, $class;
    $self->{_parent} = $_parent;
    $self->{_root} = $_root || $self;;

    $self->_read();

    return $self;
}

sub _read {
    my ($self) = @_;

    $self->{codepoints} = ();
    while (!$self->{_io}->is_eof()) {
        push @{$self->{codepoints}}, Utf8String::Utf8Codepoint->new($self->{_io}, $self, $self->{_root});
    }
}

sub codepoints {
    my ($self) = @_;
    return $self->{codepoints};
}

########################################################################
package Utf8String::Utf8Codepoint;

our @ISA = 'IO::KaitaiStruct::Struct';

sub from_file {
    my ($class, $filename) = @_;
    my $fd;

    open($fd, '<', $filename) or return undef;
    binmode($fd);
    return new($class, IO::KaitaiStruct::Stream->new($fd));
}

sub new {
    my ($class, $_io, $_parent, $_root) = @_;
    my $self = IO::KaitaiStruct::Struct->new($_io);

    bless $self, $class;
    $self->{_parent} = $_parent;
    $self->{_root} = $_root || $self;;

    $self->_read();

    return $self;
}

sub _read {
    my ($self) = @_;

    $self->{bytes} = $self->{_io}->read_bytes($self->len_bytes());
}

sub raw1 {
    my ($self) = @_;
    return $self->{raw1} if ($self->{raw1});
    if ($self->len_bytes() >= 2) {
        $self->{raw1} = (unpack('C', substr($self->bytes(), 1, 1)) & 63);
    }
    return $self->{raw1};
}

sub len_bytes {
    my ($self) = @_;
    return $self->{len_bytes} if ($self->{len_bytes});
    $self->{len_bytes} = (($self->byte0() & 128) == 0 ? 1 : (($self->byte0() & 224) == 192 ? 2 : (($self->byte0() & 240) == 224 ? 3 : (($self->byte0() & 248) == 240 ? 4 : -1))));
    return $self->{len_bytes};
}

sub raw3 {
    my ($self) = @_;
    return $self->{raw3} if ($self->{raw3});
    if ($self->len_bytes() >= 4) {
        $self->{raw3} = (unpack('C', substr($self->bytes(), 3, 1)) & 63);
    }
    return $self->{raw3};
}

sub value_as_int {
    my ($self) = @_;
    return $self->{value_as_int} if ($self->{value_as_int});
    $self->{value_as_int} = ($self->len_bytes() == 1 ? $self->raw0() : ($self->len_bytes() == 2 ? (($self->raw0() << 6) | $self->raw1()) : ($self->len_bytes() == 3 ? ((($self->raw0() << 12) | ($self->raw1() << 6)) | $self->raw2()) : ($self->len_bytes() == 4 ? (((($self->raw0() << 18) | ($self->raw1() << 12)) | ($self->raw2() << 6)) | $self->raw3()) : -1))));
    return $self->{value_as_int};
}

sub raw0 {
    my ($self) = @_;
    return $self->{raw0} if ($self->{raw0});
    $self->{raw0} = (unpack('C', substr($self->bytes(), 0, 1)) & ($self->len_bytes() == 1 ? 127 : ($self->len_bytes() == 2 ? 31 : ($self->len_bytes() == 3 ? 15 : ($self->len_bytes() == 4 ? 7 : 0)))));
    return $self->{raw0};
}

sub byte0 {
    my ($self) = @_;
    return $self->{byte0} if ($self->{byte0});
    my $_pos = $self->{_io}->pos();
    $self->{_io}->seek($self->ofs());
    $self->{byte0} = $self->{_io}->read_u1();
    $self->{_io}->seek($_pos);
    return $self->{byte0};
}

sub raw2 {
    my ($self) = @_;
    return $self->{raw2} if ($self->{raw2});
    if ($self->len_bytes() >= 3) {
        $self->{raw2} = (unpack('C', substr($self->bytes(), 2, 1)) & 63);
    }
    return $self->{raw2};
}

sub bytes {
    my ($self) = @_;
    return $self->{bytes};
}

sub ofs {
    my ($self) = @_;
    return $self->{ofs};
}

1;