读取ERC-20代币的事件日志
首先，创建ERC-20智能合约的事件日志的interface文件 erc20.sol:
pragma solidity ^0.4.24;
contract ERC20 {
event Transfer(address indexed from, address indexed to, uint tokens);
event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
}
然后在给定abi使用abigen创建Go包
solc --abi erc20.sol
abigen --abi=erc20_sol_ERC20.abi --pkg=token --out=erc20.go
现在在我们的Go应用程序中，让我们创建与ERC-20事件日志签名类型相匹配的结构类型：
type LogTransfer struct {
From common.Address
To common.Address
Tokens *big.Int
}
type LogApproval struct {
TokenOwner common.Address
Spender common.Address
Tokens *big.Int
}
初始化以太坊客户端
client, err := ethclient.Dial("https://cloudflare-eth.com")
if err != nil {
log.Fatal(err)
}
按照ERC-20智能合约地址和所需的块范围创建一个“FilterQuery”。这个例子我们会用ZRX 代币:
// 0x Protocol (ZRX) token address
contractAddress := common.HexToAddress("0xe41d2489571d322189246dafa5ebde1f4699f498")
query := ethereum.FilterQuery{
FromBlock: big.NewInt(6383820),
ToBlock: big.NewInt(6383840),
Addresses: []common.Address{
contractAddress,
},
}
用FilterLogs来过滤日志：
logs, err := client.FilterLogs(context.Background(), query)
if err != nil {
log.Fatal(err)
}
接下来我们将解析JSON abi，稍后我们将使用解压缩原始日志数据：
contractAbi, err := abi.JSON(strings.NewReader(string(token.TokenABI)))
if err != nil {
log.Fatal(err)
}
为了按某种日志类型进行过滤，我们需要弄清楚每个事件日志函数签名的keccak256哈希值。 事件日志函数签名哈希始终是topic [0]，我们很快就会看到。 以下是使用go-ethereumcrypto包计算keccak256哈希的方法：
logTransferSig := []byte("Transfer(address,address,uint256)")
LogApprovalSig := []byte("Approval(address,address,uint256)")
logTransferSigHash := crypto.Keccak256Hash(logTransferSig)
logApprovalSigHash := crypto.Keccak256Hash(LogApprovalSig)
现在我们将遍历所有日志并设置switch语句以按事件日志类型进行过滤：
for _, vLog := range logs {
fmt.Printf("Log Block Number: %d\n", vLog.BlockNumber)
fmt.Printf("Log Index: %d\n", vLog.Index)
switch vLog.Topics[0].Hex() {
case logTransferSigHash.Hex():
//
case logApprovalSigHash.Hex():
//
}
}
现在要解析Transfer事件日志，我们将使用abi.Unpack将原始日志数据解析为我们的日志类型结构。 解包不会解析indexed事件类型，因为它们存储在topics下，所以对于那些我们必须单独解析，如下例所示：
fmt.Printf("Log Name: Transfer\n")
var transferEvent LogTransfer
err := contractAbi.Unpack(&transferEvent, "Transfer", vLog.Data)
if err != nil {
log.Fatal(err)
}
transferEvent.From = common.HexToAddress(vLog.Topics[1].Hex())
transferEvent.To = common.HexToAddress(vLog.Topics[2].Hex())
fmt.Printf("From: %s\n", transferEvent.From.Hex())
fmt.Printf("To: %s\n", transferEvent.To.Hex())
fmt.Printf("Tokens: %s\n", transferEvent.Tokens.String())
Approval 日志也是类似的方法：
fmt.Printf("Log Name: Approval\n")
var approvalEvent LogApproval
err := contractAbi.Unpack(&approvalEvent, "Approval", vLog.Data)
if err != nil {
log.Fatal(err)
}
approvalEvent.TokenOwner = common.HexToAddress(vLog.Topics[1].Hex())
approvalEvent.Spender = common.HexToAddress(vLog.Topics[2].Hex())
fmt.Printf("Token Owner: %s\n", approvalEvent.TokenOwner.Hex())
fmt.Printf("Spender: %s\n", approvalEvent.Spender.Hex())
fmt.Printf("Tokens: %s\n", approvalEvent.Tokens.String())
最后，把所有的步骤放一起：
Log Block Number: 6383829
Log Index: 20
Log Name: Transfer
From: 0xd03dB9CF89A9b1f856a8E1650cFD78FAF2338eB2
To: 0x924CD9b60F4173DCDd5254ddD38C4F9CAB68FE6b
Tokens: 2804000000000000000000
Log Block Number: 6383831
Log Index: 62
Log Name: Approval
Token Owner: 0xDD3b9186Da521AbE707B48B8f805Fb3Cd5EEe0EE
Spender: 0xCf67d7A481CEEca0a77f658991A00366FED558F7
Tokens: 10000000000000000000000000000000000000000000000000000000000000000
Log Block Number: 6383838
Log Index: 13
Log Name: Transfer
From: 0xBA826fEc90CEFdf6706858E5FbaFcb27A290Fbe0
To: 0x4aEE792A88eDDA29932254099b9d1e06D537883f
Tokens: 2863452144424379687066
我们可以把解析的日志与etherscan的数据对比: https://etherscan.io/tx/0x0c3b6cf604275c7e44dc7db400428c1a39f33f0c6cbc19ff625f6057a5cb32c0#eventlog
完整代码
Commands
solc --abi erc20.sol
abigen --abi=erc20_sol_ERC20.abi --pkg=token --out=erc20.go
pragma solidity ^0.4.24;
contract ERC20 {
event Transfer(address indexed from, address indexed to, uint tokens);
event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
}
package main
import (
"context"
"fmt"
"log"
"math/big"
"strings"
token "./contracts_erc20" // for demo
"github.com/ethereum/go-ethereum"
"github.com/ethereum/go-ethereum/accounts/abi"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/crypto"
"github.com/ethereum/go-ethereum/ethclient"
)
// LogTransfer ..
type LogTransfer struct {
From common.Address
To common.Address
Tokens *big.Int
}
// LogApproval ..
type LogApproval struct {
TokenOwner common.Address
Spender common.Address
Tokens *big.Int
}
func main() {
client, err := ethclient.Dial("https://cloudflare-eth.com")
if err != nil {
log.Fatal(err)
}
// 0x Protocol (ZRX) token address
contractAddress := common.HexToAddress("0xe41d2489571d322189246dafa5ebde1f4699f498")
query := ethereum.FilterQuery{
FromBlock: big.NewInt(6383820),
ToBlock: big.NewInt(6383840),
Addresses: []common.Address{
contractAddress,
},
}
logs, err := client.FilterLogs(context.Background(), query)
if err != nil {
log.Fatal(err)
}
contractAbi, err := abi.JSON(strings.NewReader(string(token.TokenABI)))
if err != nil {
log.Fatal(err)
}
logTransferSig := []byte("Transfer(address,address,uint256)")
LogApprovalSig := []byte("Approval(address,address,uint256)")
logTransferSigHash := crypto.Keccak256Hash(logTransferSig)
logApprovalSigHash := crypto.Keccak256Hash(LogApprovalSig)
for _, vLog := range logs {
fmt.Printf("Log Block Number: %d\n", vLog.BlockNumber)
fmt.Printf("Log Index: %d\n", vLog.Index)
switch vLog.Topics[0].Hex() {
case logTransferSigHash.Hex():
fmt.Printf("Log Name: Transfer\n")
var transferEvent LogTransfer
err := contractAbi.Unpack(&transferEvent, "Transfer", vLog.Data)
if err != nil {
log.Fatal(err)
}
transferEvent.From = common.HexToAddress(vLog.Topics[1].Hex())
transferEvent.To = common.HexToAddress(vLog.Topics[2].Hex())
fmt.Printf("From: %s\n", transferEvent.From.Hex())
fmt.Printf("To: %s\n", transferEvent.To.Hex())
fmt.Printf("Tokens: %s\n", transferEvent.Tokens.String())
case logApprovalSigHash.Hex():
fmt.Printf("Log Name: Approval\n")
var approvalEvent LogApproval
err := contractAbi.Unpack(&approvalEvent, "Approval", vLog.Data)
if err != nil {
log.Fatal(err)
}
approvalEvent.TokenOwner = common.HexToAddress(vLog.Topics[1].Hex())
approvalEvent.Spender = common.HexToAddress(vLog.Topics[2].Hex())
fmt.Printf("Token Owner: %s\n", approvalEvent.TokenOwner.Hex())
fmt.Printf("Spender: %s\n", approvalEvent.Spender.Hex())
fmt.Printf("Tokens: %s\n", approvalEvent.Tokens.String())
}
fmt.Printf("\n\n")
}
}
solc version used for these examples
$ solc --version
0.4.24+commit.e67f0147.Emscripten.clang