Code shared from the Rust Playground

playground.rs

fn main() {
    let mut last_commit_hash = HashValue::zero(); // Genesis hash
    let mut last_commit_round = 0;

    fn get_and_check(untrusted_store: BlockStore, hash: HashValue) -> Result<Block, Error> {
        let block_candidate = untrusted_store
            .get(hash)
            .ok_or(format_err!("Block store is incomplete, lacks {}", hash))?;
        // this calls BlockHasher::hash()
        if block_candidate.hash() == hash {
            Ok(block_candidate)
        } else {
            Err(format_err!("Block store tampered with at {}", hash))
        }
    }

    fn process_commit(
        untrusted_store: BlockStore,
        trusted_new_commmit: HashValue,
    ) -> Result<Vec<Block>, Error> {
        let mut target_block = get_and_check(untrusted_store, trusted_new_commit)?;
        let initial_target_round = target_block.round();
        let mut committed_blocks = vec![target_block];
        while (target_block.round() > last_commit_round || target_block.id() != last_commit_hash) {
            let new_block = get_and_check(untrusted_store, target_block.parent())?;
            // important to guarantee we will exit this loop
            if new_block.round() >= target_block.round() {
                return Err(format_err!("Voting rules violation at {:?}", new_block));
            } else {
                committed_blocks.push(target_block);
                target_block = new_block();
            }
        }
        last_commit_hash = trusted_new_commit;
        last_commit_round = initial_target_round;
        committed_blocks.reverse()
    }

    // Optional: how to retrieve a trusted commit block id from a block proposal without the `committed_block_id` field
    fn process_qc(untrusted_store: BlockStore, block: Block) -> Result<Vec<Block>, Error> {
        // call
        // ValidatorVerifier.verify(block.parent_id(), block.quorum_cert().ledger_info_with_signatures().signatures)
        // + other checks if it hasn't been done before
        let qced_block = get_and_check(untrusted_store, block.parent_id())?;
        if (block.round() = qced_block.round() + 1) {
            let qc_parent = get_and_check(untrusted_store, qced_block.parent_id())?;
            if (qc_parent.round() = qc_parent.round() + 1) {
                // we're gonna retrieve this block twice, 
                // but for communication purposes, I had to show how to 
                // write process_commit taking a hash argument, not a block argument
                process_commit(untrusted_store, qc_parent.id());
            }
        }
        Ok([])
    }
    // Optional
}