library/std/src/io/impls.rs - toolchain/rustc - Git at Google

 #[cfg(test)]
 mod tests;

 use crate::alloc::Allocator;
 use crate::collections::VecDeque;
 use crate::io::{self, BorrowedCursor, BufRead, IoSlice, IoSliceMut, Read, Seek, SeekFrom, Write};
 use crate::{cmp, fmt, mem, str};

 // =============================================================================
 // Forwarding implementations

 #[stable(feature = "rust1", since = "1.0.0")]
 impl<R: Read + ?Sized> Read for &mut R {
     #[inline]
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         (**self).read(buf)
     }

     #[inline]
     fn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> io::Result<()> {
         (**self).read_buf(cursor)
     }

     #[inline]
     fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
         (**self).read_vectored(bufs)
     }

     #[inline]
     fn is_read_vectored(&self) -> bool {
         (**self).is_read_vectored()
     }

     #[inline]
     fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
         (**self).read_to_end(buf)
     }

     #[inline]
     fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
         (**self).read_to_string(buf)
     }

     #[inline]
     fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
         (**self).read_exact(buf)
     }
     #[inline]
     fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> io::Result<()> {
         (**self).read_buf_exact(cursor)
     }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<W: Write + ?Sized> Write for &mut W {
     #[inline]
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         (**self).write(buf)
     }

     #[inline]
     fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
         (**self).write_vectored(bufs)
     }

     #[inline]
     fn is_write_vectored(&self) -> bool {
         (**self).is_write_vectored()
     }

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

     #[inline]
     fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
         (**self).write_all(buf)
     }

     #[inline]
     fn write_fmt(&mut self, fmt: fmt::Arguments<'_>) -> io::Result<()> {
         (**self).write_fmt(fmt)
     }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<S: Seek + ?Sized> Seek for &mut S {
     #[inline]
     fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
         (**self).seek(pos)
     }

     #[inline]
     fn stream_position(&mut self) -> io::Result<u64> {
         (**self).stream_position()
     }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<B: BufRead + ?Sized> BufRead for &mut B {
     #[inline]
     fn fill_buf(&mut self) -> io::Result<&[u8]> {
         (**self).fill_buf()
     }

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

     #[inline]
     fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> io::Result<usize> {
         (**self).read_until(byte, buf)
     }

     #[inline]
     fn read_line(&mut self, buf: &mut String) -> io::Result<usize> {
         (**self).read_line(buf)
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl<R: Read + ?Sized> Read for Box<R> {
     #[inline]
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         (**self).read(buf)
     }

     #[inline]
     fn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> io::Result<()> {
         (**self).read_buf(cursor)
     }

     #[inline]
     fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
         (**self).read_vectored(bufs)
     }

     #[inline]
     fn is_read_vectored(&self) -> bool {
         (**self).is_read_vectored()
     }

     #[inline]
     fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
         (**self).read_to_end(buf)
     }

     #[inline]
     fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
         (**self).read_to_string(buf)
     }

     #[inline]
     fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
         (**self).read_exact(buf)
     }
     #[inline]
     fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> io::Result<()> {
         (**self).read_buf_exact(cursor)
     }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<W: Write + ?Sized> Write for Box<W> {
     #[inline]
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         (**self).write(buf)
     }

     #[inline]
     fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
         (**self).write_vectored(bufs)
     }

     #[inline]
     fn is_write_vectored(&self) -> bool {
         (**self).is_write_vectored()
     }

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

     #[inline]
     fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
         (**self).write_all(buf)
     }

     #[inline]
     fn write_fmt(&mut self, fmt: fmt::Arguments<'_>) -> io::Result<()> {
         (**self).write_fmt(fmt)
     }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<S: Seek + ?Sized> Seek for Box<S> {
     #[inline]
     fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
         (**self).seek(pos)
     }

     #[inline]
     fn stream_position(&mut self) -> io::Result<u64> {
         (**self).stream_position()
     }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<B: BufRead + ?Sized> BufRead for Box<B> {
     #[inline]
     fn fill_buf(&mut self) -> io::Result<&[u8]> {
         (**self).fill_buf()
     }

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

     #[inline]
     fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> io::Result<usize> {
         (**self).read_until(byte, buf)
     }

     #[inline]
     fn read_line(&mut self, buf: &mut String) -> io::Result<usize> {
         (**self).read_line(buf)
     }
 }

 // =============================================================================
 // In-memory buffer implementations

 /// Read is implemented for `&[u8]` by copying from the slice.
 ///
 /// Note that reading updates the slice to point to the yet unread part.
 /// The slice will be empty when EOF is reached.
 #[stable(feature = "rust1", since = "1.0.0")]
 impl Read for &[u8] {
     #[inline]
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         let amt = cmp::min(buf.len(), self.len());
         let (a, b) = self.split_at(amt);

         // First check if the amount of bytes we want to read is small:
         // `copy_from_slice` will generally expand to a call to `memcpy`, and
         // for a single byte the overhead is significant.
         if amt == 1 {
             buf[0] = a[0];
         } else {
             buf[..amt].copy_from_slice(a);
         }

         *self = b;
         Ok(amt)
     }

     #[inline]
     fn read_buf(&mut self, mut cursor: BorrowedCursor<'_>) -> io::Result<()> {
         let amt = cmp::min(cursor.capacity(), self.len());
         let (a, b) = self.split_at(amt);

         cursor.append(a);

         *self = b;
         Ok(())
     }

     #[inline]
     fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
         let mut nread = 0;
         for buf in bufs {
             nread += self.read(buf)?;
             if self.is_empty() {
                 break;
             }
         }

         Ok(nread)
     }

     #[inline]
     fn is_read_vectored(&self) -> bool {
         true
     }

     #[inline]
     fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
         if buf.len() > self.len() {
             // `read_exact` makes no promise about the content of `buf` if it
             // fails so don't bother about that.
             *self = &self[self.len()..];
             return Err(io::Error::READ_EXACT_EOF);
         }
         let (a, b) = self.split_at(buf.len());

         // First check if the amount of bytes we want to read is small:
         // `copy_from_slice` will generally expand to a call to `memcpy`, and
         // for a single byte the overhead is significant.
         if buf.len() == 1 {
             buf[0] = a[0];
         } else {
             buf.copy_from_slice(a);
         }

         *self = b;
         Ok(())
     }

     #[inline]
     fn read_buf_exact(&mut self, mut cursor: BorrowedCursor<'_>) -> io::Result<()> {
         if cursor.capacity() > self.len() {
             // Append everything we can to the cursor.
             cursor.append(*self);
             *self = &self[self.len()..];
             return Err(io::Error::READ_EXACT_EOF);
         }
         let (a, b) = self.split_at(cursor.capacity());

         cursor.append(a);

         *self = b;
         Ok(())
     }

     #[inline]
     fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
         let len = self.len();
         buf.try_reserve(len)?;
         buf.extend_from_slice(*self);
         *self = &self[len..];
         Ok(len)
     }

     #[inline]
     fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
         let content = str::from_utf8(self).map_err(|_| io::Error::INVALID_UTF8)?;
         let len = self.len();
         buf.try_reserve(len)?;
         buf.push_str(content);
         *self = &self[len..];
         Ok(len)
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl BufRead for &[u8] {
     #[inline]
     fn fill_buf(&mut self) -> io::Result<&[u8]> {
         Ok(*self)
     }

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

 /// Write is implemented for `&mut [u8]` by copying into the slice, overwriting
 /// its data.
 ///
 /// Note that writing updates the slice to point to the yet unwritten part.
 /// The slice will be empty when it has been completely overwritten.
 ///
 /// If the number of bytes to be written exceeds the size of the slice, write operations will
 /// return short writes: ultimately, `Ok(0)`; in this situation, `write_all` returns an error of
 /// kind `ErrorKind::WriteZero`.
 #[stable(feature = "rust1", since = "1.0.0")]
 impl Write for &mut [u8] {
     #[inline]
     fn write(&mut self, data: &[u8]) -> io::Result<usize> {
         let amt = cmp::min(data.len(), self.len());
         let (a, b) = mem::take(self).split_at_mut(amt);
         a.copy_from_slice(&data[..amt]);
         *self = b;
         Ok(amt)
     }

     #[inline]
     fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
         let mut nwritten = 0;
         for buf in bufs {
             nwritten += self.write(buf)?;
             if self.is_empty() {
                 break;
             }
         }

         Ok(nwritten)
     }

     #[inline]
     fn is_write_vectored(&self) -> bool {
         true
     }

     #[inline]
     fn write_all(&mut self, data: &[u8]) -> io::Result<()> {
         if self.write(data)? == data.len() { Ok(()) } else { Err(io::Error::WRITE_ALL_EOF) }
     }

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

 /// Write is implemented for `Vec<u8>` by appending to the vector.
 /// The vector will grow as needed.
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<A: Allocator> Write for Vec<u8, A> {
     #[inline]
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         self.extend_from_slice(buf);
         Ok(buf.len())
     }

     #[inline]
     fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
         let len = bufs.iter().map(|b| b.len()).sum();
         self.reserve(len);
         for buf in bufs {
             self.extend_from_slice(buf);
         }
         Ok(len)
     }

     #[inline]
     fn is_write_vectored(&self) -> bool {
         true
     }

     #[inline]
     fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
         self.extend_from_slice(buf);
         Ok(())
     }

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

 /// Read is implemented for `VecDeque<u8>` by consuming bytes from the front of the `VecDeque`.
 #[stable(feature = "vecdeque_read_write", since = "1.63.0")]
 impl<A: Allocator> Read for VecDeque<u8, A> {
     /// Fill `buf` with the contents of the "front" slice as returned by
     /// [`as_slices`][`VecDeque::as_slices`]. If the contained byte slices of the `VecDeque` 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_buf(&mut self, cursor: BorrowedCursor<'_>) -> io::Result<()> {
         let (ref mut front, _) = self.as_slices();
         let n = cmp::min(cursor.capacity(), front.len());
         Read::read_buf(front, cursor)?;
         self.drain(..n);
         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)?;

         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> {
         // SAFETY: We only append to the buffer
         unsafe { io::append_to_string(buf, |buf| self.read_to_end(buf)) }
     }
 }

 /// BufRead is implemented for `VecDeque<u8>` by reading bytes from the front of the `VecDeque`.
 #[stable(feature = "vecdeque_buf_read", since = "1.75.0")]
 impl<A: Allocator> BufRead for VecDeque<u8, A> {
     /// Returns the contents of the "front" slice as returned by
     /// [`as_slices`][`VecDeque::as_slices`]. If the contained byte slices of the `VecDeque` 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 `VecDeque<u8>` by appending to the `VecDeque`, growing it as needed.
 #[stable(feature = "vecdeque_read_write", since = "1.63.0")]
 impl<A: Allocator> Write for VecDeque<u8, A> {
     #[inline]
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         self.extend(buf);
         Ok(buf.len())
     }

     #[inline]
     fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
         let len = bufs.iter().map(|b| b.len()).sum();
         self.reserve(len);
         for buf in bufs {
             self.extend(&**buf);
         }
         Ok(len)
     }

     #[inline]
     fn is_write_vectored(&self) -> bool {
         true
     }

     #[inline]
     fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
         self.extend(buf);
         Ok(())
     }

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

 #[unstable(feature = "read_buf", issue = "78485")]
 impl<'a> io::Write for core::io::BorrowedCursor<'a> {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         let amt = cmp::min(buf.len(), self.capacity());
         self.append(&buf[..amt]);
         Ok(amt)
     }

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

	use crate::alloc::Allocator;
	use crate::collections::VecDeque;
	use crate::io::{self, BorrowedCursor, BufRead, IoSlice, IoSliceMut, Read, Seek, SeekFrom, Write};
	use crate::{cmp, fmt, mem, str};

	// =============================================================================
	// Forwarding implementations

	#[stable(feature = "rust1", since = "1.0.0")]
	impl<R: Read + ?Sized> Read for &mut R {
	#[inline]
	fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
	(**self).read(buf)
	}

	#[inline]
	fn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> io::Result<()> {
	(**self).read_buf(cursor)
	}

	#[inline]
	fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
	(**self).read_vectored(bufs)
	}

	#[inline]
	fn is_read_vectored(&self) -> bool {
	(**self).is_read_vectored()
	}

	#[inline]
	fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
	(**self).read_to_end(buf)
	}

	#[inline]
	fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
	(**self).read_to_string(buf)
	}

	#[inline]
	fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
	(**self).read_exact(buf)
	}
	#[inline]
	fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> io::Result<()> {
	(**self).read_buf_exact(cursor)
	}
	}
	#[stable(feature = "rust1", since = "1.0.0")]
	impl<W: Write + ?Sized> Write for &mut W {
	#[inline]
	fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
	(**self).write(buf)
	}

	#[inline]
	fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
	(**self).write_vectored(bufs)
	}

	#[inline]
	fn is_write_vectored(&self) -> bool {
	(**self).is_write_vectored()
	}

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

	#[inline]
	fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
	(**self).write_all(buf)
	}

	#[inline]
	fn write_fmt(&mut self, fmt: fmt::Arguments<'_>) -> io::Result<()> {
	(**self).write_fmt(fmt)
	}
	}
	#[stable(feature = "rust1", since = "1.0.0")]
	impl<S: Seek + ?Sized> Seek for &mut S {
	#[inline]
	fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
	(**self).seek(pos)
	}

	#[inline]
	fn stream_position(&mut self) -> io::Result<u64> {
	(**self).stream_position()
	}
	}
	#[stable(feature = "rust1", since = "1.0.0")]
	impl<B: BufRead + ?Sized> BufRead for &mut B {
	#[inline]
	fn fill_buf(&mut self) -> io::Result<&[u8]> {
	(**self).fill_buf()
	}

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

	#[inline]
	fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> io::Result<usize> {
	(**self).read_until(byte, buf)
	}

	#[inline]
	fn read_line(&mut self, buf: &mut String) -> io::Result<usize> {
	(**self).read_line(buf)
	}
	}

	#[stable(feature = "rust1", since = "1.0.0")]
	impl<R: Read + ?Sized> Read for Box<R> {
	#[inline]
	fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
	(**self).read(buf)
	}

	#[inline]
	fn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> io::Result<()> {
	(**self).read_buf(cursor)
	}

	#[inline]
	fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
	(**self).read_vectored(bufs)
	}

	#[inline]
	fn is_read_vectored(&self) -> bool {
	(**self).is_read_vectored()
	}

	#[inline]
	fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
	(**self).read_to_end(buf)
	}

	#[inline]
	fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
	(**self).read_to_string(buf)
	}

	#[inline]
	fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
	(**self).read_exact(buf)
	}
	#[inline]
	fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> io::Result<()> {
	(**self).read_buf_exact(cursor)
	}
	}
	#[stable(feature = "rust1", since = "1.0.0")]
	impl<W: Write + ?Sized> Write for Box<W> {
	#[inline]
	fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
	(**self).write(buf)
	}

	#[inline]
	fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
	(**self).write_vectored(bufs)
	}

	#[inline]
	fn is_write_vectored(&self) -> bool {
	(**self).is_write_vectored()
	}

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

	#[inline]
	fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
	(**self).write_all(buf)
	}

	#[inline]
	fn write_fmt(&mut self, fmt: fmt::Arguments<'_>) -> io::Result<()> {
	(**self).write_fmt(fmt)
	}
	}
	#[stable(feature = "rust1", since = "1.0.0")]
	impl<S: Seek + ?Sized> Seek for Box<S> {
	#[inline]
	fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
	(**self).seek(pos)
	}

	#[inline]
	fn stream_position(&mut self) -> io::Result<u64> {
	(**self).stream_position()
	}
	}
	#[stable(feature = "rust1", since = "1.0.0")]
	impl<B: BufRead + ?Sized> BufRead for Box<B> {
	#[inline]
	fn fill_buf(&mut self) -> io::Result<&[u8]> {
	(**self).fill_buf()
	}

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

	#[inline]
	fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> io::Result<usize> {
	(**self).read_until(byte, buf)
	}

	#[inline]
	fn read_line(&mut self, buf: &mut String) -> io::Result<usize> {
	(**self).read_line(buf)
	}
	}

	// =============================================================================
	// In-memory buffer implementations

	/// Read is implemented for `&[u8]` by copying from the slice.
	///
	/// Note that reading updates the slice to point to the yet unread part.
	/// The slice will be empty when EOF is reached.
	#[stable(feature = "rust1", since = "1.0.0")]
	impl Read for &[u8] {
	#[inline]
	fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
	let amt = cmp::min(buf.len(), self.len());
	let (a, b) = self.split_at(amt);

	// First check if the amount of bytes we want to read is small:
	// `copy_from_slice` will generally expand to a call to `memcpy`, and
	// for a single byte the overhead is significant.
	if amt == 1 {
	buf[0] = a[0];
	} else {
	buf[..amt].copy_from_slice(a);
	}

	*self = b;
	Ok(amt)
	}

	#[inline]
	fn read_buf(&mut self, mut cursor: BorrowedCursor<'_>) -> io::Result<()> {
	let amt = cmp::min(cursor.capacity(), self.len());
	let (a, b) = self.split_at(amt);

	cursor.append(a);

	*self = b;
	Ok(())
	}

	#[inline]
	fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
	let mut nread = 0;
	for buf in bufs {
	nread += self.read(buf)?;
	if self.is_empty() {
	break;
	}
	}

	Ok(nread)
	}

	#[inline]
	fn is_read_vectored(&self) -> bool {
	true
	}

	#[inline]
	fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
	if buf.len() > self.len() {
	// `read_exact` makes no promise about the content of `buf` if it
	// fails so don't bother about that.
	*self = &self[self.len()..];
	return Err(io::Error::READ_EXACT_EOF);
	}
	let (a, b) = self.split_at(buf.len());

	// First check if the amount of bytes we want to read is small:
	// `copy_from_slice` will generally expand to a call to `memcpy`, and
	// for a single byte the overhead is significant.
	if buf.len() == 1 {
	buf[0] = a[0];
	} else {
	buf.copy_from_slice(a);
	}

	*self = b;
	Ok(())
	}

	#[inline]
	fn read_buf_exact(&mut self, mut cursor: BorrowedCursor<'_>) -> io::Result<()> {
	if cursor.capacity() > self.len() {
	// Append everything we can to the cursor.
	cursor.append(*self);
	*self = &self[self.len()..];
	return Err(io::Error::READ_EXACT_EOF);
	}
	let (a, b) = self.split_at(cursor.capacity());

	cursor.append(a);

	*self = b;
	Ok(())
	}

	#[inline]
	fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
	let len = self.len();
	buf.try_reserve(len)?;
	buf.extend_from_slice(*self);
	*self = &self[len..];
	Ok(len)
	}

	#[inline]
	fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
	let content = str::from_utf8(self).map_err(\|_\| io::Error::INVALID_UTF8)?;
	let len = self.len();
	buf.try_reserve(len)?;
	buf.push_str(content);
	*self = &self[len..];
	Ok(len)
	}
	}

	#[stable(feature = "rust1", since = "1.0.0")]
	impl BufRead for &[u8] {
	#[inline]
	fn fill_buf(&mut self) -> io::Result<&[u8]> {
	Ok(*self)
	}

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

	/// Write is implemented for `&mut [u8]` by copying into the slice, overwriting
	/// its data.
	///
	/// Note that writing updates the slice to point to the yet unwritten part.
	/// The slice will be empty when it has been completely overwritten.
	///
	/// If the number of bytes to be written exceeds the size of the slice, write operations will
	/// return short writes: ultimately, `Ok(0)`; in this situation, `write_all` returns an error of
	/// kind `ErrorKind::WriteZero`.
	#[stable(feature = "rust1", since = "1.0.0")]
	impl Write for &mut [u8] {
	#[inline]
	fn write(&mut self, data: &[u8]) -> io::Result<usize> {
	let amt = cmp::min(data.len(), self.len());
	let (a, b) = mem::take(self).split_at_mut(amt);
	a.copy_from_slice(&data[..amt]);
	*self = b;
	Ok(amt)
	}

	#[inline]
	fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
	let mut nwritten = 0;
	for buf in bufs {
	nwritten += self.write(buf)?;
	if self.is_empty() {
	break;
	}
	}

	Ok(nwritten)
	}

	#[inline]
	fn is_write_vectored(&self) -> bool {
	true
	}

	#[inline]
	fn write_all(&mut self, data: &[u8]) -> io::Result<()> {
	if self.write(data)? == data.len() { Ok(()) } else { Err(io::Error::WRITE_ALL_EOF) }
	}

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

	/// Write is implemented for `Vec<u8>` by appending to the vector.
	/// The vector will grow as needed.
	#[stable(feature = "rust1", since = "1.0.0")]
	impl<A: Allocator> Write for Vec<u8, A> {
	#[inline]
	fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
	self.extend_from_slice(buf);
	Ok(buf.len())
	}

	#[inline]
	fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
	let len = bufs.iter().map(\|b\| b.len()).sum();
	self.reserve(len);
	for buf in bufs {
	self.extend_from_slice(buf);
	}
	Ok(len)
	}

	#[inline]
	fn is_write_vectored(&self) -> bool {
	true
	}

	#[inline]
	fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
	self.extend_from_slice(buf);
	Ok(())
	}

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

	/// Read is implemented for `VecDeque<u8>` by consuming bytes from the front of the `VecDeque`.
	#[stable(feature = "vecdeque_read_write", since = "1.63.0")]
	impl<A: Allocator> Read for VecDeque<u8, A> {
	/// Fill `buf` with the contents of the "front" slice as returned by
	/// [`as_slices`][`VecDeque::as_slices`]. If the contained byte slices of the `VecDeque` 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_buf(&mut self, cursor: BorrowedCursor<'_>) -> io::Result<()> {
	let (ref mut front, _) = self.as_slices();
	let n = cmp::min(cursor.capacity(), front.len());
	Read::read_buf(front, cursor)?;
	self.drain(..n);
	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)?;

	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> {
	// SAFETY: We only append to the buffer
	unsafe { io::append_to_string(buf, \|buf\| self.read_to_end(buf)) }
	}
	}

	/// BufRead is implemented for `VecDeque<u8>` by reading bytes from the front of the `VecDeque`.
	#[stable(feature = "vecdeque_buf_read", since = "1.75.0")]
	impl<A: Allocator> BufRead for VecDeque<u8, A> {
	/// Returns the contents of the "front" slice as returned by
	/// [`as_slices`][`VecDeque::as_slices`]. If the contained byte slices of the `VecDeque` 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 `VecDeque<u8>` by appending to the `VecDeque`, growing it as needed.
	#[stable(feature = "vecdeque_read_write", since = "1.63.0")]
	impl<A: Allocator> Write for VecDeque<u8, A> {
	#[inline]
	fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
	self.extend(buf);
	Ok(buf.len())
	}

	#[inline]
	fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
	let len = bufs.iter().map(\|b\| b.len()).sum();
	self.reserve(len);
	for buf in bufs {
	self.extend(&**buf);
	}
	Ok(len)
	}

	#[inline]
	fn is_write_vectored(&self) -> bool {
	true
	}

	#[inline]
	fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
	self.extend(buf);
	Ok(())
	}

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

	#[unstable(feature = "read_buf", issue = "78485")]
	impl<'a> io::Write for core::io::BorrowedCursor<'a> {
	fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
	let amt = cmp::min(buf.len(), self.capacity());
	self.append(&buf[..amt]);
	Ok(amt)
	}

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