Smart Contract Tutorial (1) — Ethereum Solidity

Published in

Haderech_DEV

3 min readApr 28, 2022

Introduction

In Ethereum, Smart contracts are stored in a block as bytecodes format. When a transaction which has purpose to use a smart contract is transferred to a node, then its bytecodes are executed by the EVM(Ethereum Virtual Machine).

The most widely used smart contract languages are Solidity and Vyper in Ethereum.

Solidity : Most popular, has been used for a long time and is constantly being updated.
Vyper : Highly influenced by Python, a Contract-Oriented language.

This tutorial describes the followings:
1. How to run a local testnet.
2. How to build Solidity example contract.
3. How to deploy & interact with deployed contract.

Installation Geth CLI

Ubuntu

$ add-apt-repository -y ppa:ethereum/ethereum
$ apt-get update
$ apt-get install ethereum

MacOs

$ brew tab ethereum/ethereum
$ brew install ethereum

Run Local Testnet

Create genesis block

Create signer account. Do not forget password you typed.

$ geth account new --datadir /tmp/testnet

Create genesis.json
- chainId : Testnet ID
- ethash : Use PoW algorithm
- difficulty : The difficulty of problem for mining a block. 0x200000 means there is a 1 / 2²¹ chance to mining a block.
- gasLimit : The maximum gas any blocks on this chain can support.
- alloc : set initial balance to address

$ vi genesis.json  
{   
  "config": {     
    "chainId": 15,
    "homesteadBlock": 0,
    "byzantiumBlock": 0,
    "constantinopleBlock": 0, 
    "petersburgBlock": 0,
    "istanbulBlock": 0,
    "eip150Block": 0,
    "eip155Block": 0,
    "eip158Block": 0,
    "ethash": {}   
  },   
  "difficulty": "0x200000",
  "gasLimit": "8000000",
  "alloc": {
    "17b27648b14af118df79155d268c07063a3e1c15": { 
      "balance": "100000000000" 
    },     
    "e43691995fa6abc96d29aece2213d7efe73fefb6": { 
      "balance": "400000" 
    } 
  }
}

Initialize and run

$ geth init --datadir /tmp/testnet genesis.json
$ geth --datadir /tmp/testnet --networkid 15 --nodiscover --maxpeers=0 --mine --miner.threads=1 --miner.etherbase=0x17b27648b14af118df79155d268c07063a3e1c15 --http --allow-insecure-unlock

Start Console

There are two ways to use console command line:

start geth with console
add “console” after flags same as above running command

$ geth <other-flags...> console

2. or run this command in another terminal

$ geth attach /tmp/testnet/geth.ipc <http://127.0.0.1:30303>

console example :

Welcome to the Geth JavaScript console!instance: Geth/v1.10.17-stable/darwin-amd64/go1.18
coinbase: 0x17b27648b14af118df79155d268c07063a3e1c15
at block: 0 (Thu Jan 01 1970 07:30:00 GMT+0730 (+0730))
 datadir: /tmp/testnet
 modules: admin:1.0 debug:1.0 eth:1.0 ethash:1.0 miner:1.0 net:1.0 personal:1.0 rpc:1.0 txpool:1.0 web3:1.0To exit, press ctrl-d or type exit
> eth.getBalance("17b27648b14af118df79155d268c07063a3e1c15")
300000
> eth.getBalance("e43691995fa6abc96d29aece2213d7efe73fefb6")
400000

Unlock account

You need unlock account to send transaction which requires account sign

Args
1. Account address
2. Account password
3. Unlock duration (If set 0, then it unlocks until testnet stop)

On geth console:

> personal.unlockAccount("0x17B27648B14Af118df79155d268C07063A3E1C15", <password>, 0)

Write & Deploy contract

Install Solidity

Ubuntu

$ sudo add-apt-repository ppa:ethereum/ethereum
$ sudo apt update
$ sudo apt install solc

MacOs

$ brew update
$ brew upgrade
$ brew tap ethereum/ethereum
$ brew install solidity

check version

$ solc --version
solc, the solidity compiler commandline interface
Version: 0.8.13+commit.abaa5c0e.Darwin.appleclang

If you want see other way to install solidity, visit official document page (https://docs.soliditylang.org/en/latest/installing-solidity.html)

Write contract

Example from https://solidity-by-example.org/app/ether-wallet

pragma solidity ^0.8.10;contract EtherWallet {
    address payable public owner;    constructor() {
        owner = payable(msg.sender);
    }    receive() external payable {}    function withdraw(uint _amount) external {
        require(msg.sender == owner, "caller is not owner");
        payable(msg.sender).transfer(_amount);
    }    function getBalance() external view returns (uint) {
        return address(this).balance;
    }
}

Compile
Binary & ABI will be used at deploy, interact contract

$ solc <contract_file_name>.sol --optimize --bin --abi======= ethWallet.sol:EtherWallet =======
Binary:
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
Contract JSON ABI
[{"inputs":[],"stateMutability":"nonpayable","type":"constructor"},{"inputs":[],"name":"getBalance","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"owner","outputs":[{"internalType":"address payable","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"_amount","type":"uint256"}],"name":"withdraw","outputs":[],"stateMutability":"nonpayable","type":"function"},{"stateMutability":"payable","type":"receive"}]

Deploy contract