How to build a blockchain from scratch with Go

#go #blockchain #web3 #webdev

Written by Solomon Esenyi ✏️

Blockchains are the underlying technology for many decentralized applications and cryptocurrencies. They are considered one of this generation’s most significant discoveries. Despite being in its early stages, blockchain is already applicable in many industries and is creating new job roles and opportunities for developers, artists, gamers, content writers, and many more.

This tutorial aims to teach you how blockchains work by guiding you through building one from scratch with Go. If you have heard of blockchains, but are still confused about how they work, this article is for you.

Why build a blockchain with Go?

Go provides many unique features and functionalities that make it a good fit for building a blockchain. For example, Go allows you to create highly efficient and performant applications with little effort.

Go is also excellent for building applications that require parallelism and concurrency (like blockchains) with its ability to spawn and manage thousands of Goroutines. Go implements automatic garbage collection and stack management with its runtime system.

Finally, it compiles applications to machine code and single binaries, supporting multiple OSs and processor architectures, and deploys easily on server infrastructure.

Prerequisites

To follow and understand this tutorial, you will need the following:

Working knowledge of Go
Go v1.x installed on your machine
A Go development environment (e.g., text editor, IDE)

What is a blockchain?

A blockchain is a digital record of transactions distributed and shared among the nodes of a computer network. Each transaction in the blockchain is called a block, and links to another with cryptography techniques.

Blockchains are helpful when you are trying to build a decentralized system that ensures the security and integrity of data while maintaining trust between every system user.

What is a block?

We mentioned blocks earlier, and you might be wondering what they are. Put simply, a block is a group of data, and multiple blocks come together to form a blockchain.

Every block in a blockchain possesses the following properties:

Data to record on the blockchain, e.g., transaction data
A block hash, the ID of the block generated using cryptography techniques
The previous block’s hash, which is the cryptographic hash of the last block in the blockchain. It is recorded in every block to link it to the chain and improve its security
A timestamp of when the block was created and added to the blockchain
Proof of Work (PoW), which is the amount of effort taken to derive the current block’s hash. We will explain this in depth later in the tutorial

Getting started

Let us start by creating a new Go project and importing all the necessary packages to build our blockchain. Create a file named blockchain.go and save the following code in it:

package main

import (
        "crypto/sha256"
        "encoding/json"
        "fmt"
        "strconv"
        "strings"
        "time"
)

Next, we will create a custom block type to hold our blockchain’s data. Add the following code to the blockchain.go file:

type Block struct {
        data         map[string]interface{}
        hash         string
        previousHash string
        timestamp    time.Time
        pow          int
}

Then, we will create a custom Blockchain type that contains our blocks. Add the following code to the blockchain.go file:

type Blockchain struct {
        genesisBlock Block
        chain        []Block
        difficulty   int
}

The genesisBlock property represents the first block added to the blockchain. In contrast, the difficulty property defines the minimum effort miners have to undertake to mine a block and include it in the blockchain.

Calculating the hash of a block

Like we discussed earlier, the hash of a block is its identifier generated using cryptography. We will derive the block hash for our blockchain by hashing the previous block hash, current block data, timestamp, and PoW using the SHA256 algorithm.

Let's create a method for our Block type that implements this functionality:

func (b Block) calculateHash() string {
        data, _ := json.Marshal(b.data)
        blockData := b.previousHash + string(data) + b.timestamp.String() + strconv.Itoa(b.pow)
        blockHash := sha256.Sum256([]byte(blockData))
        return fmt.Sprintf("%x", blockHash)
}

In the code above, we did the following:

Converted the block’s data to JSON format
Concatenated the block’s previous hash, data, timestamp, and proof of work (PoW)
Hashed the earlier concatenation with the SHA256 algorithm
Returned the hashing result in base 16, with lowercase letters for A-F

Mining new blocks

Mining a new block involves generating a block hash that starts with a desired number of zeros (the desired number is the mining difficulty). This means if the difficulty of the blockchain is three, you have to generate a block hash that starts with "000" e.g., "0009a1bfb506…".

Because we derive a block’s hash from its content, we need to keep changing the PoW value of the current block until we get a hash that satisfies our mining condition (starting zeros > difficulty).

To implement this, we will create a mine() method for our Block type that will keep incrementing the PoW value and calculating the block hash until we get a valid hash.