Euler Price Oracles

Euler Price Oracles is a library of modular oracle adapters and components that implement IPriceOracle, a quote-based interface compatible with ERC-7726.

• To read more about the design and motivation behind IPriceOracle and the oracles in this repo, check out the whitepaper and ERC-7726.

• To understand how Price Oracles fit into the Euler Vault Kit, check out the price oracles section of the EVK whitepaper.

• To use or develop with Euler Price Oracles, check out the Usage section.

• To find out ways to contribute to Euler Price Oracles, check out the Contributing section.

• To observe 200+ live deployments of these oracle adapters check out the dedicated Oracle Dashboard.

Euler Price Oracles has been audited by Spearbit, OpenZeppelin, ChainSecurity, Omniscia, yAudit, and Cantina.

IPriceOracle

All contracts in this library implement the IPriceOracle interface.

/// @return outAmount The amount of `quote` that is equivalent to `inAmount` of `base`.
function getQuote(
    uint256 inAmount,
    address base,
    address quote
) external view returns (uint256 outAmount);

/// @return bidOutAmount The amount of `quote` you would get for selling `inAmount` of `base`.
/// @return askOutAmount The amount of `quote` you would spend for buying `inAmount` of `base`.
function getQuotes(
    uint256 inAmount,
    address base,
    address quote
) external view returns (uint256 bidOutAmount, uint256 askOutAmount);

This interface shapes oracle interactions in an important way: it forces the consumer to think in amounts rather than prices.

A subset of this interface (getQuote) has been standardized in ERC-7726.

Quotes

Euler Price Oracles are unique in that they expose a flexible quoting interface instead of reporting a static price.

Note

Imagine a Chainlink price feed which reports the value 1 EUL/ETH, the unit price of EUL. Now consider an IPriceOracle adapter for the feed. It will fetch the unit price, multiply it by inAmount, and return the quantity inAmount EUL/ETH. We call this a quote as it functionally resembles a swap on a decentralized exchange.

The quoting interface offers several benefits to consumers:

• More intuitive queries: Oracles are commonly used in DeFi to determine the value of assets. getQuote does exactly that.
• More expressive interface: The unit price is a special case of a quote where inAmount is one whole unit of base.
• Safe and flexible integrations: Under IPriceOracle adapters are internally responsible for converting decimals. This allows consumers to decouple themselves from a particular provider as they can remain agnostic to its implementation details.

Bid/Ask Pricing

Euler Price Oracles additionally expose getQuotes which returns two prices: the selling price (bid) and the buying price (ask).

Bid/ask prices are inherently safer to use in lending markets as they can accurately reflect instantaneous price spreads. While few oracles support bid/ask prices currently, we anticipate their wider adoption in DeFi as on-chain liquidity matures.

Importantly getQuotes allows for custom pricing strategies to be built under the IPriceOracle interface:

• Querying two oracles and returning the lower and higher prices.
• Reporting two prices from a single source e.g. a TWAP and a median.
• Applying a synthetic spread or a volatility-dependent confidence interval around a mid-price.

Oracle Adapters

An adapter is a minimal, fully immutable contract that queries an external price feed. It is the atomic building block of the Euler Price Oracles library.

Design Principles

The IPriceOracle interface is permissive in that it does not prescribe a particular way to implement it. However the adapters in this library adhere to a strict set of rules that we believe are necessary to enable safe, open, and self-governed markets to flourish.

Immutable

Adapters are fully immutable without governance or upgradeability.

Minimally Responsible

An adapter connects to one pricing system and queries a single price feed in that system.

Bidirectional

An adapter works in both directions. If it supports quoting X/Y it must also support Y/X.

Observable

An adapter's parameters and acceptance logic are easily observed on-chain.

Summary of Adapters

Adapter	Type	Method	Supported Pairs	Parameters
ChainlinkOracle	External	Push	Provider feeds	feed, max staleness
ChronicleOracle	External	Push	Provider feeds	feed, max staleness
PythOracle	External	Pull	Provider feeds	feed, max staleness, max confidence interval
RedstoneCoreOracle	External	Pull	Provider feeds	feed, max staleness, cache ttl
LidoOracle	Onchain	Rate	wstETH/stETH	-
LidoFundamentalOracle	Onchain	Rate	wstETH/ETH	-
UniswapV3Oracle	Onchain	TWAP	UniV3 pools	fee, twap window
PendleOracle	Onchain	TWAP	Pendle markets	pendle market, twap window
RateProviderOracle	Onchain	Rate	Balancer rate providers	rate provider
FixedRateOracle	Onchain	Rate	Any	rate

Usage

Install

To install Price Oracles in a Foundry project:

forge install euler-xyz/euler-price-oracle

Development

Clone the repo:

git clone https://github.com/euler-xyz/euler-price-oracle.git && cd euler-price-oracle

Install forge dependencies:

forge install

[Optional] Install Node.js dependencies:

npm install

Compile the contracts:

forge build

Testing

The repo contains 4 types of tests: unit, property, bounds, fork, identified by their filename suffix.

Fork Tests

To run fork tests set the ETHEREUM_RPC_URL variable in your environment:

# File: .env
ETHEREUM_RPC_URL=...

Alternatively, to exclude fork tests:

forge test --no-match-contract Fork

Important

Tests in RedstoneCoreOracle.fork.t.sol use the ffi cheatcode to invoke a script that retrieves Redstone update data. FFI mode is not enabled by default for safety reasons. To run the Redstone Fork tests set ffi = true in foundry.toml.

Contributing

Euler Price Oracles is a free and open-source public good. We encourage you to engage and contribute.

Feel free to open a GitHub issue discussing your ideas.

Tip

Submit testing- and documentation-related PRs to development and changes under src/ to experiments.

Here are a few ideas how you can improve Euler Price Oracles:

Research and Development

• Write an adapter for a new oracle provider or an AMM such as Curve V2.
• getQuotes returns bid/ask prices, however we are not aware of any oracle providers that currently support them. Write an IPriceOracle wrapper that applies a price spread around a mid-point price. The spread could be dynamic based on proxy metrics such as liquidity, volume, (implied) volatility, correlation. We are highly interested in research towards this direction.
• ZK Coprocessors like Axiom and Lagrange allow you to verifiably compute over historical blockchain state in ZK circuits. This unlocks a new design space for trust-minimized manipulation-resistant oracles. Write a proof-of-concept oracle using a ZK Coprocessor. Some ideas: an implied volatility oracle based on Uniswap V3, a median filtering oracle over an AMM.
• Write an IPriceOracle wrapper that implements a trustless circuit-breaker mechanism that detects failure conditions. Upon detection it could switch to another oracle or redeploy the adapter with different parameters.
• Write an alternative router to EulerRouter that supports more flexible configuration.
• Research whether a DEX aggregator API can be used as a pull-based price oracle and write a proof-of-concept adapter.
• Some oracle providers are compatible with Chainlink's AggregatorV3Interface either directly or through a facade contract. Are they safe to use through ChainlinkOracle in this library?
• Write a sanity checking script that verifies an adapter is correctly configured by comparing the quote against a price API.
• Write a simulation script that generates a line plot comparing a given adapter's prices against a price API historically.

Security

• Expand the fork test suite to include more pairs and to historically backtest the adapter.
• Write fuzz and invariant tests using echidna, medusa, or foundry.
• Write formal verification tests using Certora, halmos, or kontrol.
• EulerRouter can price ERC4626 shares to assets by calling convertToAssets. Which of the currently live vaults have a manipulation-resistant pricing function?
• With pull-based oracles users control the price update flow. What is an appropriate value for maxStaleness on Ethereum considering network delays and possible censorship? Are there ways maxStaleness can be safely reduced?
• Are these oracles readily usable on the various L2s or are there additional considerations that must be had?

Technical Documentation

• Write an smart contract integration guide for Euler Price Oracles.
• Write a frontend integration guide for fetching the price of pull-based oracles.
• Write or compile risk research for a provider, detailing how it works, its failure modes and trust assumptions.

Safety

This software is experimental and is provided "as is" and "as available".

No warranties are provided and no liability will be accepted for any loss incurred through the use of this codebase.

Always include thorough tests when using Euler Price Oracles to ensure it interacts correctly with your code.

License

(c) 2024 Euler Labs Ltd.

The Euler Price Oracles code is licensed under the GPL-2.0-or-later license.