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.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) } setTxGas (txData, blockGasLimitHex, estimatedGasHex, cb) { txData.estimatedGas = estimatedGasHex const txParams = txData.txParams // 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)) } }