chainlink-data-feeds

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Chainlink Data Feeds (Hedera)

Push feed pattern: a Chainlink aggregator is updated off-chain; on-chain readers call latestRoundData() and must reject incomplete, non-positive, or stale rounds.

text

Chainlink DON → AggregatorV3Interface feed → consumer latestRoundData()

Consumers may wrap the feed behind a local interface; that is optional. Do not assume a project-specific adapter name.

Quick Reference

Piece	Role
`AggregatorV3Interface`	`latestRoundData()` + `decimals()`
Round completeness	`answeredInRound >= roundId` and `updatedAt != 0`
Price	`answer > 0` (feeds are typically signed `int256`)
Freshness	Compare `block.timestamp - updatedAt` to a max staleness
Scale	Normalize feed decimals to the consumer’s scale (often 18)
Pair identity	Prefer canonical uppercase symbols (`HBAR`, `USD`) if you hash pair keys

Hedera chain IDs: testnet 296, mainnet 295.

See references/hedera-feeds.md for where to source Hedera feed addresses. See references/examples.md for read and normalize sketches.

Critical: Completeness Then Staleness

Never return a price from a missing or unfinished round. Revert when:

Condition	Why
`answeredInRound < roundId`	Aggregator has not finished this round
`updatedAt == 0`	No successful update
`answer <= 0`	Invalid / non-positive price
`block.timestamp - updatedAt > maxStaleness`	Stale for this consumer

solidity

(uint80 roundId, int256 answer,, uint256 updatedAt, uint80 answeredInRound) =
    feed.latestRoundData();

if (answeredInRound < roundId || updatedAt == 0) revert IncompleteRound();
if (answer <= 0) revert InvalidPrice();
if (block.timestamp - updatedAt > maxStaleness) revert StalePrice(updatedAt, maxStaleness);

Critical: Hedera Feeds, Not Ethereum Addresses

Do not copy Ethereum mainnet aggregator addresses onto Hedera. Look up Hedera-specific Data Feed addresses for chain 295 / 296 and re-check docs before mainnet.

Pair maps (if you use them) should be constructor-only unless the project explicitly supports post-deploy updates.

Decimal Normalization

feed.decimals() is often 8. Convert to the scale your app uses before arithmetic:

solidity

uint256 price = normalizeToScale(uint256(answer), feed.decimals(), /* target */ 18);

Keep conversion rounding explicit (usually round down). Do not mix raw aggregator units with 18-decimal amounts.

Checklist

When implementing or reviewing Chainlink reads on Hedera:

[ ] Feed address taken from Hedera Data Feeds docs (not Ethereum)
[ ] latestRoundData completeness checks before using answer
[ ] Non-positive prices revert
[ ] Staleness bound is enforced
[ ] Decimals normalized to the consumer scale
[ ] Chain ID is 295 or 296 (or the project’s documented Hedera network)

References

references/examples.md — latestRoundData and normalize sketches
references/hedera-feeds.md — where to source Hedera aggregator addresses
Chainlink Data Feeds
Hedera price feed addresses