Smart Contracts

Published at: blockchain.andstuff.club.

Commands

# install npm dependencies
cd x-name-of-project
pnpm install

# truffle commands
pnpm exec truffle develop # start local blockchain instance
pnpm exec truffle compile # compile smart contracts
pnpm exec truffle test --migrate-none # test smart contracts
pnpm exec truffle migrate # deploy smart contracts

# 3-simple-bank-vyper: create virtual env and install vyper
python -m venv ./vyper-venv
source ./vyper-venv/bin/activate
pip install vyper

# 6-pet-shot: run web server
pnpm run dev

1. Proof of Existence

This contract allows for senders to notarize documents. A hash of the document is computed and then stored in the contract's state. Note that the content of the document is sent within the transaction to notarize it, therefore it is public and it size will impact the cost of the transaction.

Based on blog.openzeppelin.com/the-hitchhikers-guide-to-smart-contracts-in-ethereum.

2. Multisig Wallet

This contract allows a set of owners (defined during the contract's initialization) to submit, confirm and revoke transactions. A transaction is then executed if and only if it has been confirmed by a quorum of owners (also set during the initialization).

It is possible to send a transaction either to an EOA or to a contract account. In the latter case, it is possible to set the data field of the transaction (e.g. function signature and parameters). See the documentation of the ExecutionFailed event to prevent the transaction from failing.

Based on ConsenSys-Academy/multisig-wallet-exercise and ConsenSysMesh/MultiSigWallet.

3. Simple Bank

This contract acts as a simple bank, allowing users to enroll (i.e. create an account), to deposit and to withdraw funds. Written in Solidity and Vyper.

Based on ConsenSys-Academy/simple-bank-exercise and ConsenSys-Academy/simple-bank-vyper.

4. Supply Chain

This contract provides four different functions that:

1. let users to put up items for sale,
2. let users buy such items,
3. let sellers notify the buyer that an item has been shipped and
4. let buyers notify the seller that the item has been received.

Based on ConsenSys-Academy/supply-chain-exercise.

5. Event Ticket

This contract allows the owner to create events for which a given number of tickets can be sold at a given price. It is possible for the owner to end the sale of tickets for an event and to receive the proceeds to the sale. It is also possible for a buyer to get his tickets refunded.

Based on ConsenSys-Academy/event-ticket-exercise.

6. Pet Shop

This contract allows anyone to adopt a pet. A pet can only be adopted once and there are only 16 different pets. The purpose of this simple contract is to provide a simple dapp exemple for which a web interface can be written.

Based on trufflesuite.com/tutorial and truffle-box/pet-shop-box. Demo on Github Pages (contract is deployed on Ropsten).

7. Reentrancy Attack

TODO

8. Upgradeable Contract

Example of an upgradeable contract (BoxV1 and BoxV2) using OpenZeppelin's Upgrades plugin and the Transparent Proxy Pattern.

BoxV2 has a new storage variable as well as inherits from another contract (PausableUpgradeable). This poses a challenge as both of these changes will modify the storage layout. The solution used was to move the Box storage variables in a separate contract (BoxStorage) and have the Box contract inherit first from BoxStorage and then from other contracts. See comments and links in the code.

More or less based on OpenZeppelin's Upgrading smart contracts.