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MessagePack::Class

zef:jonathanstowe

MessagePack::Class

Serialize/Deserialize Raku classes to/from MessagePack blobs

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Synopsis

use MessagePack::Class;

class MyClass does MessagePack::Class {
	has Str $.some-data;
}

my Blob $pack = MyClass.new(some-data => "whatever").to-messagepack;

# Then send $pack over the network, write it to a file or something

my MyClass $obj = MyClass.from-messagepack($pack);

Description

MessagePack is a binary serialization format that is particularly efficient for transmission over a network or file storage.

This module provides a role that allows for the direct serialization of a Raku object to a MessagePack binary blob and the deserialization of that blob back to a Raku object of the same type with the same attribute values.

Under the hood it uses Data::MessagePack to serialize and deserialize data structures representing the object in a very similar manner to JSON::Marshal and JSON::Unmarshal (infact it borrows some of the internal code of both of those to construct a suitable data structure.)

For a simple case this may work with your class unchanged apart from the addition of the role composition, however for types that may not be properly constructed from their public attributes there are provided the attribute traits packed-by and unpacked-by which allow you to provide either a subroutine or a method name that will work with a representation that will round-trip properly.

A named method supplied to packed-by will be called on the object to be serialized without any arguments and should return a value suitable for serialization, and a method supplied to unpacked-by will be called on the type object with the value to be deserialized as a single positional argument and should return an object of the type.

So for instance if one had a class with an attribute of type Version one might do:

class TraitTest does MessagePack::Class {
    has Version $.version is packed-by('Str') is unpacked-by('new');
}

Where the Str method returns a string that is suitable to be passed to new to create a new Version object.

If a subroutine (or other Callable object) is passed to the traits then it should take a single argument and return a value suitable for serialization (for packed-by) or an object of the appropriate type (for unpacked-by) so the above example might become:

class TraitTest does MessagePack::Class {
    has Version $.version is packed-by(-> Version $v { $v.Str }) is unpacked-by(-> Str $v { Version.new($v)});
}

You can of course make the subroutines as complex as is required for your types.

If you need your data to be interoperable with software written in another language you may need to adjust the serialization accordingly to match the types available in that language.

Installation

Assuming you have a working Rakudo installation the you should be able to install this with zef :

zef install MessagePack::Class

# or from a local check-out:

zef install .

Though I can't see any reason this shouldn't work with any other installer that may come along in the future.

If it reports that is having trouble installing the dependency, you can do:

zef install -v --debug https://github.com/pierre-vigier/Perl6-Data-MessagePack.git

Support

If you find a problem with this module or have a suggestion please report at https://github.com/jonathanstowe/MessagePack-Class/issues - though I always prefer a pull request with tests if you can do that.

This is free software. Please see the LICENCE file in this repository.

© Jonathan Stowe 2017 - 2021