Integrate Payment Service for Web2 Projects with RedSonic ​

Introduction ​

In the digital age of Web2 projects, seamless transactions using stablecoins like USDC are paramount. This guide details constructing a USDC Payment Service using RedSonic's facilities. We'll delve into:

1. Depositing USDC into user accounts for immediate utility.
2. Understanding the core operations: Deposit, Transfer, and Withdraw.
3. A brief cart checkout scenario walkthrough.
4. Setting up a development environment, aided by Java and JavaScript expertise.
5. Demonstrative code snippets for wallet generation, fund deposits, transfers, and withdrawals.

Common Payment Service Overview ​

In a generic payment service:

1. Users first deposit USDC into their own account.
2. Once funds are credited, users can freely use their assets for transactions, such as payments to merchants.
3. This operates similarly to current digital currency virtual credit cards.

The Payment Service mainly consists of the following three operations:

• Deposit: Users deposit stable coins into their account.
• Transfer: Used during transactions or payments, e.g., when a user makes a purchase and transfers money to a merchant.
• Withdraw: Both users and merchants can withdraw their digital assets anytime.

Apart from these operations, your system might also need to log various actions and forward the aforementioned operations to RedSonic for on-chain data processing and synchronization.

Example Scenario: Cart Checkout ​

The process is divided into 6 steps:

1. User initiates a payment to the merchant.
2. Upon receiving the payment info, the merchant verifies the user's funds with the payment service and sends the payment details.
3. The Payment service processes the info and transfers user funds to the merchant via RedSonic's API.
4. After confirming the successful transfer, the Payment service sends a receipt to the merchant.
5. The merchant delivers the product to the user upon receipt.
6. RedSonic records the transaction on-chain after a certain period (8-16 hours). Note: The user, merchant, and payment service don't need to monitor this.

Now, based on the above scenario, let's implement the payment service step-by-step, focusing on code related to RedSonic interactions.

Warning: Deprecation of Goerli Testnet ​

Important Notice: The Goerli testnet has been deprecated, and RedSonic has successfully migrated to the Sepolia testnet. As a user, it's essential to be aware of this change and take appropriate action.

Starting immediately, the Goerli testnet is no longer supported by RedSonic. Any interactions or transactions on the Goerli testnet are at your own risk. We strongly recommend that you transition your activities to the Sepolia testnet to ensure uninterrupted access to RedSonic's features.

Please exercise caution and update your settings and configurations to work with the Sepolia testnet.

Prerequisites ​

• Basic knowledge of Java and Javascript. This guide uses Java for backend development and Javascript for frontend.
• The demo operates on the Ethereum goerli testnet (deprecated). Ensure you have a metamask wallet with goerli ETH and USDC tokens. USDC's contract code on goerli is 0x07865c6E87B9F70255377e024ace6630C1Eaa37F. RedSonic also allows traditional Web2 login methods, supporting web3auth and the particle network. You can incorporate these in your projects.

Java Library Integration ​

1. Create a new project (you can use IntelliJ IDEA).
2. Add the following maven configuration:

<dependency>
    <groupId>com.reddio</groupId>
    <artifactId>reddio-api</artifactId>
    <version>0.0.66</version>
</dependency>

3. Include necessary classes in your business logic:

import com.reddio.api.v1.DefaultReddioClient;
import com.reddio.api.v1.ReddioClient;
import com.reddio.api.v1.requests.ReddioTransferToApi;
import com.reddio.api.v1.requests.ReddioWithdrawalToApi;
import com.reddio.api.v1.rest.DefaultReddioRestClient;
import com.reddio.api.v1.rest.ReddioRestClient;
import com.reddio.api.v1.rest.SequenceRecord;
import com.reddio.crypto.CryptoService;

Javascript Library Integration ​

Install the official Reddio JS library:

yarn add @reddio.com/js

Initialize Reddio:

const reddio = new Reddio({
  env: 'test',
});

Detailed Steps ​

1. User Wallet Generation: The Payment Service can assist users in creating their wallets. Wallets can either be self-managed or hosted by the payment service. For this guide, we'll use the hosted wallet as an example. The following Java snippet generates a wallet:

public void generateNewWalletAddressAndKeys() {
    final BigInteger starkPrivateKey = CryptoService.getRandomPrivateKey();
    final BigInteger starkPublicKey = CryptoService.getPublicKey(starkPrivateKey);

    System.out.println("Layer2 Wallet Address: 0x" + starkPublicKey.toString(16));
    System.out.println("Layer2 Private Key: 0x" + starkPrivateKey.toString(16));
}

2. User Deposits: Since users start with zero funds but need funds to make payments, we provide an interface for them to deposit funds click here. Here's a simple deposit function using Javascript:

const depositUSDC = async (amount: number) => {
    const tx = await reddio.erc20.approve({
        tokenAddress: usdcContractAddress,
        amount,
    });
    await tx.wait();
    return reddio.apis.depositERC20({
        starkKey: key.publicKey,
        quantizedAmount: amount,
        tokenAddress: usdcContractAddress,
    });
}

3. User Payments to Merchant: Since we assume hosted wallets, the backend will facilitate the payment to the merchant's address. Below is the Java code for transfers:

public void transfer() {
    final String senderPrivateKey = "<sender-private-key>";
    final String receiverAddress = "<receiver-address>";
    final String transferAmount = "1.5";
    final String transferTokenContractAddress = "<erc20-token-address>";
    final SequenceRecord record = ReddioTransferToApi.transferERC20(
            DefaultReddioRestClient.testnet(),
            senderPrivateKey,
            transferAmount,
            transferTokenContractAddress,
            receiverAddress,
            ReddioClient.MAX_EXPIRATION_TIMESTAMP
    ).callAndPollRecord();
    System.out.println(
            "transfer txn completed, sequence id: " + record.getSequenceId()
    );
}

4. Merchant Product Delivery: Once the status from the Transfer process indicates SequenceStatusAccepted, the transaction is successful, and the merchant can deliver the product.

5. Withdrawal Process: Though the transaction generally concludes by the fourth step, withdrawals might be needed. This process involves two phases. First, assets are withdrawn to the hosted wallet, and after 8-16 hours (time for on-chain confirmation), users can perform the second on-chain withdrawal operation.

6. Backend Withdrawal: For hosted wallets, use the following Java code:

public void withdrawal() {
    final String starkPrivateKey = "<private-key>";
    final String withdrawalAddress = "<receiver-address-on-eth>";
    final String depositAmount = "1.5";
    final String tokenContractAddress = "<erc20-token-address>";

    final SequenceRecord record = ReddioWithdrawalToApi.withdrawalERC20(
            DefaultReddioRestClient.testnet(),
            starkPrivateKey,
            depositAmount,
            tokenContractAddress,
            withdrawalAddress,
            ReddioClient.MAX_EXPIRATION_TIMESTAMP
    ).callAndPollRecord();

    System.out.println(
            "withdrawal txn completed, sequenceid: " + record.getSequenceId()
    );
}

7. Frontend Withdrawal: With the Javascript SDK:

const withdrawToWallet = async (item: any) => {
    return reddio.apis.withdrawalFromL1({
        ethAddress: getAccount().address!,
        type: item.type,
        assetType: item.asset_type,
    });
}

That wraps up the integration process. With these steps and some additional configurations, your payment service will be ready. For the full frontend code, refer to the provided link. Try the frontend demo here.

Thank you for considering RedSonic for your payment service foundation!