Solidity consumer example

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

/// The one VerifierProxy function a consumer needs.
interface IVerifierProxy {
    /// Verifies a signed DataLink report and returns its report data.
    /// Reverts if the signatures or the report are not valid.
    function verify(bytes calldata payload, bytes calldata parameterPayload)
        external
        payable
        returns (bytes memory verifierResponse);
}

/// Example DataLink consumer: verifies a signed report on-chain, decodes it,
/// checks it is for the expected feed and recent enough, then stores the price.
/// EXAMPLE CODE — not audited. Review and test it before any real use.
contract DataLinkPriceConsumer {
    /// The nine fields encoded in a DataLink report (schema v1), in order.
    struct Report {
        bytes32 feedId;
        uint32 observationsTimestamp;
        int192 benchmarkPrice;
        int192 bid;
        int192 ask;
        uint64 currentBlockNum;
        bytes32 currentBlockHash;
        uint64 validFromBlockNum;
        uint64 currentBlockTimestamp;
    }

    IVerifierProxy public immutable verifierProxy;
    bytes32 public immutable feedId;
    /// Price decimals of this feed (from its report schema). Stored for reference:
    /// a price of 8157000000 with 8 decimals means 81.57.
    uint8 public immutable decimals;
    /// Oldest report accepted, in seconds.
    uint256 public immutable maxReportAge;

    int192 public latestPrice;
    int192 public latestBid;
    int192 public latestAsk;
    uint32 public latestObservationsTimestamp;

    event PriceUpdated(bytes32 indexed feedId, int192 price, uint32 observationsTimestamp);

    error WrongFeed(bytes32 expected, bytes32 received);
    error StaleReport(uint32 observationsTimestamp, uint256 currentTimestamp);
    error NotNewerThanStored(uint32 observationsTimestamp, uint32 storedTimestamp);

    constructor(address verifierProxy_, bytes32 feedId_, uint8 decimals_, uint256 maxReportAge_) {
        verifierProxy = IVerifierProxy(verifierProxy_);
        feedId = feedId_;
        decimals = decimals_;
        maxReportAge = maxReportAge_;
    }

    /// @param signedPayload The `payload` from GET /api/v1/reports/latest, with a 0x prefix.
    function updatePrice(bytes calldata signedPayload) external {
        // 1. Verify. Reverts unless the DataLink signers signed this exact report.
        //    parameterPayload is empty: no FeeManager is configured on the
        //    XDC Mainnet VerifierProxy, so no fee is paid.
        bytes memory reportData = verifierProxy.verify(signedPayload, "");

        // 2. Decode the verified report data into its nine fields.
        Report memory report = abi.decode(reportData, (Report));

        // 3. Only accept the feed this contract is for.
        if (report.feedId != feedId) revert WrongFeed(feedId, report.feedId);

        // 4. Only accept recent reports.
        if (uint256(report.observationsTimestamp) + maxReportAge < block.timestamp) {
            revert StaleReport(report.observationsTimestamp, block.timestamp);
        }

        // 5. Never replace a newer stored price with an older (or the same) report.
        if (report.observationsTimestamp <= latestObservationsTimestamp) {
            revert NotNewerThanStored(report.observationsTimestamp, latestObservationsTimestamp);
        }

        // 6. Store.
        latestPrice = report.benchmarkPrice;
        latestBid = report.bid;
        latestAsk = report.ask;
        latestObservationsTimestamp = report.observationsTimestamp;
        emit PriceUpdated(report.feedId, report.benchmarkPrice, report.observationsTimestamp);
    }
}