signTransaction() wallet adapter

Question

const {signTransaction} = useWallet()

const transaction = new Transaction()

const tx = .... //arbitrary anchor program method as transaction

transaction.add(tx)

const signature =  signTransaction(transaction) //errors out

How does the signTransaction() function from the wallet adapter work?

https://github.com/solana-labs/wallet-adapter/blob/master/packages/core/react/src/useWallet.ts

It says it takes a transaction and returns a promise but when I try to use it I get the following error.

WalletSignTransactionError: Transaction recentBlockhash required
at PhantomWalletAdapter.signTransaction

I know I can send my transaction a different way but I want to get a signed transaction object without sending it.

Answer 1

When creating a Transaction object without sending it, it is required to set recentBlockhash and feePayer fields like so:

const latestBlockhash = await connection.getLatestBlockhash();
transaction.feePayer = wallet.publicKey;
transaction.recentBlockhash = latestBlockhash.blockhash;

and only then sign the transaction. recentBlockchash is used to check by Solana whether the transaction is outdated. If, for example, you sign a transaction but send it after 5 minutes, that transaction will be rejected and you will need to resign. This is why it is part of the transaction object.

I had the same issue in the Place | Solana project. Here is how I create a transaction on the server, send the serialized transaction to client who signs it and forwards to the server for sending.