cookie.go
func (c *Cookie) Expire() time.Time {
	expire := c.expire
	if expire.IsZero() {
		expire = CookieExpireUnlimited
	}
	return expire
}
func (c *Cookie) Expire() time.Time {
	expire := c.expire
	if expire.IsZero() {
		expire = CookieExpireUnlimited
	}
	return expire
}
// Expire returns cookie expiration time.
//
// CookieExpireUnlimited is returned if cookie doesn't expire