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  4. tendermint提供的RPC接口(三)

tendermint提供的RPC接口(三)

接上两篇:

tendermint提供的RPC接口(一)

tendermint提供的RPC接口(二)

本文是系列文章第三篇,主要介绍如何自定义订阅事件。

/subscribe

说明:通过wensocket订阅事件。

想要订阅某个事件,需要提供一个字符串表达式,格式是“condition AND condition ”(只能用AND不能用OR)。condition的格式是“key operation operand”,

key是一个字符串(\t\n\r()'”=><不允许出现在key中)

operation可以是“=”,“<”,“<=”,“>”,“> =”, “CONTAINS”

operand可以是一个字符串(要用单引号转义),数字,日期或者事件。

比如:

tm.event = ‘NewBlock’ // 新区快产生
tm.event = ‘CompleteProposal’ // 完成一个提案
tm.event = ‘Tx’ AND tx.hash = ‘XYZ’ // 某一笔交易
tm.event = ‘Tx’ AND tx.height = 5 // 第五个块的所有交易
tx.height = 5 // 第五个块的所有交易

tendermint提供了几个预定义的key:tm.event,tx.hash,tx.height。但是用户可以通过重定义DeliverTx的响应来增加key,用以订阅其他的事件。例如定义以下event

types.ResponseDeliverTx{
Events: []types.Event{
{
Type: “rewards.withdraw”,
Attributes:
common.KVPairs{
common.KVPair{Key: []byte(“address”), Value: []byte(“AddrA”)},
common.KVPair{Key: []byte(“source”), Value: []byte(“SrcX”)},
common.KVPair{Key: []byte(“amount”), Value: []byte(“…”)},
common.KVPair{Key: []byte(“balance”), Value: []byte(“…”)},
},
},
{
Type: “rewards.withdraw”,
Attributes: common.KVPairs{
common.KVPair{Key: []byte(“address”), Value: []byte(“AddrB”)},
common.KVPair{Key: []byte(“source”), Value: []byte(“SrcY”)},
common.KVPair{Key: []byte(“amount”), Value: []byte(“…”)},
common.KVPair{Key: []byte(“balance”), Value: []byte(“…”)},
},
},
{
Type: “transfer”,
Attributes: common.KVPairs{
common.KVPair{Key: []byte(“sender”), Value: []byte(“AddrC”)},
common.KVPair{Key: []byte(“recipient”), Value: []byte(“AddrD”)},
common.KVPair{Key: []byte(“amount”), Value: []byte(“…”)},
},
},
},
}

所有事件都由eventType和eventAttrKey形式的符合键索引,在上面的示例中,将对以下键进行索引:

  • rewards.withdraw.address
  • rewards.withdraw.source
  • rewards.withdraw.amount
  • rewards.withdraw.balance
  • transfer.sender
  • transfer.recipient
  • transfer.amount
  • 允许多个事件类型具有重复的键,并且可以用于对唯一和不同事件进行分类。
  • 在上面的示例中,在密钥rewards.withdraw.address下索引的所有事件将具有以下存储和可查询的值:AddrA,AddrB
  • 创建各种类型的交易订阅:
  • query.MustParse(“tm.event = ‘Tx’ AND rewards.withdraw.address = ‘AddrA'”)
  • query.MustParse(“tm.event = ‘Tx’ AND rewards.withdraw.address = ‘AddrA’ AND rewards.withdraw.source = ‘Y'”)
  • query.MustParse(“tm.event = ‘Tx’ AND transfer.sender = ‘AddrA'”)
  • 这几种是无返回值的:
  • query.MustParse(“tm.event = ‘Tx’ AND transfer.sender = ‘AddrZ'”)
  • query.MustParse(“tm.event = ‘Tx’ AND rewards.withdraw.address = ‘AddrZ'”)
  • query.MustParse(“tm.event = ‘Tx’ AND rewards.withdraw.source = ‘W'”)
  • 下面是示例。
  • 自定义的event代码:
  • var events []types.Event
    if strings.HasPrefix(k,"a"){
       events = []types.Event{
          {
             Type: "string",
             Attributes: []common.KVPair{
                {Key: []byte("startWith"), Value: []byte("a")},
                {Key: []byte("key"), Value: key},
             },
          },
       }
    }
    if strings.HasPrefix(k,"b"){
       events = []types.Event{
          {
             Type: "string",
             Attributes: []common.KVPair{
                {Key: []byte("startWith"), Value: []byte("b")},
                {Key: []byte("key"), Value: key},
             },
          },
       }
    }
  • 订阅代码分为2个线程:
  • func main() {
       cli := client.NewHTTP("http://localhost:26657", "/websocket")
       err := cli.Start()
       if err != nil {
          fmt.Println(err)
          return
       }
       defer cli.Stop()
       ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
       defer cancel()
       //query := "app.key='author'"
       txs, err := cli.Subscribe(ctx, "test-client", "string.startWith = 'a'")
       if err != nil {
          fmt.Println("错误信息", err)
          return
       }
       for tx := range txs {
          fmt.Println("startWithA接收到消息:\n", tx)
       }
    }
  • func main() {
       cli := client.NewHTTP("http://localhost:26657", "/websocket")
       err := cli.Start()
       if err != nil {
          fmt.Println(err)
          return
       }
       defer cli.Stop()
       ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
       defer cancel()
       //query := "app.key='author'"
       txs, err := cli.Subscribe(ctx, "test-client", "string.startWith = 'b'")
       if err != nil {
          fmt.Println("错误信息", err)
          return
       }
       for tx := range txs {
          fmt.Println("startWithB接收到消息:\n", tx)
       }
    }

    分别发送交易:

    curl -s localhost:26657/broadcast_tx_commit?tx=\”aunt=a1234\”

    curl -s localhost:26657/broadcast_tx_commit?tx=\”buss=b5678\”

    可以看到两个窗口分别收到消息:

    attachments-2019-09-h1FsjKsq5d7778ae76464.png

    attachments-2019-09-OApWhrVI5d7778be87acc.png

    这只是一个示例,在实际使用过程中会更加复杂一些,例如对某个交易地址的监控,对大额转账的监控等等。

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