Ethereum Smart Contract with Ganache (20 pts.)

What you need

• Any computer with a Web browser.

Purpose

Ethereum Overview

Read through the introduction here:

http://truffleframework.com/tutorials/ethereum-overview

Getting Ganache

http://truffleframework.com/ganache/

Download the version for your OS, as shown below. Install it.

Launching Ganache

Ganache launches, as shown below. This is a local Ethereum testnet, with ten accounts preloaded with Ether and an automatic miner running.

The top bar lets you select the various pages: Accounts, Blocks, Transactions, Logs, and Settings (the gear on the top right).

Examine each page. To close the Settings page, click Cancel.

For a detailed explanation of each page, see

http://truffleframework.com/docs/ganache/using

Installing Node.js

https://nodejs.org/en/

Download and install the LTS version, as shown below.

Installing Git

https://gist.github.com/derhuerst/1b15ff4652a867391f03

Install Truffle

npm install -g truffle

truffle version

Creating a Truffle Project

mkdir pet-shop-tutorial
cd pet-shop-tutorial
truffle unbox pet-shop

Writing a Smart Contract

nano contracts/Adoption.sol

pragma solidity ^0.4.17;

contract Adoption {
	
address[16] public adopters;

// Adopting a pet
function adopt(uint petId) public returns (uint) {
  require(petId >= 0 && petId <= 15);

  adopters[petId] = msg.sender;

  return petId;
}

// Retrieving the adopters
function getAdopters() public view returns (address[16]) {
  return adopters;
}

}

Save the file with Ctrl+X, Y, Enter. Execute this command to compile the contract:

truffle compile

If you are using Windows, you may need to resolve naming conflicts.

Migration

Execute this command to create a contract. (If you are using Windows, replace "nano" with "notepad".)

nano migrations/2_deploy_contracts.js

var Adoption = artifacts.require("Adoption");

module.exports = function(deployer) {
  deployer.deploy(Adoption);
};

Save the file with Ctrl+X, Y, Enter. Execute this command to migrate the contract:

truffle migrate

Look at the Ganache window. Now there are 4 blocks on the blockchain, and some of your Ether has been consumed, as shown below.

Testing the Smart Contract

nano test/TestAdoption.sol

pragma solidity ^0.4.17;

import "truffle/Assert.sol";
import "truffle/DeployedAddresses.sol";
import "../contracts/Adoption.sol";

contract TestAdoption {
	
  Adoption adoption = Adoption(DeployedAddresses.Adoption());

// Testing the adopt() function
function testUserCanAdoptPet() public {
  uint returnedId = adoption.adopt(8);

  uint expected = 8;

  Assert.equal(returnedId, expected, "Adoption of pet ID 8 should be recorded.");
}

// Testing retrieval of a single pet's owner
function testGetAdopterAddressByPetId() public {
  // Expected owner is this contract
  address expected = this;

  address adopter = adoption.adopters(8);

  Assert.equal(adopter, expected, "Owner of pet ID 8 should be recorded.");
}

// Testing retrieval of all pet owners
function testGetAdopterAddressByPetIdInArray() public {
  // Expected owner is this contract
  address expected = this;

  // Store adopters in memory rather than contract's storage
  address[16] memory adopters = adoption.getAdopters();

  Assert.equal(adopters[8], expected, "Owner of pet ID 8 should be recorded.");
}

}

Save the file with Ctrl+X, Y, Enter. Execute this command to run the tests:

truffle test

Creating a User Interface: Step 1 - web3

nano src/js/app.js

In the "initWeb3" function, replace the "Replace me..." section with this code, as shown below.

    // Is there an injected web3 instance?
    if (typeof web3 !== 'undefined') {
      App.web3Provider = web3.currentProvider;
    } else {
      // If no injected web3 instance is detected, fall back to Ganache
      App.web3Provider = new Web3.providers.HttpProvider('http://localhost:7545');
    }
    web3 = new Web3(App.web3Provider);

In the "initContract" function, replace the "Replace me..." section with this code, as shown below.

    $.getJSON('Adoption.json', function(data) {
      // Get the necessary contract artifact file and instantiate it with truffle-contract
      var AdoptionArtifact = data;
      App.contracts.Adoption = TruffleContract(AdoptionArtifact);

      // Set the provider for our contract
      App.contracts.Adoption.setProvider(App.web3Provider);

      // Use our contract to retrieve and mark the adopted pets
      return App.markAdopted();
    });

In the "markAdopted" function, replace the "Replace me..." section with this code, as shown below.

    var adoptionInstance;

    App.contracts.Adoption.deployed().then(function(instance) {
      adoptionInstance = instance;

      return adoptionInstance.getAdopters.call();
    }).then(function(adopters) {
      for (i = 0; i < adopters.length; i++) {
        if (adopters[i] !== '0x0000000000000000000000000000000000000000') {
          $('.panel-pet').eq(i).find('button').text('Success').attr('disabled', true);
        }
      }
    }).catch(function(err) {
      console.log(err.message);
    });

In the "handleAdopt" function, replace the "Replace me..." section with this code, as shown below.

    var adoptionInstance;

    web3.eth.getAccounts(function(error, accounts) {
      if (error) {
        console.log(error);
      }

      var account = accounts[0];

      App.contracts.Adoption.deployed().then(function(instance) {
        adoptionInstance = instance;

        // Execute adopt as a transaction by sending account
        return adoptionInstance.adopt(petId, {from: account});
      }).then(function(result) {
        return App.markAdopted();
      }).catch(function(err) {
        console.log(err.message);
      });
    });

Save the file with Ctrl+X, Y, Enter.

Installing MetaMask

In Chrome or Firefox, go to

https://metamask.io/

Install the extension.

In your browser's address bar, click the little orange fox head.

A Privacy Notice appears, as shown below.

Click Accept, "Try beta version", and OK.

Click Continue. On the next page, click "Import with seed phrase", as shown below.

Look in your Ganache window. Copy the "Mnemonic" words, as highlighted in the image below.

In your Web browser, enter the words, and enter a password, such as P@ssw0rd, in both boxes, as shown below.

Click IMPORT.

Scroll to the bottom of the "Terms of Use" and click ACCEPT.

On the next page, at the top right, in the field displaying "Main Ethereum Network", click the down-arrow and click "Custom RPC", as shown below.

On the next page, in the "New RPC URL" field, enter:

http://127.0.0.1:7545

Enter the location into the form below to put your name on the WINNERS PAGE.

Your Name (without spaces): Location:

Sources