Use engine.io

[nicobarray]

We should use engine.io for aquedux-server if their heartbeat behaviour match our needs.

[chabou]

Apparently, we can hook add a handler onheartbeat with SockJS.
This is how Meteor uses it:
meteor/meteor@a1a6414

Current stable sockjs protocol is 3.3.3. Features explained for 0.4.X are not yet implemented : sockjs/sockjs-client#67
https://github.com/sockjs/sockjs-protocol/wiki/Heartbeats-and-SockJS

If it doesn't work as expected, we can temporarily use https://github.com/primus/primus to have some keepalive and reconnection out of the box.