上一篇介绍了使用golang进行智能合约的部署以及调用,但是使用go语言最大的一个问题是没法持续监听事件的发生.
比如我的后台程序需要监控谁给我转账了,如果使用go语言,目前就只能是轮询数据,而使用web3就简单许多,geth会把我关心的事件
主动通知给我.
- 以太坊系列之十七: 使用web3进行智能合约的部署调用以及监听事件(Event)
- token合约
- 编译token
- 部署合约
- 查询合约
- 调用合约函数
- 监听事件
token合约是官方提供的一个样例,这里给出我修改过的版本,方便演示.
contract MyToken {
/* Public variables of the token */
string public name;
string public symbol;
uint8 public decimals;
/* This creates an array with all balances */
mapping (address => uint256) public balanceOf;
mapping (address => mapping (address => uint)) public allowance;
mapping (address => mapping (address => uint)) public spentAllowance;
/* This generates a public event on the blockchain that will notify clients */
event Transfer(address indexed from, address indexed to, uint256 value);
event ReceiveApproval(address _from, uint256 _value, address _token, bytes _extraData);
/* Initializes contract with initial supply tokens to the creator of the contract */
function MyToken(uint256 initialSupply, string tokenName, uint8 decimalUnits, string tokenSymbol) {
balanceOf[msg.sender] = initialSupply; // Give the creator all initial tokens
name = tokenName; // Set the name for display purposes
symbol = tokenSymbol; // Set the symbol for display purposes
decimals = decimalUnits; // Amount of decimals for display purposes
}
/* Send coins */
function transfer(address _to, uint256 _value) {
if (balanceOf[msg.sender] < _value) throw; // Check if the sender has enough
if (balanceOf[_to] + _value < balanceOf[_to]) throw; // Check for overflows
balanceOf[msg.sender] -= _value; // Subtract from the sender
balanceOf[_to] += _value; // Add the same to the recipient
Transfer(msg.sender, _to, _value); // Notify anyone listening that this transfer took place
}
/* Allow another contract to spend some tokens in your behalf */
function approveAndCall(address _spender, uint256 _value, bytes _extraData) returns (bool success) {
allowance[msg.sender][_spender] = _value;
ReceiveApproval(msg.sender, _value, this, _extraData);
}
/* A contract attempts to get the coins */
function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {
if (balanceOf[_from] < _value) throw; // Check if the sender has enough
if (balanceOf[_to] + _value < balanceOf[_to]) throw; // Check for overflows
if (spentAllowance[_from][msg.sender] + _value > allowance[_from][msg.sender]) throw; // Check allowance
balanceOf[_from] -= _value; // Subtract from the sender
balanceOf[_to] += _value; // Add the same to the recipient
spentAllowance[_from][msg.sender] += _value;
Transfer(msg.sender, _to, _value);
}
/* This unnamed function is called whenever someone tries to send ether to it */
function () {
throw; // Prevents accidental sending of ether
}
}
通过solc编译得到的json abi以及hex编码的code,由于太长,太占地方就不放上来了.
这些会在部署以及调用的时候用到.
下面来通过web3进行合约的部署,读取数据,发起事务以及监听事件的发生.
部署合约需要创建事务,话费gas,因此相关账户必须事先解锁,web3目前没有api可以解锁账户,需要自己在控制台事先解锁才行.
首先创建合约,需要制定abi.
然后就可以部署合约了,这时候需要合约的code,
部署合约的结果可以通过异步函数来获取,例子已经给出.
var Web3 = require('web3');
var web3 = new Web3(new Web3.providers.IpcProvider("\\\\.\\pipe\\geth.ipc",net));
var eth=web3.eth;
var tokenContract = new web3.eth.Contract(MyTokenABI, null, {
from: '0x1a9ec3b0b807464e6d3398a59d6b0a369bf422fa' // 目前web3没有api来解锁账户,只能自己事先解锁
});
tokenContract.deploy({
data: MyTokenBin,
arguments: [32222, 'token on web3',0,'web3']
}).send({
from: '0x1a9ec3b0b807464e6d3398a59d6b0a369bf422fa',
gas: 1500000,
gasPrice: '30000000000000'
}, function(error, transactionHash){
console.log("deploy tx hash:"+transactionHash)
})
.on('error', function(error){ console.error(error) })
.on('transactionHash', function(transactionHash){ console.log("hash:",transactionHash)})
.on('receipt', function(receipt){
console.log(receipt.contractAddress) // contains the new contract address
})
.on('confirmation', function(confirmationNumber, receipt){console.log("receipt,",receipt)})
.then(function(newContractInstance){
console.log(newContractInstance.options.address) // instance with the new contract address
});
合约部署成功以后,有了地址就可以根据地址来查询合约的状态.
查询合约状态并不需要发起事务,也不需要花费gas,因此比较简单.
var tokenContract = new web3.eth.Contract(MyTokenABI, '0x6a0dF9E94a41fCd89d8236a8C03f9D678df5Acf9');
tokenContract.methods.name().call(null,function(error,result){
console.log("contract name "+result);
})
合约的函数除了指明返回值是constant的以外,都需要发起事务,这时候就需要指定调用者,因为要花费该账户的gas.
这里调用一下transfer函数.
tokenContract.methods.transfer("0x8c1b2e9e838e2bf510ec7ff49cc607b718ce8401",387).send({from: '0x1a9ec3b0b807464e6d3398a59d6b0a369bf422fa'})
.on('transactionHash', function(hash){
})
.on('confirmation', function(confirmationNumber, receipt){
})
.on('receipt', function(receipt){
// receipt example
console.log(receipt); //查询这里可以得到结果
})
.on('error', console.error); // If a out of gas error, the second parameter is the receipt.
刚刚调用transfer的时候还会触发合约的事件Transfer,如果程序关注谁给谁进行了转账,那么就可以通过监听该事件.
通过指定fromBlock,toBlock可以限制事件发生的范围,除了这个还有一个filter参数可以进行更详细的限制,
如有兴趣可以查询文档web3文档
tokenContract.events.Transfer({
fromBlock: 0,
toBlock:'latest'
}, function(error, event){ /*console.log("result:\n"+JSON.stringify(event)); */})
.on('data', function(event){
console.log(event); // same results as the optional callback above
})
.on('changed', function(event){
// remove event from local database
})
.on('error', console.error);
需要说明的是,这个监听不仅传送历史事件,未来所有事件也会传送.
下面的结果是首先运行程序,会先打印出来刚刚进行的转账.
然后我在通过其他途径进行转账 *** 作,这时候终端会把新的转账也打印出来.
历史转账:
{ address: '0x6a0dF9E94a41fCd89d8236a8C03f9D678df5Acf9',
blockNumber: 10680,
transactionHash: '0x27d5ab9277df504a436b1068697a444d30228584094632f10ab7ba5213a4eccc',
transactionIndex: 0,
blockHash: '0xcde734882b0d8cb7a5bf1f7e6d1ccfac5365308de2d7391ce286b45c5546f40b',
logIndex: 0,
removed: false,
id: 'log_2588a961',
returnValues:
Result {
'0': '0x1a9eC3b0b807464e6D3398a59d6b0a369Bf422fA',
'1': '0x8c1b2E9e838e2Bf510eC7Ff49CC607b718Ce8401',
'2': '387',
from: '0x1a9eC3b0b807464e6D3398a59d6b0a369Bf422fA',
to: '0x8c1b2E9e838e2Bf510eC7Ff49CC607b718Ce8401',
value: '387' },
event: 'Transfer',
signature: '0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef',
raw:
{ data: '0x0000000000000000000000000000000000000000000000000000000000000183',
topics:
[ '0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef',
'0x0000000000000000000000001a9ec3b0b807464e6d3398a59d6b0a369bf422fa',
'0x0000000000000000000000008c1b2e9e838e2bf510ec7ff49cc607b718ce8401' ] } }
实时监控到的转账
{ address: '0x6a0dF9E94a41fCd89d8236a8C03f9D678df5Acf9',
blockNumber: 10740,
transactionHash: '0xb42651720e8b8b64283cbd245aebaa7ad7e3dda58b9887f645ad6957bd7771b8',
transactionIndex: 0,
blockHash: '0xcdca97ba5a277e402a93188df03a758c916c37eea0f7498365d227ebd7cb2ee2',
logIndex: 0,
removed: false,
id: 'log_edc5dc68',
returnValues:
Result {
'0': '0x1a9eC3b0b807464e6D3398a59d6b0a369Bf422fA',
'1': '0x0000000000000000000000000000000000000001',
'2': '32',
from: '0x1a9eC3b0b807464e6D3398a59d6b0a369Bf422fA',
to: '0x0000000000000000000000000000000000000001',
value: '32' },
event: 'Transfer',
signature: '0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef',
raw:
{ data: '0x0000000000000000000000000000000000000000000000000000000000000020',
topics:
[ '0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef',
'0x0000000000000000000000001a9ec3b0b807464e6d3398a59d6b0a369bf422fa',
'0x0000000000000000000000000000000000000000000000000000000000000001' ] } }
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