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CheckpointSummary

CheckpointSummary​

class CheckpointSummary

A header for a Checkpoint on the IOTA blockchain.

On the IOTA network, checkpoints define the history of the blockchain. They are quite similar to the concept of blocks used by other blockchains like Bitcoin or Ethereum. The IOTA blockchain, however, forms checkpoints after transaction execution has already happened to provide a certified history of the chain, instead of being formed before execution.

Checkpoints commit to a variety of state including but not limited to:

  • The hash of the previous checkpoint.
  • The set of transaction digests, their corresponding effects digests, as well as the set of user signatures which authorized its execution.
  • The object's produced by a transaction.
  • The set of live objects that make up the current state of the chain.
  • On epoch transitions, the next validator committee.

CheckpointSummarys themselves don't directly include all of the above information but they are the top-level type by which all the above are committed to transitively via cryptographic hashes included in the summary. CheckpointSummarys are signed and certified by a quorum of the validator committee in a given epoch in order to allow verification of the chain's state.

BCS

The BCS serialized form for this type is defined by the following ABNF:

checkpoint-summary = u64                            ; epoch
u64                            ; sequence_number
u64                            ; network_total_transactions
digest                         ; contents_digest
(option digest)                ; previous_digest
gas-cost-summary               ; epoch_rolling_gas_cost_summary
u64                            ; timestamp_ms
(vector checkpoint-commitment) ; checkpoint_commitments
(option end-of-epoch-data)     ; end_of_epoch_data
bytes                          ; version_specific_data

init(epoch:sequenceNumber:networkTotalTransactions:contentsDigest:previousDigest:epochRollingGasCostSummary:timestampMs:checkpointCommitments:endOfEpochData:versionSpecificData:)​

convenience init(epoch: UInt64, sequenceNumber: UInt64, networkTotalTransactions: UInt64, contentsDigest: CheckpointContentsDigest, previousDigest: CheckpointDigest?, epochRollingGasCostSummary: GasCostSummary, timestampMs: UInt64, checkpointCommitments: [CheckpointCommitment], endOfEpochData: EndOfEpochData?, versionSpecificData: Data)

checkpointCommitments()​

func checkpointCommitments() -> [CheckpointCommitment]

Commitments to checkpoint-specific state.

contentsDigest()​

func contentsDigest() -> CheckpointContentsDigest

The hash of the CheckpointContents for this checkpoint.

digest()​

func digest() -> CheckpointDigest

endOfEpochData()​

func endOfEpochData() -> EndOfEpochData?

Extra data only present in the final checkpoint of an epoch.

epoch()​

func epoch() -> UInt64

Epoch that this checkpoint belongs to.

epochRollingGasCostSummary()​

func epochRollingGasCostSummary() -> GasCostSummary

The running total gas costs of all transactions included in the current epoch so far until this checkpoint.

networkTotalTransactions()​

func networkTotalTransactions() -> UInt64

Total number of transactions committed since genesis, including those in this checkpoint.

previousDigest()​

func previousDigest() -> CheckpointDigest?

The hash of the previous CheckpointSummary.

This will be only be None for the first, or genesis checkpoint.

sequenceNumber()​

func sequenceNumber() -> UInt64

The height of this checkpoint.

signingMessage()​

func signingMessage() -> Data

signingMessageHex()​

func signingMessageHex() -> String

timestampMs()​

func timestampMs() -> UInt64

Timestamp of the checkpoint - number of milliseconds from the Unix epoch Checkpoint timestamps are monotonic, but not strongly monotonic - subsequent checkpoints can have same timestamp if they originate from the same underlining consensus commit

versionSpecificData()​

func versionSpecificData() -> Data

CheckpointSummary is not an evolvable structure - it must be readable by any version of the code. Therefore, in order to allow extensions to be added to CheckpointSummary, we allow opaque data to be added to checkpoints which can be deserialized based on the current protocol version.