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A Ruby wrapper around rtosc to encode and decode OSC messages.

This also includes a fallback implementation in pure Ruby in the case that the compiled version doesn't load properly. This can be forced by setting an environment variable of FAST_OSC_USE_FALLBACK=1 where needed.


Add this line to your application's Gemfile:

gem 'fast_osc'

And then execute:

$ bundle

Or install it yourself as:

$ gem install fast_osc


Everything (single messages and bundles) can be parsed with a single method - FastOsc.decode. This outputs an array of bundles, with each bundle containing a timestamp and an array of messages. Each message contains a path and, optionally, some arguments.

# encode an OSC message with the established Ruby OSC libary
@msg ="/testpath", ["some", "args", 1, 2.0]).encode
@encoded_msg = @msg1.encode

FastOsc.decode(@encoded_msg0).each do |bundle|
  _timestamp, osc_msgs = bundle

  osc_msgs.each do |(path, args)|
    puts @path # "/testpath"
    puts args # ["some", "args", 1, 2.0]
>> FastOsc.encode_single_message("/foo", ["baz", 1, 2.0])
=> "/foo\x00\x00\x00\x00,sif\x00\x00\x00\x00baz\x00\x00\x00\x00\x01@\x00\x00\x00"
>> res = _
>> FastOsc.decode_no_bundles(res)
=> ["/foo", ["baz", 1, 2.0]]
>> FastOsc.encode_single_bundle(, "/foo", ["baz", 1, 2.0])
=> "#bundle\x00\x00\x00\x00\x00W*1\x7F\x00\x00\x00\x1C/foo\x00\x00\x00\x00,sif\x00\x00\x00\x00baz\x00\x00\x00\x00\x01@\x00\x00\x00"

A timestamp of nil is a special case meaning "immediately".

A note on types

To represent the blob type tag from the OSC spec, FastOsc uses strings with the ASCII-8BIT encoding. UTF-8 strings remain as normal string tags.

For examples of this, see the test suite.

Is it fast?

Let's see...


  • fast_osc - this gem
  • osc - osc-ruby
  • samsosc - OSC classes from Sonic Pi (which are optimised pure Ruby based on pack and unpack)

Encoding Benchmark

$ WITH_BENCHMARKS=1 rake test
Warming up --------------------------------------
            fast_osc    94.043k i/100ms
             samsosc    41.231k i/100ms
            osc-ruby    17.476k i/100ms
Calculating -------------------------------------
            fast_osc      1.186M (± 3.7%) i/s -      5.925M in   5.004014s
             samsosc    458.561k (± 4.1%) i/s -      2.309M in   5.043860s
            osc-ruby    182.051k (± 4.6%) i/s -    908.752k in   5.003313s

Decoding Bencmark

$ WITH_BENCHMARKS=1 rake test
Warming up --------------------------------------
            fast_osc   208.209k i/100ms
             samsosc    38.760k i/100ms
            osc-ruby     6.844k i/100ms
Calculating -------------------------------------
            fast_osc      3.679M (± 3.8%) i/s -     18.531M in   5.044888s
             samsosc    430.488k (± 3.0%) i/s -      2.171M in   5.046837s
            osc-ruby     70.998k (± 3.1%) i/s -    355.888k in   5.017493s

Benchmarks are now part of this repo - run WITH_BENCHMARKS=1 rake test to see the results for yourself.

Still todo

  • Make a pure ruby fallback available
  • Implement more types
  • Bring benchmarks into the repo
  • Work out cross compilation story for easier packaging
  • Implement multi message/nested bundles
  • More documentation
  • Travis, Appveyor

Development notes

This project uses Bundler v2 - get this with

gem install bundler

On linux, the only deps are apt-get install build-essentials ruby-devel. On OS X you may need XCode build tooling or similar.

bundle install
rake compile

On Windows, using RubyInstaller and setup the MSYS2 toolchain. You then need to include devkit in the compile step like so:

bundle install
bundle exec rake compile -rdevkit

Running the test suite

$ gem install minitest # or bundle install
$ rake clean && rake clobber && rake compile && rake test && FAST_OSC_USE_FALLBACK=true rake test


  1. Fork it ( )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request


A Ruby wrapper around rtosc ( to encode and decode OSC messages.





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