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0x10--智能合约开发之十分钟学会开发智能合约全流程

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本文字数： 29k 阅读时长 ≈ 26 分钟

1. 学习目标

  1. 了解智能合约
  2. 简单环境搭建
  3. 能够利用solidity编写Hello World合约
  4. 合约部署
  5. 和合约互动

2. 使用solidity语言撰写智能合约

Ethereum上的智能合约需要使用solidity语言来撰写。solidity是一种类似Javsscript的语言，而且围绕着solidity的各种开发工具链，都是使用属于Javascript生态系的npm来提供的。但solidity在语法上比较像Java或C#，因为和Javascript不同，solidity与Java或C#同属于强类型语言，、在定义函数时同样需要指定回传的类型、同样也需要先编译才能执行。这些特性都是Javascript所不具备的。

3. 开发前的准备

我们将使用当前最活跃的智能合约开发框架truffle为基础来开发。ENS（Ethereum Name Service）也是采用truffle框架。其他选择还有embark等。

开发过程中，我们将使用testrpc工具在电脑上模拟智能合约所需的以太坊内存块链测试环境。

testrpc中也包含了Javascript版本的Ethereum虚拟机（Ethereum Virtual Machine），因此可以完整地执行智能合约。

代码编辑器使用Atom，搭配solidity插件来开发。Atom是Github为开发者设计的基于Chromium的编辑器，支持NodeJS写的插件，内置Git，使用MIT协议开源发布。solidity插件除了支持语法高亮之外，也会透过Solium检查并提示基本的语法错误，相当方便。其他编辑器应该也有类似的插件可选择。

Ubuntu环境下Atom编辑器安装及使用

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sudo add-apt-repository ppa:webupd8team/atom
sudo apt-get update
sudo apt-get install atom

安装插件linter-solidity、autocomplete-solidity、linter-solium以方便solidity代码编写。

4.安装所需工具

首先安装Node.js

安装nvm

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cd ~
mkdir .nvm
cd .nvm
git clone https://github.com/creationix/nvm

等待下载完毕后source ~/.nvm/nvm/nvm.sh添加到~/.profile之类的文件中

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vim ~/.profile

并在文件末尾添加source ~/.nvm/nvm/nvm.sh

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source ~/.profile
nvm --version

检查安装是否正确

安装node

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nvm install node
node --version

安装npm

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git clone --recursive git://github.com/isaacs/npm.git
cd npm/bin
node npm-cli.js install npm -g
npm --version

安装ethereumjs-testrpc和truffle

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npm install -g ethereumjs-testrpc truffle
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zihao@zihaodeMBP:~$ npm install -g ethereumjs-testrpc truffle

/home/zihao/.nvm/nvm/versions/node/v9.3.0/bin/testrpc -> /home/zihao/.nvm/nvm/versions/node/v9.3.0/lib/node_modules/ethereumjs-testrpc/build/cli.node.js
/home/zihao/.nvm/nvm/versions/node/v9.3.0/bin/truffle -> /home/zihao/.nvm/nvm/versions/node/v9.3.0/lib/node_modules/truffle/build/cli.bundled.js
+ [email protected]
+ [email protected]
added 343 packages in 115.81s

5.启动testrpc

安装好后随时可以使用testrpc命令来启动以太坊测试环境。

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zihao@zihaodeMBP:~$ testrpc
EthereumJS TestRPC v6.0.3 (ganache-core: 2.0.2)

Available Accounts
==================
(0) 0x7e1897cec8e1a098384d17e85a9cd348ccb92b4a
(1) 0x6c96c6cb16442ab83aea0eb1bc3a183e28a922fe
(2) 0x163f0e06082c5cd14ff56658b186a30b0f6e7d9f
(3) 0x0e9558b2cb935ab26484c3d6783fbf2fe70041c8
(4) 0xa2233f08bbb7e3a826cc4c2cede22caf3a6922e6
(5) 0x3b1317510218f98946e0fb72b1a0685ac00bcbc4
(6) 0xca33f56a03e5ae86e25655f4dd7de88be12ec184
(7) 0xfb56aed85dd00908f1e0729ed80d06f456898588
(8) 0x6cfe240b49a28986057016ef2ecd9d6711f6b632
(9) 0x0e866473d6776edc39935dd5d00425b6ab2a423a

Private Keys
==================
(0) 3ae87bfaeabf103ce723b78525ab1278b2c7652b93b99a0131321adaa7000537
(1) 2f23eaef51f941b7af171a56acbd7524554ad529236b6abb6920935218f5df58
(2) 9b5b5d42786e74364e80b45ecf1a2b7201db7eafe12684f71006fbe3368e6dfe
(3) 33181b42772371fad50f29b8377f7a3de72000397f9b021677e329bede7bfcc7
(4) 3f5f366d89ab9263b92f35368840d24d562af043db8a5ad773dc8cc8f122662d
(5) 29933e3e79129da23da3cc0f5cecb03c583c3ad6c4c1ad8a39d68386fe92d91b
(6) 7e9bd47a6120bb9a240a96ce80866b98646f07cb98197bdffec389805575144b
(7) 0c7144621371a04e4ee733d06482b0a23ed775af17172e75e26f2b8915814e35
(8) 60ab702bdad5a348645f65fb0678cafec891c534964982d97b96f4a57abd78ef
(9) 8ff45f1ccb23bec8a317a6e218b3b50290646317b5c809c797e1522bcef9d031

HD Wallet
==================
Mnemonic:  vapor high liberty evoke pledge bronze critic stomach neck figure recipe mind
Base HD Path:  m/44'/60'/0'/0/{account_index}

Listening on localhost:8545

可以看到testrpc启动后自动建立了10个账号(Accounts)，与每个账号对应的私钥(Private Key)。每个账号中都有100个测试用的以太币(Ether)。要注意testrpc仅运行在内存中，因此每次重开时都会回到全新的状态。

一切就绪，我们可以开始建立第一个智能合约项目了。

6.建立项目

开启另一个终端，输入以下命令以建立项目：

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zihao@zihaodeMBP:~$ mkdir SmartContractDemo
zihao@zihaodeMBP:~$ cd SmartContractDemo/
zihao@zihaodeMBP:~/SmartContractDemo$ mkdir HelloWorld
zihao@zihaodeMBP:~/SmartContractDemo$ cd HelloWorld/
zihao@zihaodeMBP:~/SmartContractDemo/HelloWorld$ truffle init
Downloading...
Unpacking...
Setting up...
Unbox successful. Sweet!

Commands:

  Compile:    truffle compile
  Migrate:    truffle migrate
  Test contracts: truffle test
zihao@zihaodeMBP:~/SmartContractDemo/HelloWorld$ ls
contracts  migrations  test  truffle-config.js  truffle.js
zihao@zihaodeMBP:~/SmartContractDemo/HelloWorld$

目录结构

/contracts:存放智能合约原始代码的地方，可以看到里面有个Migrations.sol文件，我们的HelloWorld.sol文件就存放在这里。

/migrations:这是Truffle用来部署智能合约的功能，待会儿我们会修改2_deploy_contracts.js来部署HelloWorld.sol。

/test:测试智能合约的代码放在这里，支持js与sol测试。

truffle.js:Truffle的设置文档。

7.新建HelloWorld合约

在contracts文件夹下新建HelloWorld.sol文件，当然也可以直接在HelloWorld路径下面直接执行truffle create contract HelloWorld命令来创建HelloWorld.sol。

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zihao@zihaodeMBP:~/SmartContractDemo/HelloWorld$ ls
contracts  migrations  test  truffle-config.js  truffle.js
zihao@zihaodeMBP:~/SmartContractDemo/HelloWorld$ truffle create contract HelloWorld
zihao@zihaodeMBP:~/SmartContractDemo/HelloWorld$ cd contracts/
zihao@zihaodeMBP:~/SmartContractDemo/HelloWorld/contracts$ ls
HelloWorld.sol  Migrations.sol
zihao@zihaodeMBP:~/SmartContractDemo/HelloWorld/contracts$

HelloWorld.sol的文件内容如下：

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pragma solidity ^0.4.4;

contract HelloWorld {
  function sayHello() returns (string) {
    return ("Hello World");
  }
}

代码说明

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pragma solidity ^0.4.4;

第一行表明目前使用的solidity版本，不同版本的solidity可能会编译出不同的bytecode。^代表兼容solidity 0.4.4~0.4.9的版本。

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contract HelloWorld {
  ...
}

contract关键字类似于其他语言中较常见的class。因为solidity是专为智能合约(Contract)设计的语言，声明contract后即内置了开发智能合约所需的功能。也可以把这句理解为

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function sayHello() returns (string) {
  return ("Hello World");
}

函数的结构与其他程序类似，但如果有传入的参数或回传值，需要指定参数或回传值的类型(type)。

8.编译

现在执行truffle compile命令，我们可以将HelloWorld.sol原始码编译成Ethereum bytecode。

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zihao@zihaodeMBP:~/SmartContractDemo/HelloWorld$ ls
contracts  migrations  test  truffle-config.js  truffle.js
zihao@zihaodeMBP:~/SmartContractDemo/HelloWorld$ truffle compile
Compiling ./contracts/HelloWorld.sol...
Compiling ./contracts/Migrations.sol...

Compilation warnings encountered:

/home/zihao/SmartContractDemo/HelloWorld/contracts/HelloWorld.sol:4:3: Warning: No visibility specified. Defaulting to "public".
  function sayHello() returns (string) {
  ^
Spanning multiple lines.
,/home/zihao/SmartContractDemo/HelloWorld/contracts/HelloWorld.sol:4:3: Warning: Function state mutability can be restricted to pure
  function sayHello() returns (string) {
  ^
Spanning multiple lines.

Writing artifacts to ./build/contracts

zihao@zihaodeMBP:~/SmartContractDemo/HelloWorld$ ls
build  contracts  migrations  test  truffle-config.js  truffle.js

编译成功后，会在HelloWorld文件夹下面的build/contracts文件夹下面看见HelloWorld.json文件。

9.部署

truffle框架中提供了方便部署合约的脚本。打开migrations/2_deploy_contracts.js文件（脚本使用Javascript编写），将内容修改如下：

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var HelloWorld = artifacts.require("HelloWorld");
module.exports = function(deployer) {
  deployer.deploy(HelloWorld);
};

使用artifacts.require语句来取得准备部署的合约。使用deployer.deploy语句将合约部署到区块链上。这边HelloWorld是contract的名称而不是文件夹。因此可以用此语法读入任一.sol文件中的任一合约。

现在执行truffle migrate命令：

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zihao@zihaodeMBP:~/SmartContractDemo/HelloWorld$ truffle migrate
Compiling ./contracts/HelloWorld.sol...

Compilation warnings encountered:

/home/zihao/SmartContractDemo/HelloWorld/contracts/HelloWorld.sol:4:3: Warning: Function state mutability can be restricted to pure
  function sayHello() public constant returns (string) {
  ^
Spanning multiple lines.

Writing artifacts to ./build/contracts

Error: No network specified. Cannot determine current network.
  at Object.detect (/home/zihao/.nvm/nvm/versions/node/v9.3.0/lib/node_modules/truffle/build/cli.bundled.js:41338:23)
  at /home/zihao/.nvm/nvm/versions/node/v9.3.0/lib/node_modules/truffle/build/cli.bundled.js:202239:19
  at /home/zihao/.nvm/nvm/versions/node/v9.3.0/lib/node_modules/truffle/build/cli.bundled.js:41263:11
  at /home/zihao/.nvm/nvm/versions/node/v9.3.0/lib/node_modules/truffle/build/cli.bundled.js:41295:9
  at <anonymous>

可以发现，此时在使用truffle migrate进行智能合约test环境发布时出现异常，原因是truffle.js里面未配置链接合约发布时的环境地址，找到对应的truffle.js文件，修改代码为类似如下配置即可解决问题：

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module.exports = {
  networks: {
    development: {
    host: "localhost",
    port:8545,
    network_id:"*"  // 匹配任何network id
    }
  }
};

重新执行truffle migrate:

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zihao@zihaodeMBP:~/SmartContractDemo/HelloWorld$ truffle migrate
Using network 'development'.

Running migration: 1_initial_migration.js
  Deploying Migrations...
  ... 0xd43c42b526addb75876bb26a3086cabf79eaf9b0dbb1cd18ce3d6cc78f8e5335
  Migrations: 0x69c7674e74ee9aee187ea05b97faf08d6a7c0b94
Saving successful migration to network...
  ... 0x4aa706f72045aec809b3ab5d286489c157e6f5e73e1538a441cfb199c512f849
Saving artifacts...
Running migration: 2_deploy_contracts.js
  Deploying HelloWorld...
  ... 0x35afc83dd8e594167f1ddb9f52250b02aa72508a9b77ad15f5bd58b19a1e7275
  HelloWorld: 0x93ca4fd7d2820b2156fd88e40783ac9a41e26cfe
Saving successful migration to network...
  ... 0x12174aa188a4c47f84e071356149dfc9a51942bd81ce53d84bb22225d18d2fae
Saving artifacts...
zihao@zihaodeMBP:~/SmartContractDemo/HelloWorld$

如此以后，合约已经部署到testrpc中。切换到testrpc窗口，可以看到testrpc有反应了。

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Listening on localhost:8545
net_version
eth_accounts
eth_accounts
net_version
net_version
eth_sendTransaction

  Transaction: 0xd43c42b526addb75876bb26a3086cabf79eaf9b0dbb1cd18ce3d6cc78f8e5335
  Contract created: 0x69c7674e74ee9aee187ea05b97faf08d6a7c0b94
  Gas usage: 269607
  Block Number: 1
  Block Time: Wed Jan 10 2018 20:19:00 GMT+0800 (CST)

eth_newBlockFilter
eth_getFilterChanges
eth_getTransactionReceipt
eth_getCode
eth_uninstallFilter
eth_sendTransaction

  Transaction: 0x4aa706f72045aec809b3ab5d286489c157e6f5e73e1538a441cfb199c512f849
  Gas usage: 41981
  Block Number: 2
  Block Time: Wed Jan 10 2018 20:19:01 GMT+0800 (CST)

eth_getTransactionReceipt
eth_accounts
net_version
net_version
eth_sendTransaction

  Transaction: 0x35afc83dd8e594167f1ddb9f52250b02aa72508a9b77ad15f5bd58b19a1e7275
  Contract created: 0x93ca4fd7d2820b2156fd88e40783ac9a41e26cfe
  Gas usage: 142468
  Block Number: 3
  Block Time: Wed Jan 10 2018 20:19:01 GMT+0800 (CST)

eth_newBlockFilter
eth_getFilterChanges
eth_getTransactionReceipt
eth_getCode
eth_uninstallFilter
eth_sendTransaction

  Transaction: 0x12174aa188a4c47f84e071356149dfc9a51942bd81ce53d84bb22225d18d2fae
  Gas usage: 26981
  Block Number: 4
  Block Time: Wed Jan 10 2018 20:19:01 GMT+0800 (CST)

eth_getTransactionReceipt

10.与合约互动

truffle提供命令行工具，执行truffle console命令后，可用Javascript来和刚刚部署的合约互动。

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zihao@zihaodeMBP:~/SmartContractDemo/HelloWorld$ ls
build  contracts  migrations  test  truffle-config.js  truffle.js
zihao@zihaodeMBP:~/SmartContractDemo/HelloWorld$ truffle console
truffle(development)> let contract
undefined
truffle(development)> HelloWorld.deployed().then(instance => contract = instance)
TruffleContract {
  constructor: 
 { [Function: TruffleContract]
   _static_methods: 
  { setProvider: [Function: setProvider],
    new: [Function: new],
    at: [Function: at],
    deployed: [Function: deployed],
    defaults: [Function: defaults],
    hasNetwork: [Function: hasNetwork],
    isDeployed: [Function: isDeployed],
    detectNetwork: [Function: detectNetwork],
    setNetwork: [Function: setNetwork],
    resetAddress: [Function: resetAddress],
    link: [Function: link],
    clone: [Function: clone],
    addProp: [Function: addProp],
    toJSON: [Function: toJSON] },
   _properties: 
  { contract_name: [Object],
    contractName: [Object],
    abi: [Object],
    network: [Function: network],
    networks: [Function: networks],
    address: [Object],
    links: [Function: links],
    events: [Function: events],
    binary: [Function: binary],
    deployedBinary: [Function: deployedBinary],
    unlinked_binary: [Object],
    bytecode: [Object],
    deployedBytecode: [Object],
    sourceMap: [Object],
    deployedSourceMap: [Object],
    source: [Object],
    sourcePath: [Object],
    ast: [Object],
    compiler: [Object],
    schema_version: [Function: schema_version],
    schemaVersion: [Function: schemaVersion],
    updated_at: [Function: updated_at],
    updatedAt: [Function: updatedAt] },
   _property_values: {},
   _json: 
  { contractName: 'HelloWorld',
    abi: [Array],
    bytecode: '0x6060604052341561000f57600080fd5b6101578061001e6000396000f300606060405260043610610041576000357c0100000000000000000000000000000000000000000000000000000000900463ffffffff168063ef5fb05b14610046575b600080fd5b341561005157600080fd5b6100596100d4565b6040518080602001828103825283818151815260200191508051906020019080838360005b8381101561009957808201518184015260208101905061007e565b50505050905090810190601f1680156100c65780820380516001836020036101000a031916815260200191505b509250505060405180910390f35b6100dc610117565b6040805190810160405280600b81526020017f48656c6c6f20576f726c64000000000000000000000000000000000000000000815250905090565b6020604051908101604052806000815250905600a165627a7a72305820b98aa7cabcef6181bb855c27290b86a3ed577c3493b6cf1cebfeb4be9a990c2e0029',
    deployedBytecode: '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',
    sourceMap: '25:112:0:-;;;;;;;;;;;;;;;;;',
    deployedSourceMap: '25:112:0:-;;;;;;;;;;;;;;;;;;;;;;;;49:86;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;23:1:-1;8:100;33:3;30:1;27:2;8:100;;;99:1;94:3;90;84:5;80:1;75:3;71;64:6;52:2;49:1;45:3;40:15;;8:100;;;12:14;3:109;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;49:86:0;94:6;;:::i;:::-;108:22;;;;;;;;;;;;;;;;;;;;49:86;:::o;25:112::-;;;;;;;;;;;;;;;:::o',
    source: 'pragma solidity ^0.4.4;\n\ncontract HelloWorld {\n  function sayHello() public constant returns (string) {\n  return ("Hello World");\n  }\n}\n',
    sourcePath: '/home/zihao/SmartContractDemo/HelloWorld/contracts/HelloWorld.sol',
    ast: [Object],
    compiler: [Object],
    networks: [Object],
    schemaVersion: '1.0.1',
    updatedAt: '2018-01-10T12:19:01.841Z' },
   setProvider: [Function: bound setProvider],
   new: [Function: bound new],
   at: [Function: bound at],
   deployed: [Function: bound deployed],
   defaults: [Function: bound defaults],
   hasNetwork: [Function: bound hasNetwork],
   isDeployed: [Function: bound isDeployed],
   detectNetwork: [Function: bound detectNetwork],
   setNetwork: [Function: bound setNetwork],
   resetAddress: [Function: bound resetAddress],
   link: [Function: bound link],
   clone: [Function: bound clone],
   addProp: [Function: bound addProp],
   toJSON: [Function: bound toJSON],
   web3: 
  Web3 {
    _requestManager: [RequestManager],
    currentProvider: [Provider],
    eth: [Eth],
    db: [DB],
    shh: [Shh],
    net: [Net],
    personal: [Personal],
    bzz: [Swarm],
    settings: [Settings],
    version: [Object],
    providers: [Object],
    _extend: [Function] },
   class_defaults: 
  { from: '0x7e1897cec8e1a098384d17e85a9cd348ccb92b4a',
    gas: 6721975,
    gasPrice: 100000000000 },
   currentProvider: 
  HttpProvider {
    host: 'http://localhost:8545',
    timeout: 0,
    user: undefined,
    password: undefined,
    send: [Function],
    sendAsync: [Function],
    _alreadyWrapped: true },
   network_id: '1515578597496' },
  abi: 
 [ { constant: true,
   inputs: [],
   name: 'sayHello',
   outputs: [Array],
   payable: false,
   stateMutability: 'view',
   type: 'function' } ],
  contract: 
 Contract {
   _eth: 
  Eth {
    _requestManager: [RequestManager],
    getBalance: [Function],
    getStorageAt: [Function],
    getCode: [Function],
    getBlock: [Function],
    getUncle: [Function],
    getCompilers: [Function],
    getBlockTransactionCount: [Function],
    getBlockUncleCount: [Function],
    getTransaction: [Function],
    getTransactionFromBlock: [Function],
    getTransactionReceipt: [Function],
    getTransactionCount: [Function],
    call: [Function],
    estimateGas: [Function],
    sendRawTransaction: [Function],
    signTransaction: [Function],
    sendTransaction: [Function],
    sign: [Function],
    compile: [Object],
    submitWork: [Function],
    getWork: [Function],
    coinbase: [Getter],
    getCoinbase: [Function],
    mining: [Getter],
    getMining: [Function],
    hashrate: [Getter],
    getHashrate: [Function],
    syncing: [Getter],
    getSyncing: [Function],
    gasPrice: [Getter],
    getGasPrice: [Function],
    accounts: [Getter],
    getAccounts: [Function],
    blockNumber: [Getter],
    getBlockNumber: [Function],
    protocolVersion: [Getter],
    getProtocolVersion: [Function],
    iban: [Function],
    sendIBANTransaction: [Function: bound transfer] },
   transactionHash: null,
   address: '0x93ca4fd7d2820b2156fd88e40783ac9a41e26cfe',
   abi: [ [Object] ],
   sayHello: 
  { [Function: bound ]
    request: [Function: bound ],
    call: [Function: bound ],
    sendTransaction: [Function: bound ],
    estimateGas: [Function: bound ],
    getData: [Function: bound ],
    '': [Circular] },
   allEvents: [Function: bound ] },
  sayHello: 
 { [Function]
   call: [Function],
   sendTransaction: [Function],
   request: [Function: bound ],
   estimateGas: [Function] },
  sendTransaction: [Function],
  send: [Function],
  allEvents: [Function: bound ],
  address: '0x93ca4fd7d2820b2156fd88e40783ac9a41e26cfe',
  transactionHash: null }
truffle(development)> contract.sayHello.call()
'Hello World'
truffle(development)>

truffle console中预载了truffle-contract函数库，以方便操作部署到区块链上的合约。使用了HelloWorld.deployed().then语句来取得HelloWorld合约的Instance(实例)，并存到contract变量中，以方便后续的调用。

上面用的是Javascript ES6+的语法，这句也可以写成：

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HelloWorld.deployed().then(instance => {
  contract = instance
});

还可以用ES5的写法：

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HelloWorld.deployed().then(function(instance) {
  hello = instance;
});
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truffle(development)> contract.sayHello.call()
'Hello World'

最后通过contract.sayHello.call()成功打印出"Hello World"，这里直接调用contract.sayHello()也会得到一样的结果。truffle-contract提供使用call()来读取只读(read only)的数据，这样就不需提供gas。因此如果遇到的操作需要向区块链写入数据，我们就不能用call语句了。

这样，我们的第一个智能合约就已经写好并部署好了，也验证了合约确实可以运行。

11.加入新方法

我们在HelloWorld.sol中再加入一个echo方法，echo方法接受一个参数，并回传传送的参数。

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function echo(string name) constant returns (string) {
  return name;
}

新的echo方法中传入了一个name参数。我们也为echo方法加入一个constant声明，表示调用这个方法并不会改变区块链的状态。如此一来，透过truffle-contract来调用此方法时，会自动选用call来呼叫，也不需要额外提供gas。

由于更新了合约内容，我们需要先重新编译一次，将编译结果部署到testrpc上，再通过truffle console执行查看结果。

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zihao@zihaodeMBP:~/SmartContractDemo/HelloWorld$ truffle migrate --reset
Compiling ./contracts/HelloWorld.sol...

Compilation warnings encountered:

/home/zihao/SmartContractDemo/HelloWorld/contracts/HelloWorld.sol:4:3: Warning: Function state mutability can be restricted to pure
  function sayHello() public constant returns (string) {
  ^
Spanning multiple lines.
,/home/zihao/SmartContractDemo/HelloWorld/contracts/HelloWorld.sol:8:3: Warning: Function state mutability can be restricted to pure
  function echo(string name) public constant returns (string) {
  ^
Spanning multiple lines.

Writing artifacts to ./build/contracts

Using network 'development'.

Running migration: 1_initial_migration.js
  Replacing Migrations...
  ... 0xfc5af4b443dcae96f96206e26d2bc93b9699e7d14980dd0247baea112bd04c44
  Migrations: 0xee671e4bb1e86df24120041587b0a4841924f7bd
Saving successful migration to network...
  ... 0x1d7e34e903cc04a5e5cd6e5cca1031034841bd001dd693b488500fe75c4df9e2
Saving artifacts...
Running migration: 2_deploy_contracts.js
  Replacing HelloWorld...
  ... 0xdb8c8ef861498972ad769f947e9c03872b3f17f7292deff3fa25d5f5318ce94f
  HelloWorld: 0xace9ff211c9131362e05774335c6b3a353739119
Saving successful migration to network...
  ... 0x3a653f82abd0b92f389ea78ba654f51ff2256961f72b280874676cebac24f895
Saving artifacts...
zihao@zihaodeMBP:~/SmartContractDemo/HelloWorld$ truffle console
truffle(development)> let contract
undefined
truffle(development)> HelloWorld.deployed().then(instance => contract = instance)
TruffleContract {
  constructor: 
 { [Function: TruffleContract]
   _static_methods: 
  { setProvider: [Function: setProvider],
    new: [Function: new],
    at: [Function: at],
    deployed: [Function: deployed],
    defaults: [Function: defaults],
    hasNetwork: [Function: hasNetwork],
    isDeployed: [Function: isDeployed],
    detectNetwork: [Function: detectNetwork],
    setNetwork: [Function: setNetwork],
    resetAddress: [Function: resetAddress],
    link: [Function: link],
    clone: [Function: clone],
    addProp: [Function: addProp],
    toJSON: [Function: toJSON] },
   _properties: 
  { contract_name: [Object],
    contractName: [Object],
    abi: [Object],
    network: [Function: network],
    networks: [Function: networks],
    address: [Object],
    links: [Function: links],
    events: [Function: events],
    binary: [Function: binary],
    deployedBinary: [Function: deployedBinary],
    unlinked_binary: [Object],
    bytecode: [Object],
    deployedBytecode: [Object],
    sourceMap: [Object],
    deployedSourceMap: [Object],
    source: [Object],
    sourcePath: [Object],
    ast: [Object],
    compiler: [Object],
    schema_version: [Function: schema_version],
    schemaVersion: [Function: schemaVersion],
    updated_at: [Function: updated_at],
    updatedAt: [Function: updatedAt] },
   _property_values: {},
   _json: 
  { contractName: 'HelloWorld',
    abi: [Array],
    bytecode: '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',
    deployedBytecode: '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',
    sourceMap: '25:198:0:-;;;;;;;;;;;;;;;;;',
    deployedSourceMap: '25:198:0:-;;;;;;;;;;;;;;;;;;;;;;;;;;;;;49:86;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;23:1:-1;8:100;33:3;30:1;27:2;8:100;;;99:1;94:3;90;84:5;80:1;75:3;71;64:6;52:2;49:1;45:3;40:15;;8:100;;;12:14;3:109;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;139:82:0;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;23:1:-1;8:100;33:3;30:1;27:2;8:100;;;99:1;94:3;90;84:5;80:1;75:3;71;64:6;52:2;49:1;45:3;40:15;;8:100;;;12:14;3:109;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;49:86:0;94:6;;:::i;:::-;108:22;;;;;;;;;;;;;;;;;;;;49:86;:::o;139:82::-;191:6;;:::i;:::-;212:4;205:11;;139:82;;;:::o;25:198::-;;;;;;;;;;;;;;;:::o',
    source: 'pragma solidity ^0.4.4;\n\ncontract HelloWorld {\n  function sayHello() public constant returns (string) {\n  return ("Hello World");\n  }\n\n  function echo(string name) public constant returns (string) {\n  return name;\n  }\n}\n',
    sourcePath: '/home/zihao/SmartContractDemo/HelloWorld/contracts/HelloWorld.sol',
    ast: [Object],
    compiler: [Object],
    networks: [Object],
    schemaVersion: '1.0.1',
    updatedAt: '2018-01-10T13:34:12.869Z' },
   setProvider: [Function: bound setProvider],
   new: [Function: bound new],
   at: [Function: bound at],
   deployed: [Function: bound deployed],
   defaults: [Function: bound defaults],
   hasNetwork: [Function: bound hasNetwork],
   isDeployed: [Function: bound isDeployed],
   detectNetwork: [Function: bound detectNetwork],
   setNetwork: [Function: bound setNetwork],
   resetAddress: [Function: bound resetAddress],
   link: [Function: bound link],
   clone: [Function: bound clone],
   addProp: [Function: bound addProp],
   toJSON: [Function: bound toJSON],
   web3: 
  Web3 {
    _requestManager: [RequestManager],
    currentProvider: [Provider],
    eth: [Eth],
    db: [DB],
    shh: [Shh],
    net: [Net],
    personal: [Personal],
    bzz: [Swarm],
    settings: [Settings],
    version: [Object],
    providers: [Object],
    _extend: [Function] },
   class_defaults: 
  { from: '0x7e1897cec8e1a098384d17e85a9cd348ccb92b4a',
    gas: 6721975,
    gasPrice: 100000000000 },
   currentProvider: 
  HttpProvider {
    host: 'http://localhost:8545',
    timeout: 0,
    user: undefined,
    password: undefined,
    send: [Function],
    sendAsync: [Function],
    _alreadyWrapped: true },
   network_id: '1515578597496' },
  abi: 
 [ { constant: true,
   inputs: [],
   name: 'sayHello',
   outputs: [Array],
   payable: false,
   stateMutability: 'view',
   type: 'function' },
   { constant: true,
   inputs: [Array],
   name: 'echo',
   outputs: [Array],
   payable: false,
   stateMutability: 'view',
   type: 'function' } ],
  contract: 
 Contract {
   _eth: 
  Eth {
    _requestManager: [RequestManager],
    getBalance: [Function],
    getStorageAt: [Function],
    getCode: [Function],
    getBlock: [Function],
    getUncle: [Function],
    getCompilers: [Function],
    getBlockTransactionCount: [Function],
    getBlockUncleCount: [Function],
    getTransaction: [Function],
    getTransactionFromBlock: [Function],
    getTransactionReceipt: [Function],
    getTransactionCount: [Function],
    call: [Function],
    estimateGas: [Function],
    sendRawTransaction: [Function],
    signTransaction: [Function],
    sendTransaction: [Function],
    sign: [Function],
    compile: [Object],
    submitWork: [Function],
    getWork: [Function],
    coinbase: [Getter],
    getCoinbase: [Function],
    mining: [Getter],
    getMining: [Function],
    hashrate: [Getter],
    getHashrate: [Function],
    syncing: [Getter],
    getSyncing: [Function],
    gasPrice: [Getter],
    getGasPrice: [Function],
    accounts: [Getter],
    getAccounts: [Function],
    blockNumber: [Getter],
    getBlockNumber: [Function],
    protocolVersion: [Getter],
    getProtocolVersion: [Function],
    iban: [Function],
    sendIBANTransaction: [Function: bound transfer] },
   transactionHash: null,
   address: '0xace9ff211c9131362e05774335c6b3a353739119',
   abi: [ [Object], [Object] ],
   sayHello: 
  { [Function: bound ]
    request: [Function: bound ],
    call: [Function: bound ],
    sendTransaction: [Function: bound ],
    estimateGas: [Function: bound ],
    getData: [Function: bound ],
    '': [Circular] },
   echo: 
  { [Function: bound ]
    request: [Function: bound ],
    call: [Function: bound ],
    sendTransaction: [Function: bound ],
    estimateGas: [Function: bound ],
    getData: [Function: bound ],
    string: [Circular] },
   allEvents: [Function: bound ] },
  sayHello: 
 { [Function]
   call: [Function],
   sendTransaction: [Function],
   request: [Function: bound ],
   estimateGas: [Function] },
  echo: 
 { [Function]
   call: [Function],
   sendTransaction: [Function],
   request: [Function: bound ],
   estimateGas: [Function] },
  sendTransaction: [Function],
  send: [Function],
  allEvents: [Function: bound ],
  address: '0xace9ff211c9131362e05774335c6b3a353739119',
  transactionHash: null }
truffle(development)> contract.echo("2018-1-10 blockchain")
'2018-1-10 blockchain'
truffle(development)>

echo方法确实将我们输入的内容回传了。同时因为声明了constant，我们不需要直接调用call()方法，truffle会自动选用call来调用。

另外需要注意，如果我们还是使用truffle migrate命令，会得到如下信息：

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$ truffle migrate
Using network 'development'.

Network up to date.

Truffle会告诉你现在网络上的合约都已经是最新的，但事实上刚刚程序中新增的方法并没有更新到内存块链上。要更新内存块链上已部署的程序，需要改写migrations中的脚本，但现在还不到介绍migration的时候。还好我们开发用的内存块链是怎么修改都没关系的testrpc，可以使用truffle migrate --reset命令直接在testrpc上部署一次。

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