Blockchain: Practical dApps Development using Solidity

Remix - an IDE for Solidity Smart Contract coding, compilation, deployment and testing environment.     This is a browser based tool that do not need any installation.

This is an important development tool for Smart Contract.  You can access this tool from the website.

http://remix.ethereum.org/

In this tutorial, we will learn another DevToolL Ganache.   Ganache is a local Blockchain that you can install on your PC and use Remix to deploy and test your Smart Contracts.     We will also learn about MetaMask - a very popular browser-based e-Wallet for the interaction with Ethereum blockchain.

You can install and find out more about MetaMastk here:

   https://metamask.io/

And Ganache :

  https://www.npmjs.com/package/ganache-cli

In this session of learning Dev Tools, we are going to learn from an example of a Smart Contract - Ownership contract.   The Ownership contract is important as it is one way we can control the contract the we deployed on the blockchain.     Ownership can be transferred as needed and certain functions in a Smart Contract can only be assessed by the contract owner.

In this session we are going to learn the Web3 JavaScript library that allow us to interact with our Smart Contracts from Nodejs environment. 

You will see how by just installing Web3 and using the object functions of Web3 we can get information directly from the production Ethereum network.

You can find out more via this link:

https://www.npmjs.com/package/web3

In this session we are going to learn Truffle - a Smart Contract development framework that is quite popular with many developers. 

Unlike Remix which is a visual oriented browser based IDE, Truffle is mainly a command line based tool which provide a boilerplate structure for your contracts, compilation, deployment and testing functions.

The strength of Truffle is that it helps developers to streamline their development works and conduct testing specification.  I like the testing feature as you can re-run your past tests whenever you have a change of your code.   

So, do learn this tool well and use it together with Remix which are easy and visual for each simulation and front-end testing.

You can find information here: 

https://trufflesuite.com/index.html

In this session, we formally define and go into the development of Smart Contract.

A "smart contract" is simply a program that runs on the Ethereum blockchain.

It's a collection of code (its functions) and data (its state) that resides at a specific address on the Ethereum blockchain.

In this session we are going to write a Smart Contract for a Vending Machine! Yes, although it is virtual vending machine, the functionality and logic are the focus of the Smart Contract.    Enjoy!

Solidity - Data Types and Usage Examples.

Note:  the contract source codes in the demo exercises are provided in the Resource zip file here.    ( for all the Solidity examples )   Use it for your convenience. 

Solidity - Data Types and Usage Examples

Solidity:  Functions, Visibility,  Scope and Modifiers

Solidity:  Functions, Events, Payment and Control

Solidity - Inheritance, Payment, Event, and Access Control

Solidity:  Abstract Contracts, Inheritance and Interface

As shown in the demo tutorials, Smart Contract can be developed using Remix , compile, deploy and test within Remix.   

However, we can also use web3 in the NodeJs environment to connect to Ethereum and interact with our deployed contracts.

This is a power example and ease of use of Nodejs and web3.

Please unzip the Resource files for your convenience.

Later exercise we use React as front-end rather than NodeJS.  MetaMask thus become available as it is browser based extension.

For the ERC20 practical tutorials, please ensure you have install the following according to the instruction in the demo videos:

React:    npx create-react-app <folder_name_lowercase>

web3:    npm install web3

axios:    npm install axios   (note:  you may not need this) 

openzeppelin:    (please follow videos in the later video when we use this library)

Solidity contract development can be done on Remix

Note:  if you encounter installation or runtime error, this is a great opportunity to debug and find out solutions yourself.   

The files in the Resource folder here is for your convenient.   

You need to know where these files should replace what files in your own PC directories.

Please bear in mind that to interact with Smart Contract on Ganache or Testnets of Ethereum, you need 2 things:

1. The ABI file.    (you can get from Remix once you compile your contract)

2. The deployed Address on Blockchain of your contract.

Since this two information will be different from the resource file examples, you can expect errors if you did not change them accordingly.

Please use the resource files with understanding.

For the NFT practical tutorials, please ensure you have install the following according to the instruction in the demo videos:

React:    npx create-react-app <folder_name_lowercase>

web3:    npm install web3

axios:    npm install axios

openzeppelin:    (please follow videos in the later video when we use this library)

creating account on IPFS:  follow instruction in the last video on creating an account on Pinata | Your Home for NFT Mediahttps://www.pinata.cloud

Solidity contract development can be done on Remix

Note:  if you encounter installation or runtime error, this is a great opportunity to debug and find out solutions yourself.   

The files in the Resource folder here is for your convenient.   

You need to know where these files should replace what files in your own PC directories.

Please bear in mind that to interact with Smart Contract on Ganache or Testnets of Ethereum, you need 2 things:

1. The ABI file.    (you can get from Remix once you compile your contract)

2. The deployed Address on Blockchain of your contract.

Since this two information will be different from the resource file examples, you can expect errors if you did not change them accordingly.

Please use the resource files with understanding.

This practical session demonstrate how to use OpenZeppelin library and wizzard to generate the required Smart Contract.

https://wizard.openzeppelin.com/

The contract once generated, was tested on Truffle using the MyERC1155_Test.js statements.    As an exercise, you can code more test statements in the file and run it using:  truffle test

Note:  remember to set up truffle by creating an empty directory, and in that directory, do truffle init (as shown in the demo).  The do the truffle compile

and truffle migrate and eventually truffle test.

Preventative Techniques:

Use the pattern:  Validate-Effect-Interact 

Ensure all state changes happen before calling external contracts

Use function modifiers that prevent re-entrancy on any withdrawal functions

Here is a example of a re-entracy guard

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.3;

contract ReEntrancyGuard {

    bool internal locked;

    modifier noReentrant() {

        require(!locked, "No re-entrancy");

        locked = true;

        _;

        locked = false;

    }

}

// you can try on Remix to solve the problem explained earlier tutorial.

Escrow management demonstrate one safe way of handling Ether on Smart Contract is by 'pulling' approach rather than 'pushing' approach.  Pulling approach is to use an Escrow contract to hold Ether due to the rightful user.

The user can then activate the withdrawal from the Escrow contract.  This separation of Ether and contract logic of the Escrow contract is demonstrated in this session.     You can find the resource on the Escrow contract below.

Testing of Escrow service management contract.

Note:  the files used in the demo are in the resource below.  You have to copy the respective files to the right folder of Truffle. 

Final summary session of the course.  Thank you for working hard and reaching the last learning session.

We recap what we learned about Ethereum Blockchain technology, Smart Contracts, Solidity, Web3, Standards and Security Issues of Smart Contract.

A note about the limitation of current Blockchain technology and you need to evaluate the problem first to see if Blockchain is the best solution or using conventional full-stack client server is better.

You are encouraged to learn further by doing a real dApps project.

One website you can find and discover ideas for dApps is this:

https://dappradar.com/

Wishing you all the best for your future learning journey and success for your career.

Thank you.

Sincerely,

Abel Choy