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Merge pull request #2 from balancer-labs/simple-chainlink
feat: add a stripped down Chainlink rate provider for Polygon
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| // SPDX-License-Identifier: GPL-3.0-or-later | ||
| // This program is free software: you can redistribute it and/or modify | ||
| // it under the terms of the GNU General Public License as published by | ||
| // the Free Software Foundation, either version 3 of the License, or | ||
| // (at your option) any later version. | ||
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| // This program is distributed in the hope that it will be useful, | ||
| // but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | ||
| // GNU General Public License for more details. | ||
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| // You should have received a copy of the GNU General Public License | ||
| // along with this program. If not, see <http://www.gnu.org/licenses/>. | ||
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| pragma solidity ^0.8.0; | ||
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| import "@chainlink/contracts/src/v0.8/interfaces/AggregatorV3Interface.sol"; | ||
| import "@chainlink/contracts/src/v0.8/interfaces/FeedRegistryInterface.sol"; | ||
| import "@openzeppelin/contracts/utils/math/SafeMath.sol"; | ||
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| import "./interfaces/IRateProvider.sol"; | ||
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| /** | ||
| * @title Chainlink Registry Rate Provider | ||
| * @notice Returns a Chainlink price feed's quote for the provided currency pair | ||
| * @dev This rate provider uses the Chainlink pricefeed registry as the source of truth | ||
| * while caching the underlying feed to query in order to save gas. | ||
| */ | ||
| contract ChainlinkRegistryRateProvider is IRateProvider { | ||
| FeedRegistryInterface public immutable registry; | ||
| address public immutable base; | ||
| address public immutable quote; | ||
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| // We cache the price feed for the given currency pair on this contract | ||
| // This avoids unnecessarily querying the Chainlink registry. | ||
| AggregatorV3Interface internal _feed; | ||
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| // Rate providers are expected to respond with a fixed-point value with 18 decimals | ||
| // We then need to scale the price feed's output to match this. | ||
| uint256 internal _scalingFactor; | ||
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| /** | ||
| * @param _registry - The Chainlink price feed registry contract | ||
| * @param _base - The identifier for the currency which the quoted rate will be denominated in | ||
| * @param _quote - The identifier for the currency for which a price will be quoted | ||
| */ | ||
| constructor( | ||
| FeedRegistryInterface _registry, | ||
| address _base, | ||
| address _quote | ||
| ) { | ||
| registry = _registry; | ||
| base = _base; | ||
| quote = _quote; | ||
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| // Initialise price feed cache | ||
| _feed = _registry.getFeed(_base, _quote); | ||
| _scalingFactor = 10**SafeMath.sub(18, _feed.decimals()); | ||
| } | ||
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| /** | ||
| * @return the value of the quote currency in terms of the base currency | ||
| */ | ||
| function getRate() external view override returns (uint256) { | ||
| (, int256 price, , , ) = _feed.latestRoundData(); | ||
| require(price > 0, "Invalid price rate response"); | ||
| return uint256(price) * _scalingFactor; | ||
| } | ||
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| /** | ||
| * @notice updates cached address of Chainlink price feed used to source quotes | ||
| * @dev The cache may fall out of sync with the canonical price feed as listed on the Chainlink registry | ||
| * Any address may call this function to update the cache to match the registry. | ||
| */ | ||
| function updateCachedFeed() external { | ||
| AggregatorV3Interface priceFeed = registry.getFeed(base, quote); | ||
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| // Price feeds with more than 18 decimals are not supported. | ||
| _scalingFactor = 10**SafeMath.sub(18, priceFeed.decimals()); | ||
| _feed = priceFeed; | ||
| } | ||
| } |