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// SPDX-License-Identifier: GPL-2.0 use core::fmt::{self, Write}; use crate::error::Result; use crate::prelude::EINVAL; /// A mutable reference to a byte buffer where a string can be written into. /// /// # Invariants /// /// `buffer` is always null terminated. pub(crate) struct RawWriter<'a> { buffer: &'a mut [u8], pos: usize, } impl<'a> RawWriter<'a> { /// Create a new `RawWriter` instance. fn new(buffer: &'a mut [u8]) -> Result<RawWriter<'a>> { *(buffer.last_mut().ok_or(EINVAL)?) = 0; // INVARIANT: We null terminated the buffer above. Ok(Self { buffer, pos: 0 }) } pub(crate) fn from_array<const N: usize>( a: &'a mut [core::ffi::c_char; N], ) -> Result<RawWriter<'a>> { Self::new( // SAFETY: the buffer of `a` is valid for read and write as `u8` for // at least `N` bytes. unsafe { core::slice::from_raw_parts_mut(a.as_mut_ptr().cast::<u8>(), N) }, ) } } impl Write for RawWriter<'_> { fn write_str(&mut self, s: &str) -> fmt::Result { let bytes = s.as_bytes(); let len = bytes.len(); // We do not want to overwrite our null terminator if self.pos + len > self.buffer.len() - 1 { return Err(fmt::Error); } // INVARIANT: We are not overwriting the last byte self.buffer[self.pos..self.pos + len].copy_from_slice(bytes); self.pos += len; Ok(()) } }