> ## Documentation Index
> Fetch the complete documentation index at: https://docs.relay.link/llms.txt
> Use this file to discover all available pages before exploring further.

# RelayBridge

# Solidity API

## IRelayBridge

Interface for the RelayBridge contract

*Defines the bridge function for cross-chain asset transfers*

### bridge

```solidity theme={null}
function bridge(uint256 amount, address recipient, address poolAsset, uint256 poolGas, bytes extraData) external payable returns (uint256 nonce)
```

Bridges an asset (ERC20 token or native currency) from the origin chain to a pool chain

#### Parameters

| Name      | Type    | Description                                                       |
| --------- | ------- | ----------------------------------------------------------------- |
| amount    | uint256 | Amount of asset units to bridge (ERC20 tokens or native currency) |
| recipient | address | Address on the pool chain to receive the bridged asset            |
| poolAsset | address | Address of the asset on the pool chain to bridge to               |
| poolGas   | uint256 | Gas limit for the pool chain transaction                          |
| extraData | bytes   | Extra data passed to the bridge proxy                             |

#### Return Values

| Name  | Type    | Description                                   |
| ----- | ------- | --------------------------------------------- |
| nonce | uint256 | Unique identifier for this bridge transaction |

## RelayBridge

RelayBridge contract enabling cross-chain bridging via Hyperlane

*Bridges assets from an origin chain to a configured pool chain*

### BridgeTransaction

*Internal struct capturing parameters for a bridge transaction*

```solidity theme={null}
struct BridgeTransaction {
  uint256 amount;
  address recipient;
  address poolAsset;
  uint256 poolGas;
  bytes extraData;
  uint256 nonce;
  bytes txParams;
  uint32 poolChainId;
  bytes32 poolId;
}
```

### BridgingFailed

```solidity theme={null}
error BridgingFailed(uint256 nonce)
```

Error for failed bridging operations

#### Parameters

| Name  | Type    | Description                         |
| ----- | ------- | ----------------------------------- |
| nonce | uint256 | The nonce of the failed transaction |

### InsufficientValue

```solidity theme={null}
error InsufficientValue(uint256 received, uint256 expected)
```

Error for insufficient native value sent to cover fees or asset

#### Parameters

| Name     | Type    | Description                            |
| -------- | ------- | -------------------------------------- |
| received | uint256 | The amount of native currency received |
| expected | uint256 | The amount of native currency expected |

### FailedFeeRefund

```solidity theme={null}
error FailedFeeRefund(uint256 value)
```

Error when refunding leftover native value fails

#### Parameters

| Name  | Type    | Description                                         |
| ----- | ------- | --------------------------------------------------- |
| value | uint256 | The amount of native currency that failed to refund |

### transferNonce

```solidity theme={null}
uint256 transferNonce
```

Counter for assigning unique nonces to bridge transactions

*Incremented with each bridge transaction to ensure uniqueness*

### ASSET

```solidity theme={null}
address ASSET
```

Asset address on the origin chain being bridged (address(0) for native currency)

*Immutable to ensure the bridge always handles the same asset*

### BRIDGE\_PROXY

```solidity theme={null}
contract BridgeProxy BRIDGE_PROXY
```

BridgeProxy contract handling origin-chain transfer logic

*Uses delegatecall to execute custom bridge logic*

### HYPERLANE\_MAILBOX

```solidity theme={null}
address HYPERLANE_MAILBOX
```

Hyperlane Mailbox contract for cross-chain messaging

*Used to dispatch messages to the pool chain*

### BridgeInitiated

```solidity theme={null}
event BridgeInitiated(uint256 nonce, address sender, address recipient, address ASSET, address poolAsset, uint256 amount, contract BridgeProxy BRIDGE_PROXY)
```

Emitted when a bridge transaction is initiated on the origin chain

#### Parameters

| Name          | Type                 | Description                                                        |
| ------------- | -------------------- | ------------------------------------------------------------------ |
| nonce         | uint256              | Nonce of the transaction                                           |
| sender        | address              | Address on the origin chain that initiated the bridge              |
| recipient     | address              | Address on the pool chain to receive assets                        |
| ASSET         | address              | Asset address on the origin chain (address(0) for native currency) |
| poolAsset     | address              | Asset address on the pool chain (address(0) for native currency)   |
| amount        | uint256              | Amount of asset units bridged                                      |
| BRIDGE\_PROXY | contract BridgeProxy | BridgeProxy used                                                   |

### BridgeExecuted

```solidity theme={null}
event BridgeExecuted(uint256 nonce)
```

Emitted after a bridge transaction is executed on the pool chain

*This event would be emitted by the pool chain contract*

#### Parameters

| Name  | Type    | Description                       |
| ----- | ------- | --------------------------------- |
| nonce | uint256 | Nonce of the executed transaction |

### BridgeCancelled

```solidity theme={null}
event BridgeCancelled(uint256 nonce)
```

Emitted if a bridge transaction is cancelled prior to execution

*This event would be emitted if a bridge is cancelled*

#### Parameters

| Name  | Type    | Description                        |
| ----- | ------- | ---------------------------------- |
| nonce | uint256 | Nonce of the cancelled transaction |

### constructor

```solidity theme={null}
constructor(address asset, contract BridgeProxy bridgeProxy, address hyperlaneMailbox) public
```

Initializes the RelayBridge with asset and infrastructure contracts

*All parameters are immutable after deployment*

#### Parameters

| Name             | Type                 | Description                                                         |
| ---------------- | -------------------- | ------------------------------------------------------------------- |
| asset            | address              | Asset address on the origin chain to bridge (0 for native currency) |
| bridgeProxy      | contract BridgeProxy | BridgeProxy contract for origin-chain transfers                     |
| hyperlaneMailbox | address              | Hyperlane Mailbox address for messaging                             |

### getFee

```solidity theme={null}
function getFee(uint256 amount, address recipient, uint256 poolGas) external view returns (uint256 fee)
```

Calculates the fee required in native currency to dispatch a cross-chain message

*Uses Hyperlane's quoteDispatch to estimate the cross-chain messaging fee*

#### Parameters

| Name      | Type    | Description                                                   |
| --------- | ------- | ------------------------------------------------------------- |
| amount    | uint256 | Amount of asset units to bridge                               |
| recipient | address | Address on the pool chain that will receive the bridged asset |
| poolGas   | uint256 | Gas limit for the pool chain transaction                      |

#### Return Values

| Name | Type    | Description                                  |
| ---- | ------- | -------------------------------------------- |
| fee  | uint256 | Required fee in native currency for dispatch |

### bridge

```solidity theme={null}
function bridge(uint256 amount, address recipient, address poolAsset, uint256 poolGas, bytes extraData) external payable returns (uint256 nonce)
```

Bridges an asset (ERC20 token or native currency) from the origin chain to a pool chain

\_Executes a cross-chain bridge transaction with the following steps:

1. Validates sufficient payment for fees (and asset amount if native)
2. Transfers the asset from sender to this contract (if ERC20)
3. Executes bridge logic via delegatecall to BRIDGE\_PROXY
4. Dispatches cross-chain message via Hyperlane
5. Refunds any excess native currency to sender\_

#### Parameters

| Name      | Type    | Description                                                       |
| --------- | ------- | ----------------------------------------------------------------- |
| amount    | uint256 | Amount of asset units to bridge (ERC20 tokens or native currency) |
| recipient | address | Address on the pool chain to receive the bridged asset            |
| poolAsset | address | Address of the asset on the pool chain to bridge to               |
| poolGas   | uint256 | Gas limit for the pool chain transaction                          |
| extraData | bytes   | Extra data passed to the bridge proxy                             |

#### Return Values

| Name  | Type    | Description                                   |
| ----- | ------- | --------------------------------------------- |
| nonce | uint256 | Unique identifier for this bridge transaction |