Function solana_program_runtime::stable_log::program_return

pub fn program_return(
    log_collector: &Option<Rc<RefCell<LogCollector>>>,
    program_id: &Pubkey,
    data: &[u8]
)

Log return data as from the program itself. This line will not be present if no return data was set, or if the return data was set to zero length.

The general form is:

"Program return: <program-id> <program-generated-data-in-base64>"

That is, any program-generated output is guaranteed to be prefixed by “Program return: “