The Scroll Messenger

The Scroll Messenger contracts allow for sending arbitrary messages from L1 to L2 or vice versa. This enables executing functions on another chain in a secure and permissionless way. To send a message from L1 to L2, use the messenger smart contract deployed on L1, L1ScrollMessenger. To send a message from L2 to L1, use the contract deployed on L2, L2ScrollMessenger.

Finalizing transactions on L1

Any upcoming transactions from L2 need to be finalized using the relayMessageWithProof function on the Scroll Messenger contract. We call this process “submitting an Execute Withdrawal transaction,” and it is required for both sending arbitrary messages and transferring assets through a gateway or the router. When you use relayMessageWithProof, you’ll have to provide a Merkle inclusion proof showing your transaction is included in the trie of “withdrawal” messages, along with other parameters.

To produce this proof and these values, a batch indexing service has to be run locally: Scroll Bridge SDK. Further details on how to use this service are in the docs.

Messenger API

Please visit the npm library for the complete Scroll contract API documentation.

sendMessage

function sendMessage(
  address target,
  uint256 value,
  bytes calldata message,
  uint256 gasLimit,
  address refundAddress
) external payable;

Sends arbitrary data from one chain to another. It allows us to execute functions cross-chain.

relayMessageWithProof

function relayMessageWithProof(
  address from,
  address to,
  uint256 value,
  uint256 nonce,
  bytes memory message,
  L2MessageProof memory proof
) external;

Relay a L2 => L1 message with message proof.