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 by polling eth_blockNumber over HTTP.

function watch({ environment, onNewBlock })

  • environment Object containing environment variables (rpcHttpHost, pollingInterval) passed from the crawler configuration.

  • onNewBlock Callback function invoked with the latest block number on every poll that sees a new block.

The watch() function polls eth_blockNumber on environment.rpcHttpHost every environment.pollingInterval milliseconds and returns an unwatch() function to stop polling.

environment.rpcHttpHost can be a single URL or a list of URLs. With a list, each crawl sends its eth_getLogs requests to the next URL in turn, which spreads the load across providers (e.g. to stay within several free tiers).

Note

Versions 0.6.x subscribed to newHeads via WebSocket (environment.rpcWsHost). Since 0.7.0, watch() polls over HTTP instead, because many providers bill every newHeads event.