Query computed data from account

Question

I have an account with definition like this. How do i get result from implemented method "can_buy"?

#[account]
#[derive(Default)]
pub struct Data {
    pub time_start: i64,
    pub time_end: i64,
    pub total_sale: u64,
}

impl Data {
    pub fn can_buy(&self) {
        let now: i64 = Clock::get().unwrap().unix_timestamp;
        return self.time_start <= now <= self.time_end
    }
}

Answer 1

You can only call can_buy from an instance of Data. This means you have to fetch a Data account, deserialize its data, and then call the function. This can be done on or off-chain.

Solana does not have a strong concept of read-only contract calls, like on Ethereum. You can create an instruction that writes the result into the transaction's return data, and then read that from a simulated transaction. Here's the program code:

#[program]
mod my_program {
    pub fn get(ctx: Context<Get>) -> Result<()> {
        let my_account = ctx.accounts.my_account;
        solana_program::program::set_return_data(&[my_account.can_buy() as u8]);
        Ok(())
    }
}

#[derive(Accounts)]
pub struct Get<'info> {
    #[account(mut)]
    pub my_account: Account<'info, Data>,
}

After that, you'll have to read the returnData field from the simulation response: https://docs.solana.com/developing/clients/jsonrpc-api#simulatetransaction