How to add a new instruction to an existing transaction?

Question

I have a serialized transaction from the Jupiter Swap API from which I can create a versioned transaction.

raw_tx = VersionedTransaction.from_bytes(base64.b64decode(serialized_transaction))

But I want to add priority fees my transaction, I use the following to create the instruction:

priorityFee = set_compute_unit_price(100000)

Since the priority fee would look like this when printed out:

Instruction { program_id: ComputeBudget111111111111111111111111111111, accounts: [], data: [3, 160, 134, 1, 0, 0, 0, 0, 0] }

How would I add this to my versioned transaction which looks like this:

Message { header: MessageHeader { num_required_signatures: 2, num_readonly_signed_accounts: 1, num_readonly_unsigned_accounts: 6 }, account_keys: [FerNfB9EMGLgdKMsQpP8Q5hzQLhcQUXGRc1wuC5Ybq3Y, HVcqYDdERth6wcemnvejAY6X2AWZaex31o94TsboRfjT, 9D5b1NHqqveAF4LTTXXJJbm5mnh3ugQ2jzRu1T3auQjd, GmnWWYa4gcZihoHeNpChSF9Lq8nfSMz4AJPzC2sawSAV, GTNw5SSuVxcdGZHdKuzx7qguS6JEcQV9oSVw8vCLqfwt, 11111111111111111111111111111111, 7GCihgDB8fe6KNjn2MYtkzZcRjQy3t9GHdC8uHYmW2hr, jupoNjAxXgZ4rjzxzPMP4oxduvQsQtZzyknqvzYNrNu, So11111111111111111111111111111111111111112, SysvarRent111111111111111111111111111111111, TokenkegQfeZyiNwAJbNbGKPFXCWuBvf9Ss623VQ5DA], recent_blockhash: 3ShkR1fNXRxJV4aPtUApN6rRb6HHY8VwbGohu29RrsmQ, instructions: [CompiledInstruction { program_id_index: 7, accounts: [1, 0, 3, 4, 2, 8, 2, 7, 6, 5, 10, 9], data: [133, 110, 74, 175, 112, 159, 245, 159, 0, 45, 49, 1, 0, 0, 0, 0, 0, 48, 239, 125, 186, 2, 0, 0, 0] }] }

Do I have to create a new transaction from scratch or is there a way I can append it to the existing transaction?

Answer 1

You can always add multiple instructions in whatever order you want in a transaction (assuming it doesn't exceed the max transaction size of course). But how you do it depends on the SDK/language you're using.

Seeing the tag, seems like you're using Python's Solana.py. In that case. First add the priority fees instruction to your transaction and then the swap.

Before creating a version transaction object directly from serialized_transaction. First load it as a normal transaction using Transaction object. Then, get the instructions from data attribute and store it in an array with your priority fees instruction already stored and then finally form a version transaction using those instructions. Pseudo code example:

serialized_transaction = "your_tx_data"
loaded_tx = Transaction.from_bytes(serialized_transaction)
priorityFee = set_compute_unit_price(100000)
instructions = [priorityFee]

existing_ix = loaded_tx.data
instructions = instructions.append(existing_ix)

raw_tx = VersionedTransaction(instructions, ...other_data)

Answer 2

I used the method below and it works

priorityFee = set_compute_unit_price(priority_fee)

raw_tx = VersionedTransaction.from_bytes(base64.b64decode(serialized_transaction))

account_keys = raw_tx.message.account_keys
length_account_keys = len(account_keys)
account_keys.append(priorityFee.program_id)

raw_instructions = raw_tx.message.instructions

new_instruction = CompiledInstruction(
    program_id_index=length_account_keys,
    data=priorityFee.data,
    accounts=raw_instructions[0].accounts,
)

raw_instructions.append(new_instruction)

new_tx = Message.new_with_compiled_instructions(
    num_required_signatures=raw_tx.message.header.num_required_signatures,
    num_readonly_signed_accounts=raw_tx.message.header.num_readonly_signed_accounts,
    num_readonly_unsigned_accounts=raw_tx.message.header.num_readonly_unsigned_accounts,
    account_keys=account_keys,
    recent_blockhash=raw_tx.message.recent_blockhash,
    instructions=raw_instructions,
)