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Curve Lending: Oracles

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The source code of the CryptoFromPool.vy and all other oracle contracts can be found on GitHub.

The OneWayLendingFactory.vy has a create_from_pool method which deploys the full lending market infrastucture along with a price oracle using a stableswap-ng, twocrypto-ng or tricrypto-ng pool. These pools all have a suitable exponential moving-average (EMA) oracle, which can be used in lending markets.

Additionally, the price oracle contracts on Arbitrum take the status of the sequencer into consideration.

Example: CRV long market

In the CRV short market, CRV serves as the collateral token, while crvUSD is the borrowable token. This lending market utilizes the price oracle sourced from the TriCRV liquidity pool.

When calling the create_from_pool function, the code automatically checks the index of the tokens within the liquidity pool. Subsequently, it passes these values as constructor arguments during the creation of the oracle contract from the blueprint implementation.

__init__ 
@external
def __init__(
        pool: Pool,
        N: uint256,
        borrowed_ix: uint256,
        collateral_ix: uint256
    ):
    assert borrowed_ix != collateral_ix
    assert borrowed_ix < N
    assert collateral_ix < N
    POOL = pool
    N_COINS = N
    BORROWED_IX = borrowed_ix
    COLLATERAL_IX = collateral_ix

    no_argument: bool = False
    if N == 2:
        success: bool = False
        res: Bytes[32] = empty(Bytes[32])
        success, res = raw_call(
            pool.address,
            _abi_encode(empty(uint256), method_id=method_id("price_oracle(uint256)")),
            max_outsize=32, is_static_call=True, revert_on_failure=False)
        if not success
            no_argument = True
    NO_ARGUMENT = no_argument

# the following arguments will be passed into the `__init__` function:
pool = '0x4ebdf703948ddcea3b11f675b4d1fba9d2414a14'
N = 3
borrow_ix = 0               # crvUSD
collateral_ix = 2           # CRV

Ethereum

price

CryptoFromPool.price() -> uint256

Getter function for the price. For example, in a lending market using CRV as collateral and crvUSD as the borrowable token, it returns the price of CRV relative to crvUSD. Conversely, in the inverse market scenario, it returns the price of crvUSD relative to CRV. This function is view-only and does not modify the state.

Returns: price (uint256).

Source code 
@external
@view
def price() -> uint256:
    return self._raw_price()

@internal
@view
def _raw_price() -> uint256:
    p_borrowed: uint256 = 10**18
    p_collateral: uint256 = 10**18

    if NO_ARGUMENT:
        p: uint256 = POOL.price_oracle()
        if COLLATERAL_IX > 0:
            p_collateral = p
        else:
            p_borrowed = p

    else:
        if BORROWED_IX > 0:
            p_borrowed = POOL.price_oracle(BORROWED_IX - 1)
        if COLLATERAL_IX > 0:
            p_collateral = POOL.price_oracle(COLLATERAL_IX - 1)

    return p_collateral * 10**18 / p_borrowed

>>> CryptoFromPool.price()
458009543343504151

price_w

CryptoFromPool.price_w() -> uint256:

Function to return the price and update the state of the blockchain. This function is called whenever the _exchange function from the LLAMMA is called.

Returns: price (uint256).

Source code 
@external
def price_w() -> uint256:
    return self._raw_price()

@internal
@view
def _raw_price() -> uint256:
    p_borrowed: uint256 = 10**18
    p_collateral: uint256 = 10**18

    if NO_ARGUMENT:
        p: uint256 = POOL.price_oracle()
        if COLLATERAL_IX > 0:
            p_collateral = p
        else:
            p_borrowed = p

    else:
        if BORROWED_IX > 0:
            p_borrowed = POOL.price_oracle(BORROWED_IX - 1)
        if COLLATERAL_IX > 0:
            p_collateral = POOL.price_oracle(COLLATERAL_IX - 1)

    return p_collateral * 10**18 / p_borrowed

@internal
def _price_oracle_w() -> uint256[2]:
    p: uint256[2] = self.limit_p_o(price_oracle_contract.price_w())
    self.prev_p_o_time = block.timestamp
    self.old_p_o = p[0]
    self.old_dfee = p[1]
    return p

@internal
def _exchange(i: uint256, j: uint256, amount: uint256, minmax_amount: uint256, _for: address, use_in_amount: bool) -> uint256[2]:
    """
    @notice Exchanges two coins, callable by anyone
    @param i Input coin index
    @param j Output coin index
    @param amount Amount of input/output coin to swap
    @param minmax_amount Minimal/maximum amount to get as output/input
    @param _for Address to send coins to
    @param use_in_amount Whether input or output amount is specified
    @return Amount of coins given in and out
    """
    assert (i == 0 and j == 1) or (i == 1 and j == 0), "Wrong index"
    p_o: uint256[2] = self._price_oracle_w()  # Let's update the oracle even if we exchange 0
    if amount == 0:
        return [0, 0]
    ...

>>> CryptoFromPool.price_w()
458009543343504151

POOL

CryptoFromPool.POOL() -> address: view

Getter for the liquidity pool the from where the oracle is used.

Returns: liquidity pool (address).

Source code 
POOL: public(immutable(Pool))

@external
def __init__(
        pool: Pool,
        N: uint256,
        borrowed_ix: uint256,
        collateral_ix: uint256
    ):
    assert borrowed_ix != collateral_ix
    assert borrowed_ix < N
    assert collateral_ix < N
    POOL = pool
    N_COINS = N
    BORROWED_IX = borrowed_ix
    COLLATERAL_IX = collateral_ix

    no_argument: bool = False
    if N == 2:
        success: bool = False
        res: Bytes[32] = empty(Bytes[32])
        success, res = raw_call(
            pool.address,
            _abi_encode(empty(uint256), method_id=method_id("price_oracle(uint256)")),
            max_outsize=32, is_static_call=True, revert_on_failure=False)
        if not success:
            no_argument = True
    NO_ARGUMENT = no_argument

>>> CryptoFromPool.POOL()
'0x4eBdF703948ddCEA3B11f675B4D1Fba9d2414A14'

BORROWED_IX

CryptoFromPool.BORROWED_IX() -> uint256: view

Getter for the index of the borrowed coin in the liquidity pool from which the price oracle is taken from.

Returns: coin index (uint256).

Source code 
BORROWED_IX: public(immutable(uint256))

@external
def __init__(
        pool: Pool,
        N: uint256,
        borrowed_ix: uint256,
        collateral_ix: uint256
    ):
    assert borrowed_ix != collateral_ix
    assert borrowed_ix < N
    assert collateral_ix < N
    POOL = pool
    N_COINS = N
    BORROWED_IX = borrowed_ix
    COLLATERAL_IX = collateral_ix

    no_argument: bool = False
    if N == 2:
        success: bool = False
        res: Bytes[32] = empty(Bytes[32])
        success, res = raw_call(
            pool.address,
            _abi_encode(empty(uint256), method_id=method_id("price_oracle(uint256)")),
            max_outsize=32, is_static_call=True, revert_on_failure=False)
        if not success:
            no_argument = True
    NO_ARGUMENT = no_argument

>>> CryptoFromPool.BORROWED_IX()
0

COLLATERAL_IX

CryptoFromPool.COLLATERAL_IX() -> uint256: view

Getter for the index of the collateral coin in the liquidity pool from which the price oracle is taken from.

Returns: coin index (uint256).

Source code 
COLLATERAL_IX: public(immutable(uint256))

@external
def __init__(
        pool: Pool,
        N: uint256,
        borrowed_ix: uint256,
        collateral_ix: uint256
    ):
    assert borrowed_ix != collateral_ix
    assert borrowed_ix < N
    assert collateral_ix < N
    POOL = pool
    N_COINS = N
    BORROWED_IX = borrowed_ix
    COLLATERAL_IX = collateral_ix

    no_argument: bool = False
    if N == 2:
        success: bool = False
        res: Bytes[32] = empty(Bytes[32])
        success, res = raw_call(
            pool.address,
            _abi_encode(empty(uint256), method_id=method_id("price_oracle(uint256)")),
            max_outsize=32, is_static_call=True, revert_on_failure=False)
        if not success:
            no_argument = True
    NO_ARGUMENT = no_argument

>>> CryptoFromPool.COLLATERAL_IX()
2

N_COINS

CryptoFromPool.N_COINS() -> uint256: view

Getter for the total number of coins in the liquidity pool.

Returns: coins count (uint256).

Source code 
N_COINS: public(immutable(uint256))

@external
def __init__(
        pool: Pool,
        N: uint256,
        borrowed_ix: uint256,
        collateral_ix: uint256
    ):
    assert borrowed_ix != collateral_ix
    assert borrowed_ix < N
    assert collateral_ix < N
    POOL = pool
    N_COINS = N
    BORROWED_IX = borrowed_ix
    COLLATERAL_IX = collateral_ix

    no_argument: bool = False
    if N == 2:
        success: bool = False
        res: Bytes[32] = empty(Bytes[32])
        success, res = raw_call(
            pool.address,
            _abi_encode(empty(uint256), method_id=method_id("price_oracle(uint256)")),
            max_outsize=32, is_static_call=True, revert_on_failure=False)
        if not success:
            no_argument = True
    NO_ARGUMENT = no_argument

>>> CryptoFromPool.N_COINS()
3

NO_ARGUMENT

CryptoFromPool.NO_ARGUMENT() -> bool: view

Getter for the NO_ARGUMENT storage variable. This is an additional variable to ensure the correct price oracle is fetched from a pool with more than two coins. The variable is set to false if the pool from which the price oracle is taken has only two coins.

Returns: true or false (bool)

Source code 
NO_ARGUMENT: public(immutable(bool))

@external
def __init__(
        pool: Pool,
        N: uint256,
        borrowed_ix: uint256,
        collateral_ix: uint256
    ):
    assert borrowed_ix != collateral_ix
    assert borrowed_ix < N
    assert collateral_ix < N
    POOL = pool
    N_COINS = N
    BORROWED_IX = borrowed_ix
    COLLATERAL_IX = collateral_ix

    no_argument: bool = False
    if N == 2:
        success: bool = False
        res: Bytes[32] = empty(Bytes[32])
        success, res = raw_call(
            pool.address,
            _abi_encode(empty(uint256), method_id=method_id("price_oracle(uint256)")),
            max_outsize=32, is_static_call=True, revert_on_failure=False)
        if not success:
            no_argument = True
    NO_ARGUMENT = no_argument

>>> CryptoFromPool.NO_ARGUMENT()
'False'

Arbitrum

In addition to the aforementioned functions, oracle contracts on Arbitrum use a Chainlink Uptime Feed Oracle to monitor and validate any potential downtime of the sequencer.

Should the internal _raw_price function, responsible for fetching the price, encounter an indication from the uptime oracle that the Arbitrum sequencer is presently offline, or if it has experienced recent downtime and the DOWNTIME_WAIT period of 3988 seconds has not yet elapsed, it will revert.

interface ChainlinkOracle:
    def latestRoundData() -> ChainlinkAnswer: view

struct ChainlinkAnswer:
    roundID: uint80
    answer: int256
    startedAt: uint256
    updatedAt: uint256
    answeredInRound: uint80

@internal
@view
def _raw_price() -> uint256:
    # Check that we had no downtime
    cl_answer: ChainlinkAnswer = ChainlinkOracle(CHAINLINK_UPTIME_FEED).latestRoundData()
    assert cl_answer.answer == 0, "Sequencer is down"
    assert block.timestamp >= cl_answer.startedAt + DOWNTIME_WAIT, "Wait after downtime"
    ...

CryptoFromPool.CHAINLINK_UPTIME_FEED() -> address: view

Getter for the ChainlinkUptimeFeed contract.

Returns: uptime feed contract (address).

Source code 
CHAINLINK_UPTIME_FEED: public(constant(address)) = 0xFdB631F5EE196F0ed6FAa767959853A9F217697D

>>> CryptoFromPool.CHAINLINK_UPTIME_FEED()
'0xFdB631F5EE196F0ed6FAa767959853A9F217697D'

DOWNTIME_WAIT

CryptoFromPool.DOWNTIME_WAIT() -> uint256: view

Getter for the required time to wait after the sequencer was down.

Returns: time to wait (uint256).

Source code 
DOWNTIME_WAIT: public(constant(uint256)) = 3988  # 866 * log(100) s

>>> CryptoFromPool.DOWNTIME_WAIT()
3988