Fix Uniswap v4 Hook Integration Issues - Debug Guide

Most hook integration problems come from not understanding how Uniswap v4's singleton architecture processes hooks. Unlike v3 where each pool had its own contract, v4 runs everything through one PoolManager contract that calls your hook at specific lifecycle points. The official v4 documentation covers hook basics, but the actual implementation details tell the real story.

The Hook Permission System (Where Most People Fail)

Uniswap doesn't read your getHookPermissions() function at runtime. That's just for development tooling. The real permissions come from your deployed address:

// This determines what PoolManager actually calls:
function hasPermission(IHooks self, uint160 flag) internal pure returns (bool) {
    return uint160(address(self)) & flag != 0;
}

Why this breaks: You write a hook with beforeSwap: true, deploy it at address 0x1234...0000, and wonder why beforeSwap never executes. The address ends in 0000, so bit 0 (BEFORE_SWAP_FLAG) is not set. The Uniswap Foundation's hook deployment guide explains this requirement, and QuickNode's tutorial shows working examples.

I've debugged this exact issue at 2am more times than I want to count. The hook compiles fine, deploys fine, but silently does nothing because the address permissions don't match the code.

Flash Accounting and Delta Settlement

Uniswap v4 uses "flash accounting" - it tracks IOUs during a transaction and settles everything at the end. Your hook can modify these IOUs (deltas), but they must sum to zero. The MetaLamp architecture guide explains how this works technically, and QuillAudits' swap mechanics analysis covers the delta settlement process.

// This happens automatically:
function unlock(bytes calldata data) external override returns (bytes memory result) {
    // Your hook executes here via callback
    result = IUnlockCallback(msg.sender).unlockCallback(data);
    
    // This check kills your transaction if deltas don't balance:
    if (NonzeroDeltaCount.read() != 0) CurrencyNotSettled.selector.revertWith();
}

Had this hook taking 0.1% fees. Worked perfectly in my tests - I was so proud of the clean math. Deployed to mainnet, first real trade comes through, instant revert. Spent 3 hours debugging before realizing I calculated the delta right but never actually moved the tokens. Classic.

Fix: Every delta your hook creates must be settled:

function afterSwap(...) external returns (bytes4, BalanceDelta hookDelta, uint24 lpFeeOverride) {
    // Hook takes 0.1% fee
    int128 fee = int128(swapAmount * 10 / 10000);
    
    // Create the delta (negative = hook takes tokens)
    hookDelta = BalanceDeltaLibrary.toBalanceDelta(-fee, 0);
    
    // YOU MUST SETTLE THIS DELTA:
    // Transfer fee tokens to PoolManager
    IERC20(token0).transfer(address(poolManager), uint256(fee));
    poolManager.settle(Currency.wrap(address(token0)));
    
    return (BaseHook.afterSwap.selector, hookDelta, 0);
}

Hook Address Mining (The Annoying Part)

You need to mine for addresses with the right permission bits. This is slow and annoying, but there's no way around it. The HookMiner contract handles this, and SolidityDeveloper's integration guide shows practical deployment examples:

// Mine for address with beforeSwap + afterSwap permissions
uint160 flags = uint160(Hooks.BEFORE_SWAP_FLAG | Hooks.AFTER_SWAP_FLAG);

(address hookAddress, bytes32 salt) = HookMiner.find(
    CREATE2_DEPLOYER,
    flags,
    type(MyHook).creationCode,
    abi.encode(poolManager) // constructor args
);

// Deploy with the mined salt
MyHook hook = new MyHook{salt: salt}(poolManager);

Time costs: Finding a simple permission combo takes 30 seconds. Complex combos can take 5+ minutes. Factor this into your deployment scripts.

Security Issues That Will Bite You

CertiK's security analysis and Hacken's hook audit guide identify patterns that consistently cause problems:

Missing access control: Most hooks need onlyPoolManager modifiers on callback functions. Without this, anyone can call your hook directly:

// BAD - anyone can drain fees
function afterSwap(...) external returns (...) {
    feeToken.transfer(msg.sender, collectedFees);
}

// GOOD - only PoolManager can call
function afterSwap(...) external onlyPoolManager returns (...) {
    feeToken.transfer(owner, collectedFees);
}

Async hooks stealing funds: Async hooks completely replace Uniswap's swap logic. A malicious async hook can steal tokens instead of executing the swap:

// This hook steals your tokens instead of swapping
function beforeSwap(...) external returns (bytes4, BeforeSwapDelta, uint24) {
    // Take all the user's tokens
    int128 stolenAmount = -int128(params.amountSpecified);
    
    // Transfer to attacker instead of swapping
    IERC20(token).transfer(attacker, uint256(params.amountSpecified));
    
    return (selector, BeforeSwapDelta.wrap(stolenAmount), 0);
}

Hooks attached to fake pools: Anyone can create a pool using your hook with fake tokens. If your hook doesn't validate the pool, attackers can trigger it with malicious tokens that reenter or manipulate state.

Real talk: I've seen every one of these vulnerabilities in production. The same flexibility that makes hooks powerful will burn you if you don't understand the security model.

Fixed the basic shit? Cool. Now here's where you'll want to quit programming and become a bartender: deploying hooks that work reliably in production, handling edge cases, and not losing users' money.

Testing Strategy That Actually Catches Problems

Most hook failures happen because testing doesn't match production conditions. Here's what I learned the hard way. The Foundry documentation covers fork testing, Patrick Collins' testing guide shows practical examples, Base's Foundry testing tutorial provides comprehensive testing strategies, and QuickNode's Foundry introduction covers essential deployment patterns:

Test with real mainnet state: Use mainnet forks with current block state, not empty test networks:

// In your test setup
vm.createFork("https://mainnet.infura.io/v3/YOUR_KEY");
vm.selectFork(mainnetFork);

// Test with actual token balances and prices, not fantasy numbers
deal(USDC, user, 10000e6);  // Give user real USDC
deal(WETH, user, 5e18);     // Give user real WETH

Test gas usage under stress: Hooks that work with small amounts might fail with large trades due to gas limits:

function testLargeSwapGasUsage() public {
    uint256 gasStart = gasleft();
    
    // Test with realistic large swap amount
    swapRouter.swap(1000e18);  // 1000 ETH swap
    
    uint256 gasUsed = gasStart - gasleft();
    assertLt(gasUsed, 300000, "Hook uses too much gas for large swaps");
}

Test with broken oracles: External dependencies will fail in production. Your hook needs fallback behavior:

function testOracleFailure() public {
    // Mock oracle failure
    vm.mockRevert(address(priceOracle), abi.encodeWithSignature("getPrice(address)"), "Oracle down");
    
    // Hook should still work, maybe with cached price or safe defaults
    swapRouter.swap(1e18);  // This shouldn't revert
}

Hook Deployment Checklist (Skip These, Lose Money)

I maintain this checklist after debugging too many production failures:

✅ Permission verification:

## Verify your deployed hook has the right permissions
cast call $HOOK_ADDRESS "getHookPermissions()(uint256)"
## Compare with your deployed address permissions
echo "Address bits: $(cast to-base $(cast call $HOOK_ADDRESS "getHookPermissions()") 2)"

✅ Delta accounting audit:

// Every delta-modifying path must be tested
function testAllDeltaPaths() public {
    testSwapWithPositiveDelta();
    testSwapWithNegativeDelta();
    testSwapWithZeroDelta();
    testSwapWithExtremeDeltas();
}

✅ Access control verification:

## Try calling hook functions directly (should fail)
cast send $HOOK_ADDRESS "beforeSwap(...)" --from $RANDOM_ADDRESS
## Should revert with "Unauthorized" or similar

✅ Gas limit testing: Critical for production readiness as outlined in CoinsBench's gas optimization guide and Anciliar's developer guide:

// Test worst-case gas usage scenarios
function testGasLimits() public {
    // Max array sizes
    // Worst-case oracle calls
    // Maximum delta calculations
}

Monitoring and Alerting (Because Things Will Break)

Production hooks need monitoring. Failures are often silent - users just get reverts without understanding why. Tenderly's monitoring platform provides transaction debugging, OpenZeppelin Defender offers monitoring and alerting for smart contracts, Ethereum's security documentation covers monitoring tools, and Medium's Defender security guide explains practical monitoring setups. Guardrail's circuit breaker analysis and Olympix's comprehensive circuit breaker guide cover emergency response patterns.

Critical metrics to track:

• Hook execution success rate
• Gas usage per call type
• Delta settlement success rate
• External call failure rate

Example monitoring setup following best practices from OpenZeppelin's incident response guide:

contract MonitoredHook is BaseHook {
    event HookExecuted(string functionName, bool success, uint256 gasUsed);
    event DeltaSettlementFailed(address token, int256 amount);
    event ExternalCallFailed(address target, bytes data);

    modifier monitored(string memory functionName) {
        uint256 gasStart = gasleft();
        _;
        emit HookExecuted(functionName, true, gasStart - gasleft());
    }

    function beforeSwap(...) external monitored("beforeSwap") returns (...) {
        // Hook logic with try-catch for external calls
        try externalOracle.getPrice(token) returns (uint256 price) {
            // Use price
        } catch {
            emit ExternalCallFailed(address(externalOracle), abi.encodeWithSignature("getPrice(address)", token));
            // Use fallback logic
        }
    }
}

Common Production Failures (From War Stories)

Delta calculation errors under extreme conditions: A hook that worked fine for months started failing when SHIB went up 1000%. The fee calculation overflowed uint128:

// BROKEN - overflows with huge token amounts, will fuck you hard
int128 fee = int128(swapAmount * feeRate / 10000);

// FIXED - safe math with bounds checking because Solidity is a dick
int256 feeCalculation = (int256(swapAmount) * feeRate) / 10000;
require(feeCalculation <= type(int128).max, "Fee calculation overflow");
int128 fee = int128(feeCalculation);

Hook gets stuck when external contracts are paused: Had my hook integrated with Compound. Worked great until they paused their markets during some security scare - suddenly my hook starts reverting on every transaction. Rapid Innovation's security guide and Yos.io's fault-tolerant contracts guide explain resilient contract patterns:

// BROKEN - hard dependency on external protocol
uint256 rate = compound.getSupplyRate();

// FIXED - graceful degradation
uint256 rate = defaultRate;
try compound.getSupplyRate() returns (uint256 newRate) {
    rate = newRate;
} catch {
    emit ExternalProtocolDown(address(compound));
    // Continue with default rate
}

Permission mismatch after contract upgrade: Upgraded a hook implementation but forgot to mine a new address with updated permissions. Users got confused when new features didn't work.

Front-running attacks on fee adjustments: Hook adjusted fees based on volatility, but MEV bots front-ran the volatility detection to get favorable rates.

Emergency Response Plan

When your hook breaks in production (not if, when), you need a plan:

1. Circuit breaker pattern: Essential emergency response mechanism as outlined in Kaia's security best practices and SitePoint's smart contract safety guide:

bool public emergencyPause = false;
address public emergencyAdmin;

modifier whenNotPaused() {
    require(!emergencyPause, "Hook paused for emergency");
    _;
}

function beforeSwap(...) external whenNotPaused returns (...) {
    // Hook logic
}

function emergencyPauseHook() external {
    require(msg.sender == emergencyAdmin, "Only emergency admin");
    emergencyPause = true;
    emit EmergencyPause(block.timestamp);
}

2. Safe mode operations:

function beforeSwap(...) external returns (...) {
    if (emergencyPause) {
        // Pass through without modifications
        return (BaseHook.beforeSwap.selector, BeforeSwapDelta.wrap(0), 0);
    }
    
    // Normal hook logic
}

3. User communication plan:

• Discord/Twitter announcements
• Documentation updates
• Clear explanation of what went wrong and when it will be fixed

Real talk: I've had to use emergency procedures twice. Once for a gas optimization gone wrong, once for an oracle manipulation attack. Having these procedures ready saved users from losing funds both times. Medium's circuit breaker design patterns and Nethermind's secure coding guide provide essential patterns for emergency response, while Hedera's smart contract design patterns covers comprehensive security patterns including emergency stops.