diff --git a/library/std/src/fs.rs b/library/std/src/fs.rs
index c550378e7d6b7..55580b23a6249 100644
--- a/library/std/src/fs.rs
+++ b/library/std/src/fs.rs
@@ -249,9 +249,9 @@ pub struct DirBuilder {
pub fn read<P: AsRef<Path>>(path: P) -> io::Result<Vec<u8>> {
fn inner(path: &Path) -> io::Result<Vec<u8>> {
let mut file = File::open(path)?;
- let size = file.metadata().map(|m| m.len()).unwrap_or(0);
- let mut bytes = Vec::with_capacity(size as usize);
- io::default_read_to_end(&mut file, &mut bytes)?;
+ let size = file.metadata().map(|m| m.len() as usize).ok();
+ let mut bytes = Vec::with_capacity(size.unwrap_or(0));
+ io::default_read_to_end(&mut file, &mut bytes, size)?;
Ok(bytes)
}
inner(path.as_ref())
@@ -289,9 +289,9 @@ pub fn read<P: AsRef<Path>>(path: P) -> io::Result<Vec<u8>> {
pub fn read_to_string<P: AsRef<Path>>(path: P) -> io::Result<String> {
fn inner(path: &Path) -> io::Result<String> {
let mut file = File::open(path)?;
- let size = file.metadata().map(|m| m.len()).unwrap_or(0);
- let mut string = String::with_capacity(size as usize);
- io::default_read_to_string(&mut file, &mut string)?;
+ let size = file.metadata().map(|m| m.len() as usize).ok();
+ let mut string = String::with_capacity(size.unwrap_or(0));
+ io::default_read_to_string(&mut file, &mut string, size)?;
Ok(string)
}
inner(path.as_ref())
@@ -732,12 +732,12 @@ impl fmt::Debug for File {
}
/// Indicates how much extra capacity is needed to read the rest of the file.
-fn buffer_capacity_required(mut file: &File) -> usize {
- let size = file.metadata().map(|m| m.len()).unwrap_or(0);
- let pos = file.stream_position().unwrap_or(0);
+fn buffer_capacity_required(mut file: &File) -> Option<usize> {
+ let size = file.metadata().map(|m| m.len()).ok()?;
+ let pos = file.stream_position().ok()?;
// Don't worry about `usize` overflow because reading will fail regardless
// in that case.
- size.saturating_sub(pos) as usize
+ Some(size.saturating_sub(pos) as usize)
}
#[stable(feature = "rust1", since = "1.0.0")]
@@ -761,14 +761,16 @@ impl Read for File {
// Reserves space in the buffer based on the file size when available.
fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
- buf.reserve(buffer_capacity_required(self));
- io::default_read_to_end(self, buf)
+ let size = buffer_capacity_required(self);
+ buf.reserve(size.unwrap_or(0));
+ io::default_read_to_end(self, buf, size)
}
// Reserves space in the buffer based on the file size when available.
fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
- buf.reserve(buffer_capacity_required(self));
- io::default_read_to_string(self, buf)
+ let size = buffer_capacity_required(self);
+ buf.reserve(size.unwrap_or(0));
+ io::default_read_to_string(self, buf, size)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
@@ -817,14 +819,16 @@ impl Read for &File {
// Reserves space in the buffer based on the file size when available.
fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
- buf.reserve(buffer_capacity_required(self));
- io::default_read_to_end(self, buf)
+ let size = buffer_capacity_required(self);
+ buf.reserve(size.unwrap_or(0));
+ io::default_read_to_end(self, buf, size)
}
// Reserves space in the buffer based on the file size when available.
fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
- buf.reserve(buffer_capacity_required(self));
- io::default_read_to_string(self, buf)
+ let size = buffer_capacity_required(self);
+ buf.reserve(size.unwrap_or(0));
+ io::default_read_to_string(self, buf, size)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
index 020c723925aeb..b3b5803bf59c3 100644
--- a/library/std/src/io/mod.rs
+++ b/library/std/src/io/mod.rs
@@ -357,9 +357,17 @@ where
// of data to return. Simply tacking on an extra DEFAULT_BUF_SIZE space every
// time is 4,500 times (!) slower than a default reservation size of 32 if the
// reader has a very small amount of data to return.
-pub(crate) fn default_read_to_end<R: Read + ?Sized>(r: &mut R, buf: &mut Vec<u8>) -> Result<usize> {
+pub(crate) fn default_read_to_end<R: Read + ?Sized>(
+ r: &mut R,
+ buf: &mut Vec<u8>,
+ size_hint: Option<usize>,
+) -> Result<usize> {
let start_len = buf.len();
let start_cap = buf.capacity();
+ // Optionally limit the maximum bytes read on each iteration.
+ // This adds an arbitrary fiddle factor to allow for more data than we expect.
+ let max_read_size =
+ size_hint.and_then(|s| s.checked_add(1024)?.checked_next_multiple_of(DEFAULT_BUF_SIZE));
let mut initialized = 0; // Extra initialized bytes from previous loop iteration
loop {
@@ -367,7 +375,12 @@ pub(crate) fn default_read_to_end<R: Read + ?Sized>(r: &mut R, buf: &mut Vec<u8>
buf.reserve(32); // buf is full, need more space
}
- let mut read_buf: BorrowedBuf<'_> = buf.spare_capacity_mut().into();
+ let mut spare = buf.spare_capacity_mut();
+ if let Some(size) = max_read_size {
+ let len = cmp::min(spare.len(), size);
+ spare = &mut spare[..len]
+ }
+ let mut read_buf: BorrowedBuf<'_> = spare.into();
// SAFETY: These bytes were initialized but not filled in the previous loop
unsafe {
@@ -419,6 +432,7 @@ pub(crate) fn default_read_to_end<R: Read + ?Sized>(r: &mut R, buf: &mut Vec<u8>
pub(crate) fn default_read_to_string<R: Read + ?Sized>(
r: &mut R,
buf: &mut String,
+ size_hint: Option<usize>,
) -> Result<usize> {
// Note that we do *not* call `r.read_to_end()` here. We are passing
// `&mut Vec<u8>` (the raw contents of `buf`) into the `read_to_end`
@@ -429,7 +443,7 @@ pub(crate) fn default_read_to_string<R: Read + ?Sized>(
// To prevent extraneously checking the UTF-8-ness of the entire buffer
// we pass it to our hardcoded `default_read_to_end` implementation which
// we know is guaranteed to only read data into the end of the buffer.
- unsafe { append_to_string(buf, |b| default_read_to_end(r, b)) }
+ unsafe { append_to_string(buf, |b| default_read_to_end(r, b, size_hint)) }
}
pub(crate) fn default_read_vectored<F>(read: F, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
@@ -709,7 +723,7 @@ pub trait Read {
/// [`std::fs::read`]: crate::fs::read
#[stable(feature = "rust1", since = "1.0.0")]
fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
- default_read_to_end(self, buf)
+ default_read_to_end(self, buf, None)
}
/// Read all bytes until EOF in this source, appending them to `buf`.
@@ -752,7 +766,7 @@ pub trait Read {
/// [`std::fs::read_to_string`]: crate::fs::read_to_string
#[stable(feature = "rust1", since = "1.0.0")]
fn read_to_string(&mut self, buf: &mut String) -> Result<usize> {
- default_read_to_string(self, buf)
+ default_read_to_string(self, buf, None)
}
/// Read the exact number of bytes required to fill `buf`.
diff --git a/library/std/src/io/tests.rs b/library/std/src/io/tests.rs
index f4a886d889a99..6d30f5e6c6c8d 100644
--- a/library/std/src/io/tests.rs
+++ b/library/std/src/io/tests.rs
@@ -314,7 +314,7 @@ fn bench_read_to_end(b: &mut test::Bencher) {
b.iter(|| {
let mut lr = repeat(1).take(10000000);
let mut vec = Vec::with_capacity(1024);
- super::default_read_to_end(&mut lr, &mut vec)
+ super::default_read_to_end(&mut lr, &mut vec, None)
});
}
diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
index 98fcc76aa98f6..318a46d1b637e 100644
--- a/library/std/src/lib.rs
+++ b/library/std/src/lib.rs
@@ -289,6 +289,7 @@
#![feature(float_next_up_down)]
#![feature(hasher_prefixfree_extras)]
#![feature(hashmap_internals)]
+#![feature(int_roundings)]
#![feature(ip)]
#![feature(ip_in_core)]
#![feature(maybe_uninit_slice)]