Socket.IO Server Runtime Error/Exception - node.js

Question

I have this code in a file named server.js:
var app = require('express')();
var server = require('http').createServer(app);
var io = require('socket.io')(server);
io.on('connection', function(){
console.log("a client connected");
});
server.listen(80);
When i run node server.js in the terminal (cmd), it throws this error:
events.js:72
throw er; // Unhandled 'error' event
^
Error: listen EACCES
at errnoException (net.js:904:11)
at Server._listen2 (net.js:1023:19)
at listen (net.js:1064:10)
at Server.listen (net.js:1138:5)
at Object.<anonymous> (C:\inetpub\wwwroot\socketio\server.js:9:8)
at Module._compile (module.js:456:26)
at Object.Module._extensions..js (module.js:474:10)
at Module.load (module.js:356:32)
at Function.Module._load (module.js:312:12)
at Function.Module.runMain (module.js:497:10)
Do you have an idea of what could be the problem? Thanks!
Note: I already have socket.io and express installed.

Answer 1

It seems you are not allowed to open a serversocket on port 80.
See this line in the error message
C:\inetpub\wwwroot\socketio\server.js:9:8
Socket addresses smaller than 1024 are reserved for system use. Try this:
var app = require('express')();
var server = require('http').createServer(app);
var io = require('socket.io')(server);
io.on('connection', function(){
console.log("a client connected");
});
server.listen(3000);

Answer 2

Looks like the port 80, is invalid or unacceptable. I tried to change it to another port (8000) and it worked.
server.listen(8000);
The exception is gone. I hope I can find a way to distinguish between valid/invalid ports at run-time.