event事件

Event 事件是EVM上日志的抽象，具有两大特点：

1. emit 触发事件，可以直接过滤、订阅事件
2. 经济友好，通过 Event 存储数据，每次存储大概花销 2000gas

event Transfer(address indexed from, address indexed to, uint256 value);

事件Transfer内部参数表示需要记录在链上的变量类型和参数名称

• 通过 indexed 关键字，单独将事件参数作为一个 topic 进行存储和索引
• 一个 Event 最多拥有三个 indexed 数据
• 没有 indexed 关键字修饰的参数作为 data 变量存储在 data 域中，作为参数解析

Golang 解析 event事件

func ParseLogFromReceipet(contract, txhash string) {
    receipet, err := client.TransactionReceipt(context.Background(), common.HexToHash(txhash))
    if err != nil {
       log.Fatalf("Error in get TransactionReceipt: %s", err)
    }
    if receipet.Status == 0 {
       fmt.Printf("Tx has failed\n")
       return
    }
    logs := receipet.Logs
    ParseLogs(logs, contract)
}

func ParseLogs(logs []*types.Log, contract string) bool {
    for _, logData := range logs {
       if logData.Address != common.HexToAddress(contract) {
          continue
       }
       Sender := common.HexToAddress(logData.Topics[1].Hex())
       types, _ := strconv.ParseInt(hexutil.Encode(logData.Topics[2].Bytes())[2:], 16, 64)
       uuid, _ := strconv.ParseInt(hexutil.Encode(logData.Topics[3].Bytes())[2:], 16, 64)
       fmt.Printf("Contract: %s, Sender: %s, types: %d, uuid: %d\n", contract, Sender, types, uuid)
       return true
    }
    return false
}

event topic过滤

同时过滤topic1 + topic2 的 logs

for startBlockHeight < latestblockNum {
		toblock := startBlockHeight + 10000
		if toblock > latestblockNum {
			toblock = latestblockNum
		}
		query := ethereum.FilterQuery{
			FromBlock: big.NewInt(startBlockHeight),
			ToBlock:   big.NewInt(toblock),
			Addresses: []common.Address{common.HexToAddress(contract)},
			Topics:    [][]common.Hash{{common.HexToHash("topic1"), common.HexToHash("topic2")}},
		}
		logs, err := mainnetLPClient.FilterLogs(context.Background(), query)
		if err != nil {
			fmt.Printf("Error in filter logs: error:%v", err)
			return
		}
}