> ## Documentation Index
> Fetch the complete documentation index at: https://docs.cow.bleu.builders/llms.txt
> Use this file to discover all available pages before exploring further.

# GPv2VaultRelayer

> The intermediary contract between CoW Protocol settlement and Balancer Vault

# GPv2VaultRelayer Contract

The `GPv2VaultRelayer` contract serves as an intermediary between the settlement contract and Balancer Vault, enabling secure token transfers and batch swaps while maintaining strict access controls.

## Overview

The relayer acts as an intermediary between the settlement contract and Balancer Vault with specialized functions for handling user fund interactions safely. Only the settlement contract can initiate transfers.

## State Variables

| Variable  | Type                  | Description                                               |
| --------- | --------------------- | --------------------------------------------------------- |
| `creator` | `address` (immutable) | The settlement contract address with exclusive privileges |
| `vault`   | `IVault` (immutable)  | The Balancer Vault instance                               |

## Access Control

All external functions use the `onlyCreator` modifier, restricting operations to the settlement contract that deployed the relayer:

```solidity theme={null}
modifier onlyCreator {
    require(msg.sender == creator, "GPv2: not creator");
    _;
}
```

## Main Functions

### transferFromAccounts()

Moves sell token amounts from user accounts to the settlement contract, supporting three balance types:

```solidity theme={null}
function transferFromAccounts(
    GPv2Transfer.Data[] calldata transfers
) external onlyCreator;
```

**Supported balance types:**

* **ERC20** - Standard ERC20 token transfers
* **External** - Balancer Vault external balances
* **Internal** - Balancer Vault internal balances

### batchSwapWithFee()

Executes Balancer batch swaps on behalf of users while simultaneously collecting protocol fees:

```solidity theme={null}
function batchSwapWithFee(
    IVault.BatchSwapStep[] calldata swaps,
    IERC20[] calldata tokens,
    IVault.FundManagement calldata funds,
    int256[] calldata limits,
    uint256 deadline,
    GPv2Transfer.Data calldata feeTransfer
) external onlyCreator returns (int256[] memory tokenDeltas);
```

The function returns token deltas indicating amounts sent and received.

## Security Architecture

The contract implements layered protection:

* **Creator-only access** prevents unauthorized vault interactions
* **Immutable references** prevent state tampering post-deployment
* **User approvals remain isolated** since only the settlement contract can trigger transfers
* **No direct user interaction pathway** exists -- users never call this contract directly

## Integration Point

The vault relayer operates within the settlement workflow, handling token transfers before and after batch swaps. It is automatically instantiated by the settlement contract during deployment.

<Note>
  Users approve the Balancer Vault, not the VaultRelayer directly. The relayer leverages existing vault approvals to move tokens.
</Note>