Send back to back signed raw transaction

Question

I have to send multiple signed transactions and from a specific account with nonce via web3.eth.getTransactionCount. Because the call may come parallel, I either get

replacement transaction underpriced

or

Transaction was not mined within 50 blocks, please make sure your transaction was properly send.

What is the best way to calculate nonce and make every transaction unique?

I am using web3

Answer 1

I had a similar issue and used a global variable to remember the last nonce that was used. If the nonce you get from web3.eth.getTransactionCount is lower than that you can adjust the nonce accordingly. In code, it looks somehow like this:

var curnonce = web3.eth.getTransactionCount(account);
while (curnonce <= lastnonce) curnonce++;
lastnonce = curnonce;

Works fine and very reliable in my scenario.