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= MessagePack
MessagePack[http://msgpack.org] is an efficient binary serialization format.
It lets you exchange data among multiple languages like JSON but it's faster and smaller.
For example, small integers (like flags or error code) are encoded into a single byte,
and typical short strings only require an extra byte in addition to the strings themselves.
If you ever wished to use JSON for convenience (storing an image with metadata) but could
not for technical reasons (binary data, size, speed...), MessagePack is a perfect replacement.
require 'msgpack'
msg = [1,2,3].to_msgpack #=> "\x93\x01\x02\x03"
MessagePack.unpack(msg) #=> [1,2,3]
Use RubyGems to install:
gem install msgpack
or build msgpack-ruby and install:
bundle
rake
gem install --local pkg/msgpack
= Use cases
* Create REST API returing MessagePack using Rails + [RABL](https://github.com/nesquena/rabl)
* Store objects efficiently serialized by msgpack on memcached or Redis
* In fact Redis supports msgpack in EVAL-scripts[http://redis.io/commands/eval]
* Upload data in efficient format from mobile devices such as smartphones
* MessagePack works on iPhone/iPad and Android. See also Objective-C[https://github.com/msgpack/msgpack-objectivec] and Java[https://github.com/msgpack/msgpack-java] implementations
* Design a portable protocol to communicate with embedded devices
* Check also Fluentd[http://fluentd.org/] which is a log collector which uses msgpack for the log format (they say it uses JSON but actually it's msgpack, which is compatible with JSON)
* Exchange objects between software components written in different languages
* You'll need a flexible but efficient format so that components exchange objects while keeping compatibility
= Portability
MessagePack for Ruby should run on x86, ARM, PowerPC, SPARC and other CPU architectures.
And it works with MRI (CRuby) and Rubinius.
Patches to improve portability is highly welcomed.
= Serializing objects
Use *MessagePack.pack* or *to_msgpack*:
require 'msgpack'
msg = MessagePack.pack(obj) # or
msg = obj.to_msgpack
== Streaming serialization
Packer provides advanced API to serialize objects in streaming style:
# serialize a 2-element array [e1, e2]
pk = MessagePack::Packer.new(io)
pk.write_array_header(2).write(e1).write(e2).flush
See {API reference}[http://ruby.msgpack.org/MessagePack/Packer.html] for details.
= Deserializing objects
Use *MessagePack.unpack*:
require 'msgpack'
obj = MessagePack.unpack(msg)
== Streaming deserialization
Unpacker provides advanced API to deserialize objects in streaming style:
# deserialize objects from an IO
u = MessagePack::Unpacker.new(io)
u.each do |obj|
# ...
end
or event-driven style which works well with EventMachine:
# event-driven deserialization
def on_read(data)
@u ||= MessagePack::Unpacker.new
@u.feed_each(data) {|obj|
# ...
}
end
See {API reference}[http://ruby.msgpack.org/MessagePack/Unpacker.html] for details.
= Serializing and deserializing symbols
By default, symbols are serialized as strings:
packed = :symbol.to_msgpack # => "\xA6symbol"
MessagePack.unpack(packed) # => "symbol"
This can be customized by registering an extension type for them:
MessagePack::DefaultFactory.register_type(0x00, Symbol)
# symbols now survive round trips
packed = :symbol.to_msgpack # => "\xc7\x06\x00symbol"
MessagePack.unpack(packed) # => :symbol
The extension type for symbols is configurable like any other extension type.
For example, to customize how symbols are packed you can just redefine
Symbol#to_msgpack_ext. Doing this gives you an option to prevent symbols from
being serialized altogether by throwing an exception:
class Symbol
def to_msgpack_ext
raise "Serialization of symbols prohibited"
end
end
MessagePack::DefaultFactory.register_type(0x00, Symbol)
[1, :symbol, 'string'].to_msgpack # => RuntimeError: Serialization of symbols prohibited
= Extension Types
Packer and Unpacker support {Extension types of MessagePack}[https://github.com/msgpack/msgpack/blob/master/spec.md#types-extension-type].
# register how to serialize custom class at first
pk = MessagePack::Packer.new(io)
pk.register_type(0x01, MyClass1, :to_msgpack_ext) # equal to pk.register_type(0x01, MyClass)
pk.register_type(0x02, MyClass2){|obj| obj.how_to_serialize() } # blocks also available
# almost same API for unpacker
uk = MessagePack::Unpacker.new()
uk.register_type(0x01, MyClass1, :from_msgpack_ext)
uk.register_type(0x02){|data| MyClass2.create_from_serialized_data(data) }
MessagePack::Factory is to create packer and unpacker which have same extention types.
factory = MessagePack::Factory.new
factory.register_type(0x01, MyClass1) # same with next line
factory.register_type(0x01, MyClass1, packer: :to_msgpack_ext, unpacker: :from_msgpack_ext)
pk = factory.packer(options_for_packer)
uk = factory.unpacker(options_for_unpacker)
For *MessagePack.pack* and *MessagePack.unpack*, default packer/unpacker refer *MessagePack::DefaultFactory*. Call *MessagePack::DefaultFactory.register_type* to enable types process globally.
MessagePack::DefaultFactory.register_type(0x03, MyClass3)
MessagePack.unpack(data_with_ext_typeid_03) #=> MyClass3 instance
= Buffer API
MessagePack for Ruby provides a buffer API so that you can read or write data by hand, not via Packer or Unpacker API.
This {MessagePack::Buffer}[http://ruby.msgpack.org/MessagePack/Buffer.html] is backed with a fixed-length shared memory pool which is very fast for small data (<= 4KB),
and has zero-copy capability which significantly affects performance to handle large binary data.
= How to build and run tests
Before building msgpack, you need to install bundler and dependencies.
gem install bundler
bundle install
Then, you can run the tasks as follows:
* Build
bundle exec rake build
* Run tests
bundle exec rake spec
* Generating docs
bundle exec rake doc
== How to build -mingw32 rubygems
MessagePack mingw32/64 rubygems build process uses {rake-compiler-dock}[https://github.com/rake-compiler/rake-compiler-dock]. Run:
rake build:windows
Once this step successes, target gems exist in pkg/msgpack-*-{x86,x64}-mingw32.gem.
== Updating documents
Online documents (http://ruby.msgpack.org) is generated from gh-pages branch.
Following commands update documents in gh-pages branch:
bundle exec rake doc
git checkout gh-pages
cp doc/* ./ -a
= Copyright
Author:: Sadayuki Furuhashi <frsyuki@gmail.com>
Copyright:: Copyright (c) 2008-2015 Sadayuki Furuhashi
License:: Apache License, Version 2.0
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