Node JS - How Can You Tell If A Socket Is Already Open With The Einaros WS Socket Module?
asynchronous, events, javascript, node.js, websocket
Solution
`socket.readyState` will tell you what the socket thinks its state is. There is no other, more accurate property that you can consult than `socket.readyState`.
If what you want to know is when the socket has finished connecting and is now considered open, then you can register an event handler for the `open` event. This will tell you when it has finished connecting.
If you want a real-time notification when the socket closes or experiences an error, you can use an event listener for the `error` or `close` events. The `close` event just means that socket is closing and the `socket.readyState` value is now changing to closed.
A more guaranteed to be up-to-date method of checking the socket is to first check `socket.readyState` and, if that says the socket is open, then you can send a test packet to the other end and only when you get a response back from the test packet will you truly know that socket is operational.
The `socket.io` library (built on top of webSockets) does exactly this, sending regular keep-alive packets and listening for responses. If it goes some period of time with no response, then it will close the existing socket and attempt to re-establish a new connection (figuring the prior connection was lost somehow). In this way, the `socket.io` library can even survive a server reboot or a temporary drop in client internet connectivity as it will see that the connection was lost and then transparently re-establish a new connection in its place.
Problem
I'm currently using einaros' NodeJS WS module to create a websocket client. When initializing the socket client, I use the 'open' event to determine when the connection is open, but once it's open, how would I be able to check if it's still open? Is there a property on the 'WebSocket' object that I can use to quickly check the status of the socket? Is - websocketInstance.readyState - adequate?