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const async = require('async')
const EthQuery = require('eth-query')
const ethUtil = require('ethereumjs-util')
const BN = ethUtil.BN
/*
tx-utils are utility methods for Transaction manager
its passed a provider and that is passed to ethquery
and used to do things like calculate gas of a tx.
*/
module.exports = class txProviderUtils {
constructor (provider) {
this.provider = provider
this.query = new EthQuery(provider)
}
analyzeGasUsage (txData, cb) {
var self = this
this.query.getBlockByNumber('latest', true, (err, block) => {
if (err) return cb(err)
async.waterfall([
self.estimateTxGas.bind(self, txData, block.gasLimit),
self.checkForTxGasError.bind(self, txData),
self.setTxGas.bind(self, txData, block.gasLimit),
], cb)
})
}
estimateTxGas (txData, blockGasLimitHex, cb) {
const txParams = txData.txParams
// check if gasLimit is already specified
txData.gasLimitSpecified = Boolean(txParams.gas)
// if not, fallback to block gasLimit
if (!txData.gasLimitSpecified) {
txParams.gas = blockGasLimitHex
}
// run tx, see if it will OOG
this.query.estimateGas(txParams, cb)
}
checkForTxGasError (txData, estimatedGasHex, cb) {
txData.estimatedGas = estimatedGasHex
// all gas used - must be an error
if (estimatedGasHex === txData.txParams.gas) {
txData.simulationFails = true
}
cb()
}
setTxGas (txData, blockGasLimitHex, cb) {
const txParams = txData.txParams
// if OOG, nothing more to do
if (txData.simulationFails) {
cb()
return
}
// if gasLimit was specified and doesnt OOG,
// use original specified amount
if (txData.gasLimitSpecified) {
txData.estimatedGas = txParams.gas
cb()
return
}
// if gasLimit not originally specified,
// try adding an additional gas buffer to our estimation for safety
const estimatedGasBn = new BN(ethUtil.stripHexPrefix(txData.estimatedGas), 16)
const blockGasLimitBn = new BN(ethUtil.stripHexPrefix(blockGasLimitHex), 16)
const estimationWithBuffer = new BN(this.addGasBuffer(estimatedGasBn), 16)
// added gas buffer is too high
if (estimationWithBuffer.gt(blockGasLimitBn)) {
txParams.gas = txData.estimatedGas
// added gas buffer is safe
} else {
const gasWithBufferHex = ethUtil.intToHex(estimationWithBuffer)
txParams.gas = gasWithBufferHex
}
cb()
return
}
addGasBuffer (gas) {
const gasBuffer = new BN('100000', 10)
const bnGas = new BN(ethUtil.stripHexPrefix(gas), 16)
const correct = bnGas.add(gasBuffer)
return ethUtil.addHexPrefix(correct.toString(16))
}
}
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