L1CrossDomainMessenger Interop

Table of Contents

• Overview
• Constants
• Function Specification
  • relayUndeliveredMessage
  • syncETHLiquidityPause

Overview

With interop, the L1CrossDomainMessenger gains two functions. Each sends one fixed call to one fixed L2 target, as a deposit, with the L1CrossDomainMessenger itself as the L1 sender:

• relayUndeliveredMessage passes on word that a message was not relayed, for message expiry.
• syncETHLiquidityPause sends this chain's pause state to ETHLiquidity, for the ETHLiquidity pause.

L2 trusts the L1CrossDomainMessenger as the sender of these calls (see iME-003). relayMessage refuses messages that target the messenger itself or its portal, so a relayed message cannot make the messenger the L1 sender. The rest of the messenger is unchanged; see Messengers.

Constants

Function Specification

relayUndeliveredMessage

Passes on, to this chain, word from another chain that it has not relayed a message sent from this chain.

function relayUndeliveredMessage(bytes32 _messageHash, uint256 _undeliveredAt) external;

• MUST revert with L1CrossDomainMessenger_InteropNotEnabled unless this chain's SystemConfig has the INTEROP feature enabled.
• MUST revert with L1CrossDomainMessenger_Paused while this chain is paused, as relayMessage does.
• MUST revert unless all of these hold. When the caller's getters return, the revert is L1CrossDomainMessenger_NotInteropMessenger.
  • the SystemConfig of the caller's portal names the caller as its l1CrossDomainMessenger;
  • this chain's ETHLockbox authorizes the caller's portal;
  • the caller's xDomainMessageSender() is the UndeliveredMessageExporter.
• MUST send L2ToL2CrossDomainMessenger.expireMessage(_messageHash, _undeliveredAt) to this chain as a deposit, as itself, with a minimum gas limit of EXPIRE_MESSAGE_GAS_LIMIT.

It does not check which chain the message hash names as its destination. That binding comes from the exporter; see aME-001.

If relayUndeliveredMessage reverts, such as when it runs out of gas, the calling messenger records it as a failed message, and it can be replayed. A caller that shares this chain's ETHLockbox pauses together with this chain, so it cannot relay the call while this chain is paused.

syncETHLiquidityPause

Sends this chain's pause state to ETHLiquidity.

function syncETHLiquidityPause() external;

• MUST be callable by anyone.
• MUST revert with L1CrossDomainMessenger_InteropNotEnabled unless this chain's SystemConfig has the INTEROP feature enabled.
• MUST NOT revert while this chain is paused.
• MUST send ETHLiquidity.setPaused(paused(), nonce) to this chain as a deposit, as itself, with a minimum gas limit of SET_ETH_LIQUIDITY_PAUSED_GAS_LIMIT, where nonce is the versioned nonce of that message.