const EthQuery = require('ethjs-query') const { hexToBn, BnMultiplyByFraction, bnToHex, } = require('../../lib/util') const { addHexPrefix } = require('ethereumjs-util') const SIMPLE_GAS_COST = '0x5208' // Hex for 21000, cost of a simple send. /** tx-gas-utils are gas utility methods for Transaction manager its passed ethquery and used to do things like calculate gas of a tx. @param {Object} provider - A network provider. */ class TxGasUtil { constructor (provider) { this.query = new EthQuery(provider) } /** @param txMeta {Object} - the txMeta object @returns {object} the txMeta object with the gas written to the txParams */ async analyzeGasUsage (txMeta) { const block = await this.query.getBlockByNumber('latest', true) let estimatedGasHex try { estimatedGasHex = await this.estimateTxGas(txMeta, block.gasLimit) } catch (err) { txMeta.simulationFails = { reason: err.message, } return txMeta } this.setTxGas(txMeta, block.gasLimit, estimatedGasHex) return txMeta } /** Estimates the tx's gas usage @param txMeta {Object} - the txMeta object @param blockGasLimitHex {string} - hex string of the block's gas limit @returns {string} the estimated gas limit as a hex string */ async estimateTxGas (txMeta, blockGasLimitHex) { const txParams = txMeta.txParams // check if gasLimit is already specified txMeta.gasLimitSpecified = Boolean(txParams.gas) // if it is, use that value if (txMeta.gasLimitSpecified) { return txParams.gas } // if recipient has no code, gas is 21k max: const recipient = txParams.to const hasRecipient = Boolean(recipient) let code if (recipient) code = await this.query.getCode(recipient) if (hasRecipient && (!code || code === '0x')) { txParams.gas = SIMPLE_GAS_COST txMeta.simpleSend = true // Prevents buffer addition return SIMPLE_GAS_COST } // if not, fall back to block gasLimit const blockGasLimitBN = hexToBn(blockGasLimitHex) const saferGasLimitBN = BnMultiplyByFraction(blockGasLimitBN, 19, 20) txParams.gas = bnToHex(saferGasLimitBN) // run tx return await this.query.estimateGas(txParams) } /** Writes the gas on the txParams in the txMeta @param txMeta {Object} - the txMeta object to write to @param blockGasLimitHex {string} - the block gas limit hex @param estimatedGasHex {string} - the estimated gas hex */ setTxGas (txMeta, blockGasLimitHex, estimatedGasHex) { txMeta.estimatedGas = addHexPrefix(estimatedGasHex) const txParams = txMeta.txParams // if gasLimit was specified and doesnt OOG, // use original specified amount if (txMeta.gasLimitSpecified || txMeta.simpleSend) { txMeta.estimatedGas = txParams.gas return } // if gasLimit not originally specified, // try adding an additional gas buffer to our estimation for safety const recommendedGasHex = this.addGasBuffer(txMeta.estimatedGas, blockGasLimitHex) txParams.gas = recommendedGasHex return } /** Adds a gas buffer with out exceeding the block gas limit @param initialGasLimitHex {string} - the initial gas limit to add the buffer too @param blockGasLimitHex {string} - the block gas limit @returns {string} the buffered gas limit as a hex string */ addGasBuffer (initialGasLimitHex, blockGasLimitHex) { const initialGasLimitBn = hexToBn(initialGasLimitHex) const blockGasLimitBn = hexToBn(blockGasLimitHex) const upperGasLimitBn = blockGasLimitBn.muln(0.9) const bufferedGasLimitBn = initialGasLimitBn.muln(1.5) // if initialGasLimit is above blockGasLimit, dont modify it if (initialGasLimitBn.gt(upperGasLimitBn)) return bnToHex(initialGasLimitBn) // if bufferedGasLimit is below blockGasLimit, use bufferedGasLimit if (bufferedGasLimitBn.lt(upperGasLimitBn)) return bnToHex(bufferedGasLimitBn) // otherwise use blockGasLimit return bnToHex(upperGasLimitBn) } } module.exports = TxGasUtil