Clients need to be able to synchronize their local state with that of the operator. However, this process is somewhat non-trivial as clients may be simultaneously connected to multiple plasma chains.

The actual process for synchronizing a client can generally be determined by the client implementer. However, we’re going to go through some recommendations that will ensure that the client is as feature-complete as possible.

Deposit and Commitment Contracts

Our plasma construction makes use of deposit contracts that store the assets that users transact on the plasma chain. These deposit contracts act like their own individual plasma chains. For example, the range (0, 100) will be valid on two different deposit contracts but will refer to different assets.

Furthermore, we’re generally using a single deposit contract per asset type to simplify things for the client. It’s therefore very likely that a client will be interested in transactions on several different deposit contracts. As a result, clients SHOULD be able to send and receive transactions on multiple deposit contracts simultanously.

We’re also using the new concept of commitment contracts that store plasma block commitments instead of throwing all of this logic inside the deposit contract. Each deposit contract points to a specific commitment contract, and it’s possible for multiple deposit contracts to point to the same contract. Therefore a client SHOULD also be able to watch for commitments to multiple commitment contracts and SHOULD maintain a mapping between commitment contracts and deposit contracts.

Receiving Transactions

Transactions are unique to a given deposit contract, but blocks are unique to a commitment contract. For each commitment contract the client is interested in, clients SHOULD watch for new blocks being published to Ethereum.

It’s important to note that, unlike in previous plasma constructions, there’s no easy way for an operator to tell that a given address will be interested in a specific transaction. Instead, clients SHOULD, upon seeing the publication of a new block, send a `state query`_ to the operator for all state updates the client is interested in.

For example, imagine we have a predicate that allows anyone to mutate a state object as long as they have the pre-image to some hash. Without the pre-image, the operator has no way to know which user “owns” that state object. A client would have to specifically form a query for all state objects that use that predicate and lock the state object with a specific hash.