@attestate/crawler-call-block-logs

A @attestate/crawler strategy to extract and transform Ethereum block event logs from the JSON-RPC API.

Context

A key concept of Ethereum are the event logs emitted from smart contracts. They are used to signal historic calls to specific smart contract functions and can hence be used to keep a local application synchronized to the latest state of a smart contract on the Ethereum mainnet.

Source code: github.com/attestate/crawler-call-block-logs.

Installation

Assuming you already have the crawler set up, install the strategy via npm:

npm i @attestate/crawler-call-block-logs

Usage

import { resolve } from "path";
import { env } from "process";
import * as blockLogs from "@attestate/crawler-call-block-logs";

const range = {
  start: 16370086,
  end: 16370087, // start + 1
  stepSize: 1
};

const address = "0x24da31e7bb182cb2cabfef1d88db19c2ae1f5572";
const topics = [
  "0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef",
  "0x0000000000000000000000000000000000000000000000000000000000000000",
];

export default [
  {
    name: "call-block-logs",
    extractor: {
      module: blockLogs.extractor,
      args: [range.start, range.end, address, topics, range.stepSize],
      output: {
        path: resolve(env.DATA_DIR, "call-block-logs-extraction"),
      },
    },
    transformer: {
      module: blockLogs.transformer,
      args: [/* topics, address */],
      input: {
        path: resolve(env.DATA_DIR, "call-block-logs-extraction"),
      },
      output: {
        path: resolve(env.DATA_DIR, "call-block-logs-transformation"),
      },
    },
  },
];

References

Extractor module

// NOTE: address and topics can be used to filter events at the Ethereum node
//  level.
function init(start = 0, end, address, topics, stepSize = 1);

start Start block as a decimal-base number (default: 0).
end End block as a decimal-base number.
address “0x”- prefixed Ethereum address of where an event log originates from.
topics Array containing up to three 32 byte long “0x”-prefixed topic hashes related to the event.
stepSize The distance between fromBlock and toBlock (default: 1).

Transformer module

export function onLine(line, topics = [], address) {

line Cannot be user-defined. Is a respective line defined in the crawl path’s input path.
address “0x”- prefixed Ethereum address of where an event log originates from.
topics Array containing up to three 32 byte long “0x”-prefixed topic hashes related to the event.