15.03.04 이더리움 서울 밋업의(Ethereum Seoul) 개발자 스터디 발표 자료. https://dappsforbeginners.wordpress.com 에 있는 tutorial 중에서 Your first Dapp, Typing and Your Contracts Storage, JavaScript API 1 의 중요한 내용을 요약하고 설명.

1. 이더리움 개발자 스터디
15.03.04 Ethereum Seoul
서울 비트코인 센터
심지홍 (tx3sim@gmail.com)

2. Setting up your development environment
• Alethzero
• POC 8
• 컴파일러, 자바스크립트 콘솔 내장
• 블록체인 상태 조회 가능
• MIX
• javascript, html, contract 통합개발툴
• contract 작성시 step-by-step debugging 가능
• Mist
• end user 대상
• Dapp store 탑제

3. Your first Dapp
• mapping (address=>uint) balances;
• contract의 storage에 address, uint 타입으
로 balances를 참조로 mapping
• balances[msg.sender] = 10000
• msg.sender : msg는 전역변수이고
transaction 발신자의 160bit public
address를 의미
• sha-3 알고리즘으로 암호화
• key/value pair data type
contract metaCoin {
mapping (address => uint) balances;
function metaCoin() {
balances[msg.sender] = 10000;
}
function sendCoin(address receiver, uint
amount) returns(bool sufficient) {
if (balances[msg.sender] < amount)
return false;
balances[msg.sender] -= amount;
balances[receiver] += amount;
return true;
}
}

4. Your first Dapp
• function metaCoin(){}
• 모든 contract의 초기화 함수
• contract name과 같아야 함
• contract가 실행될 때 단 한번 실행되고 다시는 실
행될 수 없음
• function sendCoin(address receiver, uint
amount) returns(bool sufficient) {}
• 모든 함수는 ABI (Application Byte Interface)를
가짐
• 함수를 호출할 때 ABI, receiver, amount 가 필요
contract metaCoin {
mapping (address => uint) balances;
function metaCoin() {
balances[msg.sender] = 10000;
}
function sendCoin(address receiver, uint
amount) returns(bool sufficient) {
if (balances[msg.sender] < amount)
return false;
balances[msg.sender] -= amount;
balances[receiver] += amount;
return true;
}
}

5. Typing and Your Contracts Storage
• hash: 256-bit, 32-byte data chunk, indexable into bytes and operable
with bitwise operations.
• uint: 256-bit unsigned integer, operable with bitwise and unsigned
arithmetic operations.
• int: 256-bit signed integer, operable with bitwise and signed arithmetic
operations.
• string32: zero-terminated ASCII string of maximum length 32-bytes (256-
bit).
• address: account identifier, similar to a 160-bit hash type.
• bool: two-state value.

6. Typing and Your Contracts Storage - Structs
• Structs
• 정의된 structs는 스토리지에
아무것도 쓰지 않음
• 스토리지에 데이타를 쓰기 위
해 structs를 선언하고
instance를 생성해야함
• key 는 0x0 부터 저장
contract Test{
struct coinWallet {
uint redCoin;
uint greenCoin;
}
coinWallet myWallet;
function Test(){
myWallet.redCoin = 500;
myWallet.greenCoin = 250;
}
}

7. Typing and Your Contracts Storage - Structs
• mapping + struct로 테이블 구조 구현 가능
• mapping(type => struct name)
mappingName
• balances[msg.sender].redCoin = 10000
contract metaCoin {
struct coinWallet {
uint redCoin;
uint greenCoin;
}
mapping (address => coinWallet) balances;
function metaCoin() {
balances[msg.sender].redCoin = 10000;
balances[msg.sender].greenCoin = 5000;
}
function sendRed(address receiver, uint amount) returns(bool successful) {
if (balances[msg.sender].redCoin < amount) return false;
balances[msg.sender].redCoin -= amount;
balances[receiver].redCoin += amount;
return true;
}
function sendGreen(address receiver, uint amount) returns(bool successful) {
if (balances[msg.sender].greenCoin < amount) return false;
balances[msg.sender].greenCoin -= amount;
balances[receiver].greenCoin += amount;
return true;
}
}
sha3(address)
redCoin
(sha3(address))
greenCoin
(sha3(address)+1)
blueCoin
(sha3(address)+2)
0x0046.. 10000 10000 10000
0xd203.. 5000 9000 2000
0xc343. 3000 6000 10000

8. Typing and Your Contracts Storage - Structs
• mapping을 중첩 선언 함으로써
key 를 2개 갖는 structs 구현
• ex) data[4][9].b
• sha3(uint256(9) . sha3(uint256(4) . uint(256(1))) + 1.
contract c {
struct S { uint a; uint b; }
uint x;
mapping(uint => mapping(uint => S)) data;
}

9. Typing and Your Contracts Storage
contract rainbowCoin {
mapping (address => mapping (uint => uint)) balances;
function rainbowCoin() {
balances[msg.sender][0] = 10000; ///red coin
balances[msg.sender][1] = 10000; ///orange coin
balances[msg.sender][2] = 10000; ///yellow coin
balances[msg.sender][3] = 10000; ///green coin
balances[msg.sender][4] = 10000; ///blue coin
balances[msg.sender][5] = 10000; ///indigo coin
balances[msg.sender][6] = 10000; ///violet coin
}
function sendCoin(address receiver, uint amount, uint coin) returns(bool successful) {
if (balances[msg.sender][coin] < amount) return false;
balances[msg.sender][coin] -= amount;
balances[receiver][coin] += amount;
return true;
}
}

10. Typing and Your Contracts Storage -Accessor Functions
• Accessor Functions : 접근자
• ex) mapping (address => mapping (uint => uint)) public balances;
• mapping name 앞에 public을 선언
• 외부에서 ABI를 통해 mapping에 접근해 스토리지를 제어 할
수 있음

11. JavaScript API 1
• web3.eth.watch : 블록체인 모니터링
• web3.eth.watch(‘chain’) , web3.eth.watch(‘pending’)
• web3.eth.watch(‘chain').changed(function(){})
• 블록체인의 상태가 변하면 실행하여 프론트랜드를 동적으로 컨트롤 가능
• web3.eth.coinbase
• 마이닝하거나 트렌젝션을 보낼 때 사용하는 본인의 어카운트
• web3.eth.storageAt(contractAddress)
• 컨트랙의 스토리지지의 모든 내용을 JSON 객체로 리턴
• var storageObject = web3.eth.storageAt(contractAddress);

12. JavaScript API 1
web3.eth.watch('chain').changed(function(){
var coinbase = web3.eth.coinbase;
document.getElementById('coinbase').innerText = coinbase;
var balance = web3.eth.balanceAt(coinbase);
document.getElementById('balance').innerText = balance;
});
web3.eth.watch('pending').changed(function(){
var coinbase = web3.eth.coinbase;
document.getElementById('coinbase').innerText = coinbase;
var balance = web3.eth.balanceAt(coinbase);
document.getElementById('balance').innerText = web3.toDecimal(balance);
});
///Insert your contract address var here:
var contractAddress = "0x8026692b5e9c0e9a7ee3c3c13187a1d5efbc423c";
web3.eth.watch('pending').changed(function(){
var blockNumber = web3.eth.number;
document.getElementById('latestBlock').innerText = blockNumber;
var hash = web3.eth.block(blockNumber).hash;
document.getElementById('latestBlockHash').innerText = hash;
var timeStamp = web3.eth.block(blockNumber).timestamp;
document.getElementById('latestBlockTimestamp').innerText = Date(timeStamp);
var contractString = JSON.stringify(web3.eth.storageAt(contractAddress))
document.getElementById('contractString').innerText = contractString;
var storageObject = web3.eth.storageAt(contractAddress);
document.getElementById('fullName').innerText = web3.toAscii(storageObject['0x']) + ' ' + web3.toAscii(storageObject['0x01']);
});