generic_arraydeque/

io.rs

use core::str::from_utf8;
use std::io::{self, BufRead, IoSlice, Read, Write};

use super::{ArrayDeque, ArrayLength};

impl<N: ArrayLength> ArrayDeque<u8, N> {
  #[inline(always)]
  fn extend_bytes(&mut self, buf: &[u8]) {
    let written = unsafe {
      self.write_iter_wrapping(
        self.to_physical_idx(self.len),
        buf.iter().copied(),
        buf.len(),
      )
    };

    debug_assert_eq!(
      buf.len(),
      written,
      "The number of items written to VecDeque doesn't match the TrustedLen size hint"
    );
  }
}

/// Read is implemented for `ArrayDeque<u8>` by consuming bytes from the front of the `ArrayDeque`.
impl<N: ArrayLength> Read for ArrayDeque<u8, N> {
  /// Fill `buf` with the contents of the "front" slice as returned by
  /// [`as_slices`][`ArrayDeque::as_slices`]. If the contained byte slices of the `ArrayDeque` are
  /// discontiguous, multiple calls to `read` will be needed to read the entire content.
  #[inline]
  fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
    let (ref mut front, _) = self.as_slices();
    let n = Read::read(front, buf)?;
    self.drain(..n);
    Ok(n)
  }

  #[inline]
  fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
    let (front, back) = self.as_slices();

    // Use only the front buffer if it is big enough to fill `buf`, else use
    // the back buffer too.
    match SplitAtMut::split_at_mut_checked(buf, front.len()) {
      None => buf.copy_from_slice(&front[..buf.len()]),
      Some((buf_front, buf_back)) => match SplitAt::split_at_checked(back, buf_back.len()) {
        Some((back, _)) => {
          buf_front.copy_from_slice(front);
          buf_back.copy_from_slice(back);
        }
        None => {
          // Leave the buffered data in place — matches `VecDeque`'s
          // behavior and lets the caller retry or fall back to `read`.
          return Err(io::Error::new(
            io::ErrorKind::UnexpectedEof,
            "failed to fill whole buffer",
          ));
        }
      },
    }

    self.drain(..buf.len());
    Ok(())
  }

  #[inline]
  fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
    // The total len is known upfront so we can reserve it in a single call.
    let len = self.len();
    buf
      .try_reserve(len)
      .map_err(|_| io::ErrorKind::OutOfMemory)?;

    let (front, back) = self.as_slices();
    buf.extend_from_slice(front);
    buf.extend_from_slice(back);
    self.clear();
    Ok(len)
  }

  #[inline]
  fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
    // A single UTF-8 codepoint may straddle the ring's split point, so
    // validate the concatenated byte stream rather than each half.
    // `make_contiguous` reorganizes the physical buffer in place; after it,
    // `as_slices` returns everything in the front slice.
    let bytes = self.make_contiguous();
    let s = match from_utf8(bytes) {
      Ok(s) => s,
      Err(_) => {
        return Err(io::Error::new(
          io::ErrorKind::InvalidData,
          "stream did not contain valid UTF-8",
        ));
      }
    };

    buf
      .try_reserve(s.len())
      .map_err(|_| io::ErrorKind::OutOfMemory)?;

    let len = s.len();
    buf.push_str(s);
    // Match the `Read::read_to_string` contract: the source is consumed.
    self.clear();
    Ok(len)
  }
}

/// BufRead is implemented for `ArrayDeque<u8>` by reading bytes from the front of the `ArrayDeque`.
impl<N: ArrayLength> BufRead for ArrayDeque<u8, N> {
  /// Returns the contents of the "front" slice as returned by
  /// [`as_slices`][`ArrayDeque::as_slices`]. If the contained byte slices of the `ArrayDeque` are
  /// discontiguous, multiple calls to `fill_buf` will be needed to read the entire content.
  #[inline]
  fn fill_buf(&mut self) -> io::Result<&[u8]> {
    let (front, _) = self.as_slices();
    Ok(front)
  }

  #[inline]
  fn consume(&mut self, amt: usize) {
    self.drain(..amt);
  }
}

/// Write is implemented for `ArrayDeque<u8>` by appending to the `ArrayDeque`, growing it as needed.
impl<N: ArrayLength> Write for ArrayDeque<u8, N> {
  #[inline]
  fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
    let remaining = self.remaining_capacity();
    if remaining == 0 || buf.is_empty() {
      return Ok(0);
    }

    let n = remaining.min(buf.len());
    self.extend_bytes(&buf[..n]);
    Ok(n)
  }

  #[inline]
  fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
    // Behave like `write` concatenated over the buffers: write as much as
    // fits and report the actual byte count. Returning `WriteZero` when
    // the combined length exceeds capacity would be inconsistent with the
    // scalar `write`, which performs partial writes.
    let mut written = 0;
    for buf in bufs {
      let remaining = self.remaining_capacity();
      if remaining == 0 {
        break;
      }
      let n = remaining.min(buf.len());
      if n == 0 {
        continue;
      }
      self.extend_bytes(&buf[..n]);
      written += n;
      if n < buf.len() {
        // Ran out of room mid-buffer; a further `write` would return 0.
        break;
      }
    }
    Ok(written)
  }

  #[inline]
  fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
    if buf.len() > self.remaining_capacity() {
      return Err(io::Error::new(
        io::ErrorKind::WriteZero,
        "not enough capacity to write buffer",
      ));
    }
    self.extend_bytes(buf);
    Ok(())
  }

  #[inline]
  fn flush(&mut self) -> io::Result<()> {
    Ok(())
  }
}

trait SplitAt {
  #[allow(unstable_name_collisions)]
  fn split_at_checked(&self, mid: usize) -> Option<(&Self, &Self)>;
}

trait SplitAtMut {
  #[allow(unstable_name_collisions)]
  fn split_at_mut_checked(&mut self, mid: usize) -> Option<(&mut Self, &mut Self)>;
}

impl<T> SplitAt for [T] {
  #[allow(unstable_name_collisions)]
  #[inline(always)]
  fn split_at_checked(&self, mid: usize) -> Option<(&Self, &Self)> {
    <[T]>::split_at_checked(self, mid)
  }
}

impl<T> SplitAtMut for [T] {
  #[allow(unstable_name_collisions)]
  #[inline(always)]
  fn split_at_mut_checked(&mut self, mid: usize) -> Option<(&mut Self, &mut Self)> {
    <[T]>::split_at_mut_checked(self, mid)
  }
}

#[cfg(test)]
mod tests {
  use crate::{
    ArrayDeque,
    typenum::{U2, U4, U6, U8},
  };
  use std::{
    io::{self, BufRead, IoSlice, Read, Write},
    string::String,
    vec::Vec,
  };

  #[test]
  fn read_consumes_front_slice() {
    let mut deque = ArrayDeque::<u8, U8>::new();
    for byte in b"hello" {
      assert!(deque.push_back(*byte).is_none());
    }

    let mut buf = [0u8; 3];
    let read = Read::read(&mut deque, &mut buf).unwrap();
    assert_eq!(read, 3);
    assert_eq!(&buf[..read], b"hel");
    assert_eq!(deque.into_iter().collect::<Vec<_>>(), b"lo".to_vec());
  }

  #[test]
  fn read_exact_handles_wrapped_storage() {
    let mut deque = ArrayDeque::<u8, U4>::new();
    for byte in b"abcd" {
      assert!(deque.push_back(*byte).is_none());
    }
    assert_eq!(deque.pop_front(), Some(b'a'));
    assert!(deque.push_back(b'e').is_none());

    let mut buf = [0u8; 3];
    deque.read_exact(&mut buf).unwrap();
    assert_eq!(&buf, b"bcd");
    assert_eq!(deque.into_iter().collect::<Vec<_>>(), vec![b'e']);
  }

  #[test]
  fn read_exact_reports_eof() {
    let mut deque = ArrayDeque::<u8, U4>::new();
    assert!(deque.push_back(b'x').is_none());

    let mut buf = [0u8; 2];
    let err = Read::read_exact(&mut deque, &mut buf).unwrap_err();
    assert_eq!(err.kind(), io::ErrorKind::UnexpectedEof);
    // The buffered byte must remain in the deque — matches `VecDeque`.
    assert_eq!(deque.len(), 1);
    assert_eq!(deque.pop_front(), Some(b'x'));
  }

  #[test]
  fn read_to_end_and_string_clear_buffer() {
    let mut deque = ArrayDeque::<u8, U6>::new();
    for byte in b"abc" {
      assert!(deque.push_back(*byte).is_none());
    }
    let mut buf = Vec::new();
    deque.read_to_end(&mut buf).unwrap();
    assert_eq!(buf, b"abc");
    assert!(deque.is_empty());

    for byte in b"de" {
      assert!(deque.push_back(*byte).is_none());
    }
    let mut string = String::new();
    deque.read_to_string(&mut string).unwrap();
    assert_eq!(string, "de");
    // `read_to_string` consumes the source, like the `Read` contract demands.
    assert!(deque.is_empty());

    deque.clear();
    deque.push_back(0xFF);
    let mut invalid = String::new();
    let err = deque.read_to_string(&mut invalid).unwrap_err();
    assert_eq!(err.kind(), io::ErrorKind::InvalidData);
  }

  #[test]
  fn bufread_fill_and_consume() {
    let mut deque = ArrayDeque::<u8, U4>::new();
    for byte in b"abcd" {
      assert!(deque.push_back(*byte).is_none());
    }

    let buf = BufRead::fill_buf(&mut deque).unwrap();
    assert_eq!(buf, b"abcd");
    BufRead::consume(&mut deque, 3);
    assert_eq!(deque.into_iter().collect::<Vec<_>>(), vec![b'd']);
  }

  #[test]
  fn write_variants_respect_capacity() {
    let mut deque = ArrayDeque::<u8, U4>::new();
    let written = Write::write(&mut deque, b"abcdef").unwrap();
    assert_eq!(written, 4);
    assert_eq!(deque.len(), 4);

    let mut deque = ArrayDeque::<u8, U8>::new();
    let slices = [IoSlice::new(b"ab"), IoSlice::new(b"cd")];
    assert_eq!(Write::write_vectored(&mut deque, &slices).unwrap(), 4);
    assert_eq!(deque.len(), 4);
    // When the combined length exceeds remaining capacity, `write_vectored`
    // performs a partial write (matching scalar `write`) rather than erroring.
    let overflow = [IoSlice::new(b"1234"), IoSlice::new(b"5678")];
    let written = Write::write_vectored(&mut deque, &overflow).unwrap();
    assert_eq!(written, 4);
    assert_eq!(deque.len(), 8);

    let mut deque = ArrayDeque::<u8, U4>::new();
    Write::write_all(&mut deque, b"wxyz").unwrap();
    let err = Write::write_all(&mut deque, b"overflow").unwrap_err();
    assert_eq!(err.kind(), io::ErrorKind::WriteZero);

    let mut deque = ArrayDeque::<u8, U2>::new();
    Write::flush(&mut deque).unwrap();
  }

  // Regression: previously, `read_to_string` validated front and back slices
  // independently, so a codepoint whose bytes straddled the ring boundary
  // was rejected as InvalidData.
  #[test]
  fn read_to_string_accepts_utf8_across_ring_boundary() {
    let mut deque = ArrayDeque::<u8, U4>::new();
    // Push 3 padding bytes then `é`'s leading byte; rotate head so `é`
    // ends up split across the physical buffer boundary.
    for _ in 0..3 {
      assert!(deque.push_back(b'x').is_none());
    }
    assert!(deque.push_back(0xC3).is_none());
    for _ in 0..3 {
      deque.pop_front();
    }
    assert!(deque.push_back(0xA9).is_none());
    // Confirm the bytes are actually split (each half is invalid UTF-8 alone).
    let (front, back) = deque.as_slices();
    assert_eq!(front, &[0xC3]);
    assert_eq!(back, &[0xA9]);

    let mut s = String::new();
    let n = deque.read_to_string(&mut s).unwrap();
    assert_eq!(n, 2);
    assert_eq!(s, "é");
    assert!(deque.is_empty());
  }

  // Regression: `write_vectored` used to return `WriteZero` when the combined
  // buffers exceeded remaining capacity, while `write` did partial writes.
  #[test]
  fn write_vectored_does_partial_writes() {
    let mut deque = ArrayDeque::<u8, U4>::new();
    let slices = [IoSlice::new(b"12"), IoSlice::new(b"345")];
    let n = Write::write_vectored(&mut deque, &slices).unwrap();
    assert_eq!(n, 4);
    assert_eq!(deque.len(), 4);
    assert_eq!(deque.iter().copied().collect::<Vec<_>>(), b"1234");
  }

  #[test]
  fn read_exact_from_front_slice_only() {
    // Exercise the `split_at_mut_checked` → None arm where `buf` fits entirely
    // within the front slice.
    let mut deque = ArrayDeque::<u8, U4>::new();
    for byte in b"abcd" {
      assert!(deque.push_back(*byte).is_none());
    }
    let mut buf = [0u8; 2];
    deque.read_exact(&mut buf).unwrap();
    assert_eq!(&buf, b"ab");
    assert_eq!(deque.iter().copied().collect::<Vec<_>>(), b"cd");
  }

  #[test]
  fn write_on_full_and_empty_buf_returns_zero() {
    // `remaining == 0` branch.
    let mut deque = ArrayDeque::<u8, U4>::new();
    for byte in b"abcd" {
      assert!(deque.push_back(*byte).is_none());
    }
    assert_eq!(Write::write(&mut deque, b"xx").unwrap(), 0);

    // `buf.is_empty()` branch.
    let mut deque = ArrayDeque::<u8, U4>::new();
    assert_eq!(Write::write(&mut deque, b"").unwrap(), 0);
  }

  #[test]
  fn write_vectored_skips_empty_slices() {
    // Exercise the `n == 0 { continue }` arm without hitting the full-capacity
    // break first.
    let mut deque = ArrayDeque::<u8, U4>::new();
    let slices = [IoSlice::new(b""), IoSlice::new(b"ab")];
    let n = Write::write_vectored(&mut deque, &slices).unwrap();
    assert_eq!(n, 2);
    assert_eq!(deque.iter().copied().collect::<Vec<_>>(), b"ab");
  }
}