Handling commands

Our handle_cmd() method does nothing, for now, so let's update it. First of all, we'll need a method to send a response to a client:

impl Client {
    #[async]
    fn send(mut self, answer: Answer) -> Result<Self> {
        self.writer = await!(self.writer.send(answer))?;
        Ok(self)
    }
}

This simply calls the send() method of the writer. Since it consumes it, we reassign the result to the attribute.

Now, we'll handle the USER FTP command:

#[async]
fn handle_cmd(mut self, cmd: Command) -> Result<Self> {
    println!("Received command: {:?}", cmd);
    match cmd {
        Command::User(content) => {
            if content.is_empty() {
                self = await! 
          (self.send(Answer::new(ResultCode::InvalidParameterOrArgument, "Invalid  
           username")))?;
            } else {
                self = await!(self.send(Answer::new(ResultCode::UserLoggedIn,  
                &format!("Welcome {}!", content))))?;
            }
  ...