1 files changed, 84 insertions, 0 deletions
diff --git a/app/scripts/lib/tx-gas-utils.js b/app/scripts/lib/tx-gas-utils.js
new file mode 100644
index 000000000..41f67e230
--- /dev/null
+++ b/app/scripts/lib/tx-gas-utils.js
@@ -0,0 +1,84 @@
+const EthQuery = require('ethjs-query')
+const {
+  hexToBn,
+  BnMultiplyByFraction,
+  bnToHex,
+} = require('./util')
+
+/*
+tx-utils are utility methods for Transaction manager
+its passed ethquery
+and used to do things like calculate gas of a tx.
+*/
+
+module.exports = class txProvideUtil {
+  constructor (provider) {
+    this.query = new EthQuery(provider)
+  }
+
+  async analyzeGasUsage (txMeta) {
+    const block = await this.query.getBlockByNumber('latest', true)
+    let estimatedGasHex
+    try {
+      estimatedGasHex = await this.estimateTxGas(txMeta, block.gasLimit)
+    } catch (err) {
+      if (err.message.includes('Transaction execution error.')) {
+        txMeta.simulationFails = true
+        return txMeta
+      }
+    }
+    this.setTxGas(txMeta, block.gasLimit, estimatedGasHex)
+    return txMeta
+  }
+
+  async estimateTxGas (txMeta, blockGasLimitHex) {
+    const txParams = txMeta.txParams
+    // check if gasLimit is already specified
+    txMeta.gasLimitSpecified = Boolean(txParams.gas)
+    // if not, fallback to block gasLimit
+    if (!txMeta.gasLimitSpecified) {
+      const blockGasLimitBN = hexToBn(blockGasLimitHex)
+      const saferGasLimitBN = BnMultiplyByFraction(blockGasLimitBN, 19, 20)
+      txParams.gas = bnToHex(saferGasLimitBN)
+    }
+    // run tx
+    return await this.query.estimateGas(txParams)
+  }
+
+  setTxGas (txMeta, blockGasLimitHex, estimatedGasHex) {
+    txMeta.estimatedGas = estimatedGasHex
+    const txParams = txMeta.txParams
+
+    // if gasLimit was specified and doesnt OOG,
+    // use original specified amount
+    if (txMeta.gasLimitSpecified) {
+      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
+  }
+
+  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)
+  }
+
+  async validateTxParams (txParams) {
+    if (('value' in txParams) && txParams.value.indexOf('-') === 0) {
+      throw new Error(`Invalid transaction value of ${txParams.value} not a positive number.`)
+    }
+  }
+}
+\ No newline at end of file