New WebSocket event subscription endpoints

[shramee]

Since v0.5.6 of Pathfinder, an experimental feature to subscribe to real time updates via Websockets has been added.
This feature currently allows getting real-time updates when new headers are appended to the chain.

This discussion is to debate on which new subscription endpoints would be more useful and prioritise their development.

Poll from Telegram,

[fracek]

For Starknet React the two main sources of polling calls are blocks and transaction status.

• Blocks: we use this to check for new blocks (latest or pending). This hook is super important because it drives the refresh of other hooks.
• Transaction Status: this data is also refreshed on every block. It would be extremely useful to be able to subscribe to multiple transaction statuses in a single connection.

[Mirko-von-Leipzig]

From a node perspective the concern would be that a client holds the websocket open indefinitely as a form of DoS 🤷 so if the node knows there is no more info to output, it might want to close the socket and move on with life 😀

Maybe one can output a Complete notification or something to indicate that 🤔

[shramee]

But, the socket could stay open if client provides new transactions to start watching?

[Mirko-von-Leipzig]

But, the socket could stay open if client provides new transactions to start watching?

Right, the socket yes, I suppose I meant the subscription and not the socket itself.

[shramee]

Ahh yeah, Closing the subscription with a Complete notif sounds good to me.

[fracek]

I think a Complete message is good.

[Mirko-von-Leipzig]

Another thing that should be easy to implement is an event subscription. We re-use the event filter as defined in the starknet RPC specification. I've been told this is pretty important for some users.