carrierwave_direct.rb

# config/initializers/carrierwave_direct.rb
require "carrierwave_direct"

module CarrierWaveDirect
  module SignatureFixMonkeyPatch
    def policy(options = {})
      options[:expiration] ||= upload_expiration
      options[:min_file_size] ||= min_file_size
      options[:max_file_size] ||= max_file_size

      @policy ||= generate_policy(options)
    end

    def clear_policy!
      @policy = nil
    end

    private
    def generate_policy(options)
      conditions = [
        ["starts-with", "$utf8", ""],
        ["starts-with", "$key", key.sub(/#{Regexp.escape(FILENAME_WILDCARD)}\z/, "")]
      ]

      conditions << ["starts-with", "$Content-Type", ""] if will_include_content_type
      conditions << {"bucket" => fog_directory}
      conditions << {"acl" => acl}

      if use_action_status
        conditions << {"success_action_status" => success_action_status}
      else
        conditions << {"success_action_redirect" => success_action_redirect}
      end

      conditions << ["content-length-range", options[:min_file_size], options[:max_file_size]]

      Base64.encode64(
        {
          'expiration' => Time.now.utc + options[:expiration],
          'conditions' => conditions
        }.to_json
      ).gsub("\n","")
    end
  end
end

CarrierWaveDirect::Uploader.send(:include, CarrierWaveDirect::SignatureFixMonkeyPatch)