手把手教你搭建智能合约测试环境、开发、编译、部署以及如何通过JS调用合约方法

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学习目标

了解智能合约

简单环境搭建

能够利用solidity编写Hello World合约

合约部署

和合约互动

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。虽然还有其他能用来撰写智能合约的语言如Serpent（类Python）、lll（类Fortran），但目前看到所有公开的智能合约都是使用solidity撰写。

宣传上说，solidity是一种类似Javascript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。但我觉得solidity还是比较像Java或C#。因为和Javascript不同，solidity与Java或C#同属于强类型（Strong Type，在定义变数时需要指定类型）语言、在定义函式（function）时同样需指定回传的类型（type）、同样也需要先编译才能执行。这些特性都是Javascript所不具备的。

开发前的准备

本文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。

就像一般网站或App开发一样，在提供公开服务之前，开发者会在自己用于写程序的电脑（又称作本机）或透过测试网络来测试程序执行的效果，测试完成后，才会部署到公开的网络上提供服务。开发区块链智能合约（程序）的过程也是如此。特别是公开链上所有写入或读取计算结果的操作都需要真金白银（虚拟代币），而且根据网络状况，每个公开链上的操作都需要要一小段反应时间（15秒~数分钟），这些等待颇浪费宝贵的开发时间⏳。因此在开发的过程中，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。

此外，开发前还需准备一个合手的编辑器。我目前是使用Atom搭配solidity插件来开发。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。

安装所需工具

首先开发机上必须装好Node.js，再使用以下命令安装所需的工具：

$ npm install -g ethereumjs-testrpc truffle

liyuechun:~ yuechunli$ npm install -g ethereumjs-testrpc truffle

/usr/local/bin/testrpc -> /usr/local/lib/node_modules/ethereumjs-testrpc/build/cli.node.js

/usr/local/bin/truffle -> /usr/local/lib/node_modules/truffle/build/cli.bundled.js

• [email protected]

• [email protected]

added 1 package and updated 7 packages in 76.132s

liyuechun:~ yuechunli$

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。

liyuechun:~ yuechunli$ testrpc

EthereumJS TestRPC v4.1.3 (ganache-core: 1.1.3)

Available Accounts

==================

(0) 0xbbd414b340f2255dab9d923428c97f0b65d9df81

(1) 0xe9869e3cf29b6fca81762c314df229c7c4fea25e

(2) 0xc79e72362a4511b9e499d186654332c4d6f569be

(3) 0x9a6f0651907c149d4173c03927144dbbba1473d4

(4) 0x5b13a5d6788752b26dd4e338aae2e01058ee145e

(5) 0xfc7f56d942ad5260be23ecee92a344aba1b7e7d8

(6) 0xc48dc22c6bacd6ade4421ab54f25bc45c1c51142

(7) 0x3fe2b7d4141dd0a456661f77086d055cbaf3b78f

(8) 0x567979fed26ca85e9d1b4ac919c840e3fc9857e2

(9) 0xb2eafe245f098eef1c2c1f466d9a8dcd58764c62

Private Keys

==================

(0) 947ab78e91133103612ca099d60e6c38cac5bb769f7f097c82d003cf058500bd

(1) 8ffe0ba8dc53e16944a17dddd3378b5fba0379cd84df4e5237b8b46d05b8762f

(2) ffe2e04e43e4106b247407656f5233bcc3e0c49730972d0df9c1d1093375e2ef

(3) a20e453dc44c76aaca6a22efdbb605c2ed9eea64c11317e683461e11bd105ea7

(4) 4748268ff1b828868dc56d07a1b121b427e1bdede5dbb3c14ef1254d9d26b1a5

(5) f9957e68c6d20d38b81604a0509e6c4591478bc754f87d5682564073705fbb46

(6) 34e648b23c0ace6b2b0893651d87f70be8496f97ecf6b7b4607b2acc4e05c9bd

(7) d2477cedec217e3fb19a5981dafbc125ef66ccc9dc7df29301d08a24da843cf5

(8) d319f85ccd80e55b2e707e05f09662632564c297248f8b96f82ea5eeaeef0851

(9) 88c33ac9f1062b82f9e82f86a0ce307e3bd8fcf683b9751232c2f193f5bdc668

HD Wallet

==================

Mnemonic: hire custom clinic expect fury fantasy try dress source spy viable flag

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个帐号（Accounts），与每个帐号对应的私钥（Private Key）。每个帐号中都有100个测试用的以太币（Ether）。要注意testrpc仅运行在內存中，因此每次重开时都会回到全新的状态。

一切准备就绪，我们可以开始建立第一份智能合约项目了。

建立项目

开启另一个终端窗口，输入以下命令以建立项目：

liyuechun:Desktop yuechunli$ mkdir SmartContractDemo

liyuechun:Desktop yuechunli$ cd SmartContractDemo/

liyuechun:SmartContractDemo yuechunli$ mkdir HelloWorld

liyuechun:SmartContractDemo yuechunli$ cd HelloWorld/

liyuechun:HelloWorld yuechunli$ truffle init

Downloading project…

Project initialized.

Documentation: http://truffleframework.com/docs

Commands:

Compile: truffle compile

Migrate: truffle migrate

Test: truffle test

liyuechun:HelloWorld yuechunli$ ls

contracts migrations test truffle.js

目录结构：

/contracts:存放智能合约原始代码的地方，可以看到里面已经有三个sol文件，我们开发的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。

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。

HelloWorld.sol文件內容如下：

pragma solidity ^0.4.4;

contract HelloWorld {

function sayHello() returns (string) {

return ("Hello World");

}

}

讲解

pragma solidity ^0.4.4;

第一行指名目前使用的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。

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（Contact）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class HelloWorld extends Contract。

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）。

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。

liyuechun:HelloWorld yuechunli$ ls

contracts migrations test truffle.js

liyuechun:HelloWorld yuechunli$ truffle compile

Compiling ./contracts/ConvertLib.sol…

Compiling ./contracts/HelloWorld.sol…

Compiling ./contracts/MetaCoin.sol…

Compiling ./contracts/Migrations.sol…

Writing artifacts to ./build/contracts

liyuechun:HelloWorld yuechunli$ ls

build contracts migrations test truffle.js

liyuechun:HelloWorld yuechunli$ cd build/

liyuechun:build yuechunli$ ls

contracts

liyuechun:build yuechunli$ cd contracts/

liyuechun:contracts yuechunli$ ls

ConvertLib.json HelloWorld.json MetaCoin.json Migrations.json

liyuechun:contracts yuechunli$ cat HelloWorld.json

{

“contract_name”: “HelloWorld”,

“abi”: [

{

  "inputs": [],

  "payable": false,

  "type": "constructor"

}

],

“unlinked_binary”: “0x60606040523415600e57600080fd5b5b5b5b603680601e6000396000f30060606040525b600080fd00a165627a7a723058203ee98a767948e9bc08094df4a46ab0361f068b2a559032cf968df5bbf63e91430029”,

“networks”: {},

“schema_version”: “0.0.5”,

“updated_at”: 1505805826302

}

liyuechun:contracts yuechunli$

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。

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：

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的名称而不是文件名。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：

liyuechun:HelloWorld yuechunli$ ls

build contracts migrations test truffle.js

liyuechun:HelloWorld yuechunli$ truffle migrate

Compiling ./contracts/HelloWorld.sol…

Writing artifacts to ./build/contracts

Using network ‘development’.

Running migration: 1_initial_migration.js

Deploying Migrations…

… 0x218431f16a5cadc6347449808d981887c90b3872898af7cc9dc9b3280c07c184

Migrations: 0x64e9673cf962d21642a08635e6654fb7f2ea9bcd

Saving successful migration to network…

… 0xd9ec788c106df36b8491c95a0ab02ff1e5ef22c1965c910a2576e8259a00535c

Saving artifacts…

Running migration: 2_deploy_contracts.js

Deploying HelloWorld…

… 0x17774b4914d7bc7ab2505a53c59bda6a1fce30c9839d19d735290ca9140450ea

HelloWorld: 0x471a22ffe2bddd02e82853059871067e4c07a7f4

Saving successful migration to network…

… 0xe5e2e11cf5a63ca4517221c68dadb3cae2ca42cbfed93c09c575b6d5f275fc8b

Saving artifacts…

liyuechun:HelloWorld yuechunli$

如此一来合约已经部署到testrpc中。切换到testrpc窗口，可以看到testrpc有反应了。

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。

liyuechun:HelloWorld yuechunli$ ls

build contracts migrations test truffle.js

liyuechun:HelloWorld yuechunli$ truffle console

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],

    abi: [Object],

    network: [Function: network],

    networks: [Function: networks],

    address: [Object],

    links: [Function: links],

    events: [Function: events],

    binary: [Function: binary],

    unlinked_binary: [Object],

    schema_version: [Function: schema_version],

    updated_at: [Function: updated_at] },

_property_values: {},

_json:

  { contract_name: 'HelloWorld',

    default_network: undefined,

    abi: [Array],

    unlinked_binary: '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',

    networks: [Object],

    schema_version: '0.0.5',

    updated_at: 1505806918535 },

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: [Object],

    currentProvider: [Object],

    eth: [Object],

    db: [Object],

    shh: [Object],

    net: [Object],

    personal: [Object],

    bzz: [Object],

    settings: [Object],

    version: [Object],

    providers: [Object],

    _extend: [Object] },

class_defaults:

  { from: '0xbbd414b340f2255dab9d923428c97f0b65d9df81',

    gas: 4712388,

    gasPrice: 100000000000 },

currentProvider:

  HttpProvider {

    host: 'http://localhost:8545',

    timeout: 0,

    send: [Function],

    sendAsync: [Function],

    _alreadyWrapped: true },

network_id: '1505794143155' },

abi:

[ { constant: false,

  inputs: [],

  name: 'sayHello',

  outputs: [Array],

  payable: false,

  type: 'function' } ],

contract:

Contract {

_eth:

  Eth {

    _requestManager: [Object],

    getBalance: [Object],

    getStorageAt: [Object],

    getCode: [Object],

    getBlock: [Object],

    getUncle: [Object],

    getCompilers: [Object],

    getBlockTransactionCount: [Object],

    getBlockUncleCount: [Object],

    getTransaction: [Object],

    getTransactionFromBlock: [Object],

    getTransactionReceipt: [Object],

    getTransactionCount: [Object],

    call: [Object],

    estimateGas: [Object],

    sendRawTransaction: [Object],

    signTransaction: [Object],

    sendTransaction: [Object],

    sign: [Object],

    compile: [Object],

    submitWork: [Object],

    getWork: [Object],

    coinbase: [Getter],

    getCoinbase: [Object],

    mining: [Getter],

    getMining: [Object],

    hashrate: [Getter],

    getHashrate: [Object],

    syncing: [Getter],

    getSyncing: [Object],

    gasPrice: [Getter],

    getGasPrice: [Object],

    accounts: [Getter],

    getAccounts: [Object],

    blockNumber: [Getter],

    getBlockNumber: [Object],

    protocolVersion: [Getter],

    getProtocolVersion: [Object],

    iban: [Object],

    sendIBANTransaction: [Function: bound transfer] },

transactionHash: null,

address: '0x471a22ffe2bddd02e82853059871067e4c07a7f4',

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: ‘0x471a22ffe2bddd02e82853059871067e4c07a7f4’,

transactionHash: null }

truffle(development)> contract.sayHello.call()

‘Hello World’

truffle(development)>

讲解

HelloWorld.deployed().then(instance => contract = instance)

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。

这边使用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：

HelloWorld.deployed().then(instance => {

contract = instance

});

还可以用ES5的写法：

HelloWorld.deployed().then(function(instance) {

hello = instance;

});

truffle(development)> contract.sayHello.call()

‘Hello World’

这里直接呼叫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。

如此一来，我们已写好并部署完成了第一个智能合约，也验证了合约确实可以运作。

加入新方法

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

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，我们需要先重新新编译一次，将编译结果部署到testrpc上，再透过truffle console执行看看结果。

liyuechun:HelloWorld yuechunli$ ls

build contracts migrations test truffle.js

liyuechun:HelloWorld yuechunli$ truffle compile

Compiling ./contracts/HelloWorld.sol…

Writing artifacts to ./build/contracts

liyuechun:HelloWorld yuechunli$ truffle migrate --reset

Using network ‘development’.

Running migration: 1_initial_migration.js

Replacing Migrations…

… 0x64cdc42e08a7e3f8070c46d4877ba246d95cbbccbfe1b9abd2450cfc02b48eda

Migrations: 0x42843f6a470b84e2669f19686a223c1bdefb6f4d

Saving successful migration to network…

… 0x57042b767c0f40a4f88ce855e39549010d6d5ae5f880771a45c1f7f36ea0e5b3

Saving artifacts…

Running migration: 2_deploy_contracts.js

Replacing HelloWorld…

… 0x2330e3264aae9d6be3744d8fc71d235fc6dc2934d33ff5159ae209df4cf8f12b

HelloWorld: 0xbf68789cdd6be1577339e8c739abfa1190c31b6c

Saving successful migration to network…

… 0xb4b706d7004654215067ea5954a32f0562b32724d1c646dc43b688b466b10159

Saving artifacts…

liyuechun:HelloWorld yuechunli$ 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],

    abi: [Object],

    network: [Function: network],

    networks: [Function: networks],

    address: [Object],

    links: [Function: links],

    events: [Function: events],

    binary: [Function: binary],

    unlinked_binary: [Object],

    schema_version: [Function: schema_version],

    updated_at: [Function: updated_at] },

_property_values: {},

_json:

  { contract_name: 'HelloWorld',

    default_network: undefined,

    abi: [Array],

    unlinked_binary: '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',

    networks: [Object],

    schema_version: '0.0.5',

    updated_at: 1505809278810 },

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: [Object],

    currentProvider: [Object],

    eth: [Object],

    db: [Object],

    shh: [Object],

    net: [Object],

    personal: [Object],

    bzz: [Object],

    settings: [Object],

    version: [Object],

    providers: [Object],

    _extend: [Object] },

class_defaults:

  { from: '0xbbd414b340f2255dab9d923428c97f0b65d9df81',

    gas: 4712388,

    gasPrice: 100000000000 },

currentProvider:

  HttpProvider {

    host: 'http://localhost:8545',

    timeout: 0,

    send: [Function],

    sendAsync: [Function],

    _alreadyWrapped: true },

network_id: '1505794143155' },

abi:

[ { constant: false,

  inputs: [],

  name: 'sayHello',

  outputs: [Array],

  payable: false,

  type: 'function' },

{ constant: true,

  inputs: [Array],

  name: 'echo',

  outputs: [Array],

  payable: false,

  type: 'function' } ],

contract:

Contract {

_eth:

  Eth {

    _requestManager: [Object],

    getBalance: [Object],

    getStorageAt: [Object],

    getCode: [Object],

    getBlock: [Object],

    getUncle: [Object],

    getCompilers: [Object],

    getBlockTransactionCount: [Object],

    getBlockUncleCount: [Object],

    getTransaction: [Object],

    getTransactionFromBlock: [Object],

    getTransactionReceipt: [Object],

    getTransactionCount: [Object],

    call: [Object],

    estimateGas: [Object],

    sendRawTransaction: [Object],

    signTransaction: [Object],

    sendTransaction: [Object],

    sign: [Object],

    compile: [Object],

    submitWork: [Object],

    getWork: [Object],

    coinbase: [Getter],

    getCoinbase: [Object],

    mining: [Getter],

    getMining: [Object],

    hashrate: [Getter],

    getHashrate: [Object],

    syncing: [Getter],

    getSyncing: [Object],

    gasPrice: [Getter],

    getGasPrice: [Object],

    accounts: [Getter],

    getAccounts: [Object],

    blockNumber: [Getter],

    getBlockNumber: [Object],

    protocolVersion: [Getter],

    getProtocolVersion: [Object],

    iban: [Object],

    sendIBANTransaction: [Function: bound transfer] },

transactionHash: null,

address: '0xbf68789cdd6be1577339e8c739abfa1190c31b6c',

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: ‘0xbf68789cdd6be1577339e8c739abfa1190c31b6c’,

transactionHash: null }

truffle(development)> contract.echo(“春哥微信:liyc1215”)

‘春哥微信:liyc1215’

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来呼叫。

另一点需要注意的，是这次如果还是用truffle migrate命令，我们会得到如下信息：

$ truffle migrate

Using network ‘development’.

Network up to date.

Truffle会告诉你现在网络上的合约都已是最新的，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命令直接重新在testrpc上部署一次。