Express middleware "connect-timeout" causes "Can't set headers after they are sent."

Question

My code:

timeout = require('connect-timeout')

app.get('/', timeout('5s'), function(req, res){
  ##DO SOMETHING 1
  ##DO SOMETHING 2
  ##DO SOMETHING 3
  res.send('ok'); ##line 7
});

When user requesting. Node.js processes "DO SOMETHING1-3". But before it processed. Timeout middleware response because it has been set for 5 seconds. After that in line 7 routing try to response again. And Its causes Error "Can't set headers after they are sent."

How to handle the problem ?

Answer 1

I had a feeling this would be a common problem, so I searched the GitHub repository and found this issue.

In this answer, I will outline the two possible solutions proposed in the issue I linked above:

1. You could check to see if the request has timed out via the req.timedout property before calling res.send:

   app.get('/', timeout('5s'), function(req, res){
     ##DO SOMETHING 1
     ##DO SOMETHING 2
     ##DO SOMETHING 3
     if (!req.timedout) {
       res.send('ok'); ##line 7
     }
   });
   

2. Or you could mount some top-level middleware which effectively suppresses the error:

   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();
   });