02 Plugin (PLI) oracle feeds on XDC

What a consumer sees

• Plugin publishes price feeds on XDC mainnet as proxy contracts
• Read API is AggregatorV3-style:

interface IPluginFeed {
    function decimals() external view returns (uint8);
    function description() external view returns (string memory);
    function latestRoundData() external view returns (
        uint80 roundId, int256 answer, uint256 startedAt,
        uint256 updatedAt, uint80 answeredInRound);
}

Gotchas observed on mainnet feeds

• Decimals differ per feed: most live feeds use 16, some older ones 18 (Plugin's contracts allow others, such as 25) — always read decimals()
• Heartbeats differ: crypto pairs ~1800 s, FX / equities / metals 86400 s (market hours)
• Some proxies revert "No access" (whitelisted) or revert empty (broken / access-controlled)
• Example: XDC/USDT 0x896CC6fE8AD04dF9f481332606c445768e286076 (16 dp)

The five checks every consumer needs

• answer > 0
• updatedAt != 0
• updatedAt <= block.timestamp
• block.timestamp - updatedAt <= maxStaleness (per feed!)
• answeredInRound >= roundId

Optional: min/max bounds, max deviation vs. last accepted price

Scaling to 18 decimals

uint256 p = latestPrice();
if (feedDecimals < 18) return p * 10 ** (18 - feedDecimals);
return p / 10 ** (feedDecimals - 18);

Testing feeds

• Unit tests: a mock feed you control (set(answer, updatedAt), setRounds, setNoAccess)
• Integration: read-only fork of mainnet

XDC_FORK_RPC=https://rpc.xinfin.network forge test --match-path 'test/fork/*'

• vm.warp past the heartbeat to prove your staleness check works

→ Lab 2