Getting Started with the `v4-template` by Saucepoint

From the coding zone, Saucepoint's digital dojo.

Introduction

When Uniswap Labs previewed v4, the limitless flexibility of hooks stirred a million different ideas. From trading order types, to oracles, to bizarre permissioned trading, Uniswap v4 opens up an entirely new programming space for developers. To quickly experiment, iterate, and test ideas, having a starter template goes a long way.

v4-template particulary focuses on providing clean abstractions while being minimally lightweight and unopinonated. Overall, it reduces developer friction by defining:

  • A minimal hook contract with swap and modifyPosition hooks
  • Some test setup - deploys the v4 PoolManager, test tokens, the router contracts, and the hook
  • A deployment script for local and testnet deployments

By covering the basics, hook developers can start and validate what matters most -- the hook logic

Setup

To use the template, all that is required is the foundry toolkit

And create a new repo from the template

Screenshot 2023-10-03 at 4 44 41 PM

With the repo cloned locally, you can install the Uniswap v4 codebase:

forge install

To verify correct setup:

forge test

# output:
[ā ¢] Compiling...
[ā ƒ] Compiling 3 files with 0.8.20
[ā Š] Solc 0.8.20 finished in 2.72s
Compiler run successful!

Running 1 test for test/Counter.t.sol:CounterTest
[PASS] testCounterHooks() (gas: 218915)
Test result: ok. 1 passed; 0 failed; 0 skipped; finished in 16.68ms

Ran 1 test suites: 1 tests passed, 0 failed, 0 skipped (1 total tests)

Developing your first hook

The template provides three primary files to boostrap hook development

v4-template
ā”œā”€ā”€ script
ā”‚   ā””ā”€ā”€ Counter.s.sol      // Deployment script
ā”œā”€ā”€ src
ā”‚   ā””ā”€ā”€ Counter.sol        // Hook contract
ā””ā”€ā”€ test
    ā”œā”€ā”€ Counter.t.sol      // Tests
    ā””ā”€ā”€ utils
        ā””ā”€ā”€ ...

Counter.sol - the Hook Contract

The contract defines beforeSwap, afterSwap, beforeModifyPosition, and afterModifyPosition. All four hook functions are not mandatory, and any combination of hooks can be used

i.e. don't forget hooks for initialize and donate are also available!

The provided hook functions are simply counting how often a pool recieves a swap or an LP modification

    function afterSwap(address, PoolKey calldata key, IPoolManager.SwapParams calldata, BalanceDelta, bytes calldata)
        external
        override
        returns (bytes4)
    {
        afterSwapCount[key.toId()]++;
        return BaseHook.afterSwap.selector;
    }

    function testCounterHooks() public {
        assertEq(counter.afterSwapCount(poolKey.toId()), 0);

        // Perform a test swap //
        int256 amount = 100;
        bool zeroForOne = true;
        swap(poolKey, amount, zeroForOne);
        // ------------------- //

        assertEq(counter.afterSwapCount(poolKey.toId()), 1);
    }

Specifying which functions your Hook supports

Specifying Hook functionality

To communicate which hook functions are implemented, the Hook contract will return the information with getHookCalls()

If hook implements afterSwap and afterModifyPosition:

  function getHooksCalls() public pure override returns (Hooks.Calls memory) {
      return Hooks.Calls({
          beforeInitialize: false,
          afterInitialize: false,
          beforeModifyPosition: false,
          afterModifyPosition: true,
          beforeSwap: false,
          afterSwap: true,
          beforeDonate: false,
          afterDonate: false
      });
  }

and update the flags during test deployment:

uint160 flags = uint160(
  Hooks.AFTER_SWAP_FLAG | Hooks.AFTER_MODIFY_POSITION_FLAG
);

You should be able to start modifying the hook function bodies:

    function afterSwap(address sender, PoolKey calldata key, IPoolManager.SwapParams calldata params, BalanceDelta delta, bytes calldata hookData)
        external
        override
        returns (bytes4)
    {
        // -----------------------
        // DEFINE YOUR LOGIC
        // -----------------------

        return BaseHook.afterSwap.selector;
    }
A note on hook design

Hooks should be singletons!

A hook contract should service multiple trading pairs. One single hook contract, deployed once, should be able to serve both ETH/USDC and ETH/USDT

To support multiple trading pairs/pools, most state variables should be stored in a mapping -- keyed by the PoolId type. This is the case for the Counter hook, which stores the swap count for each pool

mapping(uint256 => uint256) public afterSwapCount;

Testing

Unit tests will be the easiest way to validate your hook behavior. The template's provided test will setup external dependencies -- the v4 PoolManager, test tokens, swap routers, LP router, etc

All you need to do is

  1. Deploy the hook
  2. Create a pool with the hook
  3. Provide liquidity to the pool
  4. Perform a swap

See Counter.t.sol for more

function setUp() public {
    // creates the pool manager, test tokens, and other utility routers
    HookTest.initHookTestEnv();

    // Deploy the hook to an address with the correct flags
    uint160 flags = uint160(
        Hooks.BEFORE_SWAP_FLAG | Hooks.AFTER_SWAP_FLAG | Hooks.BEFORE_MODIFY_POSITION_FLAG
            | Hooks.AFTER_MODIFY_POSITION_FLAG
    );
    (address hookAddress, bytes32 salt) =
        HookMiner.find(address(this), flags, 0, type(Counter).creationCode, abi.encode(address(manager)));
    counter = new Counter{salt: salt}(IPoolManager(address(manager)));
    require(address(counter) == hookAddress, "CounterTest: hook address mismatch");

    // Create the pool
    poolKey = PoolKey(Currency.wrap(address(token0)), Currency.wrap(address(token1)), 3000, 60, IHooks(counter));
    manager.initialize(poolKey, SQRT_RATIO_1_1, ZERO_BYTES);

    // Provide liquidity to the pool (full range)
    modifyPositionRouter.modifyPosition(
        poolKey, IPoolManager.ModifyPositionParams(TickMath.minUsableTick(60), TickMath.maxUsableTick(60), 10 ether)
    );
}

function testCounterHooks() public {
    assertEq(counter.beforeSwapCount(poolId), 0);
    assertEq(counter.afterSwapCount(poolId), 0);

    // Perform a test swap //
    int256 amount = 100;
    bool zeroForOne = true;
    swap(poolKey, amount, zeroForOne);
    // ------------------- //

    assertEq(counter.beforeSwapCount(poolId), 1);
    assertEq(counter.afterSwapCount(poolId), 1);
}

Troubleshooting

Permission Denied

When installing dependencies with forge install, Github may throw a Permission Denied error

This is typically caused by missing Github SSH keys, and can be resolved by following the steps here or adding the keys to your ssh-agent, if you have already uploaded SSH keys link

Hook deployment failures

Hook deployment failures are typically caused by incorrect flags or salt mining

  1. Verify the flags are in agreement:
    • getHookCalls() returns the correct flags
    • flags provided to HookMiner.find(...)
    • In obscure cases where you're deploying multiple hooks (with the same flags), try setting seed=1000 for HookMiner.find
  2. Verify salt mining is correct:
    • In forge test: the deployer for: new Hook{salt: salt}(...) and HookMiner.find(deployer, ...) are the same. This will be address(this) if not using vm.prank. If using vm.prank, the deployer will be the pranking address
    • In forge script: the deployer must be the CREATE2 Proxy: 0x4e59b44847b379578588920cA78FbF26c0B4956C
      • If anvil does not have the CREATE2 deployer, your foundry may be out of date. You can update it with foundryup

Conclusion and Future

Hopefully with this guide, your hook development journey is smooth! The possibilities are intentionally open-ended and ambigious, and the template should let you focus on the hook implementation without getting in the way.

Even if v4-template is not for you, and you prefer rolling-your-own environment, the template offers examples of the Hook development process:

Feedback and contributions are always welcome. For now, the template will strive to stay up to date with the latest v4 changes. And as new best-practices arise, expect the template to reflect and enshrine these patterns!