Resolve subscription.close() once streams have been flushed.

After using the pub/sub client for test, I have found that I wanted to know when the queue was flushed before exiting. The comment in the code states that a promise is returned when no callback is provided: https://github.com/googleapis/nodejs-pubsub/blob/master/src/subscription.js#L377 but the code does not return a promise.

Environment details

• OS: OSX
• Node.js version: 8.6.0
• npm version: 5.3.0
• @google-cloud/pubsub version: 0.16.2

Steps to reproduce

1. Open a subscription
2. Close a subscription with no callback.
3. Execute .then() on the promise from the subscription close method.

Expected: the callback in the .then() is executed. Actual: Error calling .then on undefined.

I have completed a fix with a test here: https://github.com/STeveShary/nodejs-pubsub/commit/2bf9c33f92bd43f1020f5467c58c48a796348309 . Your contribution guide doesn’t recommend a PR yet, but I can create one quickly.

[callmehiphop]

Ah, I see. In most cases that queue isn’t actually used. Its primary function is to act as a backup in case we’re unable to make a streaming connection. I’d need to investigate a bit more, but it might be possible to implement a flush (or similar) event to listen to.

[callmehiphop]

@STeveShary we’ve got a fix prepared for this (#92) if you have the bandwidth to test it out that would be fantastic! Otherwise we should have it released within the next day or two.