Most server-side-scripting languages have an exec function (node, php, ruby, etc). This allows the programming language to interact with the shell.
I wish to use exec() in node.js to run large processes, things I used to do with AJAX requests in the browser. I would like a simple progress / loading bar to display to the user the progress.
I found out the hard way in the example below that the callback / asynchronous nature of the exec function will make this example take over 5 seconds to load.
What I want is some way to get the content of browser to be updated (ajax) with the current state of the execution like a loading bar. But I don't want the ran file to be dependent on the browser.
Any idea?
my route
exports.exec = function(req,res){
// http://nodejs.org/api.html#_child_processes
var sys = require('sys')
var exec = require('child_process').exec;
var child;
child = exec("node exec/test.js", function (error, stdout, stderr) {
var o = {
"error":error,
"stdout":stdout,
"stderr":stderr,
};
o = JSON.stringify(o);
res.send(o);
});
};
my test.js file
var sys = require('sys');
var count = 0;
var interval = setInterval(
function(){
sys.print('hello'+count);
count++
if(count == 5){
clearInterval(interval);
}
},
1000);
You should use socket.io for this. Here is a demo app to get you started with socket.io
You emit an event for every 1% using socket.io, the browser listen to it and update a bar.
You can't use exec you need a streamed output.
Therefore you'd rather use child_process.
On the server.
var spawn = require('child_process').spawn,
exec = spawn('node exec/test.js');
exec.stdout.on('data', function (message) {
socket.emit('process', message);
});
On the sub process:
console.log('10%')
// ...
console.log('20%')
// ...
console.log('30%')
If your sub process is a node script you could do something a lot more elegant. Rather than having to talk with a stream stdout you could use the cluster module of node to send messages between the master and the slaves process.
I made a fork of the previous demo app adding a route /exec which demonstrate how to achieve this.
When I'll have more time I'll make another demo app, this is a quite interesting and educational test. Thanks for the idea :D.