Architecture
CoW Protocol’s settlement system revolves around three interconnected contracts. The architecture leverages Balancer V2’s Vault infrastructure while maintaining a permissioned solver network to execute batch auctions with MEV protection.
Core Components
- GPv2Settlement - Central orchestration contract handling trade execution, order validation, and settlement logic
- GPv2VaultRelayer - Intermediary managing token transfers between users and the Balancer Vault
- GPv2AllowListAuthentication - Access control system governing the permissioned solver network
Architecture Diagram
Contract Relationships
GPv2Settlement
Serves as the protocol’s entry point with key responsibilities:
- Order Validation - Verifies signatures, expiry, and prices
- Trade Execution - Processes clearing prices and batched trades
- Interaction Hooks - Enables arbitrary pre/post-settlement calls
- Reentrancy Protection - Inherits from
ReentrancyGuard
GPv2VaultRelayer
Acts as a trusted intermediary. Only the creator (GPv2Settlement) can call this contract to manage token transfers.
GPv2AllowListAuthentication
Implements solver permissions through an allowlist mapping. Only addresses added to the solver allowlist by the manager can call settle().
Token Flow
The token transfer process follows four stages:
- User Approval - Users approve the Balancer Vault (not the settlement contract) to spend tokens
- Inbound Transfers - Tokens are pulled from users into the settlement contract
- Interactions - Optional arbitrary contract calls (e.g., DEX aggregators)
- Outbound Transfers - Tokens are distributed to order receivers
Security Features
| Feature | Description |
|---|
| Reentrancy Protection | Settlement contract uses nonReentrant modifier on entry points |
| Solver Authorization | onlySolver modifier restricts execution to allowlisted addresses |
| Interaction Restrictions | VaultRelayer cannot be called as an interaction target |
| Creator-Only Access | VaultRelayer enforces sole settlement contract invocation |
Design Principles
- Separation of concerns across specialized contracts
- Minimal trust model - users approve only the Balancer Vault
- Gas efficiency through batch settlement amortization
- Extensibility via interaction hooks
- MEV protection through uniform clearing prices
Last modified on March 4, 2026
