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) {
const simulationFailed = (
err.message.includes('Transaction execution error.') ||
err.message.includes('gas required exceeds allowance or always failing transaction')
)
if (simulationFailed) {
txMeta.simulationFails = true
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
