"Invalid subscription" panic in runtime_service

[tomaka]

When starting the demo and connecting to Polkadot, Kusama and Westend all together, I occasionally have a panic here:

smoldot/bin/light-base/src/runtime_service.rs

Line 403 in 1b229e9

panic!("Invalid subscription")

[tomaka]

So this is actually subtle.

If the sync service closes the blocks subscription, the runtime service also automatically closes all its active block subscriptions, which makes sense.
But when doing so, the runtime service automatically unpins all the blocks that were pinned by these subscriptions.
The problem is that, in parallel, another piece of code on top of the runtime service isn't aware of the fact that the subscription has been killed and tries to use the pinned blocks. This leads to this panic.

[melekes]

The problem is that, in parallel, another piece of code on top of the runtime service isn't aware of the fact that the subscription has been killed and tries to use the pinned blocks.

And the solution is for "another piece of code" to check if the block they are trying to use is still pinned or not, isn't it?

[tomaka]

This is a good solution from the point of view of the runtime service, but it's not clear to me whether the API users would be able to handle this error properly.