sockets.io emit messages are delayed till post is finished - sockets

Question

I am uploading a file (using multer) and doing some processing on it and i want to show progress while i am working on it. my issue is that the client receives all the updates after the processing is finished. so the progress bar goes from 0 to 100% instead of incrementally updating as the code progresses.
The server side
var multer = require('multer')
var uploading = multer({ dest: 'uploads/' })
app.post('/result', uploading.single('audio'), function(req, res) {
var oldPath = req.file.path;
var newPath = req.file.destination + req.file.originalname;
fs.renameSync(oldPath, newPath)
var ext = newPath.substring(newPath.length-3);
io.emit('message',{'message': 'upload completed !'});
console.log('1st update');
if (ext =='mp3' || ext == 'wav')
{
//console.log('running audio code');
io.emit('update',{'step': 'Converting Audio',percent: 2/10});
audio_code(newPath );
//res.render('Results_Audio', { });
}
else if (ext =='avi' || ext == 'mp4')
{
console.log('run video code');
res.render('Results_Video', { });
}
});
on the client side
socket.on('update',function(data) {
console.log(data);
Update(data);});
function Update(data){
document.getElementById('NameArea').innerHTML = data.step;
console.log(data.percent*100);
document.getElementById('ProgressBar').style.width = data.percent*100 + '%';
document.getElementById('percent').innerHTML = (Math.round((data.percent*100))) + '%';
}

Answer 1

As soon as your post hits the server it will run the block
app.post('/result', uploading.single('audio'), function(req, res) {
...
}
Which means you will immediately get
io.emit('message',{'message': 'upload completed !'});
io.emit('update',{'step': 'Converting Audio',percent: 2/10});
Then you wait while this runs
audio_code(newPath );
Nothing is output.
then when audio_code completes you will get
to the finish.
Are you emitting any progress inside of audio_code ? If not then that's why you get no progress increments.

Answer 2

I solved the issue. switching from socket to primus showed me that since my code was a bit computationally intensive and running synchronously it blocked the server for a time long enough for the websocket to timeout and close. so all i had to do is increase the time allowed for the server to respond to the ping pong check before timing out.