process.nextTick（function（）{throw err;}）;エラー：送信後にヘッダーを設定できません

Node.jsファイルのMongoDBからデータを取得しようとしています。
私はこのエラーを取得しています：process.nextTick（function（）{throw err;}）;エラー：送信後にヘッダーを設定できません

/home/jay/node_project/user_data_manag/node_modules/mongodb/lib/utils.js:98
process.nextTick(function() { throw err; });

Error: Can't set headers after they are sent.
at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:335:11)
at ServerResponse.header (/home/jay/node_project/user_data_manag/node_modules/express/lib/response.js:719:10)
at ServerResponse.json (/home/jay/node_project/user_data_manag/node_modules/express/lib/response.js:247:10)
at ServerResponse.send (/home/jay/node_project/user_data_manag/node_modules/express/lib/response.js:152:21)
at /home/jay/node_project/user_data_manag/routes/api.js:42:13
at /home/jay/node_project/user_data_manag/node_modules/mongodb/lib/cursor.js:777:7
at handleCallback (/home/jay/node_project/user_data_manag/node_modules/mongodb/lib/utils.js:96:12)
at /home/jay/node_project/user_data_manag/node_modules/mongodb/lib/cursor.js:741:16
at handleCallback (/home/jay/node_project/user_data_manag/node_modules/mongodb/lib/utils.js:96:12)
at /home/jay/node_project/user_data_manag/node_modules/mongodb/lib/cursor.js:675:5

// Dependencies 
var express = require('express'); 
var router = express.Router(); 
var mongo = require('mongodb').MongoClient; 
var objectId = require('mongodb').ObjectID; 
var assert = require('assert'); 

var url = 'mongodb://localhost/rest_test'; 


router.post('/user', function(req, res, next) { 
    if (req.body.name == "Login") { 
    var result = []; 
    mongo.connect(url, function(err, db) { 
     var data = db.collection('products').find(); 
     data.forEach(function(doc, err) { 
     result.push(doc); 
     }, function() { 
     db.close(); 
     res.send({ 
      iteamd: result 
     }); 
     }); 
    }); 
    } else { 
    res.send("data"); 
    } 
    res.end(); 
}); 

//insert data 
router.post('/put-data', function(req, res, next) { 

    var item = { 
    title: req.body.name, 
    content: req.body.sku, 
    author: req.body.price 
    }; 
    var data = req.body.name; 

    mongo.connect(url, function(err, db) { 
    var cursor = db.collection('products').find({ 
     "name": data 
    }); 
    res.send(cursor.toString); 
    }); 

}); 


// Return router 
module.exports = router;

出典

2016-10-05 Chaudhary Jayesh