code: def unpack_values(format_string, stream, verifier=None):
      
      try:
          message_bytes = stream.read(struct.calcsize(format_string))
          if verifier:
              verifier.update(message_bytes)
          values = struct.unpack(format_string, message_bytes)
      except struct.error as error:
          raise SerializationError("Unexpected deserialization error", type(error), error.args)
      return values
docs: Helper function to unpack struct data from a stream and update the signature verifier.
  
      :param str format_string: Struct format string
      :param stream: Source data stream
      :type stream: io.BytesIO
      :param verifier: Signature verifier object
      :type verifier: aws_encryption_sdk.internal.crypto.Verifier
      :returns: Unpacked values
      :rtype: tuple