CBOR for Ruby

This is a Ruby implementation of the CBOR encoding, based on the (polished) high-performance msgpack-ruby code.

Documentation will follow, but generally, if you replace MessagePack and msgpack with CBOR and cbor in the text cited from MessagePack below, you will be on the right track. For a starter:

require 'cbor'
s = [1, 2, 33.5, 4].to_cbor  #=> "\x84\x01\x02\xF9P0\x04"
CBOR.decode(s)  #=> [1, 2, 33.5, 4]

Use RubyGems to install:

gem install cbor

CBOR is an object representation format defined by the IETF. The specification is an IETF Standards-Track specification and has been published as RFC 7049.

This is all based on wonderful work by frsyuki, and I have no idea how to acknowledge him appropriately. This gem is not intended to fork or supersede MessagePack, which has a vibrant ecosystem. It is just making use of the high-quality code that is available in this community. If MessagePack works for you, go for it. If you need CBOR, you need this.


  • This code has not yet been fully optimized, so it is still a few percent slower than msgpack-ruby.

  • Properly document things, in particular the classes CBOR::Simple and CBOR::Tagged. If you check out the source, you can rake doc to get some documentation in the directory doc (see index.html there).

  • Cover more rubies.

    • [✔✔✔✔] tested on MRI (1.9.3, 2.0.0, 2.1.10, 2.2.10, 2.3.7, 2.4.4 and 2.5.1).

    • ([✔] There now also is some basic MRI 1.8.7 compatibility, however 1.8.7 does not support differentiation between byte and text strings.)

    • [✔] tested on Rubinius 2.4.1.

    • [_] Publish the pure-ruby version and make it work the same way on JRuby.

  • Find and implement good ways to offer CBOR’s indefinite length (“streaming”) capability at the Ruby API level. (Decoding is fully supported, just no streaming or indefinite length encoding.)

  • Rename some of the internals from msgpack to cbor. Right now, much of the code still uses the name msgpack in its identifiers, to facilitate merging upstream fixes. (The msgpack and cbor gems coexist nicely in one MRI instance due to the magic in renamer.h.)

Same Apache 2.0 License applies to the changes as to the original. For the changes:


Carsten Bormann <[email protected]>


Copyright © 2013, 2014 Carsten Bormann


Apache License, Version 2.0

<img src=“https://travis-ci.org/cabo/cbor-ruby.svg?branch=master” /> <img src=“https://badge.fury.io/rb/cbor.svg” alt=“Gem Version” />

For the original, see below.


MessagePack 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:

gem install --local pkg/msgpack

Use cases

  • Store objects efficiently serialized by msgpack on memcached or Redis

  • Upload data in efficient format from mobile devices such as smartphones

    • MessagePack works on iPhone/iPad and Android. See also Objective-C and Java implementations

  • Design a portable protocol to communicate with embedded devices

    • Check also Fluentd 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


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)

See API reference 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|
  # ...

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|
     # ...

See API reference for details.

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 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



Sadayuki Furuhashi <[email protected]>


Copyright © 2008-2013 Sadayuki Furuhashi


Apache License, Version 2.0