Module for active Paperclip Url Upload

has_paperclip_url_upload.rb

# In your model after declaring your attachments, add:
# include HasPaperclipUrlUpload

# Thanks to https://gist.github.com/1502777

require 'open-uri'

module HasPaperclipUrlUpload
  def self.included(base)
    base.attachment_definitions.collect{|key, values| key}.each do |key|
      base.class_eval <<-EOS

        attr_accessor :#{key}_url
        before_validation :download_remote_#{key}, :if => :#{key}_url_provided?

        validates_presence_of :#{key}_remote_url, :if => :#{key}_url_provided?, :message => 'is invalid or inaccessible'

        def #{key}_remote_url
          if self.#{key}_url.present?
            self.#{key}_url
          else
            self.#{key}.url if !new_record? and self.#{key}?
          end
        end

        def #{key}_remote_url=(remote_url)
          self.#{key}_url = remote_url
        end

        private

        def #{key}_url_provided?
          !self.#{key}_remote_url.blank?
        end

        def download_remote_#{key}
          io = open(URI.parse(#{key}_url))
          self.#{key}_file_name = io.base_uri.path.split('/').last
          self.#{key} = io
        rescue # catch url errors with validations instead of exceptions (Errno::ENOENT, OpenURI::HTTPError, etc...)
        end
      EOS
    end
  end
end