Block import notification for literally every imported block even when the chain is not synced to the tip

[liuchengxu]

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Description of bug

I'm looking for a block import notification that is fired on every imported block, the existing client.import_notification_stream() is fired only when on the tip or there is a re-org.

substrate/client/service/src/client/client.rs

Lines 774 to 775 in dfc9223

	// We only notify when we are already synced to the tip of the chain
	// or if this import triggers a re-org

In subspace, we have the consensus chain and execution chain, the execution chain is entirely driven by the consensus chain. Each domain block is derived from a consensus block in a deterministic way, we need a block notification of every single consensus block to build the execution chain accordingly even if the consensus chain is not fully synced.

Currently, we're using a custom block notification sent during the stage of consensus-level block import, but it has an issue (autonomys/subspace#1143) that some states might be unusable when the notification is received by the handler because the block import pipeline is not yet completed.

Steps to reproduce

No response

[bkchr]

I would accept a pr adding a second method import_notification_stream_good_name that gives you the opportunity to get such a stream. Internally we should then have two vecs of notification receivers based on what kind of condition they are receiving block notifications.

[liuchengxu]

Any chance we can change the semantic of import_notification_stream, concretely speaking,

• partial_import_notification_stream: Fired when the chain is synced to the tip or there is a re-org.
• import_notification_stream: Fired on every single block no matter what the sync state is.

This clearly requires larger changes, but I do think partial_import_notification_stream (or recent_import_notification_stream?) describes better the current behavior, the bigger reason is that I honestly don't a good concise name for import_notification_stream_good_name, naming is hard :P