I am trying to use an upload program to upload my files. The code that I use is

app.post('/photos',loadUser, function(req, res) {
  var post = new Post();
  req.form.complete(function(err, fields, files) {
    if(err) {
      console.log(err);
      next(err);
    } else {
      ins = fs.createReadStream(files.file.path);
      ous = fs.createWriteStream(__dirname + '/public/uploads/photos/' + files.file.filename);
      post.filename=files.file.filename;
      post.file=files.file.path;
      util.pump(ins, ous, function(err) {
        if(err) {
          next(err);
        } else {
          post.save(function(err,docs) { 
        req.flash('info', 'information  Saved');
            res.redirect('/photos');
          });
        }
      });
    }
  });
});

When I remove loadUser method everything is working fine, but when I use the loadUser method it is giving me an error. The console information of the error is:

Error: parser error, 0 of 4344 bytes parsed
at IncomingForm.write (/home/darhamid/node_modules/formidable/lib/incoming_form.js:141:17)
at IncomingMessage. (/home/darhamid/node_modules/formidable/lib/incoming_form.js:91:12)
at IncomingMessage.emit (events.js:67:17)
at HTTPParser.onBody (http.js:121:23)
at Socket.ondata (http.js:1349:22)
at TCP.onread (net_uv.js:312:27)

The error is caused only when i use loadUser function, if i remove the loadUser Funciton everything is working fine. I don't know the reason behind this and am stuck. Can anyone help me please?

You are trying to perform database operation before everything, which is creating problems for you. Try the following code:

app.post('/potos', function(req, res, next) {
  //req.form.pause();
  req.form.complete(function(err, fields, files) {
    if(err) {
      next(err);
    } else {
      ins = fs.createReadStream(files.file.path);
      ous = fs.createWriteStream(__dirname + '/public/uploads/photos/' + files.file.filename);
      var post = new Post();
      post.filename=files.file.filename;
      post.file=files.file.path;
      post.created_at = new Date();
      post.user_id = req.session.user_id;

      function postCreationFailed() {
        req.flash('error', 'Unable to Download ');
        res.render('photos/new', {
          locals: {
             post: new Post(),currentUser: req.session.user_id
          }
        });
      }

      util.pump(ins, ous, function(err) {
        if(err) {
          next(err);
        } else { 
                 console.log('\nuploaded %s to %s',  files.file.filename, files.file.path);
                 post.save(function(err) {
                   if (err)
                return postCreationFailed();
                   req.flash('info', 'photos Succesfully Uploaded');
               res.redirect('/user/photos/'+post.user_id);
                });
              }
      });
    }
  });
  req.form.on('progress', function(bytesReceived, bytesExpected){
    var percent = (bytesReceived / bytesExpected * 100) | 0;
    process.stdout.write('Uploading: %' + percent + '\r');
  });

});

Good luck...