Proposed check for port already in use

[rkulla]

When express.js generates app.js to start the Express server on a port (default 3000), it throws an exception if the port is already in use. So instead, the error could be caught with the following check and produce a more descriptive error message, by changing:

http.createServer(app).listen(app.get('port'), function(){
  console.log("Express server listening on port " + app.get('port'));
});

to:

server = http.createServer(app);
server.once('error', function(err) {
  if (err.code == 'EADDRINUSE') {
    console.log(err.code + ': ' + app.get('port') + ' already in use');
  }
});
server.listen(app.get('port'), function(){
  console.log("Express server listening on port " + app.get('port'));
});

[tj]

EADDRINUSE is pretty descriptive IMO, even if it's just an all caps errno, any changes to make things more descriptive should be in node core, I'd love to actually patch node to display things like EADDRINUSE: http://localhost:3000 is already in use, when you have a lot of services running it can get pretty difficult to see what failed

[tj]

@isaacs do you think it would be reasonable to add something like ^ that in core? similar to the original patches to show the filename of file related errors I think this would help quite a bit

[isaacs]

Yeah, we could add something helpful there, like the port/host/path you passed to listen(). Patch welcome.

[tj]

@isaacs cool thanks for the confirmation I'll send a patch when I have a minute