chainlink-oracles
Use when integrating Chainlink price feeds, building oracle-dependent contracts, or implementing staleness checks. Covers AggregatorV3Interface, decimal handling, L2 sequencer uptime, heartbeat validation, and safe price feed wrappers.
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- chainlink-oracles
- description
- Use when integrating Chainlink price feeds, building oracle-dependent contracts, or implementing staleness checks. Covers AggregatorV3Interface, decimal handling, L2 sequencer uptime, heartbeat validation, and safe price feed wrappers.
# Chainlink Oracle Integration
## Core Interface
```solidity
import {AggregatorV3Interface} from
"@chainlink/contracts/src/v0.8/interfaces/AggregatorV3Interface.sol";
interface AggregatorV3Interface {
function latestRoundData() external view returns (
uint80 roundId,
int256 answer, // price (check decimals!)
uint256 startedAt,
uint256 updatedAt, // critical for staleness
uint80 answeredInRound
);
function decimals() external view returns (uint8);
function description() external view returns (string memory);
}
```
## Complete Safe Price Feed Wrapper
```solidity
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;
import {AggregatorV3Interface} from
"@chainlink/contracts/src/v0.8/interfaces/AggregatorV3Interface.sol";
contract ChainlinkPriceFeed {
error StalePrice(uint256 updatedAt, uint256 maxAge);
error InvalidPrice(int256 price);
error SequencerDown();
error SequencerGracePeriod(uint256 timeSinceUp);
AggregatorV3Interface public immutable priceFeed;
AggregatorV3Interface public immutable sequencerFeed; // L2 only
uint256 public immutable maxStaleness;
uint256 public constant SEQUENCER_GRACE_PERIOD = 3600; // 1 hour
constructor(
address _priceFeed,
address _sequencerFeed, // address(0) on L1
uint256 _maxStaleness
) {
priceFeed = AggregatorV3Interface(_priceFeed);
sequencerFeed = AggregatorV3Interface(_sequencerFeed);
maxStaleness = _maxStaleness;
}
function getPrice() external view returns (uint256) {
_checkSequencer();
(
uint80 roundId,
int256 answer,
,
uint256 updatedAt,
uint80 answeredInRound
) = priceFeed.latestRoundData();
if (answer <= 0) revert InvalidPrice(answer);
if (updatedAt == 0) revert InvalidPrice(answer);
if (block.timestamp - updatedAt > maxStaleness) {
revert StalePrice(updatedAt, maxStaleness);
}
if (answeredInRound < roundId) revert StalePrice(updatedAt, maxStaleness);
return uint256(answer);
}
function _checkSequencer() internal view {
if (address(sequencerFeed) == address(0)) return; // L1, skip
(, int256 answer, , uint256 startedAt, ) = sequencerFeed.latestRoundData();
// answer == 0: sequencer is up; answer == 1: sequencer is down
if (answer != 0) revert SequencerDown();
uint256 timeSinceUp = block.timestamp - startedAt;
if (timeSinceUp < SEQUENCER_GRACE_PERIOD) {
revert SequencerGracePeriod(timeSinceUp);
}
}
function decimals() external view returns (uint8) {
return priceFeed.decimals();
}
}
```
## Decimal Handling
Chainlink feeds have varying decimals:
| Feed Type | Decimals | Example |
|-----------|----------|---------|
| USD pairs | 8 | ETH/USD = 3500.00000000 |
| ETH pairs | 18 | USDC/ETH = 0.000285... |
| Non-USD | varies | Check `decimals()` |
```solidity
function normalizePrice(
AggregatorV3Interface feed,
uint8 targetDecimals
) internal view returns (uint256) {
(, int256 answer, , , ) = feed.latestRoundData();
uint8 feedDecimals = feed.decimals();
if (feedDecimals < targetDecimals) {
return uint256(answer) * 10 ** (targetDecimals - feedDecimals);
} else {
return uint256(answer) / 10 ** (feedDecimals - targetDecimals);
}
}
```
## Staleness Thresholds by Feed
| Feed | Heartbeat | Recommended maxStaleness |
|------|-----------|--------------------------|
| ETH/USD | 1 hour | 3600 + buffer (3900s) |
| BTC/USD | 1 hour | 3900s |
| USDC/USD | 24 hours | 86400 + buffer |
| Stablecoin pairs | 24 hours | 90000s |
| L2 feeds | varies | Check docs per chain |
## L2 Sequencer Uptime Feed
On Arbitrum, Optimism, and other L2s, the sequencer can go down. After it comes back, prices may be stale:
```
Arbitrum Sequencer Feed: 0xFdB631F5EE196F0ed6FAa767959853A9F217697D
Optimism Sequencer Feed: 0x371EAD81c9102C9BF4874A9075FFFf170F2Ee389
```
Always check the sequencer feed on L2 before trusting price data.
## Multi-Oracle Pattern
For critical price dependencies, use multiple oracles with a fallback:
```solidity
function getPrice() external view returns (uint256) {
try this._getChainlinkPrice() returns (uint256 price) {
return price;
} catch {
return _getFallbackPrice(); // Uniswap TWAP, Redstone, etc.
}
}
```
## Checklist
- [ ] Validate `answer > 0` from `latestRoundData()`
- [ ] Check `updatedAt` against a staleness threshold
- [ ] Verify `answeredInRound >= roundId`
- [ ] Handle decimal normalization between feeds and your contract
- [ ] On L2: check sequencer uptime feed + grace period
- [ ] Set staleness threshold based on feed's heartbeat (with buffer)
- [ ] Never hardcode prices or assume 8 decimals
- [ ] Consider a fallback oracle for critical price paths
- [ ] Test oracle failure modes (stale price, zero price, sequencer down)
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