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L2 Relayer

The Relayer contract acts as a middleman, receiving messages from the Broadcaster and relaying them to the according Agent (ownership, parameter, or emergency).

Relayer.vy

The source code for the Relayer.vy contract slightly differ depending on the chain its deployed to.

A comprehensive list of all deployed contracts is available here .

The Relayer receives the broadcasted message and forwards the message to the appropriate agent. The Agents are then responsible for executing the calldata of the message.

Upgradability of Agents

A Relayer's agent addresses cannot be altered. Once chosen, there is no way back. In the case of any issues, a new Relayer contract has to be deployed.

Relaying Messages

The actual structure of the relay function may vary slightly depending on the chain-specific Relayer used. However, the general concept remains consistent:

A message is broadcast through the Broadcaster contract from Ethereum to the L2, where the Relayer relays the message and executes it via the corresponding Agent.

relay

Relayer.relay(_agent: Agent, _messages: DynArray[Message, MAX_MESSAGES]):

Function to receive a message from the Broadcaster and relay the message to the according agent. This function is automatically called by the MESSENGER contract of the according chain. There is no need to manually call this function, which would actually revert as it is a guarded function.

Input Type Description
_agent address Token to transfer
_messages address Destination of the asset
Source code 
@external
def relay(_agent: Agent, _messages: DynArray[Message, MAX_MESSAGES]):
    """
    @notice Receive messages for an agent and relay them.
    @param _agent The agent to relay messages to.
    @param _messages The sequence of messages to relay.
    """
    assert IArbSys(ARBSYS).wasMyCallersAddressAliased()
    assert IArbSys(ARBSYS).myCallersAddressWithoutAliasing() == self

    IAgent(self.agent[_agent]).execute(_messages)

@external
def relay(_agent: Agent, _messages: DynArray[Message, MAX_MESSAGES]):
    """
    @notice Receive messages for an agent and relay them.
    @param _agent The agent to relay messages to.
    @param _messages The sequence of messages to relay.
    """
    assert msg.sender == MESSENGER
    assert IMessenger(MESSENGER).xDomainMessageSender() == self

    IAgent(self.agent[_agent]).execute(_messages)

@external
def relay(_agent: Agent, _messages: DynArray[Message, MAX_MESSAGES]):
    """
    @notice Receive messages for an agent and relay them.
    @param _agent The agent to relay messages to.
    @param _messages The sequence of messages to relay.
    """
    assert msg.sender == self.messenger

    IAgent(self.agent[_agent]).execute(_messages)

Agents

The contract contains the addresses of the Agents that are responsible for executing the messages.

OWNERSHIP_AGENT

Relayer.OWNERSHIP_AGENT() -> address: view

Getter for the ownership agent.

Returns: ownership agent (address).

Source code 
OWNERSHIP_AGENT: public(immutable(address))

This examples returns the ownership agents for the Arbitrum and Optimism chains.

>>> ArbitrumRelayer.OWNERSHIP_AGENT()
'0x452030a5D962d37D97A9D65487663cD5fd9C2B32'    # arbitrum

>>> OptimismRelayer.OWNERSHIP_AGENT()
'0x28c4A1Fa47EEE9226F8dE7D6AF0a41C62Ca98267'    # optimism

PARAMETER_AGENT

Relayer.PARAMETER_AGENT() -> address: view

Getter for the parameter agent.

Returns: parameter agent (address).

Source code 
PARAMETER_AGENT: public(immutable(address))

This examples returns the parameter agents for the Arbitrum and Optimism chains.

>>> ArbitrumRelayer.PARAMETER_AGENT()
'0x5ccbB27FB594c5cF6aC0670bbcb360c0072F6839'    # arbitrum

>>> OptimismRelayer.PARAMETER_AGENT()
'0xE7F2B72E94d1c2497150c24EA8D65aFFf1027b9b'    # optimism

EMERGENCY_AGENT

Relayer.EMERGENCY_AGENT() -> address: view

Getter for the emergency agent.

Returns: emergency agent (address).

Source code 
EMERGENCY_AGENT: public(immutable(address))

This examples returns the emergency agents for the Arbitrum and Optimism chains.

>>> ArbitrumRelayer.EMERGENCY_AGENT()
'0x2CB6E1Adf22Af1A38d7C3370441743a123991EC3'    # arbitrum

>>> OptimismRelayer.EMERGENCY_AGENT()
'0x9fF1ddE4BE9BbD891836863d227248047B3D881b'    # optimism