You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: message.rs
    path of file: ./repos/freenet-core/crates/core/src
    
    the code of the file until where you have to start completion: //! Network messaging between peers.
    
    fn elapsed(&self) -> Duration {
        let current_unix_epoch_ts = SystemTime::now()
            .duration_since(SystemTime::UNIX_EPOCH)
            .expect("now should be always be later than unix epoch")
            .as_millis() as u64;
        let this_tx_creation = self.id.timestamp_ms();
        if current_unix_epoch_ts < this_tx_creation {
            Duration::new(0, 0)
        } else {
            let ms_elapsed = current_unix_epoch_ts - this_tx_creation;
            Duration::from_millis(ms_elapsed)
        }
    }