Express-Web3-API

A simple example of locally exposing API endpoints using Express that read data from Smart Contracts deployed on a local blockchain test network.

Getting Started

Clone the Repo from Git

Start Ganache from Blockchain-Dev directory (may have to run yarn install first, please let me know)

node_modules/.bin/ganache-cli

In Another Terminal run Node Console

node

Deploy our example Smart Contract, Voting.sol in Node Console

> Web3 = require('web3')
> web3 = new Web3(new Web3.providers.HttpProvider("http://localhost:8545"));
> web3.eth.accounts
> code = fs.readFileSync('Voting.sol').toString()
> solc = require('solc')
> compiledCode = solc.compile(code)
> abiDefinition = JSON.parse(compiledCode.contracts[':Voting'].interface)
> VotingContract = web3.eth.contract(abiDefinition)
> byteCode = compiledCode.contracts[':Voting'].bytecode
> deployedContract = VotingContract.new(['Rama','Nick','Jose'],{data: byteCode, from: web3.eth.accounts[0], gas: 4700000})

IMPORTANT! - Retrieve contract's address and save

> deployedContract.address 
> contractInstance = VotingContract.at(deployedContract.address)

In Another Terminal edit server.js and change the address to the address you just saved

const contractInstance = VotingContract.at('YOUR_ADDRESS_HERE');

And again in index.js ...

contractInstance = VotingContract.at('YOUR_ADDRESS_HERE');

Start server from Blockchain-Dev directory

yarn server

and test it works by navigating to http://localhost:5000/api/hello

Navigate to http://localhost:5000/api/votes/Rama to validate the API returns 0 votes.

In another Terminal open the index.html to see a simple UI

open index.html

In this UI you can add votes to the candidates. Try 'Rama' and click Vote button. Go back to the http://localhost:5000/api/votes/Rama endpoint to confirm change.

TODO:

• Update Readme with Prereqs, installation steps, running tests, etc
• Replace Voting.Sol with a generic smart contract
• Update smart contract deploy process to Truffle
• Possibly update Express server to Webpack
• Authentication
• Deploy and connect on testnet rather than Ganache (make this a configurable environment variable)

Dev Notes:

• Need to check if UI code can hit the server (may need to provide proxy)

Resources

• https://medium.freecodecamp.org/how-to-make-create-react-app-work-with-a-node-backend-api-7c5c48acb1b0
• https://medium.com/@mvmurthy/full-stack-hello-world-voting-ethereum-dapp-tutorial-part-1-40d2d0d807c2