Settlement
CoW Protocol’s settlement mechanism executes batch auctions at uniform clearing prices, contrasting with traditional sequential AMM processing where each trade affects the next price.
Unlike AMMs where each trade impacts the next price, CoW Protocol uses a price vector where all trades in a batch settle at predetermined rates, ensuring equitable execution across participants.
This eliminates MEV opportunities within batches, as all participants receive the same price for the same token pair.
Core Settlement Function
The settle() function batches multiple orders and executes them atomically with identical clearing prices:
function settle(
IERC20[] calldata tokens,
uint256[] calldata clearingPrices,
GPv2Trade.Data[] calldata trades,
GPv2Interaction.Data[][3] calldata interactions
) external nonReentrant onlySolver;
Three-Phase Execution
Settlement involves three interaction phases:
- Pre-interactions - Setup tasks (e.g., permit approvals, token wrapping)
- Intra-interactions - DEX trades for liquidity sourcing (e.g., Uniswap, Balancer swaps)
- Post-interactions - Cleanup operations (e.g., token unwrapping, fee distribution)
Price Verification
Orders validate through the equation:
sellAmount * sellPrice >= buyAmount * buyPrice
Partial Fills
Orders can be marked partiallyFillable, enabling gradual execution across multiple settlements for large positions. The filledAmount mapping tracks how much of each order has been filled, preventing overfilling.
Balancer Integration
A swap() function provides optimized direct trading against Balancer V2 pools:
function swap(
IVault.SingleSwap calldata swap,
GPv2Trade.Data calldata trade
) external nonReentrant onlySolver returns (int256);
Security Invariants
The protocol enforces critical security invariants:
| Invariant | Description |
|---|
| Signature Verification | All orders must have valid signatures |
| Balance Validation | Users must have sufficient token balances |
| Limit Price Compliance | Clearing prices must respect order limits |
| Overfill Prevention | filledAmount mapping prevents double-execution |
| Atomicity | Entire settlement reverts if any trade fails |
| Reentrancy Protection | nonReentrant modifier on all entry points |
Interactions cannot target the VaultRelayer to prevent exploitation of user token approvals.
