How to let users decide between transactions

Question

I am building an API that will send out signed transactions to users and allow them to submit the transactions themselves.

I am attempting to send a user three different transactions however I would like the user to select between these options and select only one.

Question is; once the user submits one of these transactions, how do I prevent the others being sent?

I was attempting to use sequence numbers to prevent this but cannot figure out how to assign the same sequence id to all transactions on the javascript SDK so that only one is accepted.

Is there a better way to do this and if not how can I set the sequence number with the JS-sdk?

Answer 1

The same sequence number is the solution for this case. I also had the similar issue setting up same sequence number for multiple transactions, here's a sample js sdk code I used to set same sequence number,

// This method is not recommended but seems to be only working options
// I could find at the time.

// load account, which will have initial sequence number
var account = await server.loadAccount(public);

const transaction1 = new StellarSdk.TransactionBuilder(account)
    .addOperation(...).build();

// the sequence number has increased, I had tried many methods for setting
// the same sequence number, but nothing seems to work,

// Solution I used, load the account again

account = await server.loadAccount(public);

const transaction2 = new StellarSdk.TransactionBuilder(account)
    .addOperation(...).build();

// This transaction has same sequence number

Answer 2

Having the same sequence number for each transaction is the perfect solution. (Well almost perfect. This will get you at most one, rather than exactly one).

In regard to managing the sequence number, the docs state:

There are two ways to ensure correct sequence numbers:

1. Read the source account’s sequence number before submitting a transaction
2. Manage the sequence number locally

I read this to mean that the JS library will not automatically update the sequence number each time a transaction is built. You should be OK to fetch the sequence number once (from Horizon or your app's local store if you are keeping track) and build 3 transactions with that sequence number.

Answer 3

TransactionBuilder takes an Account object as its first parameter, an Account consists of a public key, and a sequence number.

You can do loadAccount once, to get the current sequence number, and then simply re-use it (the sequence number) for the next transactions.

const account = await server.loadAccount(accoundId);
const sequenceNumber = account.sequenceNumber();

then every time you want to create a transaction:

const account = new StellarSdk.Account(accountId, sequenceNumber); 
const builder = new StellarSdk.TransactionBuilder(account);