Client status commitment

[aeryz]

The light clients can be in 3 state at all times:

1. Active
2. Expired
3. Frozen

The light client is only usable at the Active state. And this status matters the most for the update_client function because we definitely don't want to add a new state to a frozen or expired client.

Currently, if the client is frozen, we write it under ClientState of the corresponding client. And if its expired, we don't commit it at all since it is calculated dynamically at the time where the GetStatus query is called. We want to create a commitment for the clients where we commit the status as well. This is going to be very useful for the state lens clients since they will need to guarantee that the client is not frozen.

Right after a call to the misbehaviour, update_client, and right after the execution of migrate_state, we should query the status of the client and commit it since these are the only entrypoints where we might have a state change.

[benluelo]

we probably shouldn't commit on every call, but rather have an entrypoint to commit the status of a client at a certain consensus height. this will save a lot of gas and storage costs

[aeryz]

Yeah that makes sense. Btw, to be more specific about how to save the status to the storage. Note that the status is being saved for the counterparty chains to be able to verify. We call these things commitments which are "the stored items that can be verified" and we strictly write it under Commitments storage. This Commitments storage uses the prefix 0x00 and all the chains and the light clients use this exact prefix for proof verification.

Hence, you will not need to create a separate storage for Status but rather write it under Commitments by defining a new path for it. You can take ClientStatePath as an example:

pub struct ClientStatusPath {
    client_id: u32
}

And also note that the value that is going to be saved must be canonical across all chains as well which I would just do:

#[repr(u8)]
pub enum Status {}

And then call .to_le_bytes() when committing the value.