List licences for a given Ruby project based on the Gemfile

license_checker.rb

require "bundler"
require "net/http"
require "json"

output = []

debug_mode = ARGV[0] == "--debug"

gems = Bundler::LockfileParser.new(Bundler.read_file(Bundler.default_lockfile))

dependencies = 
  Bundler::Definition.build('Gemfile', 'Gemfile.lock', nil)
  .dependencies
  .each_with_object(Hash.new { |h,k| h[k] = [] }) do |dep, obj|
    dep.groups.each do |group|
      obj[group] << dep.name
    end
  end

gems.specs.each do |spec|
  # We only want gems that are used in production, which means the :default group
  next unless dependencies[:default].include? spec.name
  
  puts "Fetching license info for #{spec.name}" if debug_mode

  uri = URI("https://rubygems.org/api/v1/gems/#{spec.name}.json")
  response = Net::HTTP.get_response(uri)
  
  if response.code != "200"
    # We use a few internal gems that are not published on RubyGems 
    # and do not need to be included here either
    # If you see another gem being skipped, please check what's going on
    puts "Skipping #{spec.name}" if debug_mode
    next
  end

  parsed_body = JSON.parse(response.body)

  spec_info = [
    spec.name,
    spec.version,
    parsed_body["licenses"].to_a.join(" + "),
    parsed_body["metadata"]["source_code_uri"]
  ]

  output << spec_info.join(";")
end

puts output.join("\n")