Unable to set headers after sending them to express

Question

I like the general question here. But I could not find a solution on all sides. here is my code: if the line is not empty, then draw the code page, otherwise do another action.

app.get('/send',function(req,res){
  var code=req.query['c']; // -- get request from input
  connection.query("use mynum");
  var strQuery = "select * from table WHERE code='"+code+"' LIMIT 1";   
  connection.query( strQuery, function(err, rows){
    if(err) {
      throw err;
    }else{
      if(rows.length==1){
        res.render('pages/code', {code : rows[0].code});
        connection.end();
        res.end();
      }else {
        // here is some actions
      }
    }
  });
  res.end();
});

stack trace:

Error: Can't set headers after they are sent.
at ServerResponse.OutgoingMessage.setHeader (http.js:690:11)
at ServerResponse.header (C:\wamp\www\vin_number\node_modules\express\lib\re
sponse.js:666:10)
at ServerResponse.res.contentType.res.type (C:\wamp\www\vin_number\node_modu
les\express\lib\response.js:532:15)
at ServerResponse.send (C:\wamp\www\vin_number\node_modules\express\lib\resp
onse.js:121:14)
at fn (C:\wamp\www\vin_number\node_modules\express\lib\response.js:900:10)
at View.exports.renderFile [as engine] (C:\wamp\www\vin_number\node_modules\
ejs\lib\ejs.js:323:3)
at View.render (C:\wamp\www\vin_number\node_modules\express\lib\view.js:93:8
)
at EventEmitter.app.render (C:\wamp\www\vin_number\node_modules\express\lib\
application.js:530:10)
at ServerResponse.res.render (C:\wamp\www\vin_number\node_modules\express\li
b\response.js:904:7)
at Query._callback (C:\wamp\www\vin_number\server.js:102:6)

Answer 1

You send a response twice through res.end(). Get rid of the second, and you will be fine. In addition, the call res.end()after is res.render()redundant, as it res.render()automatically terminates the response with the default result provided.

Answer 2

! , , :

app.use(function(req,res,next){
  var _send = res.send;
  var sent = false;
  res.send = function(data){
    if(sent) return;
    _send.bind(res)(data);
    sent = true;
};
  next();
});