Option to periodicaly ping idle websockets to keep proxies happy

[takluyver]

We have a mixin class in Jupyter which primarily adds periodic pinging to a websocket handler. This is useful when websockets are used behind proxies, as some proxy servers will kill the connection if it's unused for a set amount of time - 60 seconds in nginx (see #1070).

This seems like a generally applicable bit of functionality for websockets. Are you interested in including it in tornado? I imagine that this would be disabled by default, but could be enabled by a setting websocket_ping_interval. I am happy to work on this if you think it's in scope for tornado.

[bdarnell]

Yes, I think it's a good idea. It's a common need, and it's useful both for keeping proxies from shutting down the connection and for quicker detection of dropped connections.

From a quick look at the linked code, my one quibble with Jupyter's implementation is that I prefer to specify intervals in either floating-point seconds or timedelta objects instead of milliseconds (with some legacy exceptions notably including PeriodicCallback).

[awong1900]

Yes, very useful. I have a question, can add method ping() on WebSocketClientConnection class?

[takluyver]

The server side of the pinging is awaiting review in #1642. :-)