Log Trigger：事件驱动的 Workflow

今天的重要新概念：Log Trigger。它让你的 workflow 能够自动响应链上事件。

熟悉该 capability

EVM Log Trigger在智能合约发出特定事件时触发。你可以通过调用 EVMClient.logTrigger() 并传入配置来创建 Log Trigger，配置中指定要监听的合约地址和事件 topic。

这很有用，因为：

• 响应式：只在链上发生某件事时才运行 workflow
• 高效：无需轮询或定期检查
• 精确：可按合约地址、事件签名和 topic 过滤

创建 trigger

import { cre, getNetwork } from "@chainlink/cre-sdk";
import { keccak256, toHex } from "viem";

// Get the network
const network = getNetwork({
  chainFamily: "evm",
  chainSelectorName: "ethereum-testnet-sepolia",
  isTestnet: true,
});

const evmClient = new cre.capabilities.EVMClient(network.chainSelector.selector);

// Compute the event signature hash
const eventHash = keccak256(toHex("Transfer(address,address,uint256)"));

// Create the trigger
const trigger = evmClient.logTrigger({
  addresses: ["0x..."], // Contract addresses to watch
  topics: [{ values: [eventHash] }], // Event signatures to filter
  confidence: "CONFIDENCE_LEVEL_FINALIZED", // Wait for finality
});

配置

logTrigger() 方法接受一个配置对象：

Log Trigger 与 CRON Trigger

我们的事件：SettlementRequested

回忆一下，我们的智能合约会发出该事件：

event SettlementRequested(uint256 indexed marketId, string question);

我们希望 CRE：

1. 检测该事件何时发出
2. 解码 marketId 与 question
3. 运行我们的 settlement workflow

理解 EVMLog Payload

当 CRE 触发你的 callback 时，会提供：

解码 Topics

对于 SettlementRequested(uint256 indexed marketId, string question)：

• topics[0] = 事件签名哈希
• topics[1] = marketId（indexed，因此在 topics 中）
• data = question（非 indexed）

创建 logCallback.ts

新建文件 my-workflow/logCallback.ts，写入事件解码逻辑：

// prediction-market/my-workflow/logCallback.ts

import {
  type Runtime,
  type EVMLog,
  bytesToHex,
} from "@chainlink/cre-sdk";
import { decodeEventLog, parseAbi } from "viem";

type Config = {
  deepseekModel: string;
  evms: Array<{
    marketAddress: string;
    chainSelectorName: string;
    gasLimit: string;
  }>;
};

const EVENT_ABI = parseAbi([
  "event SettlementRequested(uint256 indexed marketId, string question)",
]);

export function onLogTrigger(runtime: Runtime<Config>, log: EVMLog): string {
  // Convert topics to hex format for viem
  const topics = log.topics.map((t: Uint8Array) => bytesToHex(t)) as [
    `0x${string}`,
    ...`0x${string}`[]
  ];
  const data = bytesToHex(log.data);

  // Decode the event
  const decodedLog = decodeEventLog({ abi: EVENT_ABI, data, topics });

  // Extract the values
  const marketId = decodedLog.args.marketId as bigint;
  const question = decodedLog.args.question as string;

  runtime.log(`Settlement requested for Market #${marketId}`);
  runtime.log(`Question: "${question}"`);

  // Continue with EVM Read, AI, EVM Write (next chapters)...
  return "Processed";
}

更新 main.ts

更新 my-workflow/main.ts，注册 Log Trigger：

// prediction-market/my-workflow/main.ts

import { cre, Runner, getNetwork, logTriggerConfig } from "@chainlink/cre-sdk";
import { keccak256, toHex } from "viem";
import { onHttpTrigger } from "./httpCallback";
import { onLogTrigger } from "./logCallback";

// Config type (matches config.staging.json structure)
type Config = {
  deepseekModel: string;
  evms: Array<{
    marketAddress: string;
    chainSelectorName: string;
    gasLimit: string;
  }>;
};

const SETTLEMENT_REQUESTED_SIGNATURE = "SettlementRequested(uint256,string)";

const initWorkflow = (config: Config) => {
  // Initialize HTTP capability
  const httpCapability = new cre.capabilities.HTTPCapability();
  const httpTrigger = httpCapability.trigger({});

  // Get network for Log Trigger
  const network = getNetwork({
    chainFamily: "evm",
    chainSelectorName: config.evms[0].chainSelectorName,
    isTestnet: true,
  });

  if (!network) {
    throw new Error(`Network not found: ${config.evms[0].chainSelectorName}`);
  }

  const evmClient = new cre.capabilities.EVMClient(network.chainSelector.selector);
  const eventHash = keccak256(toHex(SETTLEMENT_REQUESTED_SIGNATURE));

  return [
    // Day 1: HTTP Trigger - Market Creation
    cre.handler(httpTrigger, onHttpTrigger),
    
    // Day 2: Log Trigger - Event-Driven Settlement ← NEW!
    cre.handler(
      evmClient.logTrigger(
        logTriggerConfig({
          addresses: [config.evms[0].marketAddress as `0x${string}`],
          topics: [[eventHash]],
          confidence: "FINALIZED",
        })
      ),
      onLogTrigger
    ),
  ];
};

export async function main() {
  const runner = await Runner.newRunner<Config>();
  await runner.run(initWorkflow);
}

main();

模拟 Log Trigger

1. 先在合约上请求 settlement

cast send $MARKET_ADDRESS \
  "requestSettlement(uint256)" \
  0 \
  --rpc-url "https://ethereum-sepolia-rpc.publicnode.com" \
  --private-key $CRE_ETH_PRIVATE_KEY

请保存交易哈希！

2. 运行 simulation

# From the prediction-market directory
cre workflow simulate my-workflow

3. 选择 Log Trigger

🚀 Workflow simulation ready. Please select a trigger:
1. http-trigger@1.0.0-alpha Trigger
2. evm:ChainSelector:16015286601757825753@1.0.0 LogTrigger

Enter your choice (1-2): 2

4. 输入交易详情

🔗 EVM Trigger Configuration:
Please provide the transaction hash and event index for the EVM log event.
Enter transaction hash (0x...):

粘贴步骤 1 中的交易哈希。

5. 输入 event index

Enter event index (0-based): 0

输入0。

预期输出

[SIMULATION] Running trigger trigger=evm:ChainSelector:16015286601757825753@1.0.0
[USER LOG] Settlement requested for Market #0
[USER LOG] Question: "Will Argentina win the 2022 World Cup?"

Workflow Simulation Result:
 "Processed"

[SIMULATION] Execution finished signal received

要点回顾

• Log Trigger会自动响应链上事件
• 使用 keccak256(toHex("EventName(types)")) 计算事件哈希
• 使用 Viem 的 decodeEventLog 解码事件
• 测试流程：先在链上触发事件，再用 tx hash 进行 simulation

下一步

接下来在结算之前，我们需要从合约读取更多数据。