Api Compatibility Check

api_compatibility_checker.rb

class ApiCompatibilityChecker

  class CheckApiCompatibilityError < StandardError; end

  SERVER_API_VERSION = '1.0.0'
  VERSION_REGEXP = /\A(?<major>\d{1,5})\.(?<minor>\d{1,5})\.(?<patch>\d{1,5})\z/

  attr_reader :request, :env

  def initialize(request)
    @request = request
    @env = request.env
  end

  def check!
    client_api_version = request.params[:client_api_version]
    return true unless client_api_version
    result = VERSION_REGEXP.match(client_api_version) rescue nil
    client_major = Integer(result[:major]) rescue nil
    server_major = Integer(VERSION_REGEXP.match(SERVER_API_VERSION)[:major])
    ApiV2::CompatibilityCheckerController.action(:invalid_client_version_format).call(env) and return unless client_major
    return true unless server_major != client_major
    env['client_api_version'] = client_api_version
    ApiV2::CompatibilityCheckerController.action(:client_needs_to_be_upgraded).call(env) and return if client_major < server_major
    ApiV2::CompatibilityCheckerController.action(:server_needs_to_be_upgraded).call(env) and return if server_major < client_major
    raise CheckApiCompatibilityError
  end

end

compatibility_checker_controller.rb

module ApiV2
  class CompatibilityCheckerController < BaseController

    SERVER_API_VERSION = ApiCompatibilityChecker::SERVER_API_VERSION

    def invalid_client_version_format
      respond_with ({ errors: [{error: 'Invalid client version format.'}],
                      server_api_version: SERVER_API_VERSION }),
                   status: :bad_request, root: 'api_compatibility_check'
    end

    def client_needs_to_be_upgraded
      respond_with ({ errors: [{error: 'Client needs to be upgraded.'}],
                      server_api_version: SERVER_API_VERSION, client_api_version: env['client_api_version'] }),
                   status: :bad_request, root: 'api_compatibility_check'
    end

    def server_needs_to_be_upgraded
      respond_with ({ errors: [{error: 'Server needs to be upgraded.'}],
                        server_api_version: SERVER_API_VERSION, client_api_version: env['client_api_version'] }),
                     status: :internal_server_error, root: 'api_compatibility_check'
    end
  end
end

routes.rb

# ...
api_compatibility_check = lambda { |request| ApiCompatibilityChecker.new(request).check! }
# ...
scope constraints: api_compatibility_check do
  # Here be API routes
end