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  • the big picture

    • what we will build in this course ?

      • a fully decentralize voting app which :
        • smart contract is deployed to ethereum test network : ropsten, rinkeby
        • webui is deployed to distributed file system called : ipfs
      • why voting app is perfect to demo decentralize app ?
        • ethereum blockchain make sure that no one could change data after it is made
        • we do not want any people could change vote result once it is made
        • and we do not want any people change the logic behind back end

    • structure of decentralize application:

      • dapp like other web application, it contains:
        • webui
        • html layout : be updated dynamically by App.js javascript code
        • App.js will communicate with blockchain and get back data when ever transaction happen
        • backend is not any web server but is smart contract which is deployed to blockchain

  • installation

  • start project

    • truffle doc --> https://truffleframework.com/docs

    • create a empty folder --> mkdir C:\election

    • truffle prepare for us some template to speed up development process

    • we will use pet-shop template --> truffle unbox pet-shop

    • explain about what petshop have

      • src : contain webui code html,css,js
      • contracts and migrations folder
      • test folder
      • truffle.js file contain blockchain information for deploy smart contract

    • if you on windows --> create truffle-config.js then copy all content from truffle.js, then delete truffle.js file

    • if you on mac --> just use truffle.js file

    • this file describe how we will connect to blockchain

    • start ganache

    • create new contract name Election.sol with very simple content

      contract Election { string public candidate; constructor() public { candidate = "candidate 1"; } }

    • create a new migration file call 2_deploy_election.js

    • deploy start contract to local blockchain --> truffle migrate

    • try to interact with smart contract --> truffle console --> Election.deployed().then(function(i){instance=i}) --> instance.candidate()

  • smart contract coding

    • design contract component

      • data for contract

        • need a struct to model a candidate
        • need to manage multiple candidates
        • need to manage multiple voters and state of vote

      • function for contract

        • add candidate function
        • constructor function
        • vote function

      • event for communicate between contract and webui

    • coding contract and deploy to local blockchain document about default value http://solidity.readthedocs.io/en/develop/control-structures.html#default-value

  • interact with smart contract from truffle console

    • get contract instance --> Election.deployed().then(function(i){instance=i})
    • show contract address --> instance.address
    • get candidate count --> instance.candidatesCount().then(function(count){vcount=count})
    • get candidate name --> instance.candidates(1).then(function(candidate){name=candidate[1]})
    • do vote using account 0 --> instance.vote(1, {from:web3.eth.accounts[0]})
    • get voter state --> instance.voters(web3.eth.accounts[0])
    • get vote count --> instance.candidates(1).then(function(candidate){voteCount=candidate[2]})
    • vote with other voter --> instance.vote(1, {from:web3.eth.accounts[2]})
    • event --> instance.vote(1, {from:web3.eth.accounts[8]}).then(function(result){console.log(result.logs[0].args._candidateId)})

  • automation test smart contract

    • why automation test with dapp is very important ?

    • contract test structure

    • check init number of candidate *

      • check init value for each candidate
      • check vote function
      • check require candidate id condition for vote function
      • check require voter not yet vote condition
      • check voters change after vote
      • check vote count after vote
      • check event happen

    • write automation test

  • html layout

    • header
    • table
    • select from
    • account information

  • js app to communicate with smart contract

    • init web3js
    • init contract
    • init render
      • candidates information
      • candidates selection
    • vote function
    • hide vote form when user already vote
    • event binding so app auto refresh after vote

  • deploy to rinkeby network with geth node

    • download geth clien from --> https://geth.ethereum.org/downloads/

    • install geth and binary will go to --> C:\Program Files\Geth

    • start node and syncing use rinkeby network ---> geth --rinkeby

    • attach to console javascript ---> geth attach ipc:\.\pipe\geth.ipc

    • check syncing status (need to wait until all sync complete) --> eth.syncing (should return false)

    • create new account --> personal.newAccount()

    • list account --> eth.accounts

    • get some free eth from faucet --> https://faucet.rinkeby.io/

    • check account balance with console --> eth.getBalance(your account address)

    • check account balance and convert to ether --> web3.fromWei(your account address,"ether")

    • start geth again with command --> geth --rinkeby --rpc --rpcapi db,eth,net,web3,personal

    • add define for rinkeby network config to truffle-config.js rinkeby: { host: "127.0.0.1", port: 8545, network_id: 4, from: "your account address" }

    • unlock account before deploy to test network --> personal.unlockAccount(your account address)

    • deploy to rinkeby network after unlock accont ----> truffle migrate --reset --network rinkeby

    • switch to rinkeby network on metamask

    • improt rinkeby account to metamask ----> C:\Users\TAN\AppData\Roaming\Ethereum\rinkeby\keystore

    • scan information after deploy and do vote ----> https://rinkeby.etherscan.io

    • register user on infura --> https://infura.io

    • go to dashboard and copy the api url with key and use in App.js

    • change app.js to use infura host

  • deploy to testnet with hdwallet and infura

  • working with ipfs

    • install ipfs --> https://dist.ipfs.io/#go-ipfs

    • init a ipfs node --> ipfs init

    • run as long service --> ipfs daemon

    • check the peer --> ipfs swarm peers

    • add all dist folder --> ipfs add -r dist/

    • publish the hash--> ipfs name publish "hash of dist"

    • access dapp from internet --> gateway.ipfs.io/ipfs/"hash of dist"

  • some other good read

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