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use crate::io::{self, ErrorKind, Read, Write};
use crate::mem::MaybeUninit;
/// Copies the entire contents of a reader into a writer.
///
/// This function will continuously read data from `reader` and then
/// write it into `writer` in a streaming fashion until `reader`
/// returns EOF.
///
/// On success, the total number of bytes that were copied from
/// `reader` to `writer` is returned.
///
/// If you’re wanting to copy the contents of one file to another and you’re
/// working with filesystem paths, see the [`fs::copy`] function.
///
/// [`fs::copy`]: crate::fs::copy
///
/// # Errors
///
/// This function will return an error immediately if any call to [`read`] or
/// [`write`] returns an error. All instances of [`ErrorKind::Interrupted`] are
/// handled by this function and the underlying operation is retried.
///
/// [`read`]: Read::read
/// [`write`]: Write::write
///
/// # Examples
///
/// ```
/// use std::io;
///
/// fn main() -> io::Result<()> {
/// let mut reader: &[u8] = b"hello";
/// let mut writer: Vec<u8> = vec![];
///
/// io::copy(&mut reader, &mut writer)?;
///
/// assert_eq!(&b"hello"[..], &writer[..]);
/// Ok(())
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn copy<R: ?Sized, W: ?Sized>(reader: &mut R, writer: &mut W) -> io::Result<u64>
where
R: Read,
W: Write,
{
cfg_if::cfg_if! {
if #[cfg(any(target_os = "linux", target_os = "android"))] {
crate::sys::kernel_copy::copy_spec(reader, writer)
} else {
generic_copy(reader, writer)
}
}
}
/// 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>
where
R: Read,
W: Write,
{
let mut buf = MaybeUninit::<[u8; super::DEFAULT_BUF_SIZE]>::uninit();
// 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 {
reader.initializer().initialize(buf.assume_init_mut());
}
let mut written = 0;
loop {
let len = match reader.read(unsafe { buf.assume_init_mut() }) {
Ok(0) => return Ok(written),
Ok(len) => len,
Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
Err(e) => return Err(e),
};
writer.write_all(unsafe { &buf.assume_init_ref()[..len] })?;
written += len as u64;
}
}
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