How to deserialize VoteState account from on-chain program

Question

I would like to deserialize VoteState account in Solana on-chain program. https://github.com/solana-labs/solana/blob/v1.17.10/sdk/program/src/vote/state/mod.rs#L285

From what I can see it's not possible to be done with VoteState::deserialize as the deserialize is not implemented for sbf compilation (if I understand correctly). https://github.com/solana-labs/solana/blob/v1.17.10/sdk/program/src/vote/state/mod.rs#L358

I found an issue related to that https://github.com/solana-labs/solana/pull/30515

While I do not understand if there is some simple way to get deserialized data or not and some manual deserialization is needed.

Would you somebody know?

Answer 1

You did all the right research! The VoteState struct is too big to deserialize on-chain because its size is greater than the stack size of any function in the VM, as evidenced by the error:

Stack offset of 6344 exceeded max offset of 4096 by 2248 bytes, please minimize large stack variables

Your best bet is to write a limited deserializer just for the fields that you care about. For example, if you want to fetch the authorized_withdrawer in the account, you'll need to get bytes 36-68 in the account (4 bytes for the enum discriminant, then 4 bytes for the node_pubkey), which would mean:

let authorized_withdrawer = Pubkey::try_from(&vote_account_data[36..68]).unwrap();

The current VoteState is defined at: https://github.com/solana-labs/solana/blob/8330dee95d025dcf6e75a3d5ac538bda9a3d9e70/sdk/program/src/vote/state/mod.rs#L290