web3-provider-engine/subproviders/nonce-tracker.js

A JavaScript library for composing Ethereum provider objects using middleware modules

const inherits = require('util').inherits
const { TransactionFactory } = require('@ethereumjs/tx')
const ethUtil = require('@ethereumjs/util')
const Subprovider = require('./subprovider.js')
const blockTagForPayload = require('../util/rpc-cache-utils').blockTagForPayload

module.exports = NonceTrackerSubprovider

// handles the following RPC methods:
//   eth_getTransactionCount (pending only)
//
// observes the following RPC methods:
//   eth_sendRawTransaction
//   evm_revert (to clear the nonce cache)

inherits(NonceTrackerSubprovider, Subprovider)

function NonceTrackerSubprovider(){
  const self = this

  self.nonceCache = {}
}

NonceTrackerSubprovider.prototype.handleRequest = function(payload, next, end){
  const self = this

  switch(payload.method) {

    case 'eth_getTransactionCount':
      var blockTag = blockTagForPayload(payload)
      var address = payload.params[0].toLowerCase()
      var cachedResult = self.nonceCache[address]
      // only handle requests against the 'pending' blockTag
      if (blockTag === 'pending') {
        // has a result
        if (cachedResult) {
          end(null, cachedResult)
        // fallthrough then populate cache
        } else {
          next(function(err, result, cb){
            if (err) return cb()
            if (self.nonceCache[address] === undefined) {
              self.nonceCache[address] = result
            }
            cb()
          })
        }
      } else {
        next()
      }
      return

    case 'eth_sendRawTransaction':
      // allow the request to continue normally
      next(function(err, result, cb){
        // only update local nonce if tx was submitted correctly
        if (err) return cb()
        // parse raw tx
        var rawTx = payload.params[0]
        var rawData = Buffer.from(ethUtil.stripHexPrefix(rawTx), 'hex')
        const tx = TransactionFactory.fromSerializedData(rawData)
        // extract address
        var address = tx.getSenderAddress().toString('hex').toLowerCase()
        // extract nonce and increment
        var nonce = ethUtil.bufferToInt(tx.nonce)
        nonce++
        // hexify and normalize
        var hexNonce = nonce.toString(16)
        if (hexNonce.length%2) hexNonce = '0'+hexNonce
        hexNonce = '0x'+hexNonce
        // dont update our record on the nonce until the submit was successful
        // update cache
        self.nonceCache[address] = hexNonce
        cb()
      })
      return

   // Clear cache on a testrpc revert
   case 'evm_revert':
      self.nonceCache = {}
      next()
      return

    default:
      next()
      return

  }
}