mv std libs to library/
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mark
308
library/std/src/io/util.rs
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308
library/std/src/io/util.rs
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#![allow(missing_copy_implementations)]
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use crate::fmt;
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use crate::io::{self, BufRead, ErrorKind, Initializer, IoSlice, IoSliceMut, 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`]: ../fs/fn.copy.html
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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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/// # 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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let mut buf = MaybeUninit::<[u8; super::DEFAULT_BUF_SIZE]>::uninit();
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// FIXME(#53491): This is calling `get_mut` and `get_ref` on an uninitialized
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// `MaybeUninit`. Revisit this once we decided whether that is valid or not.
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// This is still technically undefined behavior due to creating a reference
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// to uninitialized data, but within libstd we can rely on more guarantees
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// than if this code were in an external lib.
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unsafe {
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reader.initializer().initialize(buf.get_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.get_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.get_ref()[..len] })?;
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written += len as u64;
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}
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}
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/// A reader which is always at EOF.
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///
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/// This struct is generally created by calling [`empty`]. Please see
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/// the documentation of [`empty()`][`empty`] for more details.
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///
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/// [`empty`]: fn.empty.html
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#[stable(feature = "rust1", since = "1.0.0")]
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pub struct Empty {
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_priv: (),
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}
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/// Constructs a new handle to an empty reader.
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///
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/// All reads from the returned reader will return [`Ok`]`(0)`.
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///
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/// [`Ok`]: ../result/enum.Result.html#variant.Ok
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///
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/// # Examples
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///
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/// A slightly sad example of not reading anything into a buffer:
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///
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/// ```
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/// use std::io::{self, Read};
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///
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/// let mut buffer = String::new();
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/// io::empty().read_to_string(&mut buffer).unwrap();
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/// assert!(buffer.is_empty());
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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pub fn empty() -> Empty {
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Empty { _priv: () }
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl Read for Empty {
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#[inline]
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fn read(&mut self, _buf: &mut [u8]) -> io::Result<usize> {
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Ok(0)
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}
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#[inline]
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unsafe fn initializer(&self) -> Initializer {
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Initializer::nop()
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl BufRead for Empty {
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#[inline]
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fn fill_buf(&mut self) -> io::Result<&[u8]> {
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Ok(&[])
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}
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#[inline]
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fn consume(&mut self, _n: usize) {}
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}
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#[stable(feature = "std_debug", since = "1.16.0")]
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impl fmt::Debug for Empty {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.pad("Empty { .. }")
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}
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}
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/// A reader which yields one byte over and over and over and over and over and...
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///
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/// This struct is generally created by calling [`repeat`][repeat]. Please
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/// see the documentation of `repeat()` for more details.
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///
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/// [repeat]: fn.repeat.html
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#[stable(feature = "rust1", since = "1.0.0")]
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pub struct Repeat {
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byte: u8,
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}
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/// Creates an instance of a reader that infinitely repeats one byte.
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///
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/// All reads from this reader will succeed by filling the specified buffer with
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/// the given byte.
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///
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/// # Examples
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///
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/// ```
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/// use std::io::{self, Read};
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///
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/// let mut buffer = [0; 3];
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/// io::repeat(0b101).read_exact(&mut buffer).unwrap();
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/// assert_eq!(buffer, [0b101, 0b101, 0b101]);
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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pub fn repeat(byte: u8) -> Repeat {
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Repeat { byte }
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl Read for Repeat {
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#[inline]
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fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
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for slot in &mut *buf {
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*slot = self.byte;
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}
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Ok(buf.len())
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}
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#[inline]
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fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
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let mut nwritten = 0;
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for buf in bufs {
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nwritten += self.read(buf)?;
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}
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Ok(nwritten)
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}
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#[inline]
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fn is_read_vectored(&self) -> bool {
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true
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}
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#[inline]
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unsafe fn initializer(&self) -> Initializer {
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Initializer::nop()
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}
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}
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#[stable(feature = "std_debug", since = "1.16.0")]
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impl fmt::Debug for Repeat {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.pad("Repeat { .. }")
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}
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}
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/// A writer which will move data into the void.
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///
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/// This struct is generally created by calling [`sink`][sink]. Please
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/// see the documentation of `sink()` for more details.
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///
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/// [sink]: fn.sink.html
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#[stable(feature = "rust1", since = "1.0.0")]
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pub struct Sink {
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_priv: (),
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}
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/// Creates an instance of a writer which will successfully consume all data.
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///
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/// All calls to `write` on the returned instance will return `Ok(buf.len())`
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/// and the contents of the buffer will not be inspected.
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///
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/// # Examples
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///
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/// ```rust
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/// use std::io::{self, Write};
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///
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/// let buffer = vec![1, 2, 3, 5, 8];
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/// let num_bytes = io::sink().write(&buffer).unwrap();
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/// assert_eq!(num_bytes, 5);
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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pub fn sink() -> Sink {
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Sink { _priv: () }
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl Write for Sink {
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#[inline]
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fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
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Ok(buf.len())
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}
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#[inline]
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fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
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let total_len = bufs.iter().map(|b| b.len()).sum();
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Ok(total_len)
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}
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#[inline]
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fn is_write_vectored(&self) -> bool {
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true
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}
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#[inline]
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fn flush(&mut self) -> io::Result<()> {
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Ok(())
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}
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}
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#[stable(feature = "std_debug", since = "1.16.0")]
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impl fmt::Debug for Sink {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.pad("Sink { .. }")
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}
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}
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#[cfg(test)]
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mod tests {
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use crate::io::prelude::*;
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use crate::io::{copy, empty, repeat, sink};
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#[test]
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fn copy_copies() {
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let mut r = repeat(0).take(4);
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let mut w = sink();
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assert_eq!(copy(&mut r, &mut w).unwrap(), 4);
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let mut r = repeat(0).take(1 << 17);
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assert_eq!(copy(&mut r as &mut dyn Read, &mut w as &mut dyn Write).unwrap(), 1 << 17);
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}
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#[test]
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fn sink_sinks() {
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let mut s = sink();
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assert_eq!(s.write(&[]).unwrap(), 0);
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assert_eq!(s.write(&[0]).unwrap(), 1);
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assert_eq!(s.write(&[0; 1024]).unwrap(), 1024);
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assert_eq!(s.by_ref().write(&[0; 1024]).unwrap(), 1024);
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}
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#[test]
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fn empty_reads() {
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let mut e = empty();
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assert_eq!(e.read(&mut []).unwrap(), 0);
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assert_eq!(e.read(&mut [0]).unwrap(), 0);
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assert_eq!(e.read(&mut [0; 1024]).unwrap(), 0);
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assert_eq!(e.by_ref().read(&mut [0; 1024]).unwrap(), 0);
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}
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#[test]
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fn repeat_repeats() {
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let mut r = repeat(4);
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let mut b = [0; 1024];
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assert_eq!(r.read(&mut b).unwrap(), 1024);
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assert!(b.iter().all(|b| *b == 4));
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}
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#[test]
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fn take_some_bytes() {
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assert_eq!(repeat(4).take(100).bytes().count(), 100);
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assert_eq!(repeat(4).take(100).bytes().next().unwrap().unwrap(), 4);
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assert_eq!(repeat(1).take(10).chain(repeat(2).take(10)).bytes().count(), 20);
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}
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}
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