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Add a limit to the maximum number of chainHead_unstable_follow subscriptions #962

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merged 2 commits into from
Jul 26, 2023
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Add a limit to the maximum number of chainHead_unstable_follow subscriptions #962

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Add a limit to the maximum number of `chainHead_unstable_follow` subs…
tomaka Jul 26, 2023
f351d3c
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tomaka Jul 26, 2023
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35 changes: 26 additions & 9 deletions light-base/src/json_rpc_service/background/chain_head.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -95,6 +95,32 @@ impl<TPlat: PlatformRef> Background<TPlat> {
unreachable!()
};

let (mut subscription, rx) = {
let mut lock = self.chain_head_follow_tasks.lock().await;

// As mentioned in the spec, the JSON-RPC server accepts 2 or more subscriptions per
// JSON-RPC client. We choose to accept only exactly 2 in order to make sure that
// JSON-RPC client implementations are made aware of this limit. This number of 2 might
// be relaxed and/or configurable in the future.
if lock.len() >= 2 {
log::warn!(
target: &self.log_target,
"Rejected `chainHead_unstable_follow` subscription due to limit reached."
);
request.fail(json_rpc::parse::ErrorResponse::ApplicationDefined(
-32100,
"Maximum number of `chainHead_unstable_follow` subscriptions reached",
));
return;
}

let (tx, rx) = service::deliver_channel();
let subscription = request.accept();
lock.insert(subscription.subscription_id().to_owned(), tx);
(subscription, rx)
};
let subscription_id = subscription.subscription_id().to_owned();

let events = if with_runtime {
let subscribe_all = self
.runtime_service
Expand All @@ -106,15 +132,6 @@ impl<TPlat: PlatformRef> Background<TPlat> {
either::Right(self.sync_service.subscribe_all(32, false).await)
};

let (mut subscription, rx) = {
let (tx, rx) = service::deliver_channel();
let mut lock = self.chain_head_follow_tasks.lock().await;
let subscription = request.accept();
lock.insert(subscription.subscription_id().to_owned(), tx);
(subscription, rx)
};
let subscription_id = subscription.subscription_id().to_owned();

let (non_finalized_blocks, pinned_blocks_headers, events) = {
let mut pinned_blocks_headers =
HashMap::with_capacity_and_hasher(0, Default::default());
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4 changes: 4 additions & 0 deletions wasm-node/CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,10 @@

## Unreleased

### Changed

- A JSON-RPC error is now returned if the JSON-RPC client tries to open more than two simultaneous `chainHead_unstable_follow` subscriptions, in accordance with the latest changes in the JSON-RPC API specification. ([#962](https://github.com/smol-dot/smoldot/pull/962))

## 1.0.13 - 2023-07-16

### Added
Expand Down