DataLab UI creating duplicate socket.io connection to server

[drewbryant]

Found during end-to-end testing that the client/UI will open a second socket.io connection to the server under some circumstances. Not clear on mechanism/trigger for this yet, as Angular is expected to managed the socket.io connection singleton for a given page (and enforce that only a single instance exists at any given point in time).

[drewbryant]

After digging into this a bit more, it turns out there is only a single socket.io connection between client-server (good) and that the issue is with socket.io firing duplicate connect and disconnect events. The duplicate connect events cause a socket.io connection to be added a second time to the session (causing the session to see two separate connections instead of one).

Found some reports in the wild of others seeing this issue with socket.io (socketio/socket.io#430, socketio/socket.io#474).

Simple fix for this is to make the server robust to multiple connect / disconnect events for a given socket.io connection; the socket.io connection maintains an id attribute that can be used to uniquely identify each socket.io connection.

[drewbryant]

Addressed by #354