Method write_error

clock-bound-ffi/src/lib.rs:68–100

Write over the `clockbound_err` memory. This function is the interface between Rust `ClockBoundError` and its C version. The C caller allocates memory and pass a pointer to the `clockbound_err`, which is updated here.

(&mut self, error: ClockBoundError)

    /// This function is the interface between Rust `ClockBoundError` and its C version. The C
    /// caller allocates memory and pass a pointer to the `clockbound_err`, which is updated here.
    fn write_error(&mut self, error: ClockBoundError) {
        // Kind and errno values are set
        self.kind = clockbound_err_kind::from(error.kind);
        self.errno = error.errno.0;

        // The detail String has to be converted to a CString, ensuring it is null terminated.
        let c_string = match CString::new(error.detail) {
            Ok(c_string) => c_string,
            Err(_) => {
                // Hopefully, we never insert null terminators in the middle of an error message,
                // and should never hit that branch.
                CString::new("No detail available").unwrap()
            }
        };

        // Copy bytes including null terminator if it fits, and truncate if required.
        // Possible cast from u8 (bytes) into i8 (c_char) but is platform dependent
        let src_ptr = c_string.as_ptr();
        let dst_ptr = self.detail.as_mut_ptr();
        let copy_len = c_string
            .as_bytes_with_nul()
            .len()
            .min(CLOCKBOUND_ERROR_DETAIL_SIZE);
        // Safety: rely on the user passing a valid pointer
        unsafe {
            ptr::copy_nonoverlapping(src_ptr, dst_ptr, copy_len);
        }

        // Ensure null termination if we had to truncate.
        if copy_len >= CLOCKBOUND_ERROR_DETAIL_SIZE {
            self.detail[CLOCKBOUND_ERROR_DETAIL_SIZE - 1] = 0;
        }
    }
}

/// The clockbound context given to the caller.