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Is there a way to handle the `close` frame received via a websocket connection?
Or is listening to exception the only way to do that (not ideal since I don't listen to frames I just emit them, maybe the `ClosedSendChannelException` works for that but it's not mentioned in the docs)

You can either catch the `CancellationException` and `ClosedSendChannelException`  in a WebSockets handler or use raw WebSockets to manually send and receive the close frames.

When do these exceptions get thrown precisely?

The `CancellationException` is thrown when the channel for outgoing frames is cancelled after receiving a close frame.

<https://github.com/ktorio/ktor/blob/1cf4dc84a88a125205c0c41a25df153489798e35/ktor-http/ktor-http-cio/jvm/src/io/ktor/http/cio/websocket/DefaultWebSocketSessionImpl.kt#L164|https://github.com/ktorio/ktor/blob/1cf4dc84a88a125205c0c41a25df153489798e35/ktor-[…]m/src/io/ktor/http/cio/websocket/DefaultWebSocketSessionImpl.kt>