type Conn struct {
	wc    io.WriteCloser
	tasks sync.WaitGroup
	// ... other internal state ...
}

func NewConn(rwc io.ReadWriteCloser) *Conn {
	c := &Conn{wc: rwc}
	c.tasks.Add(1)
	go func() {
		defer c.tasks.Done()
		c.receive(rwc)
	}()
	return c
}

func (c *Conn) receive(r io.Reader) {
	for {
		msg, err := decode(r)
		if err != nil {
			return
		}
		// ... Process message ...
	}
}

func (c *Conn) Close() error {
	err := c.wc.Close()
	c.tasks.Wait()
	return err
}