Functions and "onDisconnect", best practices?

[feildmaster]

So I seem to be having a unique issue that no one really expects to run into in cloud functions. reference.onDisconnect has a very sporadic handling in cloud functions, it either works when an error is thrown, or doesn't work until the process decides to randomly exit (maybe?). I don't know. I haven't waited around long enough to find out when it would finally trigger the disconnect.

I suppose I should begin with showing my use case, which is an asynchronous external response handler (wow that's a mouthful).

module.exports = functions.https.onRequest((req, res) => {
  // Start off by reading from the database, telling 
  return root.child(`responses`).once('value').then((value) => {
    // do some value magic, in my case I look for "listeners".
    const listeners = value.val();
    const dataRef = root.child('data');
    dataRef.onDisconnect().remove(); // I want this to be removed on disconnect
    // I then apply the key to the listeners
    listeners.forEach((id) => {
      const key = value.ref.child(`keys/${dataRef.key}`);
      key.onDisconnect().remove();
      key.set(true);
    });
    return dataRef;
  })
  .then((dataRef) => new Promise(() => {
    // By this point I now have at least 2 references waiting to be deleted on disconnect
    // and I want to do some async things
    const waitOnThis = dataRef.child('status');
    // Timeout after 5 seconds, for if something is misconfigured
    setTimeout(() => {exit(504), 5000});
    // Listen for data
    hookStatus.on('value', (snapshot) => {
      if (snapshot.val() === null) return;
      hookStatus.off('value'); // Stop listening so the process can end, I hoped
      exit(snapshot.val());
    });
    function exit(code) {
      res.send(code);
      resolve();
    }
  }))
  // This is the wacky part, Now I either have to go offline/online or do process.exit()
  // in order to trigger the ref.onDisconnect()'s, without throwing an error to exit the process.
  .then(() => {
    // Go offline/online, possibly keep process for later use?
    admin.database().goOffline();
    admin.database().goOnline();
    // Or exit() and possibly have firebase complain about it for some reason
    process.exit();
  });
});

For a working version, please refer to webhooks.js.

I guess what I'm really positing here is:
What is the best way to handle this situation?
What are the repercussions of process.exit()?
Why does the process (potentially) stick around? Does it get reused?

[laurenzlong]

firebase-talk Google group is a better place to ask questions like this: https://groups.google.com/forum/#!forum/firebase-talk