🧾 BalancerLiquidity Smart Contract

Overview

The BalancerLiquidity smart contract provides a lightweight interface to interact with the Balancer RETH/WETH liquidity pool. It allows users to:

• Join the pool by depositing RETH, WETH, or both.
• Exit the pool by redeeming Balancer Pool Tokens (BPT) for RETH.

The contract is designed for composability, simplicity, and trustless use with no admin roles or upgrade mechanisms.

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Dependencies

import { IERC20 } from "../interface/IERC20.sol";
import { IRETH } from "../interface/rocket-pool/IRETH.sol";
import { IVault } from "../interface/IVault.sol";
import {
  WETH, RETH, BALANCER_VAULT,
  BALANCER_POOL_RETH_WETH, BALANCER_POOL_ID_RETH_WETH
} from "./Constants.sol";

User Flow

Joining the Pool

1. User calls join() with RETH and/or WETH.
2. Contract transfers and approves tokens to the Vault.
3. Liquidity is added and BPT is minted.
4. Any unused tokens are refunded.

Exiting the Pool

1. User calls exit() with the amount of BPT to redeem.
2. Contract transfers BPT to the Vault.
3. RETH is redeemed and sent to the user.

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Key Imports:

• IERC20: Standard ERC-20 interface
• IRETH: Rocket Pool's RETH token interface
• IVault: Balancer Vault interface
• Constants: Immutable addresses used for tokens and pools

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Security Considerations

• Minimal token approvals (per call)
• Token refund for unused balances
• Slippage protection using minAmountsOut
• Token ordering enforced (RETH before WETH)

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Recommended Improvements

The current implementation is minimal by design. However, the following enhancements are recommended to improve safety, flexibility, and interoperability.

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1. nonReentrant Modifier

Purpose:
Protect against potential reentrancy via token callbacks or future changes.

Suggestion:
Use OpenZeppelin’s ReentrancyGuard on join() and exit().

import "@openzeppelin/contracts/security/ReentrancyGuard.sol";

contract BalancerLiquidity is ReentrancyGuard {
    function join(...) external nonReentrant { ... }
    function exit(...) external nonReentrant { ... }
}

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2. Configurable Token Withdrawal on Exit

Current:
Only RETH is returned on exit().

Improvement:
Allow users to specify:

• Desired token index (0 for RETH, 1 for WETH), or
• Use EXACT_BPT_IN_FOR_TOKENS_OUT to receive both tokens proportionally.

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3. Generalized Join/Exit Modes

Current:
Hardcoded join/exit strategies.

Improvement:
Expose JoinKind, ExitKind, and userData to enable:

• Proportional joins
• More efficient exits
• DEX aggregator integrations

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4. Emit Events

Current:
No on-chain events for off-chain tracking.

Improvement:
Emit Joined and Exited events for better UX and indexing.

event Joined(address indexed user, uint256 rethIn, uint256 wethIn, uint256 bptOut);
event Exited(address indexed user, uint256 bptIn, uint256 rethOut, uint256 wethOut);

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5. Emergency Token Recovery

Problem:
No way to recover mistakenly sent tokens.

Improvement:
Implement a sweep() function restricted to a trusted role or DAO.

Only allow non-core tokens (not RETH/WETH/BPT) to be swept.

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License

MIT

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