一步一步學區塊鏈（5）智能合約__區塊鏈

以太坊區塊鏈技術2.0版本對於行業應用的開發最主要特性就是實現了智能合約，本質上講智能合約是由事件驅動的、
具有狀態的、運行在一個複製的、分享的賬本之上的、且能夠保管賬本上資產的程式。
它是一個可以被信任，總是按照事先的規則執行的操作。但與此同時，智能合約部署完之後無法修改也會帶來其他問題，這是另一個議題。下面直接上乾貨。
本篇內容是基於go用戶端通過命令列完成智能合約的編寫、發布、調用。
可參考的項目地址:http://www.ethdocs.org/en/latest/contracts-and-transactions/contracts.html
1、安裝solidity智能合約開發語言 

brew tap ethereum/ethereumbrew install soliditywhich solc

2、開啟命令列，進入之前建立的私鏈，並設定日誌輸出檔案

jwter-WIFI:csdnBlog jwter$ geth --datadir "privateChain" console 2>> log_outputWelcome to the Geth JavaScript console!instance: Geth/v1.4.18-stable-c72f5459/darwin/go1.7.3coinbase: 0x56a957bbde2b2dcb6321c9aceb11c21d6dfe68f9at block: 164 (Sat, 03 Dec 2016 16:29:24 CST) datadir: privateChain modules: admin:1.0 debug:1.0 eth:1.0 miner:1.0 net:1.0 personal:1.0 rpc:1.0 txpool:1.0 web3:1.0> 

3、設定編譯環境

> web3.eth.getCompilers()["Solidity"]> admin.setSolc("/usr/local/bin/solc")"solc, the solidity compiler commandline interface\nVersion: 0.4.2+commit.af6afb04.Darwin.appleclang\n\npath: /usr/local/bin/solc"

4、編寫智能合約並編譯

> contractSource  = "contract test { function multiply(uint a) returns(uint d) { return a * 7; } }""contract test { function multiply(uint a) returns(uint d) { return a * 7; } }"> contract = eth.compile.solidity(contractSource).test{  code: "0x606060405260308060106000396000f3606060405260e060020a6000350463c6888fa18114601c575b6002565b346002576007600435026060908152602090f3",  info: {    abiDefinition: [{        constant: false,        inputs: [...],        name: "multiply",        outputs: [...],        payable: false,        type: "function"    }],    compilerOptions: "--bin --abi --userdoc --devdoc --add-std --optimize -o /var/folders/c6/1vhz7hcd7w9g883rwrn4vzvr0000gn/T/solc271136546",    compilerVersion: "0.4.2",    developerDoc: {      methods: {}    },    language: "Solidity",    languageVersion: "0.4.2",    source: "contract test { function multiply(uint a) returns(uint d) { return a * 7; } }",    userDoc: {      methods: {}    }  }}

5、定義智能合約abi並編譯

> abi = [{constant:false , inputs:{name:'a',type:'uint256'}}][{    constant: false,    inputs: {      name: "a",      type: "uint256"    }}]> myabi = eth.contract(abi)

6、部署前準備：解鎖賬戶、監控記錄檔

> accountAddress = eth.accounts[0]"0x56a957bbde2b2dcb6321c9aceb11c21d6dfe68f9"> personal.unlockAccount(accountAddress)Unlock account 0x56a957bbde2b2dcb6321c9aceb11c21d6dfe68f9Passphrase: true>

監控記錄檔需新開視窗，執行以下命令。用於查看部署完的智能合約是否被同步到區塊鏈網路中

jwter-WIFI:csdnBlog jwter$ tail -f log_output

7、部署智能合約

> myContract = myabi.new({from:accountAddress,data:contract.code}){  abi: [{      constant: false,      inputs: {        name: "a",        type: "uint256"      }  }],  address: undefined,  transactionHash: "0xf330f4affd3989d72a979410e3a53f3a4d2d4d832faaa6c1bb32f72998acbd4b"}

8、查看部署狀態，並同步到區塊鏈中智能合約必須開始挖礦模式才是被同步到區塊鏈中
可根據監控日誌視窗可以看到交易是否執行,來決定何時執行miner.stop()

> txpool.status{  pending: 1,  queued: 0}> miner.start()true> miner.stop()true> txpool.status{  pending: 0,  queued: 0}

9、調用智能合約

> contractABI = eth.contract(contract.info.abiDefinition)> > testContract = contractABI.at(myContract.address){  abi: [{      constant: false,      inputs: [{...}],      name: "multiply",      outputs: [{...}],      payable: false,      type: "function"  }],  address: "0xcb0895d4b3b35b2a45a31fab853614c14e7759a4",  transactionHash: null,  allEvents: function(),  multiply: function()}> testContract.multiply.call(3)21

注意：記得儲存智能合約部署完的地址，以及abi參數，因為部署完之後無法修改，
忘記地址則無法再次調用，同時部署智能合約會消耗gas，完成後可觀察使用者的餘額是否變化。