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#![cfg_attr(not(test), no_std)]
#![deny(missing_docs)]
use core::fmt::{self, Display, Formatter};
#[derive(Debug)]
pub struct WriteBuffer<const N: usize> {
buf: [u8; N],
offset: usize,
}
impl<const N: usize> WriteBuffer<N> {
pub fn new() -> Self {
let buf = [0u8; N];
WriteBuffer { buf, offset: 0 }
}
pub fn as_slice(&self) -> &[u8] {
&self.buf[..self.offset]
}
pub fn reset(&mut self) {
self.offset = 0;
}
pub fn as_str(&self) -> Option<&str> {
core::str::from_utf8(self.as_slice()).ok()
}
}
impl<const N: usize> core::fmt::Write for WriteBuffer<N> {
fn write_str(&mut self, s: &str) -> core::fmt::Result {
let bytes = s.as_bytes();
let remainder = &mut self.buf[self.offset..];
if remainder.len() < bytes.len() {
return Err(core::fmt::Error);
}
let remainder = &mut remainder[..bytes.len()];
remainder.copy_from_slice(bytes);
self.offset += bytes.len();
Ok(())
}
}
impl<const N: usize> Display for WriteBuffer<N> {
fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
write!(f, "{}", self.as_str().unwrap_or("<not utf8>"))
}
}
#[cfg(test)]
mod test {
use super::WriteBuffer;
use core::fmt::Write;
#[test]
fn test_write_wrapper() {
let x = 123;
let mut buffer: WriteBuffer<20> = WriteBuffer::new();
write!(buffer, "{}", x).unwrap();
assert_eq!(&buffer.as_slice()[0..3], b"123");
buffer.reset();
let x = 2.242424;
write!(buffer, "{:.2}", x).unwrap();
assert_eq!(buffer.as_slice(), b"2.24");
buffer.reset();
let x = 20;
write!(buffer, "Longer than {} characters sentence", x).unwrap_err();
buffer.reset();
write!(buffer, "{}", "1").unwrap();
write!(buffer, "{}", "2").unwrap();
assert_eq!(buffer.as_slice(), b"12");
}
#[test]
fn test_display() {
let x = 123;
let mut buffer: WriteBuffer<20> = WriteBuffer::new();
write!(buffer, "{}", x).unwrap();
assert_eq!("123", format!("{}", buffer));
}
}