Repository: google/OpenSK
File: third_party/libtock-drivers/src/nfc.rs (Rust)

Code before:
            DRIVER_NUMBER,
            subscribe_nr::SELECT,
            &mut is_selected_alarm,
        );
        if subscription.is_err() {
            return false;
        }

        util::yieldk_for(|| is_selected.get());
        true
    }

    /// Configure the tag type command.
    pub fn configure(tag_type: u8) -> bool {
        syscalls::command(DRIVER_NUMBER, command_nr::CONFIGURE, tag_type as usize, 0).is_ok()
    }

    /// Set the maximum frame delay value to support transmission with the reader.
    pub fn set_framedelaymax(delay: u32) -> bool {
        syscalls::command(DRIVER_NUMBER, command_nr::FRAMEDELAYMAX, delay as usize, 0).is_ok()
    }

    /// 1. Share with the driver a buffer.
    /// 2. Subscribe to having a successful receive callback.
    /// 3. Issue the request for reception.
    pub fn receive(buf: &mut [u8; 256]) -> TransOrRecvStatus {
        let result = syscalls::allow(DRIVER_NUMBER, allow_nr::RECEIVE, buf);
        if result.is_err() {
            return TransOrRecvStatus::InvalidBuffer;
        }

        let done = Cell::new(false);
        let mut alarm = || done.set(true);
        let subscription = syscalls::subscribe::<callback::Identity0Consumer, _>(
            DRIVER_NUMBER,
            subscribe_nr::RECEIVE,
            &mut alarm,
        );
        if subscription.is_err() {
            return TransOrRecvStatus::Error;
        }

        let result_code =
            unsafe { syscalls::raw::command(DRIVER_NUMBER, command_nr::RECEIVE, 0, 0) };
        match result_code {
            SUCCESS => (),
            ENOMEM => return TransOrRecvStatus::OOM,
            _ => return TransOrRecvStatus::Error,
        }

        util::yieldk_for(|| done.get());

Review comment (suggestion):
If this status wouldn't contain the success, it would instead return
`Result<(), TransOrRecvError>`
or
`Result<(), WhateverLibtockError>`
and you'd have access to `Result` magic like the `?` operator later.

Code after:
    /// Configure the tag type command.
    pub fn configure(tag_type: u8) -> bool {
        syscalls::command(DRIVER_NUMBER, command_nr::CONFIGURE, tag_type as usize, 0).is_ok()
    }

    /// 1. Share with the driver a buffer.
    /// 2. Subscribe to having a successful receive callback.
    /// 3. Issue the request for reception.
    pub fn receive(buf: &mut [u8; 256]) -> TockResult<RecvOp> {
        let result = syscalls::allow(DRIVER_NUMBER, allow_nr::RECEIVE, buf)?;
        // set callback with 2 arguments, to receive ReturnCode and RX Amount
        let recv_data = Cell::new(None);
        let mut callback = |result, amount| {
            recv_data.set(Some(RecvOp {
                result_code: result,
                recv_amount: amount,
            }))
        };
        let subscription = syscalls::subscribe::<callback::Identity2Consumer, _>(
            DRIVER_NUMBER,
            subscribe_nr::RECEIVE,
            &mut callback,
        )?;
        syscalls::command(DRIVER_NUMBER, command_nr::RECEIVE, 0, 0)?;
        util::yieldk_for(|| recv_data.get().is_some());
        mem::drop(subscription);
        mem::drop(result);
        Ok(recv_data.get().unwrap())
    }

    /// 1. Share with the driver a buffer containing the app's reply.
    /// 2. Subscribe to having a successful transmission callback.
    /// 3. Issue the request for transmitting.
    pub fn transmit(buf: &mut [u8], amount: usize) -> TockResult<usize> {
        let result = syscalls::allow(DRIVER_NUMBER, allow_nr::TRANSMIT, buf)?;
        // set callback with 1 argument, to receive ReturnCode
        let result_code = Cell::new(None);
        let mut callback = |result| result_code.set(Some(result));
        let subscription = syscalls::subscribe::<callback::Identity1Consumer, _>(
            DRIVER_NUMBER,
            subscribe_nr::TRANSMIT,
            &mut callback,
        )?;
        syscalls::command(DRIVER_NUMBER, command_nr::TRANSMIT, amount, 0)?;
        util::yieldk_for(|| result_code.get().is_some());
        mem::drop(subscription);
        mem::drop(result);
        Ok(result_code.get().unwrap())
    }
}