I keep reading about ping/pong messages in websockets to keep the connection alive, but I’m not sure what they are. Is it a distinct frame type? (I don’t see any methods on a javascript WebSocket object in chrome related to ping-pong). Or is it just a design pattern (e.g. I literally send "ping" or any other string to the server and have it respond). Is ping-pong at all related to continuation frames?
The reason I ask is I’m using a python framework that runs behind Mongrel2, so I’m wondering if there’s a way to send Mongrel2 a specific ping/pong message that would tell it to keep the connection alive without my python app needing to worry about it. Analogous to a having a separate HTTP method for it, I guess. And I imagine a dedicated ping/pong message frame could be simpler (less load on server and network) than the string "ping", though that probably wouldn’t matter too much.
EDIT: I just looked at RFC 6455 and it looks like Ping and Pong are definitely control frame types with their own opcodes. So how do I send a Ping frame from javascript in Chrome?
There is no Javascript API to send ping frames or receive pong frames. This is either supported by your browser, or not. There is also no API to enable, configure or detect whether the browser supports and is using ping/pong frames. There was discussion about creating a Javascript ping/pong API for this. There is a possibility that pings may be configurable/detectable in the future, but it is unlikely that Javascript will be able to directly send and receive ping/pong frames.
However, if you control both the client and server code, then you can easily add ping/pong support at a higher level. You will need some sort of message type header/metadata in your message if you don’t have that already, but that’s pretty simple. Unless you are planning on sending pings hundreds of times per second or have thousands of simultaneous clients, the overhead is going to be pretty minimal to do it yourself.