instance method get_data_and_digest_from

# File activesupport/lib/active_support/message_verifier.rb, line 221
      def get_data_and_digest_from(signed_message)
        return if signed_message.nil? || !signed_message.valid_encoding? || signed_message.empty?

        separator_index = separator_index_for(signed_message)
        return if separator_index.nil?

        data = signed_message[0...separator_index]
        digest = signed_message[separator_index + SEPARATOR_LENGTH..-1]

        [data, digest]
      end