const ObservableStore = require('obs-store') const extend = require('xtend') const EthQuery = require('eth-query') const log = require('loglevel') const pify = require('pify') class RecentBlocksController { /** * Controller responsible for storing, updating and managing the recent history of blocks. Blocks are back filled * upon the controller's construction and then the list is updated when the given block tracker gets a 'latest' event * (indicating that there is a new block to process). * * @typedef {Object} RecentBlocksController * @param {object} opts Contains objects necessary for tracking blocks and querying the blockchain * @param {BlockTracker} opts.blockTracker Contains objects necessary for tracking blocks and querying the blockchain * @param {BlockTracker} opts.provider The provider used to create a new EthQuery instance. * @property {BlockTracker} blockTracker Points to the passed BlockTracker. On RecentBlocksController construction, * listens for 'latest' events so that new blocks can be processed and added to storage. * @property {EthQuery} ethQuery Points to the EthQuery instance created with the passed provider * @property {number} historyLength The maximum length of blocks to track * @property {object} store Stores the recentBlocks * @property {array} store.recentBlocks Contains all recent blocks, up to a total that is equal to this.historyLength * */ constructor (opts = {}) { const { blockTracker, provider } = opts this.blockTracker = blockTracker this.ethQuery = new EthQuery(provider) this.historyLength = opts.historyLength || 40 const initState = extend({ recentBlocks: [], }, opts.initState) this.store = new ObservableStore(initState) this.blockTracker.on('latest', this.processBlock.bind(this)) this.backfill() } /** * Sets store.recentBlocks to an empty array * */ resetState () { this.store.updateState({ recentBlocks: [], }) } /** * Receives a new block and modifies it with this.mapTransactionsToPrices. Then adds that block to the recentBlocks * array in storage. If the recentBlocks array contains the maximum number of blocks, the oldest block is removed. * * @param {object} newBlock The new block to modify and add to the recentBlocks array * */ async processBlock (newBlockNumberHex) { const newBlockNumber = Number.parseInt(newBlockNumberHex, 16) const newBlock = await this.getBlockByNumber(newBlockNumber) const block = this.mapTransactionsToPrices(newBlock) const state = this.store.getState() state.recentBlocks.push(block) while (state.recentBlocks.length > this.historyLength) { state.recentBlocks.shift() } this.store.updateState(state) } /** * Receives a new block and modifies it with this.mapTransactionsToPrices. Adds that block to the recentBlocks * array in storage, but only if the recentBlocks array contains fewer than the maximum permitted. * * Unlike this.processBlock, backfillBlock adds the modified new block to the beginning of the recent block array. * * @param {object} newBlock The new block to modify and add to the beginning of the recentBlocks array * */ backfillBlock (newBlock) { const block = this.mapTransactionsToPrices(newBlock) const state = this.store.getState() if (state.recentBlocks.length < this.historyLength) { state.recentBlocks.unshift(block) } this.store.updateState(state) } /** * Receives a block and gets the gasPrice of each of its transactions. These gas prices are added to the block at a * new property, and the block's transactions are removed. * * @param {object} newBlock The block to modify. It's transaction array will be replaced by a gasPrices array. * @returns {object} The modified block. * */ mapTransactionsToPrices (newBlock) { const block = extend(newBlock, { gasPrices: newBlock.transactions.map((tx) => { return tx.gasPrice }), }) delete block.transactions return block } /** * On this.blockTracker's first 'latest' event after this RecentBlocksController's instantiation, the store.recentBlocks * array is populated with this.historyLength number of blocks. The block number of the this.blockTracker's first * 'latest' event is used to iteratively generate all the numbers of the previous blocks, which are obtained by querying * the blockchain. These blocks are backfilled so that the recentBlocks array is ordered from oldest to newest. * * Each iteration over the block numbers is delayed by 100 milliseconds. * * @returns {Promise} Promises undefined */ async backfill() { this.blockTracker.once('latest', async (blockNumberHex) => { const currentBlockNumber = Number.parseInt(blockNumberHex, 16) const blocksToFetch = Math.min(currentBlockNumber, this.historyLength) const prevBlockNumber = currentBlockNumber - 1 const targetBlockNumbers = Array(blocksToFetch).fill().map((_, index) => prevBlockNumber - index) await Promise.all(targetBlockNumbers.map(async (targetBlockNumber) => { try { const newBlock = await this.getBlockByNumber(targetBlockNumber) if (newBlock) { this.backfillBlock(newBlock) } } catch (e) { log.error(e) } })) }) } /** * Uses EthQuery to get a block that has a given block number. * * @param {number} number The number of the block to get * @returns {Promise} Promises A block with the passed number * */ async getBlockByNumber (number) { const blockNumberHex = '0x' + number.toString(16) return await pify(this.ethQuery.getBlockByNumber).call(this.ethQuery, blockNumberHex, true) } } module.exports = RecentBlocksController