¡Hola habr! Recientemente noté que hay muy pocos tutoriales para que la audiencia de habla rusa ingrese al mundo de blockchain y se desarrolle allí. Decidí compartir un artículo sobre contratos inteligentes en Ethereum. Este artículo una vez me ayudó mucho a profundizar en el mundo de blockchain y desarrollar contratos inteligentes allí. El artículo original en este enlace .
Es posible que haya oído hablar de subastas en las que puede comprar y vender cosas. Si bien esto es muy conveniente, los vendedores cuestan alrededor del 10% de sus ganancias para pagar una tarifa de mantenimiento a la empresa de gestión de subastas.
Si una empresa hace trampa en algunas de las transacciones y recibe un pago, ¿cómo puede saber si ha sido estafado?
Aquí es donde la instalación descentralizada es la solución óptima.
Si no hay un tercero, los vendedores pueden ganar más de forma segura.
Lista de características
Creando una subasta
Hacer una apuesta
Fin de la subasta
Herramientas
Contrato inteligente Solidity , Remix , Metamask
Un frontend Web3.js , Vue.js , Vieux-Klee , boostrap-vu
Prerrequisitos
Github
, :
https://github.com/openberry-ac/Auction
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- Web3.js
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Ethereum, Solidity , , -.
Remix AuctionBox.sol :
// AuctionBox.sol
// We will be using Solidity version 0.5.3
pragma solidity 0.5.3;
// Importing OpenZeppelin's SafeMath Implementation
import "https://github.com/OpenZeppelin/openzeppelin-solidity/contracts/math/SafeMath.sol";
contract AuctionBox{
Auction[] public auctions;
function createAuction (
string memory _title,
uint _startPrice,
string memory _description
) public{
// set the new instance
Auction newAuction = new Auction(msg.sender, _title, _startPrice, _description);
// push the auction address to auctions array
auctions.push(newAuction);
}
function returnAllAuctions() public view returns(Auction[] memory){
return auctions;
}
}
contract Auction {
using SafeMath for uint256;
address payable private owner;
string title;
uint startPrice;
string description;
enum State{Default, Running, Finalized}
State public auctionState;
uint public highestPrice;
address payable public highestBidder;
mapping(address => uint) public bids;
/** @dev constructor to creat an auction
* @param _owner who call createAuction() in AuctionBox contract
* @param _title the title of the auction
* @param _startPrice the start price of the auction
* @param _description the description of the auction
*/
constructor(
address payable _owner,
string memory _title,
uint _startPrice,
string memory _description
) public {
// initialize auction
owner = _owner;
title = _title;
startPrice = _startPrice;
description = _description;
auctionState = State.Running;
}
modifier notOwner(){
require(msg.sender != owner);
_;
}
/** @dev Function to place a bid
* @return true
*/
function placeBid() public payable notOwner returns(bool) {
require(auctionState == State.Running);
require(msg.value > 0);
// update the current bid
// uint currentBid = bids[msg.sender] + msg.value;
uint currentBid = bids[msg.sender].add(msg.value);
require(currentBid > highestPrice);
// set the currentBid links with msg.sender
bids[msg.sender] = currentBid;
// update the highest price
highestPrice = currentBid;
highestBidder = msg.sender;
return true;
}
function finalizeAuction() public{
//the owner and bidders can finalize the auction.
require(msg.sender == owner || bids[msg.sender] > 0);
address payable recipiant;
uint value;
// owner can get highestPrice
if(msg.sender == owner){
recipiant = owner;
value = highestPrice;
}
// highestBidder can get no money
else if (msg.sender == highestBidder){
recipiant = highestBidder;
value = 0;
}
// Other bidders can get back the money
else {
recipiant = msg.sender;
value = bids[msg.sender];
}
// initialize the value
bids[msg.sender] = 0;
recipiant.transfer(value);
auctionState = State.Finalized;
}
/** @dev Function to return the contents od the auction
* @return the title of the auction
* @return the start price of the auction
* @return the description of the auction
* @return the state of the auction
*/
function returnContents() public view returns(
string memory,
uint,
string memory,
State
) {
return (
title,
startPrice,
description,
auctionState
);
}
}
. , , «AuctionBox», !
, , AuctionBox.
Remix Ropsten.
, , Remix: AuctionBox .
!
createAuction .
returnAllAuctions !
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# git clone the project template
git clone -b boilerplate --single-branch https://github.com/openberry-ac/Auction.git
# go inside the folder
cd Auction
# install packages needed in the web application
npm install
# install web3, this is for connecting the contract
npm install -s web3@1.0.0-beta.37
# To run the app
npm run dev
web3.js
web3.js , :
// web3.js
import Web3 from 'web3';
if (window.ethereum) {
window.web3 = new Web3(ethereum);
try {
// Request account access if needed
ethereum.enable();
} catch (error) {
// User denied account access...
}
} else if (window.web3) { // Legacy dapp browsers...
window.web3 = new Web3(web3.currentProvider);
} else { // Non-dapp browsers...
console.log('Non-Ethereum browser detected. You should consider trying MetaMask!');
}
console.log(web3);
export default web3;
, web3
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MetaMask , . «» :
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ABI - , -. ABI, Remix , Compile ABI Details, :
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ABI ABI.
, AuctionBoxInstance.js AuctionInstance.js e contracts, ABI «s , :
//AuctionBoxInstance.js
import web3 from './web3';
const address = ''// THE CONTRACT ADDRESS
const abi = []// THE ABI
const instance = new web3.eth.Contract(abi, address);
export default instance;
// AuctionInstance.js
import web3 from './web3';
const abi = []// THE ABI
// Here is just only abi because we haven't created auction yet.
export default (address) => {
const instance = new web3.eth.Contract(abi, address);
return instance;
};
, , . , , . App.vue src !
beforeMount
, .
// App.vue
beforeMount() {
// get auctionBox method: returnAllAuctions()
auctionBox.methods
.returnAllAuctions()
.call()
.then((auctions) => {
console.log(auctions);
// set the amount of auctions
this.amount = auctions.length;
});
},
, , .
// App.vue
createAuction() {
// get accounts
web3.eth.getAccounts().then((accounts) => {
// convert 'ether' to 'wei'
const startPrice = web3.utils.toWei(this.startPrice, 'ether');
// createAuction in AuctionBox contract
this.isLoad = true;
return auctionBox.methods.createAuction(this.title, startPrice, this.description)
.send({ from: accounts[0] });
}).then(() => {
// initialize forms
this.isLoad = false;
this.title = '';
this.startPrice = '';
this.description = '';
// get the previous auction
return auctionBox.methods.returnAllAuctions().call();
}).then((auctions) => {
const index = auctions.length - 1;
console.log(auctions[index]);
// get the contract address of the previous auction
this.auctionAddress = auctions[index];
// set the address as the parameter
const auctionInstance = auction(auctions[index]);
return auctionInstance.methods.returnContents().call();
})
.then((lists) => {
console.log(lists);
const auctionlists = lists;
// convert 'wei' to 'ether'
auctionlists[1] = web3.utils.fromWei(auctionlists[1], 'ether');
this.auctionCard = auctionlists;
// show up the auction at the bottom of the page
this.isShow = true;
this.amount += 1;
})
.catch((err) => {
console.log(err);
});
},
, .
// App.vue
handleSubmit() {
// convert 'ether' to 'wei'
const bidPriceWei = web3.utils.toWei(this.bidPrice, 'ether');
// get the wallet adddress
const fromAddress = web3.eth.accounts.givenProvider.selectedAddress;
// set the address as the parameter
const selectedAuction = auction(this.auctionAddress);
this.isBid = true;
// placeBid in Auction contract
selectedAuction.methods
.placeBid()
.send({
from: fromAddress,
value: bidPriceWei,
})
.then(() => {
this.isBid = false;
// increase the number of bidders
this.bidders += 1;
this.bidPrice = '';
});
},
, .
// App.vue
handleFinalize() {
// get accounts
web3.eth.getAccounts().then((accounts) => {
// set the address as the parameter
const selectedAuction = auction(this.auctionAddress);
this.isFin = true;
// finalizeAuction in Auction contract
selectedAuction.methods
.finalizeAuction()
.send({ from: accounts[0] })
.then(() => {
this.isFin = false;
this.finalizeStatus = 'finalized';
});
});
},
Remix, .
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, - web3.js. , Vue.js, .
¿Qué es lo siguiente?
Es posible que desee agregar lógica para la "fecha límite" porque esto es importante en una aplicación de subasta real. Lo omitimos por ahora para evitar la complejidad y reducir el tiempo, pero si quieres intentar construirlo, te ayudará mucho .
Si necesita el código completo para este tutorial, puede consultarlo aquí.