# TransferLibrary

This utility abstracts away the differences between transferring native ETH and ERC20 tokens by introducing a unified interface for both sending and receiving assets. It also standardizes how native ETH is represented on-chain to simplify integration logic across different components.

### ETH Representation

The constant `ETH = 0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE` ([\*\*EIP-7528](https://ethereum-magicians.org/t/eip-7528-eth-native-asset-address-convention/15989))\*\* is used as a sentinel value to distinguish native ETH from ERC20 tokens.

### Errors

* `InvalidValue()`: Thrown when the contract expects a specific `msg.value` (for native ETH transfers) but receives a different amount.

### Constants

* `ETH`: Reserved address used to represent native Ether. When passed to `sendAssets` or `receiveAssets`, the function will process ETH instead of calling token functions.

### Functions

### `sendAssets(address asset, address to, uint256 assets)`

Sends the specified asset (`assets` amount) to the recipient `to`.

* If `asset == ETH`, the function uses `Address.sendValue` to transfer native ETH.
* If `asset` is an ERC20 token, it uses `IERC20.safeTransfer`.

**Parameters:**

* `asset`: Address of the asset to transfer. Should be `ETH` for native Ether or the ERC20 token address.
* `to`: Address to send the asset to.
* `assets`: Amount of the asset to transfer.

**Reverts if:** ETH transfer fails or ERC20 transfer fails via `SafeERC20`.

### `receiveAssets(address asset, address from, uint256 assets)`

Receives assets from the caller (or a third-party) into the current contract.

* If `asset == ETH`, verifies that `msg.value == assets`.
* If `asset` is an ERC20 token, calls `IERC20.safeTransferFrom` from `from` to the current contract.

**Parameters:**

* `asset`: Address of the asset to receive. Use `ETH` for native Ether or an ERC20 token address.
* `from`: Address sending the ERC20 tokens (ignored for ETH).
* `assets`: Expected amount of the asset to receive.

**Reverts if:**

* The contract receives an incorrect `msg.value` for ETH.
* The ERC20 transfer fails.

> Calling `receiveAssets(0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE, from, assets)` multiple times within a single function call will result in incorrect asset accounting.
>
> **DO NOT** use this function in scenarios like the following:

```solidity
 function func() external payable {
     TransferLibrary.receiveAssets(0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE, msg.sender, 1 ether);
     TransferLibrary.receiveAssets(0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE, msg.sender, 1 ether);
     ...
 }
```


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