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XBlock

XBlock plays a crucial role in the Omni protocol by encapsulating cross-chain messages (XMsg) and ensuring their integrity and verifiability across the network. This section delves into the lifecycle of an XBlock, from its creation to its verification and execution on the destination chain.

Overview of XBlock Creation and Flow​

1. Validator Packaging into XBlock​

Validators group multiple XMsg into an XBlock, which includes metadata about the source chain block and the messages it contains. The XBlock structure enables efficient verification through merkle-multi-proofs and simplifies the relaying and submission process.

2. Attestation by Validators​

Omni protocol validators attest to XBlock hashes, ensuring over two-thirds consensus is reached. This attestation process is integral for validating the XBlock and its contents before relaying.

3. Relayer Role in XBlock to Submission​

Relayers collect attested XBlocks and decide on the subset of XMsg to submit to each destination chain. They generate merkle-multi-proofs for these messages and submit them as part of an EVM transaction.

Key Properties and Functions of XBlock​

  • Efficient Verification: XBlock allows for succinct verification of XMsg through merkle-multi-proofs, enabling selective message submission and cost management by relayers.
  • Consensus Optimization: Only blocks containing XMsg require Omni Consensus attestations, reducing the workload on validators and optimizing the consensus process.
  • Deterministic Creation: XBlock is deterministically generated from source chain blocks, ensuring a consistent and reproducible process across the network.

Technical Details​

XBlock Structure​

type XBlock (
  uint         SourceChainID  // Source chain ID
  uint         BlockHeight    // Height of the source chain block
  bytes32      BlockHash      // Hash of the source chain block
  XMsg[]       Msgs           // XMsg events included in the source block
  XReceipt[]   Receipts       // XReceipt events resulting from `XMsg` execution
)

Storage and Calculation​

XBlock is not stored on-chain but is deterministically calculated from source blockchain data. This approach ensures that XBlock data is always available and verifiable without requiring additional storage on the Omni network.

XStream and XMsg Ordering​

XMsg are part of an XStream, a logical connection between source and destination chains, ensuring messages are uniquely identified and strictly ordered. This structure supports exactly-once delivery guarantees and strict ordering for cross-chain communication.

Conclusion​

XBlock is a foundational component of the Omni protocol, enabling secure, efficient, and verifiable cross-chain messaging. Through its structured lifecycle and the collaborative efforts of users, validators, and relayers, XBlock facilitates seamless interoperability across diverse blockchain networks.