How to get notified on unsubscribe / drop connection

[xlc]

jsonrpsee/core/src/server/rpc_module.rs

Line 828 in dab1bfc

close_notify: Option<SubscriptionPermit>,

I can't find any public API to expose this to allow me cleanup resources on drop connection. Also no public API to notify unsubscribe as well.

[niklasad1]

There is only

jsonrpsee/core/src/server/rpc_module.rs

Line 1044 in dab1bfc

pub fn is_closed(&self) -> bool {

,

I guess we could have an async fn closed I have added that in a pending PR to add backpressure.

Thus, it's on it's way but I you use pipe_from_stream it will return once the subscription is closed but assuming you need more low-level API.

[lexnv]

An alternative to that, depending on your use-case, would be to interact with the subscription.

Let's presume the client has disconnected or called the unsubscribed method.
Presume the server doesn't use the is_closed or any other future to detect the disconnect, then the server will eventually try to submit a message to the subscription. This is where the server receives Ok(false) as a result of that action.

jsonrpsee/core/src/server/rpc_module.rs

Lines 893 to 900 in dab1bfc

	/// Send a message back to subscribers.
	///
	/// Returns
	/// - `Ok(true)` if the message could be send.
	/// - `Ok(false)` if the sink was closed (either because the subscription was closed or the connection was terminated),
	/// or the subscription could not be accepted.
	/// - `Err(err)` if the message could not be serialized.
	pub fn send<T: Serialize>(&mut self, result: &T) -> Result<bool, serde_json::Error> {

To that regard, there is also this suggestion in discussion: #944, which would make things a bit more explicit to the user. Currently, you can shoot yourself in the foot with a code of those lines:

loop {
  match s.send() {
    Ok(_) => // if it is false, then we should stop.
  ..
}}

[xlc]

My use case is a JSON RPC proxy that forwards subscriptions to upstream server. So I will want to unsubscribe from upstream as soon as the downstream disconnect/unsubscribe.

So I don't want to use the sync closed method because when should I check it? and dont' want to only drop subscription on failed to send because that will just be a waste of resources on both proxy server and upstream server.

[niklasad1]

Yeah, that makes sense we should provide an async function that returns once this connection is closed or subscription is canceled.

It's useful for folks to build their own async primitives instead of using pipe_from_stream

My PR #962 will enable that.

[niklasad1]

Closed by #962

We have now introduced SubscriptionSink::closed that notifies once the subscription is closed.