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Daniel Doubrovkine

aka dB., CTO at artsy.net, fun at playplay.io, NYC

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Yet again I have to deal with 3rd party licenses, this time in RoR. It’s a pretty common thing to do for technical managers and in my last job I ended up creating 3licenses. For starters, we must know which open-source licenses are used. This can be a daunting exercise for large or complex projects. Then, you have to maintain the list and make sure it’s accurate with every release. Figuring out which licenses are used in 3rd party gems is relatively easy, because each gem spec contains a licenses array, we can do something like this.

Gem.loaded_specs.each do |key, spec|
    spec.licenses.each do |license|
        puts "#{spec} => #{license}"

But not so fast. Out of about 80 gems that we use, less than 10 had a proper license manifest. Half had a valid LICENSE file that clearly stated which license they use and others carried a license that needed review, mostly matching the MIT license word-to-word. Three turned out not to have a license at all and reaching out to the component authors was needed.

Enter gem-licenses. It’s meant to be a skeleton for a project that can effectively guess which license a project uses. I did a rudimentary regex job, but I’d like someone to contribute a much more intelligent system to identify a project’s license.

Here’s a Rake task I added to our project. It generates a list of gems and licenses, good enough to start with to make a list.

require 'gem_licenses'

task :licenses do
  Gem.licenses.each do |license, gems|
    puts "#{license}"
    gems.sort_by { |gem| gem.name }.each do |gem|
      puts "\* #{gem.name} #{gem.version} (#{gem.homepage}) - #{gem.summary}"

Finally, if you are a gem author, please take the time to specify which license your project is published under in the .gemspec. If you’re using Jeweler, specify gem.license.

Jeweler::Tasks.new do |gem|
  gem.name = "gem-licenses"
  gem.homepage = "http://github.com/dblock/gem-licenses"
  gem.license = "MIT"
  gem.summary = "List all gem licenses."
  gem.description = "Attempts to figure out what licenses various gems use."
  gem.email = "dblock@dblock.org"
  gem.authors = ["Daniel Doubrovkine"]

Now that we have the list of licenses we must ensure that we’re in compliance with the licenses. Listing those is the first step. Then we have to make sure that we’re not using any polluting licenses that require us to make any of our or our partner’s proprietary source code available. That’s something lawyers do.