Decentralized Bulletin Board

A "bulletin board" dapp using NextJS, Ethereum, and IPFS. Size of the message is determined by value of ETH sent in. Messages are stored in IPFS and the IPFS hash/path is recorded in the transaction. The motivation for this toy project was to look into Solidity, IPFS, and see how painful (or not) it would be to create a dapp without the Truffle framework.

An example of IPFS storage

This project is a bit of a contrived example of using IPFS with Ethereum since you can store text in a Smart Contract state variable. However, storing the messages on IPFS removes some load from the blockchain and would theoretically reduce gas price per transaction.

Storing IPFS path hash in a Smart Contract

When storing the IPFS hash/path into the contracts, you need to re-hash it into a 32-byte hex. Check out this SO: https://ethereum.stackexchange.com/questions/17094/how-to-store-ipfs-hash-using-bytes

export const encodeIPFSHash = (hash) => {
  const hashHex = '1220' + hash.slice(2)
  const hashBytes = Buffer.from(hashHex, 'hex')
  const hashStr = bs58.encode(hashBytes)
  return hashStr
}

export const decodeIPFSHash = (hash) => web3.utils.bytesToHex(bs58.decode(hash).slice(2))

Unpinning Data

Currently, it doesn't seem possible to unpin data using the IPFS.js library that this project is using.

Starting the Project

Start the blockchain server first. Then compile & deploy the smart contracts. If there are any changes on the smart contracts, they need to be re-compiled and re-deployed. Restart the blockchain server if you want a fresh blockchain with no stored messages.

npm install
npm run blockchain
npm run compile
npm run deploy
npm run dev

Compiling Contracts

npm run compile runs Sulk and compiles the contracts

Deploying Contracts

npm run deploy deploys the contracts onto the local eth runtime and creates the file pages/contracts/Board.sol.js which is the JS hook into the smart contracts.

Posting a Message

You need a wallet address. Copy a public key from the 10 ganache-cli will provide you after you npm run blockchain. The amount of ETH specified will affect how big the message is. When someone posts, the ETH sent in will be transferred to the owner (wallet address) of the Smart Contract.

Testing

The workflow is still WIP. When testing smart contracts, I'm using Jest and running a Web3 instance to resolve the expected values. This is not a pure Solidity test. However, it does inherently test side effects from accessing contracts via JS (async, etc). You should restart your blockchain instance when running a new test.

npm run blockchain
npm run compile
npm run deploy
npm run test