Solana token ownership

Question

is there any way to check that user A owns spl token B inside solana contract? Maybe there is safe method to check it outside.

I need it to give some privileges to users, which own mine nfts. Users would write data to program only when they have nft.

Answer 1

To check the owner of an SPL token account from within a program, you'll have to deserialize it and check the owner field, ie:

use solana_program::{
    account_info::next_account_info, account_info::AccountInfo, entrypoint,
    entrypoint::ProgramResult, pubkey::Pubkey, program_pack::Pack,
};
use spl_token::state::Account;

entrypoint!(process_instruction);

const EXPECTED_OWNER: Pubkey = Pubkey::new_from_array([1; 32]);

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

    let spl_token_account_info = next_account_info(account_info_iter)?;
    let spl_token_account_data = spl_token_account_info.try_borrow_data()?;
    let spl_token_account = Account::unpack(&spl_token_account_data)?;
    if spl_token_account.owner == EXPECTED_OWNER {
        // your logic here
    }
}

Note that I haven't tried to compile this, so use with caution!