Reference

Extractor module

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

  • start Start block as a natural number in decimal-base (default: 0).

  • end End block as a natural number in decimal-base.

  • 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 or an array of arrays containing such values.

  • blockspan The distance between fromBlock and toBlock in decimal-base (default: 1).

  • includeTimestamp Flag to include the block timestamp as block.timestamp in the result object.

  • includeValue Flag to include the transaction’s value as transaction.value in the result object.

Transformer module

function onLine({args: {topics = [], address, inputs}, state: {line}})

  • line Is an argument defined by @attestate/crawler internally. It is a line within the strategy’s input.path file.

  • 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 or an array of arrays containing such values.

  • inputs When defined, it replaces the event log’s “data” property with a parsed event log using web3-eth-abi@1.4.0’s decodeLog.

Loader module

function* order({state: {line}})

  • line Is an argument defined by @attestate/crawler internally. It is a line within the strategy’s input.path file.

order is a JavaScript generator function. As the key, it concatenates serialized blockNumber and transactionIndex to generate an identifier which defines a total order among transactionHash``es. ``value is the transactionHash.

function* direct({state: {line}})

  • line Is an argument defined by @attestate/crawler internally. It is a line within the strategy’s input.path file.

direct is a JavaScript generator function. As the key, it defines the transactionHash to generate an identifier which lets us directly access the log through value.

State module

The state module provides coordinator functionality for continuous blockchain monitoring via WebSocket subscriptions.

function watch({ environment, onNewBlock })

  • environment Object containing environment variables (e.g., rpcWsHost) passed from the crawler configuration.

  • onNewBlock Callback function invoked with the new block number when a new block is detected via WebSocket subscription.

The watch() function:

  • Establishes a WebSocket connection to the RPC endpoint specified in environment.rpcWsHost (e.g., wss://opt-mainnet.g.alchemy.com/v2/YOUR_API_KEY)

  • Subscribes to new block headers using viem’s watchBlockNumber

  • Automatically handles reconnection if the connection is lost

  • Detects and emits missed blocks with emitMissed: true

  • Returns an unwatch() function to cleanly close the subscription

The function provides real-time block notifications with ~1-2 second latency, replacing the previous polling-based approach which used an interval parameter.

Note

Prior to version 0.6.0, continuous monitoring required a polling-based interval parameter in the coordinator configuration. This has been replaced with WebSocket subscriptions via the watch() function for better performance and resource efficiency.