chore: prepare bytes v1.4.0 (#593)

When we freeze a BytesMut, we turn it into a Vec, and then convert that
to a Bytes.  Currently, this happen using Vec::into_boxed_slice, which
reallocates to a slice of the same length as the Vev if the length and
the capacity are not equal.  This can pose a performance problem if the
Vec is large or if this happens many times in a loop.

Instead, let's compare the length and capacity, and if they're the same,
continue to handle this using into_boxed_slice.  Otherwise, since we
have a type of vtable which can handle a separate capacity, the shared
vtable, let's turn our Vec into that kind of Bytes.  While this does not
avoid allocation altogether, it performs a fixed size allocation and
avoids any need to memcpy.

.github/workflows/ci.yml

@@ -157,7 +157,7 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - name: Install Rust
-        run: rustup update stable && rustup default stable
+        run: rustup update $nightly && rustup default $nightly
       - name: Build documentation
         run: cargo doc --no-deps --all-features
         env:

CHANGELOG.md

@@ -1,3 +1,18 @@
+# 1.4.0 (January 31, 2023)
+
+### Added
+
+- Make `IntoIter` constructor public (#581)
+
+### Fixed
+
+- Avoid large reallocations when freezing `BytesMut` (#592)
+
+### Documented
+
+- Document which functions require `std` (#591)
+- Fix duplicate "the the" typos (#585)
+
 # 1.3.0 (November 20, 2022)
 
 ### Added

Cargo.toml

@@ -4,7 +4,7 @@ name = "bytes"
 # When releasing to crates.io:
 # - Update CHANGELOG.md.
 # - Create "v1.x.y" git tag.
-version = "1.3.0"
+version = "1.4.0"
 license = "MIT"
 authors = [
     "Carl Lerche <[email protected]>",

README.md

@@ -36,6 +36,15 @@ Serde support is optional and disabled by default. To enable use the feature `se
 bytes = { version = "1", features = ["serde"] }
 ```
 
+## Building documentation
+
+When building the `bytes` documentation the `docsrs` option should be used, otherwise
+feature gates will not be shown. This requires a nightly toolchain:
+
+```
+RUSTDOCFLAGS="--cfg docsrs" cargo +nightly doc
+```
+
 ## License
 
 This project is licensed under the [MIT license](LICENSE).

src/buf/buf_impl.rs

@@ -160,6 +160,7 @@ pub trait Buf {
     ///
     /// [`writev`]: http://man7.org/linux/man-pages/man2/readv.2.html
     #[cfg(feature = "std")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "std")))]
     fn chunks_vectored<'a>(&'a self, dst: &mut [IoSlice<'a>]) -> usize {
         if dst.is_empty() {
             return 0;
@@ -1183,6 +1184,7 @@ pub trait Buf {
     /// assert_eq!(&dst[..11], &b"hello world"[..]);
     /// ```
     #[cfg(feature = "std")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "std")))]
     fn reader(self) -> Reader<Self>
     where
         Self: Sized,

src/buf/buf_mut.rs

@@ -1239,6 +1239,7 @@ pub unsafe trait BufMut {
     /// assert_eq!(*buf, b"hello world"[..]);
     /// ```
     #[cfg(feature = "std")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "std")))]
     fn writer(self) -> Writer<Self>
     where
         Self: Sized,

src/buf/iter.rs

@@ -2,8 +2,6 @@ use crate::Buf;
 
 /// Iterator over the bytes contained by the buffer.
 ///
-/// This struct is created by the [`iter`] method on [`Buf`].
-///
 /// # Examples
 ///
 /// Basic usage:
@@ -43,7 +41,7 @@ impl<T> IntoIter<T> {
     /// assert_eq!(iter.next(), Some(b'c'));
     /// assert_eq!(iter.next(), None);
     /// ```
-    pub(crate) fn new(inner: T) -> IntoIter<T> {
+    pub fn new(inner: T) -> IntoIter<T> {
         IntoIter { inner }
     }
 

src/bytes.rs

@@ -32,7 +32,7 @@ use crate::Buf;
 /// All `Bytes` implementations must fulfill the following requirements:
 /// - They are cheaply cloneable and thereby shareable between an unlimited amount
 ///   of components, for example by modifying a reference count.
-/// - Instances can be sliced to refer to a subset of the the original buffer.
+/// - Instances can be sliced to refer to a subset of the original buffer.
 ///
 /// ```
 /// use bytes::Bytes;
@@ -71,7 +71,7 @@ use crate::Buf;
 ///
 /// For `Bytes` implementations which point to a reference counted shared storage
 /// (e.g. an `Arc<[u8]>`), sharing will be implemented by increasing the
-/// the reference count.
+/// reference count.
 ///
 /// Due to this mechanism, multiple `Bytes` instances may point to the same
 /// shared memory region.
@@ -807,8 +807,36 @@ impl From<&'static str> for Bytes {
 
 impl From<Vec<u8>> for Bytes {
     fn from(vec: Vec<u8>) -> Bytes {
-        let slice = vec.into_boxed_slice();
-        slice.into()
+        let mut vec = vec;
+        let ptr = vec.as_mut_ptr();
+        let len = vec.len();
+        let cap = vec.capacity();
+
+        // Avoid an extra allocation if possible.
+        if len == cap {
+            return Bytes::from(vec.into_boxed_slice());
+        }
+
+        let shared = Box::new(Shared {
+            buf: ptr,
+            cap,
+            ref_cnt: AtomicUsize::new(1),
+        });
+        mem::forget(vec);
+
+        let shared = Box::into_raw(shared);
+        // The pointer should be aligned, so this assert should
+        // always succeed.
+        debug_assert!(
+            0 == (shared as usize & KIND_MASK),
+            "internal: Box<Shared> should have an aligned pointer",
+        );
+        Bytes {
+            ptr,
+            len,
+            data: AtomicPtr::new(shared as _),
+            vtable: &SHARED_VTABLE,
+        }
     }
 }
 

src/lib.rs

@@ -4,6 +4,7 @@
     attr(deny(warnings, rust_2018_idioms), allow(dead_code, unused_variables))
 ))]
 #![no_std]
+#![cfg_attr(docsrs, feature(doc_cfg))]
 
 //! Provides abstractions for working with bytes.
 //!

tests/test_bytes.rs

@@ -1163,3 +1163,48 @@ fn test_bytes_into_vec_promotable_even() {
     assert_eq!(Vec::from(b2), vec[20..]);
     assert_eq!(Vec::from(b1), vec[..20]);
 }
+
+#[test]
+fn test_bytes_vec_conversion() {
+    let mut vec = Vec::with_capacity(10);
+    vec.extend(b"abcdefg");
+    let b = Bytes::from(vec);
+    let v = Vec::from(b);
+    assert_eq!(v.len(), 7);
+    assert_eq!(v.capacity(), 10);
+
+    let mut b = Bytes::from(v);
+    b.advance(1);
+    let v = Vec::from(b);
+    assert_eq!(v.len(), 6);
+    assert_eq!(v.capacity(), 10);
+    assert_eq!(v.as_slice(), b"bcdefg");
+}
+
+#[test]
+fn test_bytes_mut_conversion() {
+    let mut b1 = BytesMut::with_capacity(10);
+    b1.extend(b"abcdefg");
+    let b2 = Bytes::from(b1);
+    let v = Vec::from(b2);
+    assert_eq!(v.len(), 7);
+    assert_eq!(v.capacity(), 10);
+
+    let mut b = Bytes::from(v);
+    b.advance(1);
+    let v = Vec::from(b);
+    assert_eq!(v.len(), 6);
+    assert_eq!(v.capacity(), 10);
+    assert_eq!(v.as_slice(), b"bcdefg");
+}
+
+#[test]
+fn test_bytes_capacity_len() {
+    for cap in 0..100 {
+        for len in 0..=cap {
+            let mut v = Vec::with_capacity(cap);
+            v.resize(len, 0);
+            let _ = Bytes::from(v);
+        }
+    }
+}