오프체인 데이터 조회 처리

Bridging On-chain & Off-chain

The Oracle Request-Response Model

Your Contract: A Chainlink Client

Initiating a Data Request

Code: Requesting Live Price Data

/*
  This is a simplified example for explanation.
  For a real deployment, replace placeholders like
  oracle address, LINK address, jobId, and fee
  with values for your chosen Chainlink network.
*/
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;

import "@chainlink/contracts/src/v0.8/ChainlinkClient.sol";

contract PriceConsumer is ChainlinkClient {
    bytes32 public lastRequestId; // Stores the ID of our last request
    uint256 public currentPrice; // Where we'll store the fetched price

    address private immutable i_oracle; // Chainlink oracle address
    bytes32 private immutable i_jobId;  // Specific job ID for the data source
    uint256 private immutable i_fee;    // Amount of LINK to pay for the request

    constructor(address _oracle, address _link, bytes32 _jobId, uint256 _fee) {
        setChainlinkToken(_link); // Set the LINK token address
        i_oracle = _oracle;
        i_jobId = _jobId;
        i_fee = _fee;
    }

    // Function to request a price from a Chainlink oracle
    function requestEthPrice() public returns (bytes32) {
        // 1. Build the Chainlink request
        Chainlink.Request memory request = buildChainlinkRequest(
            i_jobId,                      // The job ID for the oracle
            address(this),                // Our contract's address
            this.fulfillEthPrice.selector // The function the oracle will call back
        );

        // 2. Add parameters for the Chainlink node (e.g., API URL, path to data)
        request.add("get", "https://min-api.cryptocompare.com/data/price?fsym=ETH&tsyms=USD");
        request.add("path", "USD"); // Extract the USD value from the JSON response
        request.addInt("times", 100000000); // Multiply by 10^8 for fixed-point math

        // 3. Send the request to the oracle
        lastRequestId = sendChainlinkRequestTo(i_oracle, request, i_fee);
        return lastRequestId;
    }

    // The fulfillEthPrice function will be defined later!
}

Tracking Requests with IDs

Fulfilling the Data Request

Code: Implementing the Callback

/*
  This is a simplified example for explanation.
  For a real deployment, replace placeholders like
  oracle address, LINK address, jobId, and fee
  with values for your chosen Chainlink network.
*/
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;

import "@chainlink/contracts/src/v0.8/ChainlinkClient.sol";

contract PriceConsumer is ChainlinkClient {
    bytes32 public lastRequestId; // Stores the ID of our last request
    uint256 public currentPrice; // Where we'll store the fetched price

    address private immutable i_oracle; // Chainlink oracle address
    bytes32 private immutable i_jobId;  // Specific job ID for the data source
    uint256 private immutable i_fee;    // Amount of LINK to pay for the request

    constructor(address _oracle, address _link, bytes32 _jobId, uint256 _fee) {
        setChainlinkToken(_link); // Set the LINK token address
        i_oracle = _oracle;
        i_jobId = _jobId;
        i_fee = _fee;
    }

    // Function to request a price from a Chainlink oracle
    function requestEthPrice() public returns (bytes32) {
        Chainlink.Request memory request = buildChainlinkRequest(
            i_jobId,
            address(this),
            this.fulfillEthPrice.selector // Callback function
        );
        request.add("get", "https://min-api.cryptocompare.com/data/price?fsym=ETH&tsyms=USD");
        request.add("path", "USD");
        request.addInt("times", 100000000); // Multiply by 10^8
        lastRequestId = sendChainlinkRequestTo(i_oracle, request, i_fee);
        return lastRequestId;
    }

    // This is the callback function called by the Chainlink oracle
    function fulfillEthPrice(bytes32 _requestId, uint256 _price)
        public
        recordChainlinkFulfillment(_requestId) // Security modifier
    {
        // Crucial: Check if the requestId matches our last sent request
        require(lastRequestId == _requestId, "Request ID mismatch!");
        currentPrice = _price; // Store the fetched price
    }
}

Enhancing Data Integrity

Quick Check: Oracle Flow

Recap: Off-chain Data Retrieval