Solidity revert message debugging w/ Python and Parity

readme.md

Solidity Revert message debugging w/ Python and Parity

I followed the open-sourced error message decoder by etherscan. The code I modified is contained in this PR (which supports parity nodes).

The following steps are compatible with the testing workflow of the pymaker and MakerDao keepers. It will print out the RAW and Decoded error message to the CLI of a failed transaction on a local Parity testchain

1. Modify lib/pymaker/init.py to mine a failing transaction
2. Note the txhash on the failed test
3. Add debuggingRevert.js to the directory that holds the python code with the failing
4. Update debuggingRevert.js with the txhash

We are going to call debuggingRevert.js through the python code, right after the failed (but now successfully mined) transaction. To do this, I followed this stackoverflow answer.

After Naked is imported via from Naked.toolshed.shell import execute_js, muterun_js, here's an example of how I called debuggingRevert.js after spell.cast() was failing in Chief-Keeper:

spell.cast().transact(gas_price=self.gas_price())

response = muterun_js('debuggingRevert.js')
if response.exitcode == 0:
  print(response.stdout)
else:
  print(response.stderr)
  # sys.stderr.write(response.stderr)

Which yeilds the following console log within a pytest session:

b'RAW result: 0x08c379a00000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000001b64732d70617573652d64656c656761746563616c6c2d6572726f720000000000\n\nDecoded reason: "ds-pause-delegatecall-error"\n'

debuggingRevert.js

/* eslint-disable no-console */
const Web3 = require('web3')
const kovanPOA = 'https://kovan.poa.network'
const kovanInfura = 'https://kovan.infura.io/v3/c7463beadf2144e68646ff049917b716'
const mainnetInfura = 'https://mainnet.infura.io/v3/c7463beadf2144e68646ff049917b716'
const mainnetTrust = 'http://ethereum-rpc.trustwalletapp.com'
const mainnetMEW = 'https://api.mycryptoapi.com/eth'
const testnet = 'http://localhost:8545'

const web3 = new Web3(testnet)

// INSERT TXHASH THAT'S FAILING
const txHash = '0x205a25f2cf8100f33ef63a95b498d36d4f86ebe7ef6d51eeddab8edc6dad0163'
const parity = true
// INSERT TXHASH THAT's FAILING

if (parity) {
  web3.eth.extend({
    property: 'parity',
    methods: [
      {
        name: 'traceReplayTransaction',
        call: 'trace_replayTransaction',
        params: 2,
      },
    ],
  })
}

async function getResult({ hash, to, input, from, value, gas, gasPrice, blockNumber }) {
  // Parity call to get result
  if (parity) {
    return (await web3.eth.parity.traceReplayTransaction(hash, ['trace'])).output
  }

  // Geth call to get result
  return web3.eth.call(
    {
      to,
      data: input,
      from,
      value,
      gas,
      gasPrice,
    },
    blockNumber
  )
}

async function main() {

  if (!txHash.match(/^0x([A-Fa-f0-9]{64})$/)) {
    console.error('Invalid transaction hash argument. Must be a 32 byte hex string with a 0x prefix which is 64 characters in total.')
    process.exit(2)
  }

  const receipt = await web3.eth.getTransactionReceipt(txHash)

  if (!receipt) {
    console.error('Could not get transaction receipt. Are you sure it was mined?')
    process.exit(3)
  }

  if (receipt.status) {
    console.error('Transaction did not fail. Can only read the revert reason from failed transactions')
    process.exit(3)
  }

  const transaction = await web3.eth.getTransaction(txHash)

  if (receipt.gasUsed === transaction.gas) {
    console.error('Transaction failed as it ran out of gas.')
    process.exit(4)
  }

  let rawMessageData
  try {
    const result = await getResult(transaction)

    console.log('RAW result:', result)
    // Trim the 0x prefix
    rawMessageData = result.slice(2)
  } catch (e) {
    console.log('RAW error message:', e.message)

    if (e.message.startsWith('Node error: ')) {
      // Trim "Node error: "
      const errorObjectStr = e.message.slice(12)
      // Parse the error object
      const errorObject = JSON.parse(errorObjectStr)

      if (!errorObject.data) {
        throw Error('Failed to parse data field error object:' + errorObjectStr)
      }

      if (errorObject.data.startsWith('Reverted 0x')) {
        // Trim "Reverted 0x" from the data field
        rawMessageData = errorObject.data.slice(11)
      }
      else if (errorObject.data.startsWith('0x')) {
        // Trim "0x" from the data field
        rawMessageData = errorObject.data.slice(2)
      }
      else {
        throw Error('Failed to parse data field error object:' + errorObjectStr)
      }
    }
    else {
      throw Error('Failed to parse error message from Ethereum call: ' + e.message)
    }
  }

  // Get the length of the revert reason
  const strLen = parseInt(rawMessageData.slice(8 + 64, 8 + 128), 16)
  // Using the length and known offset, extract and convert the revert reason
  const reasonCodeHex = rawMessageData.slice(8 + 128, 8 + 128 + (strLen * 2))
  // Convert reason from hex to string
  const reason = web3.utils.hexToAscii('0x' + reasonCodeHex)
  console.log('\nDecoded reason: "' + reason + '"')
}

main()