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Portal Contract

Portal Contracts are a set of smart contracts that implement the on-chain logic of the Omni protocol and are deployed to all supported Rollup EVMs as well as the Omni EVM. They provide the main interface to call a cross-chain smart contract which results in a cross-chain message being emitted as a XMsg. They also provides a "pay at source" fee mechanism using the source chain’s native token. They track the omni consensus validator set, used to verify submitted cross chain message attestations (more below).

Relaying Methods​

The Portal Contract exposes both an xcall method for cross-chain calls to another chain, and an xsubmit method for receiving calls from another chain.

  • xcall is called by the omni.xcall() helper and requires the parameters listed above, with the Portal Contract emitting an XMsg Event for every call to it.
  • xsubmit accepts only calls from valid signatures (currently the Relayer) and requires the destination contract address and data (containing method and method params data).

See more on performing cross chain transactions in the developer section.

Submission Validation​

Portal Contracts keep a cursor for each source chain that:

  • Tracks the latest valid Submission’s XBlockHash that contained valid XMsgBatch to the local destination chain.
  • The total messages in that batch.
  • The index of the last message that was submitted.
  • And implicitly, whether the latest XBlock is partially or completely submitted.

They validate the AggregateAttestation data:

  • Ensuring the SourceChainID is known
  • Ensuring the ValidateSetID is known and the validator set if available.
  • If the cursor is partial, ensuring the XBlockHash matches that of the cursor.

Validate the XMsgBatch data:

  • Ensuring the TargetChainID matches the local chain ID.
  • If the cursor is complete, ensure the ParentBlockHash matches that of the cursor.
  • Ensure the included WrappedXMsg indexes start from 0 if the cursor is complete or follow on the cursor index if partial.

Verify the AggregateAttestation signatures:

  • Verify all validator signatures over the root XBlockHash
  • Ensure that quorum is reached; more than 66% validators in the set signed.
  • Verify a merke-multi-proof against the XBlockHash that proves the following fields of the XBlock:
    • All fields used in above validator.
    • All included XMsgBatch hashes.