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Part 2: Product Data Models – Ethereum Payment

In this series of articles, I’m doing a walkthrough of a hobby project I’ve worked on, a payment system for the Ethereum blockchain. Go read the intro article for more context about this project.

In this part, I will cover the following topics:

  • Product details, whitelistings, coupon codes
  • Displaying purchases and subscriptions, products available, and past purchases
  • Data models for products and whitelistings

None of what is described in this article is about web3, it’s all really web2 development. However, I do have to describe it to lay the foundation for parts 3 and 4 that will be focused on interacting with the blockchain, and with a recap of what I’ve learned about what crypto wallets and blockchain for developing mass-consumer product experiences.

Below are the data models used for products, purchases, and whitelistings and coupons (click to enlarge).

The data schemas used to represent products, purchases, and whitelists/coupons (click to zoom)

The follow diagram shows three user flows: the first flow shows products for non-signed in users, the second flow for signed in users, and a third flow just to display the current status of the access rights.

System diagram showing three user flows to display available products, past purchases, and current access rights.

Part 1: Authentication and Crypto Wallet Management – Ethereum Payment

In this series of articles, I’m doing a walkthrough of a hobby project I’ve worked on, a payment system for the Ethereum blockchain. Go read the intro article for more context about this project.

In this part, I will cover the following topics:

  • Connecting a crypto wallet via a frontend, and detecting states in MetaMask
  • Backend endpoints needed to manage wallet connections, wallet signature, and JSON Web Tokens.
  • Data models for users.

You will find that there isn’t much complexity in this article. Authenticating a crypto wallet is most about calling methods from the wallet API from the frontend, and then passing data around between the frontend and the backend for verification.

Connecting a Crypto Wallet

Whatever software you build that will have to interact with the Ethereum blockchain, either reading data or transacting, you’ll need to connect to an Ethereum node to access the Ethereum blockchain.

For most use cases, you won’t be running your own Ethereum node, and you won’t be calling directly any Ethereum node either. Instead you’ll use a third party that offers a centralized point of access to the blockchain: you connect to their backend servers, which are connected to the blockchain. It’s kind of counter-intuitive that we have to use centralized third party providers when you think about it given that one of the core tenets of the blockchain is that it’s fully decentralized, but that’s what we have to deal with these days.

As a human user of the blockchain, you need a crypto wallet to initiate various actions and execute smart contracts. Every Ethereum client implements the same JSON-RPC specifications, which is the standard that applications can rely on to interact with the blockchain.

Building a Payment System for the Ethereum Blockchain

Over the past few years, I’ve oriented the content of this blog towards engineering management and tech leadership, and consequently, I haven’t written anything purely technical for a while. Some of my most technical article series ended up finding a large audience, namely Implementing a Key-Value Store, and Coding for SSDs, and it now feels like it’s been an eternity since I wrote them.

Crypto protocols have made a serious dent in the tech space, and even more so over the past couple of years, often referred to as a whole as crypto or web3 technologies. With my personal commitment to keep upskilling myself, I have decided to make it a top priority for me to understand how blockchain technology was built and operated, and what kinds of businesses and product experiences this technology could enable in the long term.

I decided to build something basic yet complex enough that it would force me to interact with blockchain data in interesting ways. Because token transactions and crypto payments are simplest interactions on the blockchain, I settled on building a payment system.

Therefore in this series of articles, I will be sharing how I implemented a fully-functional payment system on top of the Ethereum blockchain, with the following features:

  1. Managing a list of products and time-bound subscriptions. Allowing for coupons and whitelistings.
  2. Displaying the current and past purchased products for a user.
  3. Guiding users through payment transactions on the Ethereum blockchain, by connecting their Ethereum wallets.
  4. Handling complex situations of network and service disruptions, to prevent double payments, avoid hanged transactions, and cover all other edge cases. This is mostly done by making all operations idempotent and idempotency keys.
  5. Monitoring the Ethereum blockchain to verify that payments for a particular product has been received.
  6. Once payment has been received, allowing paid users to access the private parts of a website by signing on with their Ethereum wallet to authenticate.