Light Full Node Technical Workflow

The light full node operates by checking all the full blocks or a specified suffix of the full blockchain, depending on the settings. It starts from a trusted pre-genesis digest or a digest within the blockchain.

To obtain a new digest from an old one, the light full node utilizes AD-transformations (authenticated dictionary transformations) block sections that contain batch-proof for UTXO transformations. However, it only stores a single digest and does not retain any transaction data.

For more detailed information, refer to this paper.

Additional settings:

The light full node supports the following additional settings:

• depth - from which block in the past to checktransactions (if 0, then go from genesis).
• additional-checks - light-full node trusts the previous digest and checks current digest validity by using the previous one as well as AD-transformations.
• additional-depth - depth to start additional checks from.

Workflow Steps

1. Send ErgoSyncInfo message to connected peers.
2. Get a response with an INV message containing the IDs of blocks that are better than the current best block.
3. Request headers for all the IDs received in step 2.
4. Upon receiving a header, perform the following checks:

if (History.apply(header).isSuccess) {
    if (localScore != networkScore) {
        GOTO 1
    } else {
        GOTO 5
    }
} else {
    blacklist peer
}

1. Request BlockTransactions and ADProofs starting from the specified BlocksToKeep value in the history. This is done after the node bootstrapping process and involves requesting the last header:

History.lastBestHeaders(BlocksToKeep).foreach { header =>
    send message(GetBlockTransactionsForHeader(header)) to Random full node
    send message(GetAdProofsHeader(header)) to Random full node
}

1. Upon receiving a modifier (BlockTransactions or ADProofs), perform the following checks:

if (History.apply(modifier) == Success(ProgressInfo)) {
    /* TODO if history now contains both ADProofs and BlockTransactions,
    it should return ProgressInfo with both of them. Otherwise,
    it should return an empty ProgressInfo */
    if (State().apply(ProgressInfo) == Success((newState, ADProofs))) {
        if ("mode" == "pruned-full") {
            drop BlockTransactions and ADProofs older than BlocksToKeep
        }
    } else {
        /*Drop Header from history because its transaction sequence is not valid*/
        History.drop(BlockTransactions.headerId)
    }
}