Log Trigger en Prediction Market

Cuando se solicita la liquidación de un Mercado, se utiliza Log trigger para iniciar un workflow y obtener la respuesta de Gemini AI.

El Evento: SettlementRequested

Recuerda que nuestro smart contract emite este evento:

event SettlementRequested(uint256 indexed marketId, string question);

Queremos que CRE:

1. Detecte cuando este evento se emite
2. Decodifique el marketId y la pregunta
3. Ejecute nuestro workflow de liquidación

El Payload EVMLog para SettlementRequested

Estas son las informaciones en el Payload del evento SettlementRequested(uint256 indexed marketId, string question):

• topics[0] = Hash de la firma del evento
• topics[1] = marketId (indexado, así que está en topics)
• data = question (no indexado)

Creando logCallback.ts

Crea un nuevo archivo my-workflow/logCallback.ts con la lógica de decodificación del evento:

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

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

type Config = {
  geminiModel: 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";
}

Actualizando main.ts

Actualiza my-workflow/main.ts para usar el Log Trigger:

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

import { cre, Runner, getNetwork, hexToBase64 } 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 = {
  geminiModel: 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({
        addresses: [hexToBase64(config.evms[0].marketAddress as `0x${string}`)],
        topics: [{ values: [hexToBase64(eventHash)] }],
        confidence: "CONFIDENCE_LEVEL_FINALIZED",
      }),
      onLogTrigger
    ),
  ];
};

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

main();

Simulando un Log Trigger

1. Primero, solicita la liquidación de un mercado en el smart contract

• Interactúa con el PredictionMarket.sol
• Llama a la función requestSettlement, con el parámetro 0, que es el id de la pregunta del mercado creada antes.

En una computadora con Windows, usa Git Bash para ejecutar el comando a continuación.

Ejecuta:

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

Guarda el hash de la transacción!

El resultado en nuestro contrato desplegado:

blockHash            0x123ec1ae9e4e5fcfec18edd3e76aa99a4628904c2380a6d578e5471928e71e78
blockNumber          10668469
contractAddress
cumulativeGasUsed    51861828
effectiveGasPrice    42409327
from                 0x12Fbc10072650d844492De4bcCd0298eaE07dB96
gasUsed              41125
logs                 [{"address":"0x3c01d85d7d2b7c505b1317b1e7f418334a7777bd","topics":["0x0355cdf68e24814c7dc62aff7f0f02eecf17779d969144accb1ad4b432f51dad","0x0000000000000000000000000000000000000000000000000000000000000000"],"data":"0x0000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000002657696c6c20417267656e74696e612077696e20746865203230323220576f726c64204375703f0000000000000000000000000000000000000000000000000000","blockHash":"0x123ec1ae9e4e5fcfec18edd3e76aa99a4628904c2380a6d578e5471928e71e78","blockNumber":"0xa2c9b5","blockTimestamp":"0x69e04324","transactionHash":"0x152352a8c56b67300423227010b2993d3e44c10d95d958796e0b5c8572c4700b","transactionIndex":"0xaf","logIndex":"0x803","removed":false}]
logsBloom            0x00000000000000000000000000000000000000400000000000000000000000000000800000000000000000000000000000000000000000000000000000000000000000000000000000080000000000000000000000000000000000000000000000000000020000000000000000000800000000000000000000000000000000000000004000000000000000000000000000000000000000000000002000000000000000000000000000000000800000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000000000
root
status               1 (success)
transactionHash      0x152352a8c56b67300423227010b2993d3e44c10d95d958796e0b5c8572c4700b
transactionIndex     175
type                 2
blobGasPrice
blobGasUsed
to                   0x3c01d85D7d2b7C505b1317b1e7f418334A7777bd

En este ejemplo, el hash de la transacción es 0x152352a8c56b67300423227010b2993d3e44c10d95d958796e0b5c8572c4700b

2. Ejecutar la simulación

Desde el directorio prediction-market

cre workflow simulate my-workflow

3. Seleccionar Log Trigger

Ahora el workflow tiene 2 triggers y necesitas elegir uno de ellos en una simulación.

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

Selecciona la segunda opción: evm:ChainSelector: ... LogTrigger y presiona Enter

4. Ingresar los detalles de la transacción

Continua con el hash de la transacción para el evento EVM log:

🔗 EVM Trigger Configuration:
┃ Transaction hash for the EVM log event
┃ > 0x...

Pega el hash de la transacción del Paso 1.

5. Ingresar el índice del evento

Ingresa el índice del evento (basado en 0).

Verificando los Logs de la transacción en el block explorer, puedes ver que el evento SettlementRequested es el primero, que es el índice 0.

Mira el ejemplo: SettlementRequested Log

┃ Event Index
┃ Log event index (0-based)
┃ > 0

Escribe 0 y presiona Enter.

Salida Esperada

[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

Puntos Clave

• Los Log Triggers reaccionan a eventos on-chain automáticamente
• Usa keccak256(toHex("EventName(types)")) para calcular el hash del evento
• Decodifica eventos usando decodeEventLog de Viem
• Prueba primero activando el evento on-chain, luego simulando con el hash de la transacción

Siguientes Pasos

Ahora vamos a leer más datos del contrato antes de ejecutar la liquidación de mercado solicitada.