Example to understand Chainlink Keepers, based on a web3 script

The main idea of this example is to create an auxiliary task called “keeper-simulation” to manually try and adjust the Keeper prior to registration in the keeper network.

To understand what are Chainlink Keepers please read the following docs

• Introduction to Chainlink Keepers
• Keepers Network Overview

Requirements

• NPM or YARN
• Chainlink Hardhat Box

Installation

git clone -b keeper-simulation-w-web3script https://github.com/digitalbridgekit/hardhat-starter-kit.git
cd hardhat-starter-kit

then

npm install

Or

yarn

then execute the following

cp .env.example .env

Example context

The Counter contract

The follow contract implements KeeperCompatibleInterface interface, this interface able the contract to be called by a keeper.

pragma solidity ^0.8.7;

interface KeeperCompatibleInterface {
    function checkUpkeep(bytes calldata checkData) external returns (bool upkeepNeeded, bytes memory performData);
    function performUpkeep(bytes calldata performData) external;
}
contract Counter is KeeperCompatibleInterface {
    /**
    * Public counter variable
    */
    uint public counter;
    /**
    * Use an interval in seconds and a timestamp to slow execution of Upkeep
    */
    uint public immutable interval;
    uint public lastTimeStamp;
    
    constructor(uint updateInterval) public {
      interval = updateInterval;
      lastTimeStamp = block.timestamp;
      counter = 0;
    }
    function checkUpkeep(bytes calldata checkData) external override returns (bool upkeepNeeded, bytes memory performData) {
        upkeepNeeded = (block.timestamp - lastTimeStamp) > interval;
        // We don't use the checkData in this example
        // checkData was defined when the Upkeep was registered
        performData = checkData;
    }
    function performUpkeep(bytes calldata performData) external override {
        lastTimeStamp = block.timestamp;
        counter = counter + 1;
        // We don't use the performData in this example
    }
}

The keeper-simulation task

As the Counter contract is defined to be called in external mode, it’s necessary a web3 script to call the Counter contract, simulating a Keeper call.

keeper-simulation.js

Steps to deploy and test the contract and understand how the Keepers works

The first step is run hardhat as local node

user@host:~/keeper/hardhat-starter-kit$ npx hardhat node
Started HTTP and WebSocket JSON-RPC server at http://127.0.0.1:8545/

The second step is deploy the contracts

• In a different terminal execute the following

user@host:~/keeper/hardhat-starter-kit$ npx hardhat deploy --network localhost --tags keepers

output

Compilation finished successfully
deploying "Counter" (tx: 0xe74fb4e378f4055540692272da229b22bbbafc07a8589f13118bfdd07d30e51e)...: deployed at 0x8A791620dd6260079BF849Dc5567aDC3F2FdC318 with 342119 gas
Run the following command to track the counter updates:
npx hardhat read-keepers-counter --contract 0x8A791620dd6260079BF849Dc5567aDC3F2FdC318 --network localhost
Run the following command to manually simulate a Keeper call:
npx hardhat keeper-simulation --contract 0x8A791620dd6260079BF849Dc5567aDC3F2FdC318 --network localhost
----------------------------------------------------

Then to understand how it works

The Counter contract has:

• 30 seconds as interval value
• The counter it’s initialized in 0
• lastimestamp is initalized with the timestamp of the block when the contract is deployed.

To read the current state excecute the following

user@host:~/keeper/hardhat-starter-kit$ npx hardhat read-keepers-counter --contract 0x8A791620dd6260079BF849Dc5567aDC3F2FdC318 --network localhost

output

Reading counter from Keepers contract  0x8A791620dd6260079BF849Dc5567aDC3F2FdC318  on network  localhost
Last timestamp is:  1638220869
Counter is:  0

The counter in 0 value implie that the keeper never executed the preformUpkeep function

Now after more than 30 seconds execute the follow

user@host:~/keeper/hardhat-starter-kit$ npx hardhat keeper-simulation --contract 0x8A791620dd6260079BF849Dc5567aDC3F2FdC318 --network localhost

output

Calling Counter contract simulating a Keeper call  0x8A791620dd6260079BF849Dc5567aDC3F2FdC318  on network  localhost
Contract  0x8A791620dd6260079BF849Dc5567aDC3F2FdC318  checkUpkeep:  true
Contract  0x8A791620dd6260079BF849Dc5567aDC3F2FdC318  performUpkeep was called. Transaction Hash:  0x6011322d77c46b3181098e305b9ef7cefdb7345b09097d73e791859265613e40

As the interval is greater than 30 seconds the checkUpkeep function responds true so the performUpkeep function is executed in the same way as for the keeper.

Now you can read the status again.

user@host:~/keeper/hardhat-starter-kit$ npx hardhat read-keepers-counter --contract 0x8A791620dd6260079BF849Dc5567aDC3F2FdC318 --network localhost

output

Reading counter from Keepers contract  0x8A791620dd6260079BF849Dc5567aDC3F2FdC318  on network  localhost
Last timestamp is:  1638220921
Counter is:  1

You can verify that the counter value was incremented in 1 more and the lasttimestamp changed to the current value too.

Now you need to wait more than 30 seconds again and execute the contract that simulates the keeper again

user@host:~/keeper/hardhat-starter-kit$ npx hardhat keeper-simulation --contract 0x8A791620dd6260079BF849Dc5567aDC3F2FdC318 --network localhost

output

Calling Counter contract simulating a Keeper call  0x8A791620dd6260079BF849Dc5567aDC3F2FdC318  on network  localhost
Contract  0x8A791620dd6260079BF849Dc5567aDC3F2FdC318  checkUpkeep:  true
Contract  0x8A791620dd6260079BF849Dc5567aDC3F2FdC318  performUpkeep was called. Transaction Hash:  0x740019915422734e6926879560791818ad8ac61ea5dd020fbb866289f7084a37

The result true indicates that the performUpkeep was executed again.

Reading the current Counter values.

user@host:~/keeper/hardhat-starter-kit$ npx hardhat read-keepers-counter --contract 0x8A791620dd6260079BF849Dc5567aDC3F2FdC318 --network localhost

output

Reading counter from Keepers contract  0x8A791620dd6260079BF849Dc5567aDC3F2FdC318  on network  localhost
Last timestamp is:  1638220985
Counter is:  2

The counter increment 1 more its value and the timestamp changed to the new value.

But if you execute the contract that simulates the keeper again before 30 seconds from the last execution.

user@host:~/keeper/hardhat-starter-kit$ npx hardhat keeper-simulation --contract 0x8A791620dd6260079BF849Dc5567aDC3F2FdC318 --network localhost

output

Calling Counter contract simulating a Keeper call  0x8A791620dd6260079BF849Dc5567aDC3F2FdC318  on network  localhost
Contract  0x8A791620dd6260079BF849Dc5567aDC3F2FdC318  checkUpkeep:  false

The results of checkUpkeep function is false So if you read the Counter values.

user@host:~/keeper/hardhat-starter-kit$ npx hardhat read-keepers-counter --contract 0x8A791620dd6260079BF849Dc5567aDC3F2FdC318 --network localhost

output

Reading counter from Keepers contract  0x8A791620dd6260079BF849Dc5567aDC3F2FdC318  on network  localhost
Last timestamp is:  1638220985
Counter is:  2

The state didn’t change.

When the contract reaches this testing phase and is adjusted, it can continue the process registering it at https://keepers.chain.link/

If you want to automate your own contract I suggest to learn Hardhat . The mainly files that you need to modify are KeepersCounter.sol , 04_Deploy_KeepersCounter.js , keeper-simulation.js and read-keepers-counter.js .

This is a contribution to the Chainlink Developer Expert Program that we are part of.

About Chainlink

Chainlink is the industry standard for building, accessing, and selling oracle services needed to power hybrid smart contracts on any blockchain. Chainlink oracle networks provide smart contracts with a way to reliably connect to any external API and leverage secure off-chain computations for enabling feature-rich applications. Chainlink currently secures tens of billions of dollars across DeFi, insurance, gaming, and other major industries, and offers global enterprises and leading data providers a universal gateway to all blockchains.

Learn more about Chainlink by visiting chain.link or read the documentation at docs.chain.link. To discuss an integration, reach out to an expert.

Website | Twitter | Discord | Reddit | YouTube | Telegram | Events | GitHub | Price Feeds | DeFi

About Digital Bridge

We are building trust digital bridges for business.

We are Chainlink oracles providers. Digital Bridge is interconnecting Blockchain Networks with external Computer Systems. Providing high quality information for the correct execution of smart contracts as well as communicating the results to external systems.

Working on back end and middleware development tools for DeFi protocols and blockchain ecosystems.

To find out more about us you can contact us by email to hello@digitalbridge.link. Follow us on Twitter https://twitter.com/DigitalBridgeIO and social media for future updates:

Twitter | LinkedIn | Web | Telegram | GitHub