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detects redundant imports that can be eliminated.
for #117772 :
In order to facilitate review and modification, split the checking code and
removing redundant imports code into two PR.
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unify read_to_end and io::copy impls for reading into a Vec
This ports over the initial probe (to avoid allocation) and the dynamic read sizing from the io::copy specialization to the `default_read_to_end` implementation which already had its own optimizations for different cases.
I think it should be a best-of-both now.
suggested by `@a1phyr` in https://github.com/rust-lang/rust/pull/117576#issuecomment-1803408492
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Improve rewind documentation
The persistent use of an internal cursor for readers is expected for buffer data types that aren't read all at once, but for files it leads to the confusing situation where calling `read_to_end` on the same file handle multiple times only returns the contents of the file for the first call. This PR adds a note to the documentation clarifying that in that case, `rewind()` must first be called.
I'm unsure if this is the right location for the docs update. Maybe it should also be duplicated on `File`?
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Add `BufRead::skip_until`
Alternative version of `BufRead::read_until` that simply discards data, rather than copying it into a buffer.
Useful for situations like skipping irrelevant data in a binary file format that is NUL-terminated.
<details>
<summary>Benchmark</summary>
```
running 2 tests
test bench_read_until ... bench: 123 ns/iter (+/- 6)
test bench_skip_until ... bench: 66 ns/iter (+/- 3)
```
```rs
#![feature(test)]
extern crate test;
use test::Bencher;
use std::io::{ErrorKind, BufRead};
fn skip_until<R: BufRead + ?Sized>(r: &mut R, delim: u8) -> Result<usize, std::io::Error> {
let mut read = 0;
loop {
let (done, used) = {
let available = match r.fill_buf() {
Ok(n) => n,
Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
Err(e) => return Err(e),
};
match memchr::memchr(delim, available) {
Some(i) => (true, i + 1),
None => (false, available.len()),
}
};
r.consume(used);
read += used;
if done || used == 0 {
return Ok(read);
}
}
}
const STR: &[u8] = b"Ferris\0Hello, world!\0";
#[bench]
fn bench_skip_until(b: &mut Bencher) {
b.iter(|| {
let mut io = std::io::Cursor::new(test::black_box(STR));
skip_until(&mut io, b'\0').unwrap();
let mut hello = Vec::with_capacity(b"Hello, world!\0".len());
let num_bytes = io.read_until(b'\0', &mut hello).unwrap();
assert_eq!(num_bytes, b"Hello, world!\0".len());
assert_eq!(hello, b"Hello, world!\0");
});
}
#[bench]
fn bench_read_until(b: &mut Bencher) {
b.iter(|| {
let mut io = std::io::Cursor::new(test::black_box(STR));
io.read_until(b'\0', &mut Vec::new()).unwrap();
let mut hello = Vec::with_capacity(b"Hello, world!\0".len());
let num_bytes = io.read_until(b'\0', &mut hello).unwrap();
assert_eq!(num_bytes, b"Hello, world!\0".len());
assert_eq!(hello, b"Hello, world!\0");
});
}
```
</details>
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Add Seek::seek_relative
The `BufReader` struct has a `seek_relative` method because its `Seek::seek` implementation involved dumping the internal buffer (https://github.com/rust-lang/rust/issues/31100).
Unfortunately, there isn't really a good way to take advantage of that method in generic code. This PR adds the same method to the main `Seek` trait with the straightforward default method, and an override for `BufReader` that calls its implementation.
_Also discussed in [this](https://internals.rust-lang.org/t/add-seek-seek-relative/19546) internals.rust-lang.org thread._
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Assigned new feature name `core_io_borrowed_buf` to distinguish from the
`Read::read_buf` functionality in `std::io`.
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Don't panic in `<BorrowedCursor as io::Write>::write`
Instead of panicking if the BorrowedCursor does not have enough capacity for the whole buffer, just return a short write, [like `<&mut [u8] as io::Write>::write` does](https://doc.rust-lang.org/src/std/io/impls.rs.html#349).
(cc `@ChayimFriedman2` https://github.com/rust-lang/rust/issues/78485#issuecomment-1493129588)
(I'm not sure if this needs an ACP? since it's not changing the "API", just what the function does)
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The initial probe-for-empty-source by stack_buffer_copy only detected EOF
if the source was empty but not when it was merely small which lead to
additional calls to read() after Ok(0) had already been returned
in the stack copy routine
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It now keeps track of initialized bytes to avoid reinitialization.
It also keeps track of read sizes to avoid initializing more bytes
than the reader needs. This is important when passing a huge vector to a
Read that only has a few bytes to offer and doesn't implement read_buf().
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This reduces the runtime for a simple program using `Bytes::next` to
iterate through a file from 220ms to 70ms on my Linux box.
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Inline `Bytes::next` and `Bytes::size_hint`.
This greatly increases its speed. On one small test program using `Bytes::next` to iterate over a large file, execution time dropped from ~330ms to ~220ms.
r? `@the8472`
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This greatly increases its speed.
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Implement `BufRead` for `VecDeque<u8>`
Note: it would become insta-stable
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Bump bootstrap compiler to just-released beta
https://forge.rust-lang.org/release/process.html#master-bootstrap-update-t-2-day-tuesday
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This variable seems to serve no purpose, and it's a little confusing
when reading std source code, so remove it.
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r=Mark-Simulacrum
Avoid overflow in `IoSlice::advance_slices`
Noticed in https://github.com/rust-lang/rust/issues/62726#issuecomment-1713997431.
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- Hide Docs
- Use repr_unpacked error
Signed-off-by: Ayush Singh <ayushdevel1325@gmail.com>
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add more explicit I/O safety documentation
Fixes https://github.com/rust-lang/unsafe-code-guidelines/issues/434
Cc https://github.com/rust-lang/rust/issues/114167
Cc `@Manishearth` `@sunfishcode` `@joshtriplett`
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Stabilize `io_error_other` feature
Per the FCP for https://github.com/rust-lang/rust/issues/91946.
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Move RawOsError defination to sys
This was originally a part of https://github.com/rust-lang/rust/pull/105861, but I feel it should be its own PR since the raw os error is still unstable.
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Signed-off-by: Ayush Singh <ayushdevel1325@gmail.com>
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Co-authored-by: Dan Gohman <dev@sunfishcode.online>
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`Ok(0)` is indeed something the caller may interpret as an error, but
that's the *correct* thing to return if the writer can't accept any more
bytes.
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Inline trivial (noop) flush calls
At work I noticed that `writer.flush()?` didn't get optimized away in cases where the flush is obviously a no-op, which I had expected (well, desired).
I went through and added `#[inline]` to a bunch of cases that were obviously noops, or delegated to ones that were obviously noops. I omitted platforms I don't have access to (some tier3). I didn't do this very scientifically, in cases where it was non-obvious I left `#[inline]` off.
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The extra `\0` in this commit is needed because the assertion on line 49 will fail otherwise (as `skip_until` stops reading on EOF and therefore does not read a trailing `\0`, returning 6 read bytes rather than the expected 7)
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