code: func (c *Characteristic) SetValue(b []byte) {
  	if c.ReadHandler != nil {
  		panic("charactristic has been configured with a read handler")
  	}
  	c.Property |= CharRead
  	c.Value = make([]byte, len(b))
  	copy(c.Value, b)
  }
docs: // SetValue makes the characteristic support read requests, and returns a static value.
  // SetValue must be called before the containing service is added to a server.
  // SetValue panics if the characteristic has been configured with a ReadHandler.