Rust 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 the raw transaction, then wrap it with FeePayerRawTransaction.

   let payload = EntryFunction::apt_transfer(recipient.address(), 5_000_000)?;
   let sequence_number = aptos.get_sequence_number(sender.address()).await?;
   let raw_txn = TransactionBuilder::new()
       .sender(sender.address())
       .sequence_number(sequence_number)
       .payload(payload.into())
       .chain_id(aptos.chain_id())
       .expiration_from_now(600)
       .build()?;
   let fee_payer_txn = FeePayerRawTransaction::new_simple(raw_txn, fee_payer.address());

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

   let signed_txn = sign_fee_payer_transaction(
       &fee_payer_txn,
       &sender,
       &[], // secondary signers
       &fee_payer,
   )?;

3. Submit and wait for the transaction.

   let result = aptos.submit_and_wait(&signed_txn, None).await?;

Rust Sponsored Transaction Code Sample

use aptos_sdk::{
    Aptos, AptosConfig,
    account::Ed25519Account,
    transaction::{
        EntryFunction, TransactionBuilder, builder::sign_fee_payer_transaction,
        types::FeePayerRawTransaction,
    },
};

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    let aptos = Aptos::new(AptosConfig::devnet())?;

    let sender = Ed25519Account::generate();
    let recipient = Ed25519Account::generate();
    let fee_payer = Ed25519Account::generate();

    aptos
        .fund_account(fee_payer.address(), 1_000_000_000)
        .await?;
    aptos.fund_account(sender.address(), 10_000_000).await?;

    let payload = EntryFunction::apt_transfer(recipient.address(), 5_000_000)?;
    let sequence_number = aptos.get_sequence_number(sender.address()).await?;
    let raw_txn = TransactionBuilder::new()
        .sender(sender.address())
        .sequence_number(sequence_number)
        .payload(payload.into())
        .chain_id(aptos.chain_id())
        .expiration_from_now(600)
        .build()?;

    let fee_payer_txn = FeePayerRawTransaction::new_simple(raw_txn, fee_payer.address());
    let signed_txn = sign_fee_payer_transaction(&fee_payer_txn, &sender, &[], &fee_payer)?;
    let result = aptos.submit_and_wait(&signed_txn, None).await?;
    println!("Submitted: {:?}", result.data.get("hash"));

    Ok(())
}