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FlashLender

The FlashLender.vy contract is an ERC-3156 contract that allows users to take out a flash loan for crvUSD. The flash loan must be repaid within the same transaction; otherwise, the transaction will revert.

GitHub

The source code for the FlashLender.vy contract can be found on GitHub . Additionally, a DummyFlashBorrower.vy contract showcasing a potential usage of a flash loan can also be found on GitHub.

The FlashLender.vy is deployed at 0xa7a4bb50af91f90b6feb3388e7f8286af45b299b on Ethereum.

The contract does not charge any fees on flash loans. The fee and flashFee methods are implemented to comply with the ERC-3156 standard.

flashLoan

FlashLender.flashLoan(receiver: ERC3156FlashBorrower, token: address, amount: uint256, data: Bytes[10**5]) -> bool

Function to take out a flash loan of amount of token and send them to the receiver. The receiver address must be a contract that implements the onFlashLoan(initiator: address, token: address, amount: uint256, fee: uint256, data: Bytes[10**5]) interface. A flash loan must be repaid within the same transaction; otherwise, the transaction will revert. Additionally, the method allows passing custom data to the receiver contract.

Returns: True (bool)

Emits: FlashLoan

Input Type Description
receiver ERC3156FlashBorrower Contract to receive the flash loan
token address Address of the token to take the flash loan in
amount uint256 Amount of tokens to flash loan
data Bytes[10**5] Custom data to pass to the receiver contract
Source code

The following source code includes all changes up to commit hash 53b7086; any changes made after this commit are not included.

from vyper.interfaces import ERC20

event FlashLoan:
    caller: indexed(address)
    receiver: indexed(address)
    amount: uint256

CRVUSD: immutable(address)
fee: public(constant(uint256)) = 0  # 1 == 0.01 %

@external
@nonreentrant('lock')
def flashLoan(receiver: ERC3156FlashBorrower, token: address, amount: uint256, data: Bytes[10**5]) -> bool:
    """
    @notice Loan `amount` tokens to `receiver`, and takes it back plus a `flashFee` after the callback
    @param receiver The contract receiving the tokens, needs to implement the
    `onFlashLoan(initiator: address, token: address, amount: uint256, fee: uint256, data: Bytes[10**5])` interface.
    @param token The loan currency.
    @param amount The amount of tokens lent.
    @param data A data parameter to be passed on to the `receiver` for any custom use.
    """
    assert token == CRVUSD, "FlashLender: Unsupported currency"
    crvusd_balance: uint256 = ERC20(CRVUSD).balanceOf(self)
    ERC20(CRVUSD).transfer(receiver.address, amount)
    receiver.onFlashLoan(msg.sender, CRVUSD, amount, 0, data)
    assert ERC20(CRVUSD).balanceOf(self) == crvusd_balance, "FlashLender: Repay failed"

    log FlashLoan(msg.sender, receiver.address, amount)

    return True

>>> soon

maxFlashLoan

FlashLender.maxFlashLoan(token: address) -> uint256

Getter for the maximum amount of flash-loanable tokens. This corresponds to the token balance of the contract (token.balanceOf(FlashLender)).

Returns: maximum flash-loanable amount (uint256)

Input Type Description
token address Token address to check the maximum flash-loanable amount for
Source code

The following source code includes all changes up to commit hash 53b7086; any changes made after this commit are not included.

from vyper.interfaces import ERC20

CRVUSD: immutable(address)
fee: public(constant(uint256)) = 0  # 1 == 0.01 %

@external
@view
def maxFlashLoan(token: address) -> uint256:
    """
    @notice The amount of currency available to be lent.
    @param token The loan currency.
    @return The amount of `token` that can be borrowed.
    """
    if token == CRVUSD:
        return ERC20(CRVUSD).balanceOf(self)
    else:
        return 0

Calling the function with the crvUSD address as input will return the flash-loanable amount. Calling the function with any other token than crvUSD will return 0. 

>>> FlashLender.maxFlashLoan('0xf939E0A03FB07F59A73314E73794Be0E57ac1b4E')
1000000000000000000000000

fee

FlashLender.fee() -> uint256: view

Getter for the fee charged on the flash loan. This variable is a constant set to 0 and cannot be changed. The fees for the contract will always remain at 0.

Returns: fee (uint256).

Source code

The following source code includes all changes up to commit hash 53b7086; any changes made after this commit are not included.

fee: public(constant(uint256)) = 0  # 1 == 0.01 %

>>> FlashLender.fee()
0

flashFee

FlashLender.flashFee(token: address, amount: uint256) -> uint256

Getter for the flash fee when taking out a flash loan of amount of token. This method will always return 0.

Returns: total fee charged on the flashloan (uint256).

Input Type Description
token address Address of the token for the flash loan
amount uint256 Amount of tokens to be flash loaned
Source code

The following source code includes all changes up to commit hash 53b7086; any changes made after this commit are not included.

CRVUSD: immutable(address)

@external
@view
def flashFee(token: address, amount: uint256) -> uint256:
    """
    @notice The fee to be charged for a given loan.
    @param token The loan currency.
    @param amount The amount of tokens lent.
    @return The amount of `token` to be charged for the loan, on top of the returned principal.
    """
    assert token == CRVUSD, "FlashLender: Unsupported currency"
    return 0

This method will always return 0 for any amount of flash loaned crvUSD because the fee is 0. If the function is called with any token other than crvUSD, the function will revert.

>>> FlashLender.flashFee('0xf939E0A03FB07F59A73314E73794Be0E57ac1b4E', 100000 * 10**18)
0

>>> FlashLender.flashFee('0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48', 100000 * 10**18)
reverts: "FlashLender: Unsupported currency"

supportedTokens

FlashLender.supportedTokens(token: address) -> bool

Getter for the supported token by the FlashLender. The only supported token is crvUSD. Due to the immutability of the contract, no further supported tokens can be added.

Returns: True or False (bool).

Input Type Description
token address Token address to check support status for
Source code

The following source code includes all changes up to commit hash 53b7086; any changes made after this commit are not included.

CRVUSD: immutable(address)

@external
@view
def supportedTokens(token: address) -> bool:
    return token == CRVUSD

>>> FlashLender.supportedTokens('0xf939E0A03FB07F59A73314E73794Be0E57ac1b4E')
'true'

version

FlashLender.version() -> String[8]: view

Getter for the version of the contract.

Returns: contract version (String[8]).

Source code

The following source code includes all changes up to commit hash 53b7086; any changes made after this commit are not included.

version: public(constant(String[8])) = "1.0.0"  # Initial

>>> FlashLender.version()
"1.0.0"