Transaction simulations can be spoofed; it is possible to have an accurate simulation of the execution of a transaction with a desired outcome and then observe a different outcome when executing the transaction in real time.
On Solana, transactions are comprised of multiple instructions. If any instruction in the transaction fails, the entire transaction fails. Zipper takes advantage of this.
Zipper is an on-chain program that contains a single instruction. The instruction expects a set of system and token accounts, and a set of expected balances. If the balances in the SOL account or token accounts are not at least those provided in the expected balances, the program panics and the transaction fails.
This instruction can be included after any instruction that mutates a SOL or token account to ensure that the instruction does not take more lamports than what you expect. Note that only accounts that are included in a transaction and are marked as mutable need to be included. Since these accounts are already included in your transaction, the Zipper Program is the only additional account needed. Furthermore, an ordered u64 array is used for the expected balances, which adds only 8 bytes per account to be checked.
```rust use anchorclient::{ solanasdk::instruction::Instruction, Client, Cluster, Program }; use zipper::{AccountZipper, ID as ZIPPERPROGRAMID};
// A sketchy ix that needs to mutable access to user // token accounts, for whatever reason let sketchyix: Instruction = constructsketchy_ix(/* todo */);
// Construct a zipper instruction let client: Client::newwithoptions( Cluster::Mainnet, Rc::new(todo!("keypair")), CommitmentConfig::processed(), ); let program: Program = client.program(ZIPPERPROGRAMID); let zipperix: Instruction = program.request() .accounts(AccountZipper::zipaccounts(&[ user.keypair.pubkey(), user.ata, user.ata2, ])) .args(zipper::instruction::Verify { balances: todo!(), }) .instructions() .unwrap() .remove(0);
// Zip the sketchy instruction with the zipper instruction let zippedtransaction = Transaction::newsignedwithpayer( &[sketchyix, zipperix], Some(&user.keypair.pubkey()), &[&user.keypair], get_recent_blockhash(/ todo */), );
// If the balances drop under the specified balances
// this transaction will fail
sendtransaction(&zippedtransaction)
``
See the rustspooftest inprograms/zipper/tests/spoof.rs` for an end-to-end example on testnet.
The testnet and mainnet program ID is Z1PrGTgZp5Q1WKewjF4XaTW2nHvNxvbxs7qW8p9qz5U.