golang实现的交互shell

func copyConn(readConn, writeConn *websocket.Conn, readClosed, writeClosed chan struct{}) {  var rerr error  for {    var r io.Reader    var messageType int    messageType, r, rerr = readConn.NextReader()    if rerr != nil {      break    }    w, err := writeConn.NextWriter(messageType)    if err != nil {      break    }    if _, err := io.Copy(w, r); err != nil {      break    }    if err := w.Close(); err != nil {      break    }  }  // Close the reading connection. If we broke out of the loop because of a  // normal close, then NextReader echoed the close message and we should now  // close the connection.  If it's an abnormal close, then we should give up  // and close the connection.  readConn.Close()  // Tell the other goroutine that readConn was closed.  close(readClosed)  // Did we break out of the loop because we received a close message?  if e, ok := rerr.(*websocket.CloseError); ok && e.Code != websocket.CloseAbnormalClosure {    // Forward the close message to writeConn.    var m []byte    if e.Code != websocket.CloseNoStatusReceived {      m = websocket.FormatCloseMessage(e.Code, e.Text)    }    err := writeConn.WriteMessage(websocket.CloseMessage, m)    // Did we successfully send the close message?    if err == nil {      // Wait with timeout for the other goroutine to handle the handshake.      select {      case <-writeClosed:        // The other goroutine closed writeConn.        return      case <-time.After(10 * time.Second):      }    }  }  // A blocked reader returns with an error when the connection is closed.  writeConn.Close()}