-use crate::io::{self, ErrorKind, Read, Write};
+use super::{BufWriter, ErrorKind, Read, Result, Write, DEFAULT_BUF_SIZE};
use crate::mem::MaybeUninit;
/// Copies the entire contents of a reader into a writer.
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
-pub fn copy<R: ?Sized, W: ?Sized>(reader: &mut R, writer: &mut W) -> io::Result<u64>
+pub fn copy<R: ?Sized, W: ?Sized>(reader: &mut R, writer: &mut W) -> Result<u64>
where
R: Read,
W: Write,
}
}
-/// The general read-write-loop implementation of
-/// `io::copy` that is used when specializations are not available or not applicable.
-pub(crate) fn generic_copy<R: ?Sized, W: ?Sized>(reader: &mut R, writer: &mut W) -> io::Result<u64>
+/// The userspace read-write-loop implementation of `io::copy` that is used when
+/// OS-specific specializations for copy offloading are not available or not applicable.
+pub(crate) fn generic_copy<R: ?Sized, W: ?Sized>(reader: &mut R, writer: &mut W) -> Result<u64>
where
R: Read,
W: Write,
{
- let mut buf = MaybeUninit::<[u8; super::DEFAULT_BUF_SIZE]>::uninit();
+ BufferedCopySpec::copy_to(reader, writer)
+}
+
+/// Specialization of the read-write loop that either uses a stack buffer
+/// or reuses the internal buffer of a BufWriter
+trait BufferedCopySpec: Write {
+ fn copy_to<R: Read + ?Sized>(reader: &mut R, writer: &mut Self) -> Result<u64>;
+}
+
+impl<W: Write + ?Sized> BufferedCopySpec for W {
+ default fn copy_to<R: Read + ?Sized>(reader: &mut R, writer: &mut Self) -> Result<u64> {
+ stack_buffer_copy(reader, writer)
+ }
+}
+
+impl<I: Write> BufferedCopySpec for BufWriter<I> {
+ fn copy_to<R: Read + ?Sized>(reader: &mut R, writer: &mut Self) -> Result<u64> {
+ if writer.capacity() < DEFAULT_BUF_SIZE {
+ return stack_buffer_copy(reader, writer);
+ }
+
+ // FIXME: #42788
+ //
+ // - This creates a (mut) reference to a slice of
+ // _uninitialized_ integers, which is **undefined behavior**
+ //
+ // - Only the standard library gets to soundly "ignore" this,
+ // based on its privileged knowledge of unstable rustc
+ // internals;
+ unsafe {
+ let spare_cap = writer.buffer_mut().spare_capacity_mut();
+ reader.initializer().initialize(MaybeUninit::slice_assume_init_mut(spare_cap));
+ }
+
+ let mut len = 0;
+
+ loop {
+ let buf = writer.buffer_mut();
+ let spare_cap = buf.spare_capacity_mut();
+
+ if spare_cap.len() >= DEFAULT_BUF_SIZE {
+ match reader.read(unsafe { MaybeUninit::slice_assume_init_mut(spare_cap) }) {
+ Ok(0) => return Ok(len), // EOF reached
+ Ok(bytes_read) => {
+ assert!(bytes_read <= spare_cap.len());
+ // Safety: The initializer contract guarantees that either it or `read`
+ // will have initialized these bytes. And we just checked that the number
+ // of bytes is within the buffer capacity.
+ unsafe { buf.set_len(buf.len() + bytes_read) };
+ len += bytes_read as u64;
+ // Read again if the buffer still has enough capacity, as BufWriter itself would do
+ // This will occur if the reader returns short reads
+ continue;
+ }
+ Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
+ Err(e) => return Err(e),
+ }
+ }
+
+ writer.flush_buf()?;
+ }
+ }
+}
+
+fn stack_buffer_copy<R: Read + ?Sized, W: Write + ?Sized>(
+ reader: &mut R,
+ writer: &mut W,
+) -> Result<u64> {
+ let mut buf = MaybeUninit::<[u8; DEFAULT_BUF_SIZE]>::uninit();
// FIXME: #42788
//
// - This creates a (mut) reference to a slice of