Cannot catch EADDRINUSE from server.start()

[mik01aj]

When I try to call server.start(callback), and the port is in use, the script crashes with a message:

events.js:72
        throw er; // Unhandled 'error' event
              ^
Error: listen EADDRINUSE
    at errnoException (net.js:904:11)
    at Server._listen2 (net.js:1042:14)
    at listen (net.js:1064:10)
    at net.js:1146:9
    at dns.js:72:18
    at process._tickCallback (node.js:419:13)

I would expect the callback to be called instead (with the error, of course).

[hueniverse]

We don't wrap everything in try..catch code. Only place throws are handled is in userland code called as part of request processing so that we can return a 500 page.

[mik01aj]

Well, if you don't handle errors well, then I doubt whether it's safe to use hapi in production.

EADDRINUSE is an error to be expected in the listen function and handling it is as simple as adding the callback to the listen call. The documentation even provides a detailed example on how to do this.

[ghost]

Can't you just check the exit status ($?) in your init script?

[mik01aj]

@jzorn I use forever to restart the API, to be on the safe side.

But still, letting the application crash is a bug to me. You don't know anything about the application's open database transactions, half-written files and other ongoing operations. Hapi is just a library and it should not crash the process without an important reason. And if in your opinion it's still ok, then the documentation should tell Hapi users something like:

if the connection port happens in use, your whole application will crash and you have no way to handle it.

[edimoldovan]

I am not sure I follow the reasoning behind the need to handle the EADDRINUSE at startup. It apears only at startup, right? At least I only saw it there. If this is the case, then you basically don’t have any database connections which are in use yet, because nobody could connect to the app due it failing to start.
What am I missing here?

[ghost]

Can't you use forever's -m switch and use $? I also don't think that the application crashes when it's throwing the EADDRINUSE — it refuses to start, right? That's pretty much exactly what every other service will do, e.g. superstatic.

[hueniverse]

@mik01aj If you rely on EADDRINUSE errors in production code, you have bigger problems. I have never seen an app that tries to resolve that in production. You production setup must ensure a proper port is configured and that no multiple instances are running at the same time. This is clearly not the framework's job.

In general, we cannot possibly handle every exception every function might throw. Node has made a choice to throw in async methods when the basic inputs are wrong, even when a callback is provided.

I am happy to take a pull request that states simply that the method may throw and give this as an example.

[kanongil]

EADDRINUSE is an error to be expected in the listen function and handling it is as simple as adding the callback to the listen call. The documentation even provides a detailed example on how to do this.

This is wrong. The callback is never called on errors. The only way to catch the error, is to add an error listener to the object listen is called on.

@hueniverse I agree on your point regarding relying on EADDRINUSE errors, however I am not sure I agree on the hands off approach you are pursuing in this case.

This is not a matter of adding try..catch but rather of respecting the api of the listen() call, which will either emit a listening, or an error event on the listener. You handle one case but ignore the other, which triggers the OMG no error listener! throw behavior.

Note that this issue will also trigger on this (with another error):

var server = new Hapi.Server();
server.connection({ host: 'does.not.resolve' });
server.start(function (err) {});

[hueniverse]

@kanongil fair enough. I'll take a PR.