# L2 Relayer

Source: [https://docs.curve.finance/developer/curve-dao/governance/x-gov/relayer](https://docs.curve.finance/developer/curve-dao/governance/x-gov/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.

-   [`ArbitrumRelayer.vy`](https://github.com/curvefi/curve-xgov/blob/master/contracts/arbitrum/ArbitrumRelayer.vy) for Arbitrum
-   [`OptimismRelayer.vy`](https://github.com/curvefi/curve-xgov/blob/master/contracts/optimism/OptimismRelayer.vy) for Optimism and Optimistic Rollups
-   [`XYZRelayer.vy`](https://github.com/curvefi/curve-xgov/blob/master/contracts/xyz/XYZRelayer.vy) for all other chains

A comprehensive list of all deployed contracts is available [here ↗](https://docs.curve.finance/developer/deployments.md).

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 choosen, there is no way back. In the case of any issues, a new `Relayer` contract has to be deployed.

* * *

<a id="relaying-messages"></a>

## 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`.

<a id="relay"></a>

### `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` | `Agent` | Agent to relay the message to |
| `_messages` | `DynArray[Message, MAX_MESSAGES]` | Sequence of messages to relay |

**<>Source code▼**

ArbitrumRelayer.vy

```vyper
@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)
```

OptimismRelayer.vy

```vyper
@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)
```

XYZRelayer.vy

```vyper
@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)
```

* * *

<a id="agents"></a>

## Agents

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

<a id="ownership_agent"></a>

### `OWNERSHIP_AGENT`

`Relayer.OWNERSHIP_AGENT() -> address: view`

Getter for the ownership agent.

Returns: ownership agent (`address`).

**<>Source code▼**

```vyper
OWNERSHIP_AGENT: public(immutable(address))
```

**▶Example▼**

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

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

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

<a id="parameter_agent"></a>

### `PARAMETER_AGENT`

`Relayer.PARAMETER_AGENT() -> address: view`

Getter for the parameter agent.

Returns: parameter agent (`address`).

**<>Source code▼**

```vyper
PARAMETER_AGENT: public(immutable(address))
```

**▶Example▼**

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

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

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

<a id="emergency_agent"></a>

### `EMERGENCY_AGENT`

`Relayer.EMERGENCY_AGENT() -> address: view`

Getter for the emergency agent.

Returns: emergency agent (`address`).

**<>Source code▼**

```vyper
EMERGENCY_AGENT: public(immutable(address))
```

**▶Example▼**

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

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

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