code: func (t *Transport) CloseIdleConnections() {
  	t.lk.Lock()
  	defer t.lk.Unlock()
  	if t.idleConn == nil {
  		return
  	}
  	for _, conns := range t.idleConn {
  		for _, pconn := range conns {
  			pconn.close()
  		}
  	}
  	t.idleConn = make(map[string][]*persistConn)
  }
docs: // CloseIdleConnections closes any connections which were previously
  // connected from previous requests but are now sitting idle in
  // a "keep-alive" state. It does not interrupt any connections currently
  // in use.