dd0sxx/nft-marketplace-lesson

NFT Contracts for week long Project

Introduction

This project will give engineers a stronger working knowledge of web3. It involves developing a smart contract in Solidity and deploying it to a test network. We will be working with an NFT contract along the lines of CryptoPunks (see https://github.com/larvalabs/cryptopunks/blob/master/contracts/CryptoPunksMarket.sol).

Prerequisites

This project is designed for experienced software engineers who are in the early stages of learning web3. You will be writing code in Solidity, but to get the most out of it you should already be very comfortable writing applications and tests in at least one other language. You should also have some prior knowledge of Solidity. Having previously completed the first CryptoZombies Solidity Path (https://cryptozombies.io/solidity) would be ideal. All the coding for the project is in Solidity, but the contract deployment and tests make use of JavaScript and NPM. Previous experience of these, or at least the ability to Google your way out of trouble, will help a lot. Finally, there is a front end DApp that provides a web UI based on JavaScript and React. You don't need to work on this to complete the project. However you may be interested to examine it, and your possible next steps on completion of the project include modifying or extending it.

Tasks

1. Take a look at the provided file contracts/TigerBasicNFT.sol, which contains most of the implementation of a smart contract for trading in an imaginary Tiger NFT token. The contract keeps track of who owns each token. It also tracks which Tiger tokens are currently for sale and allows participants to buy them with suitable offers. All payments are in Ether. The first task is to extend this contract to provide some missing functionality:

   • The contract holds all the Ether it receives from the sale of Tiger tokens. This Ether is held on behalf of the sellers and the contract keeps a record of how much is held on behalf of each seller address in the field pendingWithdrawals. pendingWithdrawals maps addresses to the amount of Ether held for each address. However as the contract stands there is no way for the owner of an address to transfer their Ether out of the Tiger NFT contract.
     • Add a withdrawFunds function which allows users to claim the Ether held on their behalf by moving it from the contract's address to their own address.
     • Extend the provided test file tests/TigerBasicNFT.js to add tests for your new code
   • We would like the artist to receive a royalty payment of 5% on each resale of the tokens.
     • Extend the contract to automatically deduct a 5% artist's fee from all token sales and make this available to the artist via the withdrawFunds function.
     • Extend the tests to cover this
   • The contract should also take a 1% fee for itself.
     • Extend the contract to automatically deduct a 1% service fee from all token sales and make this available for transfer to the adddress from which the contract was deployed. Movement of these fees to the contract deployer's address should also be performed via the withdrawFunds function.
     • Extend the tests to cover this

2. Take a look at the provided file contracts/TigerBuggyNFT.sol, which contains an implementation of the above requirements. However, as it's name implies, this contract has a number of defects and vulnerabilities.

   • This can be seen if the accompanying tests are run via npx hardhat test, as a number of the tests fail.
     • Try to get the failing tests to pass by fixing the defects in the contract.
     • Be warned that the contract contains some defects that are not detected by the tests. There are 10 defects in all, some of which could result in users losing their funds. See how many you can find and fix.

3. Once you have completed the project you will be provided with the file contracts/TigerNFT.sol which implements all the requirements without any of the defects. You will also be given a description of all the defects, so you can see how well you did finding them all.

Tips

• You will need to do your own research to complete the project. Some useful sources of information include

  • https://docs.soliditylang.org/
  • https://solidity-by-example.org/ (at least one of the defects in TigerBuggyNFT is described in the Hacks section here)
  • https://hardhat.org/tutorial/

• When debugging contract code the HardHat console logging facility may help. At the top of the contract, after the line

pragma solidity 0.8.2;

• add the line

import "hardhat/console.sol";

• You can then print debug output from your test runs like this:

      console.log("artist address is %s, owner of token 0 address is %s", artist, tigerOwners[0]);

Acknowledgements

The contracts are based on the original CryptoPunks:

• https://github.com/larvalabs/cryptopunks/blob/master/contracts/CryptoPunksMarket.sol

The contracts incorporate some ideas and code from the OpenZeppelin ERC721Enumerable contract:

• https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC721/extensions/ERC721Enumerable.sol
• https://docs.openzeppelin.com/contracts/2.x/api/token/erc721#ERC721Enumerable

The front end DApp includes code from HeadlessUI by Tailwind Labs:

• https://github.com/tailwindlabs/headlessui