错误：无法设置头发送之后。当自动重新连接到MongoDB的

Question

我收到以下错误：

Error: Can't set headers after they are sent. 
       at ServerResponse.OutgoingMessage.setHeader (http.js:708:11) 
       at ServerResponse.res.setHeader (/home/rahul/workspace1/iranproud/node_modules/express/node_modules/connect/lib/patch.js:63:22) 
       at next (/home/rahul/workspace1/iranproud/node_modules/express/node_modules/connect/lib/proto.js:156:13) 
       at next (/home/rahul/workspace1/iranproud/node_modules/express/node_modules/connect/lib/middleware/session.js:318:9) 
       at /home/rahul/workspace1/iranproud/node_modules/express/node_modules/connect/lib/middleware/session.js:342:9 
       at /home/rahul/workspace1/iranproud/node_modules/connect-mongo/lib/connect-mongo.js:220:17 
       at /home/rahul/workspace1/iranproud/node_modules/connect-mongo/node_modules/mongodb/lib/mongodb/collection.js:953:5 
       at Cursor.nextObject (/home/rahul/workspace1/iranproud/node_modules/connect-mongo/node_modules/mongodb/lib/mongodb/cursor.js:678:5) 
       at commandHandler (/home/rahul/workspace1/iranproud/node_modules/connect-mongo/node_modules/mongodb/lib/mongodb/cursor.js:658:14) 
       at Server.Base._callHandler (/home/rahul/workspace1/iranproud/node_modules/connect-mongo/node_modules/mongodb/lib/mongodb/connection/base.js:382:41)

我的配置如下：

我使用的连接 - 蒙戈的会话存储，并自动重新连接是真实的，即。

app.use(express.session({

 store: new MongoStore({
        url: 'mongodb://192.168.1.104:27017/db_ip',
        auto_reconnect:true

    }, function(e) {
        //code
    }),
    cookie: {
        expires: new Date(Date.now() + 7200000)
    },    
    secret: '*********'
}));

我通过手动停止mongod的服务测试此代码和URL请求，它是在（连续浏览器中运行，直到它被连接到数据库）等待状态，所以我一直对请求超时下面的代码（后4其次，它会在维护页面重定向到）。

app.use(function(req, res, next){

    res.setTimeout(4000, function(){
        console.log('Request has timed out.');

        var fullURL = req.protocol + "://" + req.get('host') + req.url;
        var client_ip = req.connection.remoteAddress;
        console.log("\nRequested Url is : " + fullURL + " :: From IP Address : " + client_ip + " : on date : " + new Date()); 
         res.render('undermaintenance');
        });

   next();

});

但是当我重新启动的mongod它会自动连接到数据库和网站工作，但在控制台中我得到这个错误：

Error: Can't set headers after they are sent.

Answer 1

我在想什么是，1 - 下一个被调用，响应被发送到客户端，但2-- 4秒钟后，你要发送res.render（）..这也得到呼吁。没有看到完整的代码我不知道如何帮助你。

app.use(function(req, res, next){



    res.setTimeout(4000, function(){
        console.log('Request has timed out.');

        var fullURL = req.protocol + "://" + req.get('host') + req.url;
        var client_ip = req.connection.remoteAddress;
        console.log("\nRequested Url is : " + fullURL + " :: From IP Address : " + client_ip + " : on date : " + new Date()); 
         res.render('undermaintenance'); // ---2

        });

   next(); ---> 1


});

Answer 2

每当你看到一个有关的事实，你不能发送头两次的消息，这意味着你要发送一个特定的HTTP请求的响应不止一次。你的代码（或依赖）的某些部分已经发送的响应。检查所有自定义的中间件，并确保在res.setTimeout()回调不执行每一次，即使是非常超时后。