Are clients notified when a subscription task exists?

[SuperFluffy]

I am writing some tests to ensure my client task reconnects if a jsonrpc subscription is dropped (I am ignoring the websocket going down for now and am just focusing on the subscription ending).

Does jsonrpsee have a mechanism to notify subscribers that the server closed the subscription? Or is that just not a thing? I was looking through the code but couldn't find anything.

For reference, this is the code where the self.command is a broadcast channel held by the server that is used to end the subscription task:

impl GethServer for GethImpl {
    async fn eth_subscribe(
        &self,
        pending: PendingSubscriptionSink,
        subscription_target: String,
        full_txs: Option<bool>,
    ) -> SubscriptionResult {
        use jsonrpsee::server::SubscriptionMessage;
        tracing::debug!("received eth_subription request");

        assert_eq!(
            ("newPendingTransactions", Some(true)),
            (&*subscription_target, full_txs),
            "the mocked geth server only supports the `eth_subscribe` RPC with
            parameters [\"newPendingTransaction\", true]",
        );
        let sink = pending.accept().await?;
        let mut rx = self.command.subscribe();
        loop {
            tokio::select!(
                biased;
                () = sink.closed() => break,
                Ok(cmd) = rx.recv() => {
                    match cmd {
                        SubscriptionCommand::Abort => {
                            tracing::debug!("abort command received; exiting eth_subscription");
                            break;
                        }
                        SubscriptionCommand::Send(tx) => {
                            let _ = sink.send(SubscriptionMessage::from_json(&tx)?).await?;
                        }
                    }
                }
            );
        }
        Ok(())
    }
}

EDIT: I can see that there used to be a function SubscriptionSink::close_with_error, but it seems to have been removed in the meanitme? #1013

[SuperFluffy]

After looking through the git history I found this PR: #1034

So the solution is to return an Err("reason".into()) as the SubscriptionResult in the handler instead of explicitly closing the connection as was done before, bascially this:

                        SubscriptionCommand::Abort => {
                            tracing::debug!("abort command received; exiting eth_subscription");
                            break Err("abort command received".into());
                        }

[niklasad1]

Yeah, we tried to explain it https://github.com/paritytech/jsonrpsee/blob/master/CHANGELOG.md#subscription-api-is-changed.

If your subscription method returns Result<(), Err> then the String impl of "Err" will be used in the "error field" or implement IntoSubscriptionCloseResponse for your own type for a customized behavior.