Signing raw transaction AssertionError: The field v must have byte length of 1

Question

I have followed every option present in net to do Raw transaction I have followed

ethereumjs-tx

let resData = {};
var Tx = require('ethereumjs-tx')
var privateKey = new Buffer('0xe331b6d69882b4cb4ea581d88e0b604039a3de5967688d3dcffdd2270c0fd109', 'hex')
var gasPrice = privateWeb3.eth.gasPrice;
var gasPriceHex = privateWeb3.toHex(gasPrice);
var nonce = privateWeb3.eth.getTransactionCount(req.body.fromAddress);
var nonceHex = privateWeb3.toHex(nonce);
var rawTx = {
    nonce: nonceHex,
    gasPrice: gasPriceHex,
    gasLimit: '0x2710000000',
    to: req.body.toAddress,
    from: req.body.fromAddress,
    data: '0x7f7465737432000000000000000000000000000000000000000000000000000000600057',
    chainId: req.body.chain
}

var tx = new Tx(rawTx)
console.log(tx.v);
tx.sign(privateKey)

var serializedTx = tx.serialize()
console.log(serializedTx.toString('hex'))

privateWeb3.eth.sendRawTransaction(serializedTx.toString('hex'), function(err, hash) {
    //  if (!err)
        console.log("hiii", err, hash); // "0x7f9fade1c0d57a7af66ab4ead79fade1c0d57a7af66ab4ead7c2c2eb7b11a91385"
});

This approach give me error in tx.sign(privateKey)

AssertionError: The field v must have byte length of 1 at Transaction.setter [as v] (node_modules/ethereumjs-util/index.js:609:9)

Answer 1

This may be caused by unexpectedly large chainId. It is used to compute tx.v.

See EIP155:

v = CHAIN_ID * 2 + 35 or v = CHAIN_ID * 2 + 36

And ethereumjs-tx source:

// sig.v = 28

if (this._chainId > 0) {
  sig.v += this._chainId * 2 + 8
}

So, to fit v into a single byte, your chainId must be less than 0x6d (109 dec).

Ropsten has chainId = 3, mainnet has chainId = 1.

Answer 2

var privateKey = new Buffer('0xe331b6d69882b4cb4ea581d88e0b604039a3de5967688d3dcffdd2270c0fd109', 'hex')

..you need to strip the 0x hex prefix:
new Buffer('e331b6d69882b4cb4ea581d88e0b604039a3de5967688d3dcffdd2270c0fd109', 'hex')

ps) you can also get rid of rawTx.from.. it has no meaning and will be ignored. the raw transaction is sent "from" the address corresponding to the privateKey used to sign it