294 lines
8.7 KiB
Rust
294 lines
8.7 KiB
Rust
use super::{BorrowedBuf, BufReader, BufWriter, Read, Result, Write, DEFAULT_BUF_SIZE};
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use crate::alloc::Allocator;
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use crate::cmp;
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use crate::collections::VecDeque;
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use crate::io::IoSlice;
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use crate::mem::MaybeUninit;
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#[cfg(test)]
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mod tests;
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/// Copies the entire contents of a reader into a writer.
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///
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/// This function will continuously read data from `reader` and then
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/// write it into `writer` in a streaming fashion until `reader`
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/// returns EOF.
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///
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/// On success, the total number of bytes that were copied from
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/// `reader` to `writer` is returned.
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///
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/// If you want to copy the contents of one file to another and you’re
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/// working with filesystem paths, see the [`fs::copy`] function.
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///
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/// [`fs::copy`]: crate::fs::copy
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///
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/// # Errors
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///
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/// This function will return an error immediately if any call to [`read`] or
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/// [`write`] returns an error. All instances of [`ErrorKind::Interrupted`] are
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/// handled by this function and the underlying operation is retried.
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///
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/// [`read`]: Read::read
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/// [`write`]: Write::write
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/// [`ErrorKind::Interrupted`]: crate::io::ErrorKind::Interrupted
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///
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/// # Examples
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///
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/// ```
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/// use std::io;
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///
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/// fn main() -> io::Result<()> {
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/// let mut reader: &[u8] = b"hello";
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/// let mut writer: Vec<u8> = vec![];
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///
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/// io::copy(&mut reader, &mut writer)?;
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///
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/// assert_eq!(&b"hello"[..], &writer[..]);
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/// Ok(())
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/// }
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/// ```
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///
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/// # Platform-specific behavior
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///
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/// On Linux (including Android), this function uses `copy_file_range(2)`,
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/// `sendfile(2)` or `splice(2)` syscalls to move data directly between file
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/// descriptors if possible.
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///
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/// Note that platform-specific behavior [may change in the future][changes].
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///
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/// [changes]: crate::io#platform-specific-behavior
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#[stable(feature = "rust1", since = "1.0.0")]
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pub fn copy<R: ?Sized, W: ?Sized>(reader: &mut R, writer: &mut W) -> Result<u64>
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where
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R: Read,
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W: Write,
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{
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cfg_if::cfg_if! {
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if #[cfg(any(target_os = "linux", target_os = "android"))] {
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crate::sys::kernel_copy::copy_spec(reader, writer)
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} else {
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generic_copy(reader, writer)
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}
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}
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}
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/// The userspace read-write-loop implementation of `io::copy` that is used when
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/// OS-specific specializations for copy offloading are not available or not applicable.
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pub(crate) fn generic_copy<R: ?Sized, W: ?Sized>(reader: &mut R, writer: &mut W) -> Result<u64>
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where
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R: Read,
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W: Write,
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{
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let read_buf = BufferedReaderSpec::buffer_size(reader);
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let write_buf = BufferedWriterSpec::buffer_size(writer);
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if read_buf >= DEFAULT_BUF_SIZE && read_buf >= write_buf {
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return BufferedReaderSpec::copy_to(reader, writer);
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}
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BufferedWriterSpec::copy_from(writer, reader)
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}
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/// Specialization of the read-write loop that reuses the internal
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/// buffer of a BufReader. If there's no buffer then the writer side
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/// should be used instead.
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trait BufferedReaderSpec {
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fn buffer_size(&self) -> usize;
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fn copy_to(&mut self, to: &mut (impl Write + ?Sized)) -> Result<u64>;
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}
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impl<T> BufferedReaderSpec for T
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where
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Self: Read,
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T: ?Sized,
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{
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#[inline]
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default fn buffer_size(&self) -> usize {
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0
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}
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default fn copy_to(&mut self, _to: &mut (impl Write + ?Sized)) -> Result<u64> {
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unreachable!("only called from specializations")
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}
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}
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impl BufferedReaderSpec for &[u8] {
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fn buffer_size(&self) -> usize {
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// prefer this specialization since the source "buffer" is all we'll ever need,
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// even if it's small
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usize::MAX
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}
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fn copy_to(&mut self, to: &mut (impl Write + ?Sized)) -> Result<u64> {
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let len = self.len();
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to.write_all(self)?;
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*self = &self[len..];
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Ok(len as u64)
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}
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}
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impl<A: Allocator> BufferedReaderSpec for VecDeque<u8, A> {
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fn buffer_size(&self) -> usize {
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// prefer this specialization since the source "buffer" is all we'll ever need,
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// even if it's small
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usize::MAX
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}
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fn copy_to(&mut self, to: &mut (impl Write + ?Sized)) -> Result<u64> {
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let len = self.len();
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let (front, back) = self.as_slices();
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let bufs = &mut [IoSlice::new(front), IoSlice::new(back)];
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to.write_all_vectored(bufs)?;
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self.clear();
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Ok(len as u64)
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}
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}
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impl<I> BufferedReaderSpec for BufReader<I>
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where
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Self: Read,
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I: ?Sized,
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{
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fn buffer_size(&self) -> usize {
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self.capacity()
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}
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fn copy_to(&mut self, to: &mut (impl Write + ?Sized)) -> Result<u64> {
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let mut len = 0;
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loop {
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// Hack: this relies on `impl Read for BufReader` always calling fill_buf
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// if the buffer is empty, even for empty slices.
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// It can't be called directly here since specialization prevents us
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// from adding I: Read
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match self.read(&mut []) {
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Ok(_) => {}
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Err(e) if e.is_interrupted() => continue,
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Err(e) => return Err(e),
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}
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let buf = self.buffer();
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if self.buffer().len() == 0 {
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return Ok(len);
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}
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// In case the writer side is a BufWriter then its write_all
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// implements an optimization that passes through large
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// buffers to the underlying writer. That code path is #[cold]
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// but we're still avoiding redundant memcopies when doing
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// a copy between buffered inputs and outputs.
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to.write_all(buf)?;
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len += buf.len() as u64;
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self.discard_buffer();
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}
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}
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}
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/// Specialization of the read-write loop that either uses a stack buffer
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/// or reuses the internal buffer of a BufWriter
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trait BufferedWriterSpec: Write {
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fn buffer_size(&self) -> usize;
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fn copy_from<R: Read + ?Sized>(&mut self, reader: &mut R) -> Result<u64>;
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}
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impl<W: Write + ?Sized> BufferedWriterSpec for W {
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#[inline]
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default fn buffer_size(&self) -> usize {
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0
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}
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default fn copy_from<R: Read + ?Sized>(&mut self, reader: &mut R) -> Result<u64> {
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stack_buffer_copy(reader, self)
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}
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}
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impl<I: Write + ?Sized> BufferedWriterSpec for BufWriter<I> {
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fn buffer_size(&self) -> usize {
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self.capacity()
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}
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fn copy_from<R: Read + ?Sized>(&mut self, reader: &mut R) -> Result<u64> {
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if self.capacity() < DEFAULT_BUF_SIZE {
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return stack_buffer_copy(reader, self);
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}
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let mut len = 0;
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let mut init = 0;
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loop {
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let buf = self.buffer_mut();
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let mut read_buf: BorrowedBuf<'_> = buf.spare_capacity_mut().into();
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unsafe {
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// SAFETY: init is either 0 or the init_len from the previous iteration.
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read_buf.set_init(init);
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}
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if read_buf.capacity() >= DEFAULT_BUF_SIZE {
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let mut cursor = read_buf.unfilled();
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match reader.read_buf(cursor.reborrow()) {
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Ok(()) => {
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let bytes_read = cursor.written();
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if bytes_read == 0 {
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return Ok(len);
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}
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init = read_buf.init_len() - bytes_read;
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len += bytes_read as u64;
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// SAFETY: BorrowedBuf guarantees all of its filled bytes are init
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unsafe { buf.set_len(buf.len() + bytes_read) };
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// Read again if the buffer still has enough capacity, as BufWriter itself would do
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// This will occur if the reader returns short reads
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}
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Err(ref e) if e.is_interrupted() => {}
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Err(e) => return Err(e),
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}
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} else {
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self.flush_buf()?;
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init = 0;
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}
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}
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}
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}
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impl BufferedWriterSpec for Vec<u8> {
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fn buffer_size(&self) -> usize {
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cmp::max(DEFAULT_BUF_SIZE, self.capacity() - self.len())
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}
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fn copy_from<R: Read + ?Sized>(&mut self, reader: &mut R) -> Result<u64> {
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reader.read_to_end(self).map(|bytes| u64::try_from(bytes).expect("usize overflowed u64"))
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}
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}
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pub fn stack_buffer_copy<R: Read + ?Sized, W: Write + ?Sized>(
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reader: &mut R,
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writer: &mut W,
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) -> Result<u64> {
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let buf: &mut [_] = &mut [MaybeUninit::uninit(); DEFAULT_BUF_SIZE];
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let mut buf: BorrowedBuf<'_> = buf.into();
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let mut len = 0;
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loop {
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match reader.read_buf(buf.unfilled()) {
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Ok(()) => {}
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Err(e) if e.is_interrupted() => continue,
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Err(e) => return Err(e),
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};
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if buf.filled().is_empty() {
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break;
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}
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len += buf.filled().len() as u64;
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writer.write_all(buf.filled())?;
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buf.clear();
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}
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Ok(len)
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}
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