# Token Bridge

The ability to send cross layer messages trustlessly between L1 and L2 can be leveraged to build a token bridge to move assets from L1 to L2 and back. Goshen provide a standard bridge for Ether and ERC20 tokens.

### Deposit Ether

To move Ether from L1 to L2, you can send a deposit transaction via `depositETH` or `depositETHTo` of `L1StandardBridge` contract. This will transfer the funds to the `L1StandardBridge` contract and will send a cross layer message to `L2StandardBridge` contract deployed on L2 to mint the same amount of funds to the specified address.

```javascript
/**
 * @dev Deposit an amount of the ETH to the caller's balance on L2.
 * @param _data Optional data to forward to L2. This data is provided
 *        solely as a convenience for external contracts. Aside from enforcing a maximum
 *        length, these contracts provide no guarantees about its content.
 */
function depositETH(bytes calldata _data) external payable;

/**
 * @dev Deposit an amount of ETH to a recipient's balance on L2.
 * @param _to L2 address to credit the withdrawal to.
 * @param _data Optional data to forward to L2. This data is provided
 *        solely as a convenience for external contracts. Aside from enforcing a maximum
 *        length, these contracts provide no guarantees about its content.
 */
function depositETHTo(address _to, bytes calldata _data) external payable;
```

### Withdraw Ether

To withdraw Ether from L2 to L1, you can send a withdraw transaction via `withdrawETH` or `withdrawETHTo` of `L2StandardBridge` contract. This will transfer the funds to the `L2StandardBridge` contract and will send a cross layer message to `L1StandardBridge` contract to transfer the same amount of funds to the specified address.

```javascript
function withdrawETH(bytes calldata _data) external payable onlyEOA ;
function withdrawETHTo(address _to, bytes calldata _data) external payable;
```

### Deposit ERC20 tokens

To move a ERC20 token from L1 to L2, you can send a deposit transaction via `depositERC20` or `depositERC20To` of `L1StandardBridge` contract. This will transfer the funds to the `L1StandardBridge` contract and will send a cross layer message to `L2StandardBridge` contract deployed on L2 to mint the same amount of funds to the specified address.

```javascript
/**
 * @dev deposit an amount of the ERC20 to the caller's balance on L2.
 * @param _l1Token Address of the L1 ERC20 we are depositing
 * @param _l2Token Address of the L1 respective L2 ERC20
 * @param _amount Amount of the ERC20 to deposit
 * @param _data Optional data to forward to L2. This data is provided
 *        solely as a convenience for external contracts. Aside from enforcing a maximum
 *        length, these contracts provide no guarantees about its content.
 */java
function depositERC20(
    address _l1Token,
    address _l2Token,
    uint256 _amount,
    bytes calldata _data
) external;

/**
 * @dev deposit an amount of ERC20 to a recipient's balance on L2.
 * @param _l1Token Address of the L1 ERC20 we are depositing
 * @param _l2Token Address of the L1 respective L2 ERC20
 * @param _to L2 address to credit the withdrawal to.
 * @param _amount Amount of the ERC20 to deposit.
 * @param _data Optional data to forward to L2. This data is provided
 *        solely as a convenience for external contracts. Aside from enforcing a maximum
 *        length, these contracts provide no guarantees about its content.
 */
function depositERC20To(
    address _l1Token,
    address _l2Token,
    address _to,
    uint256 _amount,
    bytes calldata _data
) external;
```

### Withdraw ERC20 tokens

To withdraw a ERC20 token from L2 to L1, you can send a withdraw transaction via `withdraw` or `withdrawTo` of `L2StandardBridge` contract. This will transfer the funds to the `L2StandardBridge` contract and will send a cross layer message to `L1StandardBridge` contract to transfer the same amount of funds to the specified address.

```javascript
/**
 * @dev initiate a withdraw of some tokens to the caller's account on L1
 * @param _l2Token Address of L2 token where withdrawal was initiated.
 * @param _amount Amount of the token to withdraw.
 * @param _data Optional data to forward to L1. This data is provided
 *        solely as a convenience for external contracts. Aside from enforcing a maximum
 *        length, these contracts provide no guarantees about its content.
 */
function withdraw(
    address _l2Token,
    uint256 _amount,
    bytes calldata _data
) external;

/**
 * @dev initiate a withdraw of some token to a recipient's account on L1.
 * @param _l2Token Address of L2 token where withdrawal is initiated.
 * @param _to L1 adress to credit the withdrawal to.
 * @param _amount Amount of the token to withdraw.
 * @param _data Optional data to forward to L1. This data is provided
 *        solely as a convenience for external contracts. Aside from enforcing a maximum
 *        length, these contracts provide no guarantees about its content.
 */
function withdrawTo(
    address _l2Token,
    address _to,
    uint256 _amount,
    bytes calldata _data
) external;
```


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