Improving connect promise handling

[palavrov]

A buggy device was closing the socket immediately without sending any data to be parsed so the promise was never resolved or rejected i.e. effectively deadlocking i.e. endless await telnetClinet.connect()

This PR fixes just connect method but probably other methods (send, exec, etc) needs to be fixed too.

Generally the problem comes because the underlying socket API is event based and doesn't go well with promises. Another problem comes due lack of control to socket.timeout i.e. we can't cancel it. In overall error handling is really messy and unstable. I did my best with this patch to improve but probably will be better to rewrite everything in a better way.

[mkozjak]

Hey, @palavrov, thanks for the PR. Please check if the tests pass. Something with tests exit code is not right currently so the travis seems to pass, but has stderr. Sorry about that! #135

[palavrov]

Everything seems OK.

The test warns but there is nothing wrong because it is using event based API not the promise one i.e. there is no one to consume the rejected promise which is wrong but totally expected by design.

Probably it was just luck that non handled rejections didn't occur early in the tests ... I got them all the time with telnet-client.

As said above - mixing events with promises needs better implementation.

I think we have several choices:

• to adapt the tests to handle the promise rejection
• to try to guess run time when the connection is event mode and to avoid all promises ... that will be ugly and may be not possible at all
• to separate the implementation to event based and promise based - IMHO the best way to go but will needs significantly more efforts

[palavrov]

Seems that it'll be possible to detect when someone doesn't use the promise to prevent rejections but it will be really ugly. Bluebird has nice feature for promise monitoring so we could use promiseChained event to know when someone uses .then() and probably await ... but really don't like such quick'n'dirty approach

[mkozjak]

@palavrov Ok, looks good for now! Can you please remove semicolons and add some newlines before your if statements? Just general code convention. Merging after that one.

[palavrov]

Done!

[mkozjak]

lgtm