Setting up Cache-Control for CarrierWave uploads - making sure that file names are updated to keep the cache fresh.

versioned_filename.rb

# This is for versioning files that we upload to S3.
#
# We want a unique time stamp in the name, so that we can cache files on browsers without
# worrying about cache-busting.
#
# The tricky part is deciding when to increment the version, this is accomplished
# by binding to the +before_cache+ hook.
#
# All you need to do to use this, is to call "has_versioned_filename" from an uploader,
# and add a string column "+mount_name+_version_token" to the model.

module CarrierWave::Uploader::VersionedFilename
  def has_versioned_filename
    before :cache, :clear_version_token!
    include InstanceMethods
  end

  module InstanceMethods
    def fog_attributes
      { 'Cache-Control' => 'public, max-age=315360000' }
    end

    def filename
      "#{version_token!}.#{file.extension}" if original_filename.present?
    end

    def version_token!
      col = "#{mounted_as}_version_token"

      model.send(col) || model.send("#{col}=", version_token)
    end

    def version_token
      Time.now.to_i
    end

    def clear_version_token!(file)
      model.send "#{mounted_as}_version_token=", nil
    end
  end
end

CarrierWave::Uploader::Base.send :extend, CarrierWave::Uploader::VersionedFilename