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chainlink-data-feeds

Coding & development

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Updated 10-15 18:13

About this skill

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.

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 
(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:

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