Google Protocol Buffers (protobuf): Perl parsing library

Google Protocol Buffers (AKA protobuf) is a popular data serialization scheme used for communication protocols, data storage, etc. There are implementations are available for almost every popular language. The focus points of this scheme are brevity (data is encoded in a very size-efficient manner) and extensibility (one can add keys to the structure, while keeping it readable in previous version of software).

Protobuf uses semi-self-describing encoding scheme for its messages. It means that it is possible to parse overall structure of the message (skipping over fields one can't understand), but to fully understand the message, one needs a protocol definition file (.proto). To be specific:

  • "Keys" in key-value pairs provided in the message are identified only with an integer "field tag". .proto file provides info on which symbolic field names these field tags map to.
  • "Keys" also provide something called "wire type". It's not a data type in its common sense (i.e. you can't, for example, distinguish sint32 vs uint32 vs some enum, or string from bytes), but it's enough information to determine how many bytes to parse. Interpretation of the value should be done according to the type specified in .proto file.
  • There's no direct information on which fields are optional / required, which fields may be repeated or constitute a map, what restrictions are placed on fields usage in a single message, what are the fields' default values, etc, etc.

KS implementation details

License: MIT
Minimal Kaitai Struct required: 0.7

References

This page hosts a formal specification of Google Protocol Buffers (protobuf) 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 Google Protocol Buffers (protobuf)

GoogleProtobuf.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;
use VlqBase128Le;

########################################################################
package GoogleProtobuf;

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) = @_;

    $self->{pairs} = ();
    while (!$self->{_io}->is_eof()) {
        push @{$self->{pairs}}, GoogleProtobuf::Pair->new($self->{_io}, $self, $self->{_root});
    }
}

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

########################################################################
package GoogleProtobuf::Pair;

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));
}

our $WIRE_TYPES_VARINT = 0;
our $WIRE_TYPES_BIT_64 = 1;
our $WIRE_TYPES_LEN_DELIMITED = 2;
our $WIRE_TYPES_GROUP_START = 3;
our $WIRE_TYPES_GROUP_END = 4;
our $WIRE_TYPES_BIT_32 = 5;

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) = @_;

    $self->{key} = VlqBase128Le->new($self->{_io});
    my $_on = $self->wire_type();
    if ($_on == $GoogleProtobuf::Pair::WIRE_TYPES_VARINT) {
        $self->{value} = VlqBase128Le->new($self->{_io});
    }
    elsif ($_on == $GoogleProtobuf::Pair::WIRE_TYPES_LEN_DELIMITED) {
        $self->{value} = GoogleProtobuf::DelimitedBytes->new($self->{_io}, $self, $self->{_root});
    }
    elsif ($_on == $GoogleProtobuf::Pair::WIRE_TYPES_BIT_64) {
        $self->{value} = $self->{_io}->read_u8le();
    }
    elsif ($_on == $GoogleProtobuf::Pair::WIRE_TYPES_BIT_32) {
        $self->{value} = $self->{_io}->read_u4le();
    }
}

sub wire_type {
    my ($self) = @_;
    return $self->{wire_type} if ($self->{wire_type});
    $self->{wire_type} = ($self->key()->value() & 7);
    return $self->{wire_type};
}

sub field_tag {
    my ($self) = @_;
    return $self->{field_tag} if ($self->{field_tag});
    $self->{field_tag} = ($self->key()->value() >> 3);
    return $self->{field_tag};
}

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

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

########################################################################
package GoogleProtobuf::DelimitedBytes;

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) = @_;

    $self->{len} = VlqBase128Le->new($self->{_io});
    $self->{body} = $self->{_io}->read_bytes($self->len()->value());
}

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

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

1;