router.post('/post', function(req,res){
    var currentUser = req.session.user;
    var post = new Post(currentUser.name, req.body.post);
    post.save(function(err){
        if(err){
            req.flash('error', err);
            return res.redirect('/');
        }
    req.flash('success', 'post success.');
    res.redirect('/u/'+ currentUser.name);
    });
});

用 bluebird 该怎么写呢， bluebird的api看的有点糊涂 new Promise(function(function resolve, function reject) resolver) -> Promise