The NNS ledger canister on the Internet Computer offers both Candid and Protobuf interfaces. However the candid interface is missing some important utilities, including looking up a past transaction.

To solve this problem, we provide the following missing interfaces in Candid by proxying the call to the NNS ledger and translating between the data formats:

service : {
  block : (nat64) -> (variant { Ok: variant { Ok: Block; Err: CanisterId }; Err: text });
  tip_of_chain : () -> (variant { Ok: TipOfChain; Err: text });
}

The complete interface can be found in source file ledger_candid.did or canister ockk2-xaaaa-aaaai-aaaua-cai on ic.rocks.