GPv2Interaction API

Interaction library API for executing arbitrary contract calls during settlements

GPv2Interaction API

The GPv2Interaction library enables settlement contracts to execute arbitrary external contract calls during trading settlements, supporting complex strategies like liquidity sourcing and protocol integrations.

Data Structure

struct Data {
    address target;
    uint256 value;
    bytes callData;
}

Field	Type	Description
target	address	Contract address to call
value	uint256	ETH value to send with the call
callData	bytes	Encoded function call data

Functions

execute

Performs the actual contract interaction using inline assembly for gas optimization. Propagates revert reasons if calls fail.

function execute(Data calldata interaction) internal {
    address target = interaction.target;
    uint256 value = interaction.value;
    bytes calldata callData = interaction.callData;

    // solhint-disable-next-line no-inline-assembly
    assembly {
        let freeMemoryPointer := mload(0x40)
        calldatacopy(freeMemoryPointer, callData.offset, callData.length)
        if iszero(
            call(gas(), target, value, freeMemoryPointer, callData.length, 0, 0)
        ) {
            returndatacopy(0, 0, returndatasize())
            revert(0, returndatasize())
        }
    }
}

selector

Extracts the 4-byte function selector from calldata for event logging.

function selector(Data calldata interaction) internal pure returns (bytes4);

Settlement Integration

Interactions run at three distinct phases:

Phase	Stage	Common Use Cases
Pre-settlement	interactions[0]	Approvals, permits, token wrapping
Intra-settlement	interactions[1]	DEX swaps, liquidity sourcing
Post-settlement	interactions[2]	Token unwrapping, fee distribution

Common Use Cases

• DEX swaps for liquidity sourcing (Uniswap, Balancer, Curve)
• Token wrapping/unwrapping (WETH)
• Approval grants to external protocols
• Trade routing through aggregators like 1inch
• EIP-2612 permit calls for gasless approvals

Security

Interactions cannot target the vaultRelayer contract. Only authorized solvers may submit settlements with interactions. Reentrancy guards prevent attack vectors. Misbehaving solvers face financial penalties.

Best Practices

• Order interactions by settlement phase carefully
• Ensure all calls succeed (failures cause the entire settlement to revert)
• Use type-safe encoding methods (e.g., abi.encodeWithSelector) rather than manual byte manipulation