How to Close an Account

Closing accounts enables you to reclaim the SOL that was used to open the account, but requires deleting of all information in the account. When an account is closed, make sure that the data is zeroed out in the same instruction to avoid people reopening the account in the same transaction and getting access to the data. This is because the account is not actually closed until the transaction is completed.

use solana_program::{
    account_info::next_account_info, account_info::AccountInfo, entrypoint,
    entrypoint::ProgramResult, pubkey::Pubkey,
};

entrypoint!(process_instruction);

fn process_instruction(
    _program_id: &Pubkey,
    accounts: &[AccountInfo],
    _instruction_data: &[u8],
) -> ProgramResult {
    let account_info_iter = &mut accounts.iter();

    let source_account_info = next_account_info(account_info_iter)?;
    let dest_account_info = next_account_info(account_info_iter)?;

    let dest_starting_lamports = dest_account_info.lamports();
    **dest_account_info.lamports.borrow_mut() = dest_starting_lamports
        .checked_add(source_account_info.lamports())
        .unwrap();
    **source_account_info.lamports.borrow_mut() = 0;

    let mut source_data = source_account_info.data.borrow_mut();
    source_data.fill(0);

    Ok(())
}