ChainlinkDataFeeds.s.sol

💻 The code corresponding to this page can be found on Github at ChainlinkDataFeeds.s.sol

The best way to deploy contracts using Foundry is to use the write a simple deploy script. However, we first need to set up a dotenv file to store our environment variables.

At the root of your project, create a file named .env. Fill out your environment variables like this:

# Alchemy RPC URLs
SEPOLIA_RPC_URL=

# Private Key
PRIVATE_KEY=

# Etherscan and Polygonscan API keys
ETHERSCAN_API_KEY=

1. You can get RPC URLs from Alchemy, or any other RPC provider. You can also use a public RPC URL.
2. Make sure to use the private key of a wallet that has some Sepolia ETH. You can get some from Alchemy's Sepolia faucet.
3. Get your Etherscan API key from Etherscan's website.

Once your environment variables are set up, run source .env to load them into your shell. Let us now write a script to deploy the data feeds contract.

📝 Note: This is really, really important. Whatever happens, make sure to NOT push your env variables to Github. To make sure that doesn't happen, add .env to your .gitignore file. Please note that even using a normal dotenv file is not recommended behaviour. Ideally you should be using a hardware wallet, and/or an encrypted keystore. But for the sake of simplicity, I'll be using a dotenv file throughout.

Create a file named ChainlinkDataFeeds.s.sol, and initialize a deployment contract like this:

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.19;

import "forge-std/Script.sol";
import {ChainlinkDataFeeds} from "./ChainlinkDataFeeds.sol";

contract DeployDataFeed is Script {

}

This contract is executed using the forge script command. Next, within the DeployDataFeeds contract, initialize an instance of the data feeds contract, and define a function named run():

 ChainlinkDataFeeds chainlinkDataFeeds;

    function run() external {
        
        // Using the envUint cheatcode we can read some env variables
        uint256 PrivateKey = vm.envUint("PRIVATE_KEY");

        // Anything within the broadcast cheatcodes is executed on-chain
        vm.startBroadcast(PrivateKey);
        chainlinkDataFeeds = new ChainlinkDataFeeds(0x694AA1769357215DE4FAC081bf1f309aDC325306);
        vm.stopBroadcast();
    }

A few things happen here:

1. The run() function serves as the default entry point for the script.
2. We can use the envUint() cheatcode to read environment variables from the .env file. This way we don't have to pass the private key as a command line argument.
3. The startBroadcast() and stopBroadcast() cheatcodes are used to execute the code on-chain. Anything within these two cheatcodes is executed on-chain.
4. Finally, the new instance of the data feeds contract is passed an address as an argument. This address is the address of the aggregator contract that serves the ETH/USD price feed on the Sepolia testnet.

Save everything and run forge build to make sure everything compiles correctly. To run the script, use the forge script command like this:

forge script src/Applications/Chainlink/ChainlinkDataFeeds/ChainlinkDataFeeds.s.sol:DeployDataFeed \
--rpc-url $SEPOLIA_RPC_URL \
--broadcast -vvvv

The exact params may of course differ depending on your setup. To verify the contract once it is deployed, run:

forge verify-contract <Your contract address> \
--chain-id 11155111 \
--num-of-optimizations 200 \
--watch --compiler-version v0.8.19+commit.7dd6d404 \
--constructor-args $(cast abi-encode "constructor(address)" 0x694AA1769357215DE4FAC081bf1f309aDC325306) \
src/Applications/Chainlink/ChainlinkDataFeeds/ChainlinkDataFeeds.sol:ChainlinkDataFeeds \
--etherscan-api-key $ETHERSCAN_API_KEY

📝 Note: It is possible to verify the contract your contract at the time of deployment by passing the --verify flag to the forge script command. However, this way of verification fails more often than not in my experience. You can read more about this in Foundry's docs.