code: def _non_framed_body_length(header, plaintext_length):
      
      body_length = header.algorithm.iv_len  # IV
      body_length += 8  # Encrypted Content Length
      body_length += plaintext_length  # Encrypted Content
      body_length += header.algorithm.auth_len  # Authentication Tag
      return body_length
docs: Calculates the length of a non-framed message body, given a complete header.
  
      :param header: Complete message header object
      :type header: aws_encryption_sdk.structures.MessageHeader
      :param int plaintext_length: Length of plaintext in bytes
      :rtype: int