88 lines
2.7 KiB
Rust
88 lines
2.7 KiB
Rust
use crate::io::{self, ErrorKind, Read, Write};
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use crate::mem::MaybeUninit;
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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’re wanting 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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///
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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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#[stable(feature = "rust1", since = "1.0.0")]
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pub fn copy<R: ?Sized, W: ?Sized>(reader: &mut R, writer: &mut W) -> io::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 general read-write-loop implementation of
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/// `io::copy` that is used when specializations 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) -> io::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 mut buf = MaybeUninit::<[u8; super::DEFAULT_BUF_SIZE]>::uninit();
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// FIXME: #42788
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//
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// - This creates a (mut) reference to a slice of
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// _uninitialized_ integers, which is **undefined behavior**
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//
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// - Only the standard library gets to soundly "ignore" this,
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// based on its privileged knowledge of unstable rustc
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// internals;
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unsafe {
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reader.initializer().initialize(buf.assume_init_mut());
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}
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let mut written = 0;
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loop {
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let len = match reader.read(unsafe { buf.assume_init_mut() }) {
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Ok(0) => return Ok(written),
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Ok(len) => len,
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Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
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Err(e) => return Err(e),
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};
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writer.write_all(unsafe { &buf.assume_init_ref()[..len] })?;
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written += len as u64;
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}
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}
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