Overview

Using an existing Oracle Job makes your smart contract code more succinct. This page explains how to retrieve the gas price from an existing Chainlink job that calls etherscan gas tracker API.

Topics

• Example
• Response Types
• Setting the LINK token address, Oracle, and JobId

Example

In Single Word Response Example, the example contract code declared which URL to use, where to find the data in the response, and how to convert it so that it can be represented on-chain.

This example uses an existing job that is pre-configured to make requests to get the gas price. Using specialized jobs makes your contracts succinct and more simple.

Etherscan gas oracle returns the current Safe, Proposed and Fast gas prices. To check the response, you can directly paste the following URL in your browser https://api.etherscan.io/api?module=gastracker&action=gasoracle&apikey=YourApiKeyToken or run this command in your terminal:

curl -X 'GET' \
  'https://api.etherscan.io/api?module=gastracker&action=gasoracle&apikey=YourApiKeyToken' \
  -H 'accept: application/json'

The response should be similar to the following:

{
  "status": "1",
  "result": {
    "LastBlock": "14653286",
    "SafeGasPrice": "33",
    "ProposeGasPrice": "33",
    "FastGasPrice": "35",
    "suggestBaseFee": "32.570418457",
    "gasUsedRatio": "0.366502543599508,0.15439818258491,0.9729006,0.4925609,0.999657066666667"
  }
}

For this example, we created a job that leverages the EtherScan External Adapter to fetch the SafeGasPrice , ProposeGasPrice and FastGasPrice. You can learn more about External Adapters here.
To consume an API, your contract must import ChainlinkClient.sol. This contract exposes a struct named Chainlink.Request, which your contract can use to build the API request. The request must include the following parameters:

• Link token address
• Oracle address
• Job id
• Request fee
• Task parameters
• Callback function signature

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

import '@chainlink/contracts/src/v0.8/ChainlinkClient.sol';
import '@chainlink/contracts/src/v0.8/ConfirmedOwner.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 THAT USES HARDCODED VALUES FOR CLARITY.
 * THIS IS AN EXAMPLE CONTRACT THAT USES UN-AUDITED CODE.
 * DO NOT USE THIS CODE IN PRODUCTION.
 */

contract GetGasPrice is ChainlinkClient, ConfirmedOwner {
    using Chainlink for Chainlink.Request;

    uint256 public gasPriceFast;
    uint256 public gasPriceAverage;
    uint256 public gasPriceSafe;

    bytes32 private jobId;
    uint256 private fee;

    event RequestGasPrice(
        bytes32 indexed requestId,
        uint256 gasPriceFast,
        uint256 gasPriceAverage,
        uint256 gasPriceSafe
    );

    /**
     * @notice Initialize the link token and target oracle
     *
     * Goerli Testnet details:
     * Link Token: 0x326C977E6efc84E512bB9C30f76E30c160eD06FB
     * Oracle: 0xCC79157eb46F5624204f47AB42b3906cAA40eaB7 (Chainlink DevRel)
     * jobId: 7223acbd01654282865b678924126013
     *
     */
    constructor() ConfirmedOwner(msg.sender) {
        setChainlinkToken(0x326C977E6efc84E512bB9C30f76E30c160eD06FB);
        setChainlinkOracle(0xCC79157eb46F5624204f47AB42b3906cAA40eaB7);
        jobId = '7223acbd01654282865b678924126013';
        fee = (1 * LINK_DIVISIBILITY) / 10; // 0,1 * 10**18 (Varies by network and job)
    }

    /**
     * Create a Chainlink request the gas price from Etherscan
     */
    function requestGasPrice() public returns (bytes32 requestId) {
        Chainlink.Request memory req = buildChainlinkRequest(jobId, address(this), this.fulfill.selector);
        // No need extra parameters for this job. Send the request
        return sendChainlinkRequest(req, fee);
    }

    /**
     * Receive the responses in the form of uint256
     */
    function fulfill(
        bytes32 _requestId,
        uint256 _gasPriceFast,
        uint256 _gasPriceAverage,
        uint256 _gasPriceSafe
    ) public recordChainlinkFulfillment(_requestId) {
        emit RequestGasPrice(_requestId, _gasPriceFast, _gasPriceAverage, _gasPriceSafe);
        gasPriceFast = _gasPriceFast;
        gasPriceAverage = _gasPriceAverage;
        gasPriceSafe = _gasPriceSafe;
    }

    /**
     * Allow withdraw of Link tokens from the contract
     */
    function withdrawLink() public onlyOwner {
        LinkTokenInterface link = LinkTokenInterface(chainlinkTokenAddress());
        require(link.transfer(msg.sender, link.balanceOf(address(this))), 'Unable to transfer');
    }
}

To use this contract:

1. Open the contract in Remix.

2. Compile and deploy the contract using the Injected Provider environment. The contract includes all the configuration variables for the Goerli testnet. Make sure your wallet is set to use Goerli. The constructor sets the following parameters:

   • The Chainlink Token address for Goerli by calling the setChainlinkToken function.
   • The Oracle contract address for Goerli by calling the setChainlinkOracle function.
   • The jobId: A specific job for the oracle node to run. In this case, the job is very specific to the use case as it returns the gas prices. You can find the job spec for the Chainlink node here.

3. Fund your contract with 0.1 LINK. To learn how to send LINK to contracts, read the Fund Your Contracts page.

4. Call the gasPriceFast, gasPriceAverage and gasPriceSafe functions to confirm that the gasPriceFast, gasPriceAverage and gasPriceSafe state variables are equal to zero.

5. Run the requestGasPrice function. This builds the Chainlink.Request. Note how succinct the request is.

6. After few seconds, call the gasPriceFast, gasPriceAverage and gasPriceSafe functions. You should get a non-zero responses.

Response Types

Make sure to choose an oracle job that supports the data type that your contract needs to consume. Multiple data types are available such as:

• uint256 - Unsigned integers
• int256 - Signed integers
• bool - True or False values
• string - String
• bytes32 - Strings and byte values. If you need to return a string, use bytes32. Here's one method of converting bytes32 to string. Currently, any return value must fit within 32 bytes. If the value is bigger than that, make multiple requests.
• bytes - Arbitrary-length raw byte data

Setting the LINK token address, Oracle, and JobId

The setChainlinkToken function sets the LINK token address for the network you are deploying to. The setChainlinkOracle function sets a specific Chainlink oracle that a contract makes an API call from. The jobId refers to a specific job for that node to run.

Each job is unique and returns different types of data. For example, a job that returns a bytes32 variable from an API would have a different jobId than a job that retrieved the same data, but in the form of a uint256 variable.

Check the Find Existing Jobs page to learn how to find a job suitable to your use case.