> ## 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.

# IFlashLoanRouter

> Interface for the Flash Loan Router enabling CoW Protocol solvers to request flash loans and execute settlements atomically

## Overview

The `IFlashLoanRouter` interface defines the contract API for coordinating flash loans with CoW Protocol settlements. It acts as a solver for CoW Protocol, enabling solvers to request flash loans and execute settlements in a single transaction.

## Contract Details

* **Source**: `src/interfaces/IFlashLoanRouter.sol`
* **License**: GPL-3.0-or-later
* **Solidity**: ^0.8.28

## Functions

### flashLoanAndSettle

```solidity theme={null}
function flashLoanAndSettle(
    Loan.Data[] calldata loans,
    bytes calldata settlement
) external;
```

Requests flash loans and executes a CoW Protocol settlement atomically. All specified loans are requested sequentially before the settlement is executed.

**Parameters:**

* `loans`: Array of flash loan specifications, each containing:
  * `amount` (`uint256`): Amount of tokens to borrow
  * `token` (`IERC20`): Token contract address
  * `lender` (`address`): Flash loan provider contract
  * `borrower` (`IBorrower`): Adapter contract for the lender
* `settlement`: ABI-encoded `settle()` call data for the CoW Settlement contract

**Requirements:**

* Caller must be a registered CoW Protocol solver
* No concurrent settlement in progress
* Settlement data must encode a valid `settle()` call

<Warning>
  It is the solver's responsibility to ensure the loan is specified correctly. The router does not validate that flash loan proceeds will be available for the settlement.
</Warning>

### borrowerCallBack

```solidity theme={null}
function borrowerCallBack(bytes memory loansWithSettlement) external;
```

Callback function for borrower contracts to signal flash loan receipt. The borrower must pass the encoded data back unmodified.

**Parameters:**

* `loansWithSettlement`: Encoded remaining loans and settlement data

**Requirements:**

* Caller must be the expected pending borrower
* Data must match the stored hash

### settlementContract

```solidity theme={null}
function settlementContract() external view returns (ICowSettlement);
```

Returns the CoW Protocol settlement contract address.

### settlementAuthentication

```solidity theme={null}
function settlementAuthentication() external view returns (ICowAuthentication);
```

Returns the solver authentication contract address used to verify solver identity.

## Events

### Settlement

```solidity theme={null}
event Settlement(address indexed solver);
```

Emitted when a solver initiates a flash loan settlement.

## Data Types

### Loan.Data

```solidity theme={null}
struct Data {
    uint256 amount;
    IERC20 token;
    address lender;
    IBorrower borrower;
}
```

Specification for a single flash loan request within a settlement.

## Execution Flow

1. Solver calls `flashLoanAndSettle()` with loan array and settlement data
2. Router requests each loan sequentially through borrower adapters
3. Each borrower receives funds and calls `borrowerCallBack()`
4. After all loans are obtained, the router executes the settlement
5. Settlement repays loans through borrower approvals

## Key Constraints

* Only one settlement execution per call
* Settlement data cannot be modified during execution
* Only the `settle()` function can be called during execution
* Callback data must be passed through unmodified

## Next Steps

<CardGroup cols={2}>
  <Card title="IBorrower" icon="plug" href="/flash-loan-router/contracts/interfaces/iborrower">
    Borrower interface reference
  </Card>

  <Card title="FlashLoanRouter" icon="code" href="/flash-loan-router/contracts/flash-loan-router">
    Full contract reference
  </Card>
</CardGroup>