问socket.handshake无法获得会话

EN

io.use(function(socket, next){
    signedCookieParser(socket.request, null, function(err){
        if(err){
            console.log('err parse');
            return next(new Error("cookie err"));
        }
        var connect_sid = socket.request.signedCookies['connect.sid']
        console.log('connect_sid'+connect_sid);
        if (connect_sid) {
         //通过cookie中保存的session的id获取到服务器端对应的session
             sessionStore.load(connect_sid, function(error, session){
                if (error) {
                    return next(new Error('Authentication error'));
                }
                else {
                    // save the session data and accept the connection
                    socket.request.session = session;
                    next();
             }
         });
     }
    })
})

io.sockets.on('connection', function(socket){
    var session = socket.handshake.session;  //undefined
}