Analyzing Solana Feepayer enforcement on Transaction Sanitization

Cargo.toml

[package]
name = "feepayer"
version = "0.1.0"
edition = "2024"

[dependencies]
solana-instruction = "3.0.0"
solana-pubkey = "3.0.0"
solana-sanitize = "3.0.1"
solana-transaction = { version = "3.0.1", features = ["blake3"] }

main.rs

use std::collections::HashSet;

use solana_sanitize::Sanitize;

use solana_instruction::{AccountMeta, Instruction};
use solana_pubkey::Pubkey;
use solana_transaction::{sanitized::SanitizedTransaction, Transaction};

fn sanitize_ixs(ixs: &[Instruction], payer: Option<Pubkey>, label: &str) -> Transaction {
    let tx = Transaction::new_with_payer(ixs, payer.as_ref());
    let res = tx.sanitize();
    eprintln!("{label:18}: {res:?}");
    tx
}

fn main() {
    let program = Pubkey::default();
    let payer = Pubkey::new_unique();

    // No accounts
    let ix = Instruction::new_with_bytes(program, &[], vec![]);
    sanitize_ixs(&[ix], None, "Empty Accounts");

    // Readonly Payer
    let payer_meta = AccountMeta::new_readonly(payer, false);
    let ix = Instruction::new_with_bytes(program, &[], vec![payer_meta]);
    sanitize_ixs(&[ix], None, "Readonly");

    // Readonly signing payer
    let payer_meta = AccountMeta::new_readonly(payer, true);
    let ix = Instruction::new_with_bytes(program, &[], vec![payer_meta]);
    sanitize_ixs(&[ix], None, "Readonly signing");

    // Writable Payer
    let payer_meta = AccountMeta::new(payer, false);
    let ix = Instruction::new_with_bytes(program, &[], vec![payer_meta]);
    sanitize_ixs(&[ix], None, "Writable");

    // Writable signing payer
    let payer_meta = AccountMeta::new(payer, true);
    let ix = Instruction::new_with_bytes(program, &[], vec![payer_meta]);
    let tx = sanitize_ixs(&[ix], None, "Writable signing");
    let sanitized = SanitizedTransaction::try_from_legacy_transaction(tx.clone(), &HashSet::new());
    eprintln!("                 : {sanitized:#?}");

    // Explicit payer
    let ix = Instruction::new_with_bytes(program, &[], vec![]);
    let tx = sanitize_ixs(&[ix], Some(payer), "Explicit payer");
    let sanitized = SanitizedTransaction::try_from_legacy_transaction(tx.clone(), &HashSet::new());
    eprintln!("                 : {sanitized:#?}");

    // Explicit payer used as readonly in ix
    let payer_meta = AccountMeta::new_readonly(payer, false);
    let ix = Instruction::new_with_bytes(program, &[], vec![payer_meta]);
    let tx = sanitize_ixs(
        &[ix],
        Some(payer),
        "Explicit payer included as readonly not signing",
    );
    let sanitized = SanitizedTransaction::try_from_legacy_transaction(tx.clone(), &HashSet::new());
    eprintln!("                 : {sanitized:#?}");
}