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Add more from the std

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This commit is contained in:
Julien THILLARD
2026-03-17 23:40:39 +01:00
parent 10be5b301c
commit fd0770f813
15 changed files with 4526 additions and 16 deletions
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crates/std/src/io/buffered/bufreader.rs Normal file
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mod buffer;
use buffer::Buffer;
use crate::fmt;
use crate::io::{
self, BorrowedCursor, BufRead, DEFAULT_BUF_SIZE, IoSliceMut, Read, Seek, SeekFrom, SizeHint,
SpecReadByte, uninlined_slow_read_byte,
};
/// The `BufReader<R>` struct adds buffering to any reader.
///
/// It can be excessively inefficient to work directly with a [`Read`] instance.
/// For example, every call to [`read`][`TcpStream::read`] on [`TcpStream`]
/// results in a system call. A `BufReader<R>` performs large, infrequent reads on
/// the underlying [`Read`] and maintains an in-memory buffer of the results.
///
/// `BufReader<R>` can improve the speed of programs that make *small* and
/// *repeated* read calls to the same file or network socket. It does not
/// help when reading very large amounts at once, or reading just one or a few
/// times. It also provides no advantage when reading from a source that is
/// already in memory, like a <code>[Vec]\<u8></code>.
///
/// When the `BufReader<R>` is dropped, the contents of its buffer will be
/// discarded. Creating multiple instances of a `BufReader<R>` on the same
/// stream can cause data loss. Reading from the underlying reader after
/// unwrapping the `BufReader<R>` with [`BufReader::into_inner`] can also cause
/// data loss.
///
/// [`TcpStream::read`]: crate::net::TcpStream::read
/// [`TcpStream`]: crate::net::TcpStream
///
/// # Examples
///
/// ```no_run
/// use std::io::prelude::*;
/// use std::io::BufReader;
/// use std::fs::File;
///
/// fn main() -> std::io::Result<()> {
/// let f = File::open("log.txt")?;
/// let mut reader = BufReader::new(f);
///
/// let mut line = String::new();
/// let len = reader.read_line(&mut line)?;
/// println!("First line is {len} bytes long");
/// Ok(())
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub struct BufReader<R: ?Sized> {
buf: Buffer,
inner: R,
}
impl<R: Read> BufReader<R> {
/// Creates a new `BufReader<R>` with a default buffer capacity. The default is currently 8 KiB,
/// but may change in the future.
///
/// # Examples
///
/// ```no_run
/// use std::io::BufReader;
/// use std::fs::File;
///
/// fn main() -> std::io::Result<()> {
/// let f = File::open("log.txt")?;
/// let reader = BufReader::new(f);
/// Ok(())
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn new(inner: R) -> BufReader<R> {
BufReader::with_capacity(DEFAULT_BUF_SIZE, inner)
}
pub(crate) fn try_new_buffer() -> io::Result<Buffer> {
Buffer::try_with_capacity(DEFAULT_BUF_SIZE)
}
pub(crate) fn with_buffer(inner: R, buf: Buffer) -> Self {
Self { inner, buf }
}
/// Creates a new `BufReader<R>` with the specified buffer capacity.
///
/// # Examples
///
/// Creating a buffer with ten bytes of capacity:
///
/// ```no_run
/// use std::io::BufReader;
/// use std::fs::File;
///
/// fn main() -> std::io::Result<()> {
/// let f = File::open("log.txt")?;
/// let reader = BufReader::with_capacity(10, f);
/// Ok(())
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn with_capacity(capacity: usize, inner: R) -> BufReader<R> {
BufReader { inner, buf: Buffer::with_capacity(capacity) }
}
}
impl<R: Read + ?Sized> BufReader<R> {
/// Attempt to look ahead `n` bytes.
///
/// `n` must be less than or equal to `capacity`.
///
/// The returned slice may be less than `n` bytes long if
/// end of file is reached.
///
/// After calling this method, you may call [`consume`](BufRead::consume)
/// with a value less than or equal to `n` to advance over some or all of
/// the returned bytes.
///
/// ## Examples
///
/// ```rust
/// #![feature(bufreader_peek)]
/// use std::io::{Read, BufReader};
///
/// let mut bytes = &b"oh, hello there"[..];
/// let mut rdr = BufReader::with_capacity(6, &mut bytes);
/// assert_eq!(rdr.peek(2).unwrap(), b"oh");
/// let mut buf = [0; 4];
/// rdr.read(&mut buf[..]).unwrap();
/// assert_eq!(&buf, b"oh, ");
/// assert_eq!(rdr.peek(5).unwrap(), b"hello");
/// let mut s = String::new();
/// rdr.read_to_string(&mut s).unwrap();
/// assert_eq!(&s, "hello there");
/// assert_eq!(rdr.peek(1).unwrap().len(), 0);
/// ```
#[unstable(feature = "bufreader_peek", issue = "128405")]
pub fn peek(&mut self, n: usize) -> io::Result<&[u8]> {
assert!(n <= self.capacity());
while n > self.buf.buffer().len() {
if self.buf.pos() > 0 {
self.buf.backshift();
}
let new = self.buf.read_more(&mut self.inner)?;
if new == 0 {
// end of file, no more bytes to read
return Ok(&self.buf.buffer()[..]);
}
debug_assert_eq!(self.buf.pos(), 0);
}
Ok(&self.buf.buffer()[..n])
}
}
impl<R: ?Sized> BufReader<R> {
/// Gets a reference to the underlying reader.
///
/// It is inadvisable to directly read from the underlying reader.
///
/// # Examples
///
/// ```no_run
/// use std::io::BufReader;
/// use std::fs::File;
///
/// fn main() -> std::io::Result<()> {
/// let f1 = File::open("log.txt")?;
/// let reader = BufReader::new(f1);
///
/// let f2 = reader.get_ref();
/// Ok(())
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn get_ref(&self) -> &R {
&self.inner
}
/// Gets a mutable reference to the underlying reader.
///
/// It is inadvisable to directly read from the underlying reader.
///
/// # Examples
///
/// ```no_run
/// use std::io::BufReader;
/// use std::fs::File;
///
/// fn main() -> std::io::Result<()> {
/// let f1 = File::open("log.txt")?;
/// let mut reader = BufReader::new(f1);
///
/// let f2 = reader.get_mut();
/// Ok(())
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn get_mut(&mut self) -> &mut R {
&mut self.inner
}
/// Returns a reference to the internally buffered data.
///
/// Unlike [`fill_buf`], this will not attempt to fill the buffer if it is empty.
///
/// [`fill_buf`]: BufRead::fill_buf
///
/// # Examples
///
/// ```no_run
/// use std::io::{BufReader, BufRead};
/// use std::fs::File;
///
/// fn main() -> std::io::Result<()> {
/// let f = File::open("log.txt")?;
/// let mut reader = BufReader::new(f);
/// assert!(reader.buffer().is_empty());
///
/// if reader.fill_buf()?.len() > 0 {
/// assert!(!reader.buffer().is_empty());
/// }
/// Ok(())
/// }
/// ```
#[stable(feature = "bufreader_buffer", since = "1.37.0")]
pub fn buffer(&self) -> &[u8] {
self.buf.buffer()
}
/// Returns the number of bytes the internal buffer can hold at once.
///
/// # Examples
///
/// ```no_run
/// use std::io::{BufReader, BufRead};
/// use std::fs::File;
///
/// fn main() -> std::io::Result<()> {
/// let f = File::open("log.txt")?;
/// let mut reader = BufReader::new(f);
///
/// let capacity = reader.capacity();
/// let buffer = reader.fill_buf()?;
/// assert!(buffer.len() <= capacity);
/// Ok(())
/// }
/// ```
#[stable(feature = "buffered_io_capacity", since = "1.46.0")]
pub fn capacity(&self) -> usize {
self.buf.capacity()
}
/// Unwraps this `BufReader<R>`, returning the underlying reader.
///
/// Note that any leftover data in the internal buffer is lost. Therefore,
/// a following read from the underlying reader may lead to data loss.
///
/// # Examples
///
/// ```no_run
/// use std::io::BufReader;
/// use std::fs::File;
///
/// fn main() -> std::io::Result<()> {
/// let f1 = File::open("log.txt")?;
/// let reader = BufReader::new(f1);
///
/// let f2 = reader.into_inner();
/// Ok(())
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn into_inner(self) -> R
where
R: Sized,
{
self.inner
}
/// Invalidates all data in the internal buffer.
#[inline]
pub(in crate::io) fn discard_buffer(&mut self) {
self.buf.discard_buffer()
}
}
// This is only used by a test which asserts that the initialization-tracking is correct.
#[cfg(test)]
impl<R: ?Sized> BufReader<R> {
#[allow(missing_docs)]
pub fn initialized(&self) -> usize {
self.buf.initialized()
}
}
impl<R: ?Sized + Seek> BufReader<R> {
/// Seeks relative to the current position. If the new position lies within the buffer,
/// the buffer will not be flushed, allowing for more efficient seeks.
/// This method does not return the location of the underlying reader, so the caller
/// must track this information themselves if it is required.
#[stable(feature = "bufreader_seek_relative", since = "1.53.0")]
pub fn seek_relative(&mut self, offset: i64) -> io::Result<()> {
let pos = self.buf.pos() as u64;
if offset < 0 {
if let Some(_) = pos.checked_sub((-offset) as u64) {
self.buf.unconsume((-offset) as usize);
return Ok(());
}
} else if let Some(new_pos) = pos.checked_add(offset as u64) {
if new_pos <= self.buf.filled() as u64 {
self.buf.consume(offset as usize);
return Ok(());
}
}
self.seek(SeekFrom::Current(offset)).map(drop)
}
}
impl<R> SpecReadByte for BufReader<R>
where
Self: Read,
{
#[inline]
fn spec_read_byte(&mut self) -> Option<io::Result<u8>> {
let mut byte = 0;
if self.buf.consume_with(1, |claimed| byte = claimed[0]) {
return Some(Ok(byte));
}
// Fallback case, only reached once per buffer refill.
uninlined_slow_read_byte(self)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<R: ?Sized + Read> Read for BufReader<R> {
fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
// If we don't have any buffered data and we're doing a massive read
// (larger than our internal buffer), bypass our internal buffer
// entirely.
if self.buf.pos() == self.buf.filled() && buf.len() >= self.capacity() {
self.discard_buffer();
return self.inner.read(buf);
}
let mut rem = self.fill_buf()?;
let nread = rem.read(buf)?;
self.consume(nread);
Ok(nread)
}
fn read_buf(&mut self, mut cursor: BorrowedCursor<'_>) -> io::Result<()> {
// If we don't have any buffered data and we're doing a massive read
// (larger than our internal buffer), bypass our internal buffer
// entirely.
if self.buf.pos() == self.buf.filled() && cursor.capacity() >= self.capacity() {
self.discard_buffer();
return self.inner.read_buf(cursor);
}
let prev = cursor.written();
let mut rem = self.fill_buf()?;
rem.read_buf(cursor.reborrow())?; // actually never fails
self.consume(cursor.written() - prev); //slice impl of read_buf known to never unfill buf
Ok(())
}
// Small read_exacts from a BufReader are extremely common when used with a deserializer.
// The default implementation calls read in a loop, which results in surprisingly poor code
// generation for the common path where the buffer has enough bytes to fill the passed-in
// buffer.
fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
if self.buf.consume_with(buf.len(), |claimed| buf.copy_from_slice(claimed)) {
return Ok(());
}
crate::io::default_read_exact(self, buf)
}
fn read_buf_exact(&mut self, mut cursor: BorrowedCursor<'_>) -> io::Result<()> {
if self.buf.consume_with(cursor.capacity(), |claimed| cursor.append(claimed)) {
return Ok(());
}
crate::io::default_read_buf_exact(self, cursor)
}
fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
let total_len = bufs.iter().map(|b| b.len()).sum::<usize>();
if self.buf.pos() == self.buf.filled() && total_len >= self.capacity() {
self.discard_buffer();
return self.inner.read_vectored(bufs);
}
let mut rem = self.fill_buf()?;
let nread = rem.read_vectored(bufs)?;
self.consume(nread);
Ok(nread)
}
fn is_read_vectored(&self) -> bool {
self.inner.is_read_vectored()
}
// The inner reader might have an optimized `read_to_end`. Drain our buffer and then
// delegate to the inner implementation.
fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
let inner_buf = self.buffer();
buf.try_reserve(inner_buf.len())?;
buf.extend_from_slice(inner_buf);
let nread = inner_buf.len();
self.discard_buffer();
Ok(nread + self.inner.read_to_end(buf)?)
}
// The inner reader might have an optimized `read_to_end`. Drain our buffer and then
// delegate to the inner implementation.
fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
// In the general `else` case below we must read bytes into a side buffer, check
// that they are valid UTF-8, and then append them to `buf`. This requires a
// potentially large memcpy.
//
// If `buf` is empty--the most common case--we can leverage `append_to_string`
// to read directly into `buf`'s internal byte buffer, saving an allocation and
// a memcpy.
if buf.is_empty() {
// `append_to_string`'s safety relies on the buffer only being appended to since
// it only checks the UTF-8 validity of new data. If there were existing content in
// `buf` then an untrustworthy reader (i.e. `self.inner`) could not only append
// bytes but also modify existing bytes and render them invalid. On the other hand,
// if `buf` is empty then by definition any writes must be appends and
// `append_to_string` will validate all of the new bytes.
unsafe { crate::io::append_to_string(buf, |b| self.read_to_end(b)) }
} else {
// We cannot append our byte buffer directly onto the `buf` String as there could
// be an incomplete UTF-8 sequence that has only been partially read. We must read
// everything into a side buffer first and then call `from_utf8` on the complete
// buffer.
let mut bytes = Vec::new();
self.read_to_end(&mut bytes)?;
let string = crate::str::from_utf8(&bytes).map_err(|_| io::Error::INVALID_UTF8)?;
*buf += string;
Ok(string.len())
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<R: ?Sized + Read> BufRead for BufReader<R> {
fn fill_buf(&mut self) -> io::Result<&[u8]> {
self.buf.fill_buf(&mut self.inner)
}
fn consume(&mut self, amt: usize) {
self.buf.consume(amt)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<R> fmt::Debug for BufReader<R>
where
R: ?Sized + fmt::Debug,
{
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt.debug_struct("BufReader")
.field("reader", &&self.inner)
.field(
"buffer",
&format_args!("{}/{}", self.buf.filled() - self.buf.pos(), self.capacity()),
)
.finish()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<R: ?Sized + Seek> Seek for BufReader<R> {
/// Seek to an offset, in bytes, in the underlying reader.
///
/// The position used for seeking with <code>[SeekFrom::Current]\(_)</code> is the
/// position the underlying reader would be at if the `BufReader<R>` had no
/// internal buffer.
///
/// Seeking always discards the internal buffer, even if the seek position
/// would otherwise fall within it. This guarantees that calling
/// [`BufReader::into_inner()`] immediately after a seek yields the underlying reader
/// at the same position.
///
/// To seek without discarding the internal buffer, use [`BufReader::seek_relative`].
///
/// See [`std::io::Seek`] for more details.
///
/// Note: In the edge case where you're seeking with <code>[SeekFrom::Current]\(n)</code>
/// where `n` minus the internal buffer length overflows an `i64`, two
/// seeks will be performed instead of one. If the second seek returns
/// [`Err`], the underlying reader will be left at the same position it would
/// have if you called `seek` with <code>[SeekFrom::Current]\(0)</code>.
///
/// [`std::io::Seek`]: Seek
fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
let result: u64;
if let SeekFrom::Current(n) = pos {
let remainder = (self.buf.filled() - self.buf.pos()) as i64;
// it should be safe to assume that remainder fits within an i64 as the alternative
// means we managed to allocate 8 exbibytes and that's absurd.
// But it's not out of the realm of possibility for some weird underlying reader to
// support seeking by i64::MIN so we need to handle underflow when subtracting
// remainder.
if let Some(offset) = n.checked_sub(remainder) {
result = self.inner.seek(SeekFrom::Current(offset))?;
} else {
// seek backwards by our remainder, and then by the offset
self.inner.seek(SeekFrom::Current(-remainder))?;
self.discard_buffer();
result = self.inner.seek(SeekFrom::Current(n))?;
}
} else {
// Seeking with Start/End doesn't care about our buffer length.
result = self.inner.seek(pos)?;
}
self.discard_buffer();
Ok(result)
}
/// Returns the current seek position from the start of the stream.
///
/// The value returned is equivalent to `self.seek(SeekFrom::Current(0))`
/// but does not flush the internal buffer. Due to this optimization the
/// function does not guarantee that calling `.into_inner()` immediately
/// afterwards will yield the underlying reader at the same position. Use
/// [`BufReader::seek`] instead if you require that guarantee.
///
/// # Panics
///
/// This function will panic if the position of the inner reader is smaller
/// than the amount of buffered data. That can happen if the inner reader
/// has an incorrect implementation of [`Seek::stream_position`], or if the
/// position has gone out of sync due to calling [`Seek::seek`] directly on
/// the underlying reader.
///
/// # Example
///
/// ```no_run
/// use std::{
/// io::{self, BufRead, BufReader, Seek},
/// fs::File,
/// };
///
/// fn main() -> io::Result<()> {
/// let mut f = BufReader::new(File::open("foo.txt")?);
///
/// let before = f.stream_position()?;
/// f.read_line(&mut String::new())?;
/// let after = f.stream_position()?;
///
/// println!("The first line was {} bytes long", after - before);
/// Ok(())
/// }
/// ```
fn stream_position(&mut self) -> io::Result<u64> {
let remainder = (self.buf.filled() - self.buf.pos()) as u64;
self.inner.stream_position().map(|pos| {
pos.checked_sub(remainder).expect(
"overflow when subtracting remaining buffer size from inner stream position",
)
})
}
/// Seeks relative to the current position.
///
/// If the new position lies within the buffer, the buffer will not be
/// flushed, allowing for more efficient seeks. This method does not return
/// the location of the underlying reader, so the caller must track this
/// information themselves if it is required.
fn seek_relative(&mut self, offset: i64) -> io::Result<()> {
self.seek_relative(offset)
}
}
impl<T: ?Sized> SizeHint for BufReader<T> {
#[inline]
fn lower_bound(&self) -> usize {
SizeHint::lower_bound(self.get_ref()) + self.buffer().len()
}
#[inline]
fn upper_bound(&self) -> Option<usize> {
SizeHint::upper_bound(self.get_ref()).and_then(|up| self.buffer().len().checked_add(up))
}
}