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