带你玩转以太坊智能合约的”Hello World“
-
- 学习目标
- 使用solidity语言撰写智能合约
- 开发前的准备
- Ubuntu环境下Atom编辑器安装及使用
- 安装所需工具
- 安装nvm
- 安装node
- 安装npm
- 启动testrpc
- 建立项目
- 目录结构
- 新建HelloWorld合约
- 代码说明
- 编译
- 部署
- 与合约互动
- 加入新方法
1.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
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。
4.Ubuntu环境下Atom编辑器安装及使用
sudo add -apt -repository ppa:webupd8team/atomsudo apt -get updatesudo apt -get install atom安装插件linter-solidity、autocomplete-solidity、linter-solium以方便solidity代码编写。
5.安装所需工具
首先安装Node.js
安装nvm
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
vim ~/.profile并在文件末尾添加source ~/.nvm/nvm/nvm.sh
source ~/.profile
nvm --version检查安装是否正确
安装node
nvm install node
node --version安装npm
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
npm install -g ethereumjs-testrpc trufflesily@lyg-sily:~$ npm install -g ethereumjs-testrpc truffle
/home/sily/.nvm/nvm/versions/node/v9.3.0/bin/testrpc -> /home/sily/.nvm/nvm/versions/node/v9.3.0/lib/node_modules/ethereumjs-testrpc/build/cli.node.js
/home/sily/.nvm/nvm/versions/node/v9.3.0/bin/truffle -> /home/sily/.nvm/nvm/versions/node/v9.3.0/lib/node_modules/truffle/build/cli.bundled.js
+ ethereumjs-testrpc@6.0.3
+ truffle@4.0.4
added 343 packages in 115.81s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。
sily@lyg-sily:~$ 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：
sily@lyg-sily:~$ mkdir SmartContractDemo
sily@lyg-sily:~$ cd SmartContractDemo/
sily@lyg-sily:~/SmartContractDemo$ mkdir HelloWorld
sily@lyg-sily:~/SmartContractDemo$ cd HelloWorld/
sily@lyg-sily:~/SmartContractDemo/HelloWorld$ truffle init
Downloading...
Unpacking...
Setting up...
Unbox successful. Sweet!
Commands:
Compile: truffle compile
Migrate: truffle migrate
Test contracts: truffle test
sily@lyg-sily:~/SmartContractDemo/HelloWorld$ ls
contracts migrations test truffle-config.js truffle.js
sily@lyg-sily:~/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。
sily@lyg-sily:~/SmartContractDemo/HelloWorld$ ls
contracts migrations test truffle-config.js truffle.js
sily@lyg-sily:~/SmartContractDemo/HelloWorld$ truffle create contract HelloWorld
sily@lyg-sily:~/SmartContractDemo/HelloWorld$ cd contracts/
sily@lyg-sily:~/SmartContractDemo/HelloWorld/contracts$ ls
HelloWorld.sol Migrations.sol
sily@lyg-sily:~/SmartContractDemo/HelloWorld/contracts$ HelloWorld.sol的文件内容如下：
pragma solidity ^0.4.4;
contract HelloWorld {
function sayHello() returns (string) {
return ("Hello World");
}
}代码说明
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。
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
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)。
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- 适合区块链新手的以太坊DApp实战入门教程
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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。
sily@lyg-sily:~/SmartContractDemo/HelloWorld$ ls
contracts migrations test truffle-config.js truffle.js
sily@lyg-sily:~/SmartContractDemo/HelloWorld$ truffle compile
Compiling ./contracts/HelloWorld.sol...
Compiling ./contracts/Migrations.sol...
Compilation warnings encountered:
/home/sily/SmartContractDemo/HelloWorld/contracts/HelloWorld.sol:4:3: Warning: No visibility specified. Defaulting to "public".
function sayHello() returns (string) {
^
Spanning multiple lines.
,/home/sily/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
sily@lyg-sily:~/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：
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：
sily@lyg-sily:~/SmartContractDemo/HelloWorld$ truffle migrate
Compiling ./contracts/HelloWorld.sol...
Compilation warnings encountered:
/home/sily/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/sily/.nvm/nvm/versions/node/v9.3.0/lib/node_modules/truffle/build/cli.bundled.js:41338:23)
at /home/sily/.nvm/nvm/versions/node/v9.3.0/lib/node_modules/truffle/build/cli.bundled.js:202239:19
at /home/sily/.nvm/nvm/versions/node/v9.3.0/lib/node_modules/truffle/build/cli.bundled.js:41263:11
at /home/sily/.nvm/nvm/versions/node/v9.3.0/lib/node_modules/truffle/build/cli.bundled.js:41295:9
at 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：
module.exports = {
networks: {
development: {
host: "localhost",
port:8545,
network_id:"*" // 匹配任何network id
}
}
};重新执行truffle migrate:
sily@lyg-sily:~/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...
sily@lyg-sily:~/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。
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_getTransactionReceipt10.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。
sily@lyg-sily:~/SmartContractDemo/HelloWorld$ ls
build contracts migrations test truffle-config.js truffle.js
sily@lyg-sily:~/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: '25:112:0:-;;;;;;;;;;;;;;;;;',
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/sily/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：
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'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。
如果你希望高效的学习以太坊DApp开发，可以访问汇智网提供的最热门在线互动教程：
- 适合区块链新手的以太坊DApp实战入门教程
- 区块链+IPFS+Node.js+MongoDB+Express去中心化以太坊电商应用开发实战
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。
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。
sily@lyg-sily:~/SmartContractDemo/HelloWorld$ truffle migrate --reset
Compiling ./contracts/HelloWorld.sol...
Compilation warnings encountered:
/home/sily/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/sily/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...
sily@lyg-sily:~/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/sily/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：
$ 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。
转自:
https://blog.csdn.net/rectsuly/article/details/79028766
如果你希望高效的学习以太坊DApp开发，可以访问汇智网提供的最热门在线互动教程：
- 适合区块链新手的以太坊DApp实战入门教程
- 区块链+IPFS+Node.js+MongoDB+Express去中心化以太坊电商应用开发实战
其他更多内容也可以访问这个以太坊博客。