Index / BackGeoOracle

pattern · MIT · last updated 2026-08-27

BackGeoOracle

Geomean oracle that backruns its own pool so the recorded price is not stale.

A geometric-mean TWAP oracle that solves the usual problem with in-pool oracles: the price you record is the price after someone traded against you, which is exactly the price an attacker chose. BackGeoOracle answers that by backrunning the swap itself in afterSwap and recording the corrected price, so the observation reflects a rebalanced pool rather than the post-trade extreme.

Permissions are wide but each one is doing something specific. beforeInitialize is a configuration gate: it reverts unless fee is 0 and tickSpacing is MAX_TICK_SPACING, so only one oracle pool can exist per pair and liquidity cannot fragment. afterInitialize seeds the observation array. beforeAddLiquidity rejects anything that is not full range — minUsableTick to maxUsableTick — and updates the pool first; beforeRemoveLiquidity updates too, so observations stay current across liquidity moves.

beforeSwap reverts on exact-output swaps (only exactIn is supported) and refreshes the pool. The interesting one is afterSwap, which calls _backrun to compute a corrective delta, then settles it with afterSwapReturnDelta — inverting zeroForOne and the sign of amountSpecified while keeping the specified currency the same. The fee for that correction is charged in the unspecified currency, the one the user is buying.

Every callback is onlyPoolManager. The full-range and zero-fee constraints mean this is a purpose-built oracle pool, not a hook you bolt onto a trading pool.

RigoBlock has an audit for this one — linked below — which makes it unusual among research-grade oracle hooks. Read the report, not just the excerpt.

Permission bits

These bits must match the deployed address. Confirm on-chain before you route.

beforeInitializeafterInitializebeforeAddLiquiditybeforeRemoveLiquiditybeforeSwapafterSwapafterSwapReturnDelta

Solidity

Excerpt from src/BackGeoOracle.sol. Copy the full file to implement this. Not an audit.

// SPDX-License-Identifier: MIT
// RigoBlock/back-geo-oracle — excerpt. Full file: source.url
function getHookPermissions() public pure override returns (Hooks.Permissions memory) {
    return Hooks.Permissions({
        beforeInitialize: true,
        afterInitialize: true,
        beforeAddLiquidity: true,
        afterAddLiquidity: false,
        beforeRemoveLiquidity: true,
        afterRemoveLiquidity: false,
        beforeSwap: true,
        afterSwap: true,
        beforeDonate: false,
        afterDonate: false,
        beforeSwapReturnDelta: false,
        afterSwapReturnDelta: true,
        afterAddLiquidityReturnDelta: false,
        afterRemoveLiquidityReturnDelta: false
    });
}

function _beforeInitialize(address, PoolKey calldata key, uint160)
    internal view override onlyPoolManager returns (bytes4)
{
    // This is to limit the fragmentation of pools using this oracle hook. In other words,
    // there may only be one pool per pair of tokens that use this hook. The tick spacing is set to the maximum
    // because we only allow max range liquidity in this pool.
    if (key.fee != 0 || key.tickSpacing != TickMath.MAX_TICK_SPACING) {
        revert OnlyOneOraclePoolAllowed();
    }
    return BaseHook.beforeInitialize.selector;
}

function _beforeSwap(address, PoolKey calldata key, IPoolManager.SwapParams calldata params, bytes calldata)
    internal override onlyPoolManager returns (bytes4, BeforeSwapDelta, uint24)
{
    // only exactIn swaps are supported
    if (params.amountSpecified >= 0) {
        revert NotExactIn();
    }
    _updatePool(key);
    return (BaseHook.beforeSwap.selector, BeforeSwapDeltaLibrary.ZERO_DELTA, 0);
}

function _afterSwap(address sender, PoolKey calldata key, IPoolManager.SwapParams calldata params,
    BalanceDelta swapDelta, bytes calldata)
    internal override onlyPoolManager returns (bytes4, int128)
{
    // the unspecified currency is always the one user is buying, so we charge a fee to settle the backrun
    (BalanceDelta hookDelta, bool isBackrun) = _backrun(key, params, swapDelta);
    // ... settles the corrective delta via afterSwapReturnDelta

Spec

FAQ

Can I paste this into production? The snippet is an excerpt. Use the full file at the source URL, match flags to the address, and treat this page as a map, not a guarantee.

How do I build this safely? Start with secure v4 hooks and the OpenZeppelin hooks guide.