How to set up `BaseCallFilter` to only allow a limited set of calls of one pallet to be executed?

Question

Are there examples how to set up a call filter in Substrate to allow only certain calls of a particular pallet to be executed?

Answer 1

The overarching Call enum has the following structure

enum Call {
    PalletOne(pallet_one::Call),
    PalletTwo(pallet_two::Call),
    // ... and so on
}

The implementation of Contains<Call> for a call filter can do pattern-matching on the inner values as well. For example,

impl Contains<Call> for SomeFilter {
    fn contains(call: &Call) -> bool {
        match *call {
            Call::PalletOne(pallet_one::Call::CallA(_)) => true,
            _ => false,
        }
    }
}

Answer 2

Here's an example of how we were using a BaseCallFilter in the statemint parachain to filter out calls that we did not want enabled yet:

https://github.com/paritytech/cumulus/blob/2fe7a2edba05155c6a5f0f3527e1001aad7aee2e/polkadot-parachains/statemint/src/lib.rs#L126