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Consensus Context

Provides the system context for the consensus algorithm and deals with the actual content of blocks. Responsible primarily for the creation of new blocks (populated with transactions from TransactionPool) and for content validation of proposed blocks (verifying transaction results).

Currently, a single instance per virtual chain per node.

Interacts with services

  • TransactionPool - Uses it to populate transactions in proposed blocks and validate ordering of others' proposed blocks.
  • VirtualMachine - Uses it to execute transactions and generate receipts and state diffs.
  • StateStorage - Queries the merkle root of the state for writing in proposed blocks and validating others' proposed ones.
  • Passive towards ConsensusAlgo. Provides services to it upon request.

 

Init (flow)

  • Initialize the configuration.

 

RequestOrderingCommittee (method)

Returns a sorted list of nodes (public keys) that participate in the committee for the ordering of a given block height. Called by consensus algo. Note: currently single phase consensus is used where the committee is based on RequestValidationCommittee.

 

RequestValidationCommittee (method)

Returns a sorted list of nodes (public keys) that participate in the committee for the execution validation of a given block height. Called by consensus algo.

  • The current ordered list of nodes (per block height) is retrieved by a call to getOrderedCommittee in Committee contract.
  • If the size of the requested committee is larger than total nodes, select all nodes as the committee.

 

RequestNewTransactionsBlock (method)

Performed by consensus leader only, upon request from consensus algo, to perform the ordering phase of the consensus during a live round.

Choose pending transactions

  • Get pending transactions by calling TransactionPool.GetTransactionsForOrdering.

Add trigger transaction

  • If the configuration flag TRIGGERS_ENABLED is set to TRUE:
    • Generate a trigger transaction and add it as the last transaction.

Build Transactions block

  • Current protocol version (0x1).
  • Current virtual chain.
  • Block height is given.
  • Block proposer is given.
  • Hash pointer to the previous (latest) Transactions block is given.
  • Block timestamp.
  • The merkle root hash of the transactions in the block.
  • Placeholder: metadata - holds reputation / algorithm data.
  • Hash of the block metadata.

 

RequestNewResultsBlock (method)

Performed by the leader only, upon request from consensus algo to perform the execution phase of the consensus during a live round.

Execute transactions

  • The Transactions block for this block height should be cached from a previous call to RequestNewTransactionsBlock.

  • Get the block reference timestamp from the TransactionsBlock header.

  • Execute the ordered transactions set by calling VirtualMachine.ProcessTransactionSet creating receipts and state diff.

Build Results block

  • Current protocol version (0x1).
  • Current virtual chain.
  • Block height.
  • Block proposer.
  • Hash pointer to the previous (latest) Results block.
  • Block timestamp.
  • The merkle root hash of the transaction receipts in the block.
  • The hash of the state diff in the block.
  • Hash pointer to the Transactions block of the same height.
  • Merkle root of the state prior to the block execution, retrieved by calling StateStorage.GetStateHash.
    • Called with block height equals to the last committed block height (current block height - 1)

 

ValidateTransactionsBlock (method)

Validates another node's proposed block. Performed upon a request from consensus algo when receiving a proposal during a live consensus round.

Check Transactions block header

  • Check protocol version.
  • Check virtual chain.
  • Check that the header's block height matches the provided one.
  • Check that the header's previous block hash pointer matches the provided one.
  • Check timestamp is within config.CONSENSUS_CONTEXT_SYSTEM_TIMESTAMP_ALLOWED_JITTER of current system time, and later than the previous block.
  • Check the transactions merkle root matches the transactions.
  • Check metadata hash.
  • Check that the block proposer in the block header matches the provided one.

Validate trigger transaction

  • If the configuration flag TRIGGERS_ENABLED is set to TRUE:
    • Validates that a trigger transaction is present as the last transaction.
    • Validate the trigger transaction content:
      • protocol_version = protocol version
      • virtual_chain_id = virtual_chain_id
      • timestamp = block.timestamp
      • signer = empty
      • contract_name = triggers
      • method_name = blockPost
      • input_argument_array = empty
      • signature = empty
  • If the configuration flag TRIGGERS_ENABLED is set to FALSE, verify that no trigger transaction is present.

Validate transaction choice

  • Call TransactionPool.ValidateTransactionsForOrdering to validate pre order checks, expiration and no duplication.
    • Using the provided header timestamp as a reference timestamp.
    • Remove trigger transaction (if present := if TRIGGERS_ENABLED is set to TRUE).

 

ValidateResultsBlock (method)

Validates another node's proposed block. Performed upon request from consensus algo when receiving a proposal during a live consensus round.

Check Results block header

  • Check protocol version.
  • Check virtual chain.
  • Check that the header's block height matches the provided one.
  • Check hash pointer indeed matches the given previous block hash.
  • Check timestamp equals the TransactionsBlock timestamp.
  • Check the receipts merkle root matches the receipts.
  • Check the hash of the state diff in the block.
  • Check hash pointer to the Transactions block of the same height.
  • Check merkle root of the state prior to the block execution, retrieved by calling StateStorage.GetStateHash.
    • Called with block height equals to the last committed block height (current block height - 1)
  • Check that the block proposer in the block header matches the provided one.

Validate transaction execution

  • Execute the ordered transactions set by calling VirtualMachine.ProcessTransactionSet creating receipts and state diff.
    • Using the provided header timestamp as a reference timestamp.
  • Compare the receipts merkle root hash to the one in the block.
  • Compare the state diff hash to the one in the block (supports only deterministic execution).