Python SDK - Sponsoring Transactions

Normally, the account that is executing a transaction pays for the gas fees. You can allow another account to cover those charges by sponsoring a transaction.

This can be used to help manage fees from a central account when working with complicated smart contracts.

How To Sponsor a Transaction

1. Build a raw transaction for the sender, then wrap it in FeePayerRawTransaction.

   raw_txn = await aptos.transaction.build(
       sender=alice.address,
       payload=TransactionPayload(payload),
   )
   fee_payer_txn = FeePayerRawTransaction(
       raw_txn, secondary_signers=[], fee_payer=sponsor.address
   )

2. Sign the fee-payer transaction with BOTH the sender and the fee payer.

   alice_auth = fee_payer_txn.sign(alice.private_key)
   sponsor_auth = fee_payer_txn.sign(sponsor.private_key)

3. Combine the signatures into a FeePayerAuthenticator and submit.

   authenticator = Authenticator(
       FeePayerAuthenticator(
           sender=alice_auth,
           secondary_signers=[],
           fee_payer=(sponsor.address, sponsor_auth),
       )
   )
   txn_hash = await aptos.transaction.submit(SignedTransaction(raw_txn, authenticator))

4. Wait for the transaction to execute.

   result = await aptos.transaction.wait_for_transaction(txn_hash)

Python Sponsored Transaction Code Sample

import asyncio

from aptos_sdk.v2 import Account, Aptos, AptosConfig, Network
from aptos_sdk.v2.bcs import Serializer
from aptos_sdk.v2.transactions import (
    Authenticator,
    EntryFunction,
    FeePayerAuthenticator,
    FeePayerRawTransaction,
    SignedTransaction,
    TransactionArgument,
    TransactionPayload,
)
from aptos_sdk.v2.types import StructTag, TypeTag


async def main():
    async with Aptos(AptosConfig(network=Network.DEVNET)) as aptos:
        alice = Account.generate()
        bob = Account.generate()
        sponsor = Account.generate()

        await asyncio.gather(
            aptos.faucet.fund_account(alice.address, 100_000_000),
            aptos.faucet.fund_account(bob.address, 10_000_000),
            aptos.faucet.fund_account(sponsor.address, 100_000_000),
        )

        payload = EntryFunction.natural(
            "0x1::coin",
            "transfer",
            [TypeTag(StructTag.from_str("0x1::aptos_coin::AptosCoin"))],
            [
                TransactionArgument(bob.address, Serializer.struct),
                TransactionArgument(10_000, Serializer.u64),
            ],
        )
        raw_txn = await aptos.transaction.build(
            sender=alice.address,
            payload=TransactionPayload(payload),
        )
        fee_payer_txn = FeePayerRawTransaction(
            raw_txn, secondary_signers=[], fee_payer=sponsor.address
        )

        alice_auth = fee_payer_txn.sign(alice.private_key)
        sponsor_auth = fee_payer_txn.sign(sponsor.private_key)
        authenticator = Authenticator(
            FeePayerAuthenticator(
                sender=alice_auth,
                secondary_signers=[],
                fee_payer=(sponsor.address, sponsor_auth),
            )
        )

        txn_hash = await aptos.transaction.submit(SignedTransaction(raw_txn, authenticator))
        result = await aptos.transaction.wait_for_transaction(txn_hash)
        print(f"Success: {result['success']}")
        print(f"Gas used: {result['gas_used']}")


asyncio.run(main())