如何使用 Chainlink api 调用通过 api 从 json 返回中检索字符串值答案

【问题标题】：How do I use a Chainlink api call to retrieve a string value from json returne by api如何使用 Chainlink api 调用通过 api 从 json 返回中检索字符串值
【发布时间】：2021-12-28 21:30:21
【问题描述】：

我正在尝试使用 chainlink 请求进行 api 调用，然后使用 api 调用的结果更新 volume 变量。

api 调用应该检索一个字符串。在部署和资助智能合约之后，我似乎能够成功地进行 api 调用（尽管我对此不确定）。问题是音量变量没有更新。

我从chainlink tutorial 改编了代码。原始教程代码有效，在我看来，我所做的更改也应该有效。有人可以帮忙吗？

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;

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

/**
 * Request testnet LINK and ETH here: https://faucets.chain.link/
 * Find information on LINK Token Contracts and get the latest ETH and LINK faucets here: https://docs.chain.link/docs/link-token-contracts/
 */

/**
 * THIS IS AN EXAMPLE CONTRACT WHICH USES HARDCODED VALUES FOR CLARITY.
 * PLEASE DO NOT USE THIS CODE IN PRODUCTION.
 */
contract APIConsumer is ChainlinkClient {
    using Chainlink for Chainlink.Request;
  
    string public volume;
    
    address private oracle;
    bytes32 private jobId;
    uint256 private fee;
    
    /**
     * Network: Kovan
     * Oracle: 0xc57B33452b4F7BB189bB5AfaE9cc4aBa1f7a4FD8 (Chainlink Devrel   
     * Node)
     * Job ID: d5270d1c311941d0b08bead21fea7747
     * Fee: 0.1 LINK
     */
    constructor() {
        setPublicChainlinkToken();
        oracle = 0xF405B99ACa8578B9eb989ee2b69D518aaDb90c1F;
        jobId = "c51694e71fa94217b0f4a71b2a6b565a";
        fee = 0.1 * 10 ** 18; // (Varies by network and job)
    }
    
    /**
     * Create a Chainlink request to retrieve API response, find the target
     * data, then multiply by 1000000000000000000 (to remove decimal places from data).
     */
    function requestVolumeData() public returns (bytes32 requestId) 
    {
        Chainlink.Request memory request = buildChainlinkRequest(jobId, address(this), this.fulfill.selector);
        
        // Set the URL to perform the GET request on
        request.add("get", "https://min-api.cryptocompare.com/data/pricemultifull?fsyms=ETH&tsyms=USD");
        
        // Set the path to find the desired data in the API response, where the response format is:
        // {"RAW":
        //   {"ETH":
        //    {"USD":
        //     {
        //      "VOLUME24HOUR": xxx.xxx,
        //     }
        //    }
        //   }
        //  }
        request.add("path", "RAW.ETH.USD.MARKET");
        
        // // Multiply the result by 1000000000000000000 to remove decimals
        // int timesAmount = 10**18;
        // request.addInt("times", timesAmount);
        
        // Sends the request
        return sendChainlinkRequestTo(oracle, request, fee);
    }
    
    /**
     * Receive the response in the form of uint256
     */ 
    function fulfill(bytes32 _requestId, bytes32 _volume) public recordChainlinkFulfillment(_requestId)
    {
        volume = bytes32ToString(_volume);
        
    }
    
    
    function bytes32ToString(bytes32 _bytes32) public pure returns (string memory) {
        uint8 i = 0;
        while(i < 32 && _bytes32[i] != 0) {
            i++;
        }
        bytes memory bytesArray = new bytes(i);
        for (i = 0; i < 32 && _bytes32[i] != 0; i++) {
            bytesArray[i] = _bytes32[i];
        }
        return string(bytesArray);
    }

    // function withdrawLink() external {} - Implement a withdraw function to avoid locking your LINK in the contract
}

【问题讨论】：

标签： ethereum solidity web3js chainlink

【解决方案1】：

要返回一个字符串，你实际上必须返回一个bytes32 并将其转换为链上的字符串。

你可以使用这样的东西，将 bytes32 转换为字符串：

function bytes32ToString(bytes32 _bytes32) public pure returns (string memory) {
        uint8 i = 0;
        while(i < 32 && _bytes32[i] != 0) {
            i++;
        }
        bytes memory bytesArray = new bytes(i);
        for (i = 0; i < 32 && _bytes32[i] != 0; i++) {
            bytesArray[i] = _bytes32[i];
        }
        return string(bytesArray);
    }

【讨论】：