sdk: Client ping on idle connections #2309
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kim
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Feb 26, 2025
Make the websocket loop send a `Ping` frame when the connection is idle for a while. "idle" includes missing server-side pings. Writing to the socket will detect if the remote end went away, but FIN / RST went missing for some reason. This is not detected by only reading.
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gefjon
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Feb 26, 2025
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After out-of-band discussion, we've decided we'd like to include this in the 1.0 release if possible, though if it can't go in we won't be too disappointed. It seems low-risk, and will improve visibility for networking failures, particularly in SpacetimeDB-cloud. |
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Feb 26, 2025
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Sorry, just realized: the host doesn't actually respond Pong to client Pings. crates/client-api/src/routes/subscribe.rs has:
Item::Message(ClientMessage::Ping(_message)) => {
log::trace!("Received ping from client {}", client.id);
// TODO: should we respond with a `Pong`?
}I don't think we can merge this until we complete that TODO comment. I'm worried that as-is, this patch will cause spurious disconnects.
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Nope, I'm wrong. Per this discussion, Tungstenite responds Pong to Pings automatically.
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Make the websocket loop send a
Pingframe when the connection is idle for a while. "idle" includes missing server-side pings.Writing to the socket will detect if the remote end went away, but FIN / RST went missing for some reason. This is not detected by only reading.
I haven't touched the scary server-side websocket loop, but we may consider to also make it send pings only if it doesn't have anything else to send.
Expected complexity level and risk
2
Testing
The situation can be approximated by inducing a 100% packet loss scenario.
This can be done in various ways. A convenient one is
docker compose disconnect, which disables the virtual interface of a container.Without this patch, you'll see the server timing out the connection after a while (as it did not receive pong), while the client keeps thinking that something may eventually arrive.
With this patch, both ends eventually close the connection.