func OnSend(f func(*Request, *Response)) ConnOpt {
	return func(c *Conn) { c.onSend = append(c.onSend, f) }
}
func OnSend(f func(*Request, *Response)) ConnOpt {
	return func(c *Conn) { c.onSend = append(c.onSend, f) }
}
func OnSend ( f func ( * Request , * Response ) ) ConnOpt { return func ( c * Conn ) { c . onSend = append ( c . onSend , f ) } }
// OnSend causes all requests sent on conn to invoke f(req, nil) and
// all responses to invoke f(nil, resp),
OnSend causes all requests sent on conn to invoke f ( req nil ) and all responses to invoke f ( nil resp )