Onchain Tutorial (2/2): Deploy Your Airdrop Contract

Overview

This tutorial aims at describing the process behind the deployment of Sismo Connect contracts. In this context, we will recap on what a Sismo Connect Client config is and how to impersonate accounts. Once understood, these notions will allow you to confidently deploy contracts with Sismo Connect's functionalities.

To better understand the different notions highlighted in this tutorial, we strongly advise you to go through the first tutorial, which will show you how to leverage data aggregation in your app by building a Gated Airdrop for Gitcoin Passport holders.

For this tutorial, we will again use the GitHub repository used for the gated airdrop tutorial. You can clone it and install it as described in the repository's README or in the tutorial. You don't need to clone it again if you just finished the tutorial.

Prerequisites

This tutorial requires:

• Node.js >= 18.15.0 (Latest LTS version)

• Yarn

• Foundry (see how to install it here)

• MetaMask installed in your browser

We use Foundry for our smart contract dependencies, but we also have a Hardhat library. This tutorial is focused on how to deploy your smart contracts using Foundry.

Installation

This tutorial is based on the following tutorial repository. You can clone it with the following command:

git clone https://github.com/sismo-core/sismo-connect-onchain-tutorial
cd sismo-connect-onchain-tutorial
yarn

Install contract dependencies

# updates foundry
foundryup
# install smart contract dependencies
forge install

Once these steps are done, you are well set up to use Forge, a tool provided by Foundry to test and deploy smart contracts.

Understand the Sismo Connect config

Before deploying any Sismo Connect contract, it is better to understand the Sismo Connect config and especially how to impersonate accounts.

As you may already know, Sismo Connect is the communication layer allowing any Sismo Connect app to request ZK proofs about user data and receive the expected proofs before verifying them. To be able to produce such proofs, users are required to import accounts (i.e. Data Sources) into their Data Vaults. By doing so, they will be able to prove group membership and account ownership to apps.

Such proof generation is possible (among other things) thanks to the Commitment Mapper. Therefore, we allow any developer to impersonate accounts by automatically creating a fake Commitment Mapper in the Vault app front end if the Vault object with the impersonate field is defined in the Sismo Connect configuration.

You can learn more about the Sismo Connect configuration here.

// in your frontend

export const sismoConnectConfig: SismoConnectConfig = {
  appId: "0xf4977993e52606cfd67b7a1cde717069",
  vault: {
    // this will let the Vault App create fake commitments in the Vault App frontend
    // allowing devs to create valid proofs with such fake commitments
    // you will then need to reference that you are impersonating accounts in your contract
    // to be able to verify the proofs with fake commitments
    impersonate: [
      "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045", // vitalik.eth
      "0x8ab1760889F26cBbf33A75FD2cF1696BFccDc9e6" // dhadrien.eth
    ]
  }
};

// in your contract

import "sismo-connect-solidity/SismoConnectLib.sol";

contract A is SismoConnect {
  // add your appId
  bytes16 private _appId = 0xf4977993e52606cfd67b7a1cde717069;
  // use impersonated mode for testing
  bool private _isImpersonationMode = true;

  constructor()
    // use buildConfig helper to easily build a Sismo Connect config in Solidity
    SismoConnect(buildConfig(_appId, _isImpersonationMode))
  {}
}

The deployment script

Solidity scripting is a way to declaratively deploy contracts using Solidity instead of using the more limiting and less user friendly forge create. You can look at the example displayed in the Foundry documentation if you want to learn more about it.

We are going to use a simple Solidity script to deploy our contract on our chosen network.

You can see the script used in script/Airdrop.s.sol file. Here is it:

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.13;

import "forge-std/Script.sol";
import "forge-std/console.sol";
import {Airdrop} from "src/Airdrop.sol";

contract DeployAirdrop is Script {
    function run() public {
        vm.startBroadcast();
        Airdrop airdrop = new Airdrop("My airdrop contract", "AIR");
        console.log("Airdrop Contract deployed at", address(airdrop));
        vm.stopBroadcast();
    }
}

This script is simple; it declares a new airdrop contract between vm.startBroadcast and vm.stopBroadcast, two foundry cheatcodes that will simulate the contract creation in the context you will provide.

You can simply run this command to see the simulation of your contract deployment in the context of a Mumbai fork.

forge script DeployAirdrop --rpc-url <your-mumbai-rpc-url>

# if you dont have any personal rpc url
# you can try to use https://rpc.ankr.com/polygon_mumbai

# output
== Logs ==
  Airdrop Contract deployed at 0x34A1D3fff3958843C43aD80F30b94c510645C316

EIP-3855 is not supported in one or more of the RPCs used.
Unsupported Chain IDs: 80001.
Contracts deployed with a Solidity version equal or higher than 0.8.20 might not work properly.
For more information, please see https://eips.ethereum.org/EIPS/eip-3855

## Setting up (1) EVMs.

==========================

Chain 80001

Estimated gas price: 3.000000038 gwei

Estimated total gas used for script: 5442749

Estimated amount required: 0.016328247206824462 ETH

==========================

SIMULATION COMPLETE. To broadcast these transactions, add --broadcast and wallet configuration(s) to the previous command. See forge script --help for more.

As you can see in the output logs, the simulation of the airdrop contract deployment was successful. You can even see the amount that will be required for you to deploy on the Mumbai Testnet. (You can use this Alchemy faucet if you need some testnet tokens: https://mumbaifaucet.com/)

Since we are happy with the script simulation, we can broadcast it on Mumbai by inputting an EOA private key in the command line.

We strongly advise you to use a private key from a developer account when developing, do not leak any private key linked to some accounts with real assets in it.

Here is how to deploy the airdrop smart contract on the Mumbai testnet network. We use a publicly known private key to show you how to do it.

forge script DeployAirdrop --rpc-url <your-mumbai-rpc-url> --private-key '0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80' --broadcast

# if you dont have any personal rpc url
# you can try to use https://rpc.ankr.com/polygon_mumbai

If you try to run this exact command without changing the private key, you will encounter an error since the account has no funds. You should replace the private key by your own developer private key and have some funds on your dev account (Mumbai faucet link: https://mumbaifaucet.com/).

Notice the --broadcast option, which states that you want to actually trigger the transaction on the Mumbai testnet.

Verify your contracts with --verify option

To verify your contracts, you will need to register for an Etherscan API key.

The Etherscan API Key needs to be registered from PolygonScan if you want to deploy on Mumbai: https://polygonscan.com/myaccount

You just need to directly specify the --verify option when deploying alongside your Etherscan API key.

In clear terms:

forge script DeployAirdrop \
--rpc-url <your-mumbai-rpc-url> \
--private-key '0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80' \
--broadcast \
--etherscan-api-key <your_etherscan_api_key> \
--verify \
--watch

# if you dont have any personal rpc url
# you can try to use https://rpc.ankr.com/polygon_mumbai

# output
==========================

ONCHAIN EXECUTION COMPLETE & SUCCESSFUL.
Total Paid: 0.00837346 ETH (4186730 gas * avg 2 gwei)
##
Start verification for (1) contracts
Start verifying contract `0x1465ebb35e84a307a59e9c38d9ec3e773683b706` deployed on mumbai

Submitting verification for [src/Airdrop.sol:Airdrop] "0x1465EbB35e84a307A59E9c38D9Ec3E773683b706".

Submitting verification for [src/Airdrop.sol:Airdrop] "0x1465EbB35e84a307A59E9c38D9Ec3E773683b706".

Submitting verification for [src/Airdrop.sol:Airdrop] "0x1465EbB35e84a307A59E9c38D9Ec3E773683b706".
Submitted contract for verification:
	Response: `OK`
	GUID: `cgfkzkpdki9c2jlnwpy9lzrhpuckxhadf4yyqysm38jzmqscgi`
	URL:
        https://mumbai.polygonscan.com/address/0x1465ebb35e84a307a59e9c38d9ec3e773683b706
Contract verification status:
Response: `NOTOK`
Details: `Pending in queue`
Contract verification status:
Response: `OK`
Details: `Pass - Verified`
Contract successfully verified
All (1) contracts were verified!

If you deploy the exact contract from the tutorial on Mumbai, you are likely to encounter a message reading "Already verified". As long as your contract is verified, it is totally fine!

And congrats on your deployment! You should be left with a verified contract at this point. If not, don't hesitate to reach out to us on our developer Telegram.

If you want to use the tutorial front end with your contracts, you will need to add some minor changes to the front/src/app/page.tsx file. You will first need to change how you get the contractAddress by changing 5151111 (the fork chain id) to 80001 (the Mumbai chain id) in your imports. You also have to use the polygonMumbai chain config from viem instead of mumbaiFork config for the chain.

// you are in: front/src/app/page.tsx

// import { transactions } from "../../../broadcast/Airdrop.s.sol/5151111/run-latest.json";
import { transactions } from "../../../broadcast/Airdrop.s.sol/80001/run-latest.json";
// ------------------------------------------------------------^^^^^ 
//                                                        REPLACE HERE

/* ********************  Defines the chain to use *************************** */
// replace
// const CHAIN = mumbaiFork;
const CHAIN = polygonMumbai;

Next steps

If you have any questions about integrating Sismo Connect, don’t hesitate to reach out. The team will be happy to answer any questions you may have. Any feedback is also welcomed!

Get involved in the Sismo community! 🎭

• Look out for hackathons that we are participating in
• Join our Discord or our Dev Telegram
• See the Sismo-hub contributing page