library/std/src/net/addr/display_buffer.rs

   1 use crate::fmt;
   2 use crate::mem::MaybeUninit;
   3 use crate::str;
   4
   5 /// Used for slow path in `Display` implementations when alignment is required.
   6 pub struct DisplayBuffer<const SIZE: usize> {
   7     buf: [MaybeUninit<u8>; SIZE],
   8     len: usize,
   9 }
  10
  11 impl<const SIZE: usize> DisplayBuffer<SIZE> {
  12     #[inline]
  13     pub const fn new() -> Self {
  14         Self { buf: MaybeUninit::uninit_array(), len: 0 }
  15     }
  16
  17     #[inline]
  18     pub fn as_str(&self) -> &str {
  19         // SAFETY: `buf` is only written to by the `fmt::Write::write_str` implementation
  20         // which writes a valid UTF-8 string to `buf` and correctly sets `len`.
  21         unsafe {
  22             let s = MaybeUninit::slice_assume_init_ref(&self.buf[..self.len]);
  23             str::from_utf8_unchecked(s)
  24         }
  25     }
  26 }
  27
  28 impl<const SIZE: usize> fmt::Write for DisplayBuffer<SIZE> {
  29     fn write_str(&mut self, s: &str) -> fmt::Result {
  30         let bytes = s.as_bytes();
  31
  32         if let Some(buf) = self.buf.get_mut(self.len..(self.len + bytes.len())) {
  33             MaybeUninit::write_slice(buf, bytes);
  34             self.len += bytes.len();
  35             Ok(())
  36         } else {
  37             Err(fmt::Error)
  38         }
  39     }
  40 }