1use core::iter::FromIterator;
2use core::mem::{self, ManuallyDrop, MaybeUninit};
3use core::ops::{Deref, DerefMut};
4use core::ptr::{self, NonNull};
5use core::{cmp, fmt, hash, isize, slice, usize};
6
7use alloc::{
8 borrow::{Borrow, BorrowMut},
9 boxed::Box,
10 string::String,
11 vec,
12 vec::Vec,
13};
14
15use crate::buf::{IntoIter, UninitSlice};
16use crate::bytes::Vtable;
17#[allow(unused)]
18use crate::loom::sync::atomic::AtomicMut;
19use crate::loom::sync::atomic::{AtomicPtr, AtomicUsize, Ordering};
20use crate::{offset_from, Buf, BufMut, Bytes};
21
22/// A unique reference to a contiguous slice of memory.
23///
24/// `BytesMut` represents a unique view into a potentially shared memory region.
25/// Given the uniqueness guarantee, owners of `BytesMut` handles are able to
26/// mutate the memory.
27///
28/// `BytesMut` can be thought of as containing a `buf: Arc<Vec<u8>>`, an offset
29/// into `buf`, a slice length, and a guarantee that no other `BytesMut` for the
30/// same `buf` overlaps with its slice. That guarantee means that a write lock
31/// is not required.
32///
33/// # Growth
34///
35/// `BytesMut`'s `BufMut` implementation will implicitly grow its buffer as
36/// necessary. However, explicitly reserving the required space up-front before
37/// a series of inserts will be more efficient.
38///
39/// # Examples
40///
41/// ```
42/// use bytes::{BytesMut, BufMut};
43///
44/// let mut buf = BytesMut::with_capacity(64);
45///
46/// buf.put_u8(b'h');
47/// buf.put_u8(b'e');
48/// buf.put(&b"llo"[..]);
49///
50/// assert_eq!(&buf[..], b"hello");
51///
52/// // Freeze the buffer so that it can be shared
53/// let a = buf.freeze();
54///
55/// // This does not allocate, instead `b` points to the same memory.
56/// let b = a.clone();
57///
58/// assert_eq!(&a[..], b"hello");
59/// assert_eq!(&b[..], b"hello");
60/// ```
61pub struct BytesMut {
62 ptr: NonNull<u8>,
63 len: usize,
64 cap: usize,
65 data: *mut Shared,
66}
67
68// Thread-safe reference-counted container for the shared storage. This mostly
69// the same as `core::sync::Arc` but without the weak counter. The ref counting
70// fns are based on the ones found in `std`.
71//
72// The main reason to use `Shared` instead of `core::sync::Arc` is that it ends
73// up making the overall code simpler and easier to reason about. This is due to
74// some of the logic around setting `Inner::arc` and other ways the `arc` field
75// is used. Using `Arc` ended up requiring a number of funky transmutes and
76// other shenanigans to make it work.
77struct Shared {
78 vec: Vec<u8>,
79 original_capacity_repr: usize,
80 ref_count: AtomicUsize,
81}
82
83// Assert that the alignment of `Shared` is divisible by 2.
84// This is a necessary invariant since we depend on allocating `Shared` a
85// shared object to implicitly carry the `KIND_ARC` flag in its pointer.
86// This flag is set when the LSB is 0.
87const _: [(); 0 - mem::align_of::<Shared>() % 2] = []; // Assert that the alignment of `Shared` is divisible by 2.
88
89// Buffer storage strategy flags.
90const KIND_ARC: usize = 0b0;
91const KIND_VEC: usize = 0b1;
92const KIND_MASK: usize = 0b1;
93
94// The max original capacity value. Any `Bytes` allocated with a greater initial
95// capacity will default to this.
96const MAX_ORIGINAL_CAPACITY_WIDTH: usize = 17;
97// The original capacity algorithm will not take effect unless the originally
98// allocated capacity was at least 1kb in size.
99const MIN_ORIGINAL_CAPACITY_WIDTH: usize = 10;
100// The original capacity is stored in powers of 2 starting at 1kb to a max of
101// 64kb. Representing it as such requires only 3 bits of storage.
102const ORIGINAL_CAPACITY_MASK: usize = 0b11100;
103const ORIGINAL_CAPACITY_OFFSET: usize = 2;
104
105const VEC_POS_OFFSET: usize = 5;
106// When the storage is in the `Vec` representation, the pointer can be advanced
107// at most this value. This is due to the amount of storage available to track
108// the offset is usize - number of KIND bits and number of ORIGINAL_CAPACITY
109// bits.
110const MAX_VEC_POS: usize = usize::MAX >> VEC_POS_OFFSET;
111const NOT_VEC_POS_MASK: usize = 0b11111;
112
113#[cfg(target_pointer_width = "64")]
114const PTR_WIDTH: usize = 64;
115#[cfg(target_pointer_width = "32")]
116const PTR_WIDTH: usize = 32;
117
118/*
119 *
120 * ===== BytesMut =====
121 *
122 */
123
124impl BytesMut {
125 /// Creates a new `BytesMut` with the specified capacity.
126 ///
127 /// The returned `BytesMut` will be able to hold at least `capacity` bytes
128 /// without reallocating.
129 ///
130 /// It is important to note that this function does not specify the length
131 /// of the returned `BytesMut`, but only the capacity.
132 ///
133 /// # Examples
134 ///
135 /// ```
136 /// use bytes::{BytesMut, BufMut};
137 ///
138 /// let mut bytes = BytesMut::with_capacity(64);
139 ///
140 /// // `bytes` contains no data, even though there is capacity
141 /// assert_eq!(bytes.len(), 0);
142 ///
143 /// bytes.put(&b"hello world"[..]);
144 ///
145 /// assert_eq!(&bytes[..], b"hello world");
146 /// ```
147 #[inline]
148 pub fn with_capacity(capacity: usize) -> BytesMut {
149 BytesMut::from_vec(Vec::with_capacity(capacity))
150 }
151
152 /// Creates a new `BytesMut` with default capacity.
153 ///
154 /// Resulting object has length 0 and unspecified capacity.
155 /// This function does not allocate.
156 ///
157 /// # Examples
158 ///
159 /// ```
160 /// use bytes::{BytesMut, BufMut};
161 ///
162 /// let mut bytes = BytesMut::new();
163 ///
164 /// assert_eq!(0, bytes.len());
165 ///
166 /// bytes.reserve(2);
167 /// bytes.put_slice(b"xy");
168 ///
169 /// assert_eq!(&b"xy"[..], &bytes[..]);
170 /// ```
171 #[inline]
172 pub fn new() -> BytesMut {
173 BytesMut::with_capacity(0)
174 }
175
176 /// Returns the number of bytes contained in this `BytesMut`.
177 ///
178 /// # Examples
179 ///
180 /// ```
181 /// use bytes::BytesMut;
182 ///
183 /// let b = BytesMut::from(&b"hello"[..]);
184 /// assert_eq!(b.len(), 5);
185 /// ```
186 #[inline]
187 pub fn len(&self) -> usize {
188 self.len
189 }
190
191 /// Returns true if the `BytesMut` has a length of 0.
192 ///
193 /// # Examples
194 ///
195 /// ```
196 /// use bytes::BytesMut;
197 ///
198 /// let b = BytesMut::with_capacity(64);
199 /// assert!(b.is_empty());
200 /// ```
201 #[inline]
202 pub fn is_empty(&self) -> bool {
203 self.len == 0
204 }
205
206 /// Returns the number of bytes the `BytesMut` can hold without reallocating.
207 ///
208 /// # Examples
209 ///
210 /// ```
211 /// use bytes::BytesMut;
212 ///
213 /// let b = BytesMut::with_capacity(64);
214 /// assert_eq!(b.capacity(), 64);
215 /// ```
216 #[inline]
217 pub fn capacity(&self) -> usize {
218 self.cap
219 }
220
221 /// Converts `self` into an immutable `Bytes`.
222 ///
223 /// The conversion is zero cost and is used to indicate that the slice
224 /// referenced by the handle will no longer be mutated. Once the conversion
225 /// is done, the handle can be cloned and shared across threads.
226 ///
227 /// # Examples
228 ///
229 /// ```
230 /// use bytes::{BytesMut, BufMut};
231 /// use std::thread;
232 ///
233 /// let mut b = BytesMut::with_capacity(64);
234 /// b.put(&b"hello world"[..]);
235 /// let b1 = b.freeze();
236 /// let b2 = b1.clone();
237 ///
238 /// let th = thread::spawn(move || {
239 /// assert_eq!(&b1[..], b"hello world");
240 /// });
241 ///
242 /// assert_eq!(&b2[..], b"hello world");
243 /// th.join().unwrap();
244 /// ```
245 #[inline]
246 pub fn freeze(self) -> Bytes {
247 let bytes = ManuallyDrop::new(self);
248 if bytes.kind() == KIND_VEC {
249 // Just re-use `Bytes` internal Vec vtable
250 unsafe {
251 let off = bytes.get_vec_pos();
252 let vec = rebuild_vec(bytes.ptr.as_ptr(), bytes.len, bytes.cap, off);
253 let mut b: Bytes = vec.into();
254 b.advance(off);
255 b
256 }
257 } else {
258 debug_assert_eq!(bytes.kind(), KIND_ARC);
259
260 let ptr = bytes.ptr.as_ptr();
261 let len = bytes.len;
262 let data = AtomicPtr::new(bytes.data.cast());
263 unsafe { Bytes::with_vtable(ptr, len, data, &SHARED_VTABLE) }
264 }
265 }
266
267 /// Creates a new `BytesMut` containing `len` zeros.
268 ///
269 /// The resulting object has a length of `len` and a capacity greater
270 /// than or equal to `len`. The entire length of the object will be filled
271 /// with zeros.
272 ///
273 /// On some platforms or allocators this function may be faster than
274 /// a manual implementation.
275 ///
276 /// # Examples
277 ///
278 /// ```
279 /// use bytes::BytesMut;
280 ///
281 /// let zeros = BytesMut::zeroed(42);
282 ///
283 /// assert!(zeros.capacity() >= 42);
284 /// assert_eq!(zeros.len(), 42);
285 /// zeros.into_iter().for_each(|x| assert_eq!(x, 0));
286 /// ```
287 pub fn zeroed(len: usize) -> BytesMut {
288 BytesMut::from_vec(vec![0; len])
289 }
290
291 /// Splits the bytes into two at the given index.
292 ///
293 /// Afterwards `self` contains elements `[0, at)`, and the returned
294 /// `BytesMut` contains elements `[at, capacity)`. It's guaranteed that the
295 /// memory does not move, that is, the address of `self` does not change,
296 /// and the address of the returned slice is `at` bytes after that.
297 ///
298 /// This is an `O(1)` operation that just increases the reference count
299 /// and sets a few indices.
300 ///
301 /// # Examples
302 ///
303 /// ```
304 /// use bytes::BytesMut;
305 ///
306 /// let mut a = BytesMut::from(&b"hello world"[..]);
307 /// let mut b = a.split_off(5);
308 ///
309 /// a[0] = b'j';
310 /// b[0] = b'!';
311 ///
312 /// assert_eq!(&a[..], b"jello");
313 /// assert_eq!(&b[..], b"!world");
314 /// ```
315 ///
316 /// # Panics
317 ///
318 /// Panics if `at > capacity`.
319 #[must_use = "consider BytesMut::truncate if you don't need the other half"]
320 pub fn split_off(&mut self, at: usize) -> BytesMut {
321 assert!(
322 at <= self.capacity(),
323 "split_off out of bounds: {:?} <= {:?}",
324 at,
325 self.capacity(),
326 );
327 unsafe {
328 let mut other = self.shallow_clone();
329 // SAFETY: We've checked that `at` <= `self.capacity()` above.
330 other.advance_unchecked(at);
331 self.cap = at;
332 self.len = cmp::min(self.len, at);
333 other
334 }
335 }
336
337 /// Removes the bytes from the current view, returning them in a new
338 /// `BytesMut` handle.
339 ///
340 /// Afterwards, `self` will be empty, but will retain any additional
341 /// capacity that it had before the operation. This is identical to
342 /// `self.split_to(self.len())`.
343 ///
344 /// This is an `O(1)` operation that just increases the reference count and
345 /// sets a few indices.
346 ///
347 /// # Examples
348 ///
349 /// ```
350 /// use bytes::{BytesMut, BufMut};
351 ///
352 /// let mut buf = BytesMut::with_capacity(1024);
353 /// buf.put(&b"hello world"[..]);
354 ///
355 /// let other = buf.split();
356 ///
357 /// assert!(buf.is_empty());
358 /// assert_eq!(1013, buf.capacity());
359 ///
360 /// assert_eq!(other, b"hello world"[..]);
361 /// ```
362 #[must_use = "consider BytesMut::clear if you don't need the other half"]
363 pub fn split(&mut self) -> BytesMut {
364 let len = self.len();
365 self.split_to(len)
366 }
367
368 /// Splits the buffer into two at the given index.
369 ///
370 /// Afterwards `self` contains elements `[at, len)`, and the returned `BytesMut`
371 /// contains elements `[0, at)`.
372 ///
373 /// This is an `O(1)` operation that just increases the reference count and
374 /// sets a few indices.
375 ///
376 /// # Examples
377 ///
378 /// ```
379 /// use bytes::BytesMut;
380 ///
381 /// let mut a = BytesMut::from(&b"hello world"[..]);
382 /// let mut b = a.split_to(5);
383 ///
384 /// a[0] = b'!';
385 /// b[0] = b'j';
386 ///
387 /// assert_eq!(&a[..], b"!world");
388 /// assert_eq!(&b[..], b"jello");
389 /// ```
390 ///
391 /// # Panics
392 ///
393 /// Panics if `at > len`.
394 #[must_use = "consider BytesMut::advance if you don't need the other half"]
395 pub fn split_to(&mut self, at: usize) -> BytesMut {
396 assert!(
397 at <= self.len(),
398 "split_to out of bounds: {:?} <= {:?}",
399 at,
400 self.len(),
401 );
402
403 unsafe {
404 let mut other = self.shallow_clone();
405 // SAFETY: We've checked that `at` <= `self.len()` and we know that `self.len()` <=
406 // `self.capacity()`.
407 self.advance_unchecked(at);
408 other.cap = at;
409 other.len = at;
410 other
411 }
412 }
413
414 /// Shortens the buffer, keeping the first `len` bytes and dropping the
415 /// rest.
416 ///
417 /// If `len` is greater than the buffer's current length, this has no
418 /// effect.
419 ///
420 /// Existing underlying capacity is preserved.
421 ///
422 /// The [split_off](`Self::split_off()`) method can emulate `truncate`, but this causes the
423 /// excess bytes to be returned instead of dropped.
424 ///
425 /// # Examples
426 ///
427 /// ```
428 /// use bytes::BytesMut;
429 ///
430 /// let mut buf = BytesMut::from(&b"hello world"[..]);
431 /// buf.truncate(5);
432 /// assert_eq!(buf, b"hello"[..]);
433 /// ```
434 pub fn truncate(&mut self, len: usize) {
435 if len <= self.len() {
436 // SAFETY: Shrinking the buffer cannot expose uninitialized bytes.
437 unsafe { self.set_len(len) };
438 }
439 }
440
441 /// Clears the buffer, removing all data. Existing capacity is preserved.
442 ///
443 /// # Examples
444 ///
445 /// ```
446 /// use bytes::BytesMut;
447 ///
448 /// let mut buf = BytesMut::from(&b"hello world"[..]);
449 /// buf.clear();
450 /// assert!(buf.is_empty());
451 /// ```
452 pub fn clear(&mut self) {
453 // SAFETY: Setting the length to zero cannot expose uninitialized bytes.
454 unsafe { self.set_len(0) };
455 }
456
457 /// Resizes the buffer so that `len` is equal to `new_len`.
458 ///
459 /// If `new_len` is greater than `len`, the buffer is extended by the
460 /// difference with each additional byte set to `value`. If `new_len` is
461 /// less than `len`, the buffer is simply truncated.
462 ///
463 /// # Examples
464 ///
465 /// ```
466 /// use bytes::BytesMut;
467 ///
468 /// let mut buf = BytesMut::new();
469 ///
470 /// buf.resize(3, 0x1);
471 /// assert_eq!(&buf[..], &[0x1, 0x1, 0x1]);
472 ///
473 /// buf.resize(2, 0x2);
474 /// assert_eq!(&buf[..], &[0x1, 0x1]);
475 ///
476 /// buf.resize(4, 0x3);
477 /// assert_eq!(&buf[..], &[0x1, 0x1, 0x3, 0x3]);
478 /// ```
479 pub fn resize(&mut self, new_len: usize, value: u8) {
480 let additional = if let Some(additional) = new_len.checked_sub(self.len()) {
481 additional
482 } else {
483 self.truncate(new_len);
484 return;
485 };
486
487 if additional == 0 {
488 return;
489 }
490
491 self.reserve(additional);
492 let dst = self.spare_capacity_mut().as_mut_ptr();
493 // SAFETY: `spare_capacity_mut` returns a valid, properly aligned pointer and we've
494 // reserved enough space to write `additional` bytes.
495 unsafe { ptr::write_bytes(dst, value, additional) };
496
497 // SAFETY: There are at least `new_len` initialized bytes in the buffer so no
498 // uninitialized bytes are being exposed.
499 unsafe { self.set_len(new_len) };
500 }
501
502 /// Sets the length of the buffer.
503 ///
504 /// This will explicitly set the size of the buffer without actually
505 /// modifying the data, so it is up to the caller to ensure that the data
506 /// has been initialized.
507 ///
508 /// # Examples
509 ///
510 /// ```
511 /// use bytes::BytesMut;
512 ///
513 /// let mut b = BytesMut::from(&b"hello world"[..]);
514 ///
515 /// unsafe {
516 /// b.set_len(5);
517 /// }
518 ///
519 /// assert_eq!(&b[..], b"hello");
520 ///
521 /// unsafe {
522 /// b.set_len(11);
523 /// }
524 ///
525 /// assert_eq!(&b[..], b"hello world");
526 /// ```
527 #[inline]
528 pub unsafe fn set_len(&mut self, len: usize) {
529 debug_assert!(len <= self.cap, "set_len out of bounds");
530 self.len = len;
531 }
532
533 /// Reserves capacity for at least `additional` more bytes to be inserted
534 /// into the given `BytesMut`.
535 ///
536 /// More than `additional` bytes may be reserved in order to avoid frequent
537 /// reallocations. A call to `reserve` may result in an allocation.
538 ///
539 /// Before allocating new buffer space, the function will attempt to reclaim
540 /// space in the existing buffer. If the current handle references a view
541 /// into a larger original buffer, and all other handles referencing part
542 /// of the same original buffer have been dropped, then the current view
543 /// can be copied/shifted to the front of the buffer and the handle can take
544 /// ownership of the full buffer, provided that the full buffer is large
545 /// enough to fit the requested additional capacity.
546 ///
547 /// This optimization will only happen if shifting the data from the current
548 /// view to the front of the buffer is not too expensive in terms of the
549 /// (amortized) time required. The precise condition is subject to change;
550 /// as of now, the length of the data being shifted needs to be at least as
551 /// large as the distance that it's shifted by. If the current view is empty
552 /// and the original buffer is large enough to fit the requested additional
553 /// capacity, then reallocations will never happen.
554 ///
555 /// # Examples
556 ///
557 /// In the following example, a new buffer is allocated.
558 ///
559 /// ```
560 /// use bytes::BytesMut;
561 ///
562 /// let mut buf = BytesMut::from(&b"hello"[..]);
563 /// buf.reserve(64);
564 /// assert!(buf.capacity() >= 69);
565 /// ```
566 ///
567 /// In the following example, the existing buffer is reclaimed.
568 ///
569 /// ```
570 /// use bytes::{BytesMut, BufMut};
571 ///
572 /// let mut buf = BytesMut::with_capacity(128);
573 /// buf.put(&[0; 64][..]);
574 ///
575 /// let ptr = buf.as_ptr();
576 /// let other = buf.split();
577 ///
578 /// assert!(buf.is_empty());
579 /// assert_eq!(buf.capacity(), 64);
580 ///
581 /// drop(other);
582 /// buf.reserve(128);
583 ///
584 /// assert_eq!(buf.capacity(), 128);
585 /// assert_eq!(buf.as_ptr(), ptr);
586 /// ```
587 ///
588 /// # Panics
589 ///
590 /// Panics if the new capacity overflows `usize`.
591 #[inline]
592 pub fn reserve(&mut self, additional: usize) {
593 let len = self.len();
594 let rem = self.capacity() - len;
595
596 if additional <= rem {
597 // The handle can already store at least `additional` more bytes, so
598 // there is no further work needed to be done.
599 return;
600 }
601
602 // will always succeed
603 let _ = self.reserve_inner(additional, true);
604 }
605
606 // In separate function to allow the short-circuits in `reserve` and `try_reclaim` to
607 // be inline-able. Significantly helps performance. Returns false if it did not succeed.
608 fn reserve_inner(&mut self, additional: usize, allocate: bool) -> bool {
609 let len = self.len();
610 let kind = self.kind();
611
612 if kind == KIND_VEC {
613 // If there's enough free space before the start of the buffer, then
614 // just copy the data backwards and reuse the already-allocated
615 // space.
616 //
617 // Otherwise, since backed by a vector, use `Vec::reserve`
618 //
619 // We need to make sure that this optimization does not kill the
620 // amortized runtimes of BytesMut's operations.
621 unsafe {
622 let off = self.get_vec_pos();
623
624 // Only reuse space if we can satisfy the requested additional space.
625 //
626 // Also check if the value of `off` suggests that enough bytes
627 // have been read to account for the overhead of shifting all
628 // the data (in an amortized analysis).
629 // Hence the condition `off >= self.len()`.
630 //
631 // This condition also already implies that the buffer is going
632 // to be (at least) half-empty in the end; so we do not break
633 // the (amortized) runtime with future resizes of the underlying
634 // `Vec`.
635 //
636 // [For more details check issue #524, and PR #525.]
637 if self.capacity() - self.len() + off >= additional && off >= self.len() {
638 // There's enough space, and it's not too much overhead:
639 // reuse the space!
640 //
641 // Just move the pointer back to the start after copying
642 // data back.
643 let base_ptr = self.ptr.as_ptr().sub(off);
644 // Since `off >= self.len()`, the two regions don't overlap.
645 ptr::copy_nonoverlapping(self.ptr.as_ptr(), base_ptr, self.len);
646 self.ptr = vptr(base_ptr);
647 self.set_vec_pos(0);
648
649 // Length stays constant, but since we moved backwards we
650 // can gain capacity back.
651 self.cap += off;
652 } else {
653 if !allocate {
654 return false;
655 }
656 // Not enough space, or reusing might be too much overhead:
657 // allocate more space!
658 let mut v =
659 ManuallyDrop::new(rebuild_vec(self.ptr.as_ptr(), self.len, self.cap, off));
660 v.reserve(additional);
661
662 // Update the info
663 self.ptr = vptr(v.as_mut_ptr().add(off));
664 self.cap = v.capacity() - off;
665 debug_assert_eq!(self.len, v.len() - off);
666 }
667
668 return true;
669 }
670 }
671
672 debug_assert_eq!(kind, KIND_ARC);
673 let shared: *mut Shared = self.data;
674
675 // Reserving involves abandoning the currently shared buffer and
676 // allocating a new vector with the requested capacity.
677 //
678 // Compute the new capacity
679 let mut new_cap = match len.checked_add(additional) {
680 Some(new_cap) => new_cap,
681 None if !allocate => return false,
682 None => panic!("overflow"),
683 };
684
685 unsafe {
686 // First, try to reclaim the buffer. This is possible if the current
687 // handle is the only outstanding handle pointing to the buffer.
688 if (*shared).is_unique() {
689 // This is the only handle to the buffer. It can be reclaimed.
690 // However, before doing the work of copying data, check to make
691 // sure that the vector has enough capacity.
692 let v = &mut (*shared).vec;
693
694 let v_capacity = v.capacity();
695 let ptr = v.as_mut_ptr();
696
697 let offset = offset_from(self.ptr.as_ptr(), ptr);
698
699 // Compare the condition in the `kind == KIND_VEC` case above
700 // for more details.
701 if v_capacity >= new_cap + offset {
702 self.cap = new_cap;
703 // no copy is necessary
704 } else if v_capacity >= new_cap && offset >= len {
705 // The capacity is sufficient, and copying is not too much
706 // overhead: reclaim the buffer!
707
708 // `offset >= len` means: no overlap
709 ptr::copy_nonoverlapping(self.ptr.as_ptr(), ptr, len);
710
711 self.ptr = vptr(ptr);
712 self.cap = v.capacity();
713 } else {
714 if !allocate {
715 return false;
716 }
717 // calculate offset
718 let off = (self.ptr.as_ptr() as usize) - (v.as_ptr() as usize);
719
720 // new_cap is calculated in terms of `BytesMut`, not the underlying
721 // `Vec`, so it does not take the offset into account.
722 //
723 // Thus we have to manually add it here.
724 new_cap = new_cap.checked_add(off).expect("overflow");
725
726 // The vector capacity is not sufficient. The reserve request is
727 // asking for more than the initial buffer capacity. Allocate more
728 // than requested if `new_cap` is not much bigger than the current
729 // capacity.
730 //
731 // There are some situations, using `reserve_exact` that the
732 // buffer capacity could be below `original_capacity`, so do a
733 // check.
734 let double = v.capacity().checked_shl(1).unwrap_or(new_cap);
735
736 new_cap = cmp::max(double, new_cap);
737
738 // No space - allocate more
739 //
740 // The length field of `Shared::vec` is not used by the `BytesMut`;
741 // instead we use the `len` field in the `BytesMut` itself. However,
742 // when calling `reserve`, it doesn't guarantee that data stored in
743 // the unused capacity of the vector is copied over to the new
744 // allocation, so we need to ensure that we don't have any data we
745 // care about in the unused capacity before calling `reserve`.
746 debug_assert!(off + len <= v.capacity());
747 v.set_len(off + len);
748 v.reserve(new_cap - v.len());
749
750 // Update the info
751 self.ptr = vptr(v.as_mut_ptr().add(off));
752 self.cap = v.capacity() - off;
753 }
754
755 return true;
756 }
757 }
758 if !allocate {
759 return false;
760 }
761
762 let original_capacity_repr = unsafe { (*shared).original_capacity_repr };
763 let original_capacity = original_capacity_from_repr(original_capacity_repr);
764
765 new_cap = cmp::max(new_cap, original_capacity);
766
767 // Create a new vector to store the data
768 let mut v = ManuallyDrop::new(Vec::with_capacity(new_cap));
769
770 // Copy the bytes
771 v.extend_from_slice(self.as_ref());
772
773 // Release the shared handle. This must be done *after* the bytes are
774 // copied.
775 unsafe { release_shared(shared) };
776
777 // Update self
778 let data = (original_capacity_repr << ORIGINAL_CAPACITY_OFFSET) | KIND_VEC;
779 self.data = invalid_ptr(data);
780 self.ptr = vptr(v.as_mut_ptr());
781 self.cap = v.capacity();
782 debug_assert_eq!(self.len, v.len());
783 return true;
784 }
785
786 /// Attempts to cheaply reclaim already allocated capacity for at least `additional` more
787 /// bytes to be inserted into the given `BytesMut` and returns `true` if it succeeded.
788 ///
789 /// `try_reclaim` behaves exactly like `reserve`, except that it never allocates new storage
790 /// and returns a `bool` indicating whether it was successful in doing so:
791 ///
792 /// `try_reclaim` returns false under these conditions:
793 /// - The spare capacity left is less than `additional` bytes AND
794 /// - The existing allocation cannot be reclaimed cheaply or it was less than
795 /// `additional` bytes in size
796 ///
797 /// Reclaiming the allocation cheaply is possible if the `BytesMut` has no outstanding
798 /// references through other `BytesMut`s or `Bytes` which point to the same underlying
799 /// storage.
800 ///
801 /// # Examples
802 ///
803 /// ```
804 /// use bytes::BytesMut;
805 ///
806 /// let mut buf = BytesMut::with_capacity(64);
807 /// assert_eq!(true, buf.try_reclaim(64));
808 /// assert_eq!(64, buf.capacity());
809 ///
810 /// buf.extend_from_slice(b"abcd");
811 /// let mut split = buf.split();
812 /// assert_eq!(60, buf.capacity());
813 /// assert_eq!(4, split.capacity());
814 /// assert_eq!(false, split.try_reclaim(64));
815 /// assert_eq!(false, buf.try_reclaim(64));
816 /// // The split buffer is filled with "abcd"
817 /// assert_eq!(false, split.try_reclaim(4));
818 /// // buf is empty and has capacity for 60 bytes
819 /// assert_eq!(true, buf.try_reclaim(60));
820 ///
821 /// drop(buf);
822 /// assert_eq!(false, split.try_reclaim(64));
823 ///
824 /// split.clear();
825 /// assert_eq!(4, split.capacity());
826 /// assert_eq!(true, split.try_reclaim(64));
827 /// assert_eq!(64, split.capacity());
828 /// ```
829 // I tried splitting out try_reclaim_inner after the short circuits, but it was inlined
830 // regardless with Rust 1.78.0 so probably not worth it
831 #[inline]
832 #[must_use = "consider BytesMut::reserve if you need an infallible reservation"]
833 pub fn try_reclaim(&mut self, additional: usize) -> bool {
834 let len = self.len();
835 let rem = self.capacity() - len;
836
837 if additional <= rem {
838 // The handle can already store at least `additional` more bytes, so
839 // there is no further work needed to be done.
840 return true;
841 }
842
843 self.reserve_inner(additional, false)
844 }
845
846 /// Appends given bytes to this `BytesMut`.
847 ///
848 /// If this `BytesMut` object does not have enough capacity, it is resized
849 /// first.
850 ///
851 /// # Examples
852 ///
853 /// ```
854 /// use bytes::BytesMut;
855 ///
856 /// let mut buf = BytesMut::with_capacity(0);
857 /// buf.extend_from_slice(b"aaabbb");
858 /// buf.extend_from_slice(b"cccddd");
859 ///
860 /// assert_eq!(b"aaabbbcccddd", &buf[..]);
861 /// ```
862 #[inline]
863 pub fn extend_from_slice(&mut self, extend: &[u8]) {
864 let cnt = extend.len();
865 self.reserve(cnt);
866
867 unsafe {
868 let dst = self.spare_capacity_mut();
869 // Reserved above
870 debug_assert!(dst.len() >= cnt);
871
872 ptr::copy_nonoverlapping(extend.as_ptr(), dst.as_mut_ptr().cast(), cnt);
873 }
874
875 unsafe {
876 self.advance_mut(cnt);
877 }
878 }
879
880 /// Absorbs a `BytesMut` that was previously split off.
881 ///
882 /// If the two `BytesMut` objects were previously contiguous and not mutated
883 /// in a way that causes re-allocation i.e., if `other` was created by
884 /// calling `split_off` on this `BytesMut`, then this is an `O(1)` operation
885 /// that just decreases a reference count and sets a few indices.
886 /// Otherwise this method degenerates to
887 /// `self.extend_from_slice(other.as_ref())`.
888 ///
889 /// # Examples
890 ///
891 /// ```
892 /// use bytes::BytesMut;
893 ///
894 /// let mut buf = BytesMut::with_capacity(64);
895 /// buf.extend_from_slice(b"aaabbbcccddd");
896 ///
897 /// let split = buf.split_off(6);
898 /// assert_eq!(b"aaabbb", &buf[..]);
899 /// assert_eq!(b"cccddd", &split[..]);
900 ///
901 /// buf.unsplit(split);
902 /// assert_eq!(b"aaabbbcccddd", &buf[..]);
903 /// ```
904 pub fn unsplit(&mut self, other: BytesMut) {
905 if self.is_empty() {
906 *self = other;
907 return;
908 }
909
910 if let Err(other) = self.try_unsplit(other) {
911 self.extend_from_slice(other.as_ref());
912 }
913 }
914
915 // private
916
917 // For now, use a `Vec` to manage the memory for us, but we may want to
918 // change that in the future to some alternate allocator strategy.
919 //
920 // Thus, we don't expose an easy way to construct from a `Vec` since an
921 // internal change could make a simple pattern (`BytesMut::from(vec)`)
922 // suddenly a lot more expensive.
923 #[inline]
924 pub(crate) fn from_vec(vec: Vec<u8>) -> BytesMut {
925 let mut vec = ManuallyDrop::new(vec);
926 let ptr = vptr(vec.as_mut_ptr());
927 let len = vec.len();
928 let cap = vec.capacity();
929
930 let original_capacity_repr = original_capacity_to_repr(cap);
931 let data = (original_capacity_repr << ORIGINAL_CAPACITY_OFFSET) | KIND_VEC;
932
933 BytesMut {
934 ptr,
935 len,
936 cap,
937 data: invalid_ptr(data),
938 }
939 }
940
941 #[inline]
942 fn as_slice(&self) -> &[u8] {
943 unsafe { slice::from_raw_parts(self.ptr.as_ptr(), self.len) }
944 }
945
946 #[inline]
947 fn as_slice_mut(&mut self) -> &mut [u8] {
948 unsafe { slice::from_raw_parts_mut(self.ptr.as_ptr(), self.len) }
949 }
950
951 /// Advance the buffer without bounds checking.
952 ///
953 /// # SAFETY
954 ///
955 /// The caller must ensure that `count` <= `self.cap`.
956 pub(crate) unsafe fn advance_unchecked(&mut self, count: usize) {
957 // Setting the start to 0 is a no-op, so return early if this is the
958 // case.
959 if count == 0 {
960 return;
961 }
962
963 debug_assert!(count <= self.cap, "internal: set_start out of bounds");
964
965 let kind = self.kind();
966
967 if kind == KIND_VEC {
968 // Setting the start when in vec representation is a little more
969 // complicated. First, we have to track how far ahead the
970 // "start" of the byte buffer from the beginning of the vec. We
971 // also have to ensure that we don't exceed the maximum shift.
972 let pos = self.get_vec_pos() + count;
973
974 if pos <= MAX_VEC_POS {
975 self.set_vec_pos(pos);
976 } else {
977 // The repr must be upgraded to ARC. This will never happen
978 // on 64 bit systems and will only happen on 32 bit systems
979 // when shifting past 134,217,727 bytes. As such, we don't
980 // worry too much about performance here.
981 self.promote_to_shared(/*ref_count = */ 1);
982 }
983 }
984
985 // Updating the start of the view is setting `ptr` to point to the
986 // new start and updating the `len` field to reflect the new length
987 // of the view.
988 self.ptr = vptr(self.ptr.as_ptr().add(count));
989 self.len = self.len.checked_sub(count).unwrap_or(0);
990 self.cap -= count;
991 }
992
993 fn try_unsplit(&mut self, other: BytesMut) -> Result<(), BytesMut> {
994 if other.capacity() == 0 {
995 return Ok(());
996 }
997
998 let ptr = unsafe { self.ptr.as_ptr().add(self.len) };
999 if ptr == other.ptr.as_ptr()
1000 && self.kind() == KIND_ARC
1001 && other.kind() == KIND_ARC
1002 && self.data == other.data
1003 {
1004 // Contiguous blocks, just combine directly
1005 self.len += other.len;
1006 self.cap += other.cap;
1007 Ok(())
1008 } else {
1009 Err(other)
1010 }
1011 }
1012
1013 #[inline]
1014 fn kind(&self) -> usize {
1015 self.data as usize & KIND_MASK
1016 }
1017
1018 unsafe fn promote_to_shared(&mut self, ref_cnt: usize) {
1019 debug_assert_eq!(self.kind(), KIND_VEC);
1020 debug_assert!(ref_cnt == 1 || ref_cnt == 2);
1021
1022 let original_capacity_repr =
1023 (self.data as usize & ORIGINAL_CAPACITY_MASK) >> ORIGINAL_CAPACITY_OFFSET;
1024
1025 // The vec offset cannot be concurrently mutated, so there
1026 // should be no danger reading it.
1027 let off = (self.data as usize) >> VEC_POS_OFFSET;
1028
1029 // First, allocate a new `Shared` instance containing the
1030 // `Vec` fields. It's important to note that `ptr`, `len`,
1031 // and `cap` cannot be mutated without having `&mut self`.
1032 // This means that these fields will not be concurrently
1033 // updated and since the buffer hasn't been promoted to an
1034 // `Arc`, those three fields still are the components of the
1035 // vector.
1036 let shared = Box::new(Shared {
1037 vec: rebuild_vec(self.ptr.as_ptr(), self.len, self.cap, off),
1038 original_capacity_repr,
1039 ref_count: AtomicUsize::new(ref_cnt),
1040 });
1041
1042 let shared = Box::into_raw(shared);
1043
1044 // The pointer should be aligned, so this assert should
1045 // always succeed.
1046 debug_assert_eq!(shared as usize & KIND_MASK, KIND_ARC);
1047
1048 self.data = shared;
1049 }
1050
1051 /// Makes an exact shallow clone of `self`.
1052 ///
1053 /// The kind of `self` doesn't matter, but this is unsafe
1054 /// because the clone will have the same offsets. You must
1055 /// be sure the returned value to the user doesn't allow
1056 /// two views into the same range.
1057 #[inline]
1058 unsafe fn shallow_clone(&mut self) -> BytesMut {
1059 if self.kind() == KIND_ARC {
1060 increment_shared(self.data);
1061 ptr::read(self)
1062 } else {
1063 self.promote_to_shared(/*ref_count = */ 2);
1064 ptr::read(self)
1065 }
1066 }
1067
1068 #[inline]
1069 unsafe fn get_vec_pos(&self) -> usize {
1070 debug_assert_eq!(self.kind(), KIND_VEC);
1071
1072 self.data as usize >> VEC_POS_OFFSET
1073 }
1074
1075 #[inline]
1076 unsafe fn set_vec_pos(&mut self, pos: usize) {
1077 debug_assert_eq!(self.kind(), KIND_VEC);
1078 debug_assert!(pos <= MAX_VEC_POS);
1079
1080 self.data = invalid_ptr((pos << VEC_POS_OFFSET) | (self.data as usize & NOT_VEC_POS_MASK));
1081 }
1082
1083 /// Returns the remaining spare capacity of the buffer as a slice of `MaybeUninit<u8>`.
1084 ///
1085 /// The returned slice can be used to fill the buffer with data (e.g. by
1086 /// reading from a file) before marking the data as initialized using the
1087 /// [`set_len`] method.
1088 ///
1089 /// [`set_len`]: BytesMut::set_len
1090 ///
1091 /// # Examples
1092 ///
1093 /// ```
1094 /// use bytes::BytesMut;
1095 ///
1096 /// // Allocate buffer big enough for 10 bytes.
1097 /// let mut buf = BytesMut::with_capacity(10);
1098 ///
1099 /// // Fill in the first 3 elements.
1100 /// let uninit = buf.spare_capacity_mut();
1101 /// uninit[0].write(0);
1102 /// uninit[1].write(1);
1103 /// uninit[2].write(2);
1104 ///
1105 /// // Mark the first 3 bytes of the buffer as being initialized.
1106 /// unsafe {
1107 /// buf.set_len(3);
1108 /// }
1109 ///
1110 /// assert_eq!(&buf[..], &[0, 1, 2]);
1111 /// ```
1112 #[inline]
1113 pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<u8>] {
1114 unsafe {
1115 let ptr = self.ptr.as_ptr().add(self.len);
1116 let len = self.cap - self.len;
1117
1118 slice::from_raw_parts_mut(ptr.cast(), len)
1119 }
1120 }
1121}
1122
1123impl Drop for BytesMut {
1124 fn drop(&mut self) {
1125 let kind: usize = self.kind();
1126
1127 if kind == KIND_VEC {
1128 unsafe {
1129 let off: usize = self.get_vec_pos();
1130
1131 // Vector storage, free the vector
1132 let _ = rebuild_vec(self.ptr.as_ptr(), self.len, self.cap, off);
1133 }
1134 } else if kind == KIND_ARC {
1135 unsafe { release_shared(self.data) };
1136 }
1137 }
1138}
1139
1140impl Buf for BytesMut {
1141 #[inline]
1142 fn remaining(&self) -> usize {
1143 self.len()
1144 }
1145
1146 #[inline]
1147 fn chunk(&self) -> &[u8] {
1148 self.as_slice()
1149 }
1150
1151 #[inline]
1152 fn advance(&mut self, cnt: usize) {
1153 assert!(
1154 cnt <= self.remaining(),
1155 "cannot advance past `remaining`: {:?} <= {:?}",
1156 cnt,
1157 self.remaining(),
1158 );
1159 unsafe {
1160 // SAFETY: We've checked that `cnt` <= `self.remaining()` and we know that
1161 // `self.remaining()` <= `self.cap`.
1162 self.advance_unchecked(cnt);
1163 }
1164 }
1165
1166 fn copy_to_bytes(&mut self, len: usize) -> Bytes {
1167 self.split_to(len).freeze()
1168 }
1169}
1170
1171unsafe impl BufMut for BytesMut {
1172 #[inline]
1173 fn remaining_mut(&self) -> usize {
1174 usize::MAX - self.len()
1175 }
1176
1177 #[inline]
1178 unsafe fn advance_mut(&mut self, cnt: usize) {
1179 let remaining = self.cap - self.len();
1180 if cnt > remaining {
1181 super::panic_advance(cnt, remaining);
1182 }
1183 // Addition won't overflow since it is at most `self.cap`.
1184 self.len = self.len() + cnt;
1185 }
1186
1187 #[inline]
1188 fn chunk_mut(&mut self) -> &mut UninitSlice {
1189 if self.capacity() == self.len() {
1190 self.reserve(64);
1191 }
1192 self.spare_capacity_mut().into()
1193 }
1194
1195 // Specialize these methods so they can skip checking `remaining_mut`
1196 // and `advance_mut`.
1197
1198 fn put<T: Buf>(&mut self, mut src: T)
1199 where
1200 Self: Sized,
1201 {
1202 while src.has_remaining() {
1203 let s = src.chunk();
1204 let l = s.len();
1205 self.extend_from_slice(s);
1206 src.advance(l);
1207 }
1208 }
1209
1210 fn put_slice(&mut self, src: &[u8]) {
1211 self.extend_from_slice(src);
1212 }
1213
1214 fn put_bytes(&mut self, val: u8, cnt: usize) {
1215 self.reserve(cnt);
1216 unsafe {
1217 let dst = self.spare_capacity_mut();
1218 // Reserved above
1219 debug_assert!(dst.len() >= cnt);
1220
1221 ptr::write_bytes(dst.as_mut_ptr(), val, cnt);
1222
1223 self.advance_mut(cnt);
1224 }
1225 }
1226}
1227
1228impl AsRef<[u8]> for BytesMut {
1229 #[inline]
1230 fn as_ref(&self) -> &[u8] {
1231 self.as_slice()
1232 }
1233}
1234
1235impl Deref for BytesMut {
1236 type Target = [u8];
1237
1238 #[inline]
1239 fn deref(&self) -> &[u8] {
1240 self.as_ref()
1241 }
1242}
1243
1244impl AsMut<[u8]> for BytesMut {
1245 #[inline]
1246 fn as_mut(&mut self) -> &mut [u8] {
1247 self.as_slice_mut()
1248 }
1249}
1250
1251impl DerefMut for BytesMut {
1252 #[inline]
1253 fn deref_mut(&mut self) -> &mut [u8] {
1254 self.as_mut()
1255 }
1256}
1257
1258impl<'a> From<&'a [u8]> for BytesMut {
1259 fn from(src: &'a [u8]) -> BytesMut {
1260 BytesMut::from_vec(src.to_vec())
1261 }
1262}
1263
1264impl<'a> From<&'a str> for BytesMut {
1265 fn from(src: &'a str) -> BytesMut {
1266 BytesMut::from(src.as_bytes())
1267 }
1268}
1269
1270impl From<BytesMut> for Bytes {
1271 fn from(src: BytesMut) -> Bytes {
1272 src.freeze()
1273 }
1274}
1275
1276impl PartialEq for BytesMut {
1277 fn eq(&self, other: &BytesMut) -> bool {
1278 self.as_slice() == other.as_slice()
1279 }
1280}
1281
1282impl PartialOrd for BytesMut {
1283 fn partial_cmp(&self, other: &BytesMut) -> Option<cmp::Ordering> {
1284 self.as_slice().partial_cmp(other.as_slice())
1285 }
1286}
1287
1288impl Ord for BytesMut {
1289 fn cmp(&self, other: &BytesMut) -> cmp::Ordering {
1290 self.as_slice().cmp(other.as_slice())
1291 }
1292}
1293
1294impl Eq for BytesMut {}
1295
1296impl Default for BytesMut {
1297 #[inline]
1298 fn default() -> BytesMut {
1299 BytesMut::new()
1300 }
1301}
1302
1303impl hash::Hash for BytesMut {
1304 fn hash<H>(&self, state: &mut H)
1305 where
1306 H: hash::Hasher,
1307 {
1308 let s: &[u8] = self.as_ref();
1309 s.hash(state);
1310 }
1311}
1312
1313impl Borrow<[u8]> for BytesMut {
1314 fn borrow(&self) -> &[u8] {
1315 self.as_ref()
1316 }
1317}
1318
1319impl BorrowMut<[u8]> for BytesMut {
1320 fn borrow_mut(&mut self) -> &mut [u8] {
1321 self.as_mut()
1322 }
1323}
1324
1325impl fmt::Write for BytesMut {
1326 #[inline]
1327 fn write_str(&mut self, s: &str) -> fmt::Result {
1328 if self.remaining_mut() >= s.len() {
1329 self.put_slice(src:s.as_bytes());
1330 Ok(())
1331 } else {
1332 Err(fmt::Error)
1333 }
1334 }
1335
1336 #[inline]
1337 fn write_fmt(&mut self, args: fmt::Arguments<'_>) -> fmt::Result {
1338 fmt::write(self, args)
1339 }
1340}
1341
1342impl Clone for BytesMut {
1343 fn clone(&self) -> BytesMut {
1344 BytesMut::from(&self[..])
1345 }
1346}
1347
1348impl IntoIterator for BytesMut {
1349 type Item = u8;
1350 type IntoIter = IntoIter<BytesMut>;
1351
1352 fn into_iter(self) -> Self::IntoIter {
1353 IntoIter::new(self)
1354 }
1355}
1356
1357impl<'a> IntoIterator for &'a BytesMut {
1358 type Item = &'a u8;
1359 type IntoIter = core::slice::Iter<'a, u8>;
1360
1361 fn into_iter(self) -> Self::IntoIter {
1362 self.as_ref().iter()
1363 }
1364}
1365
1366impl Extend<u8> for BytesMut {
1367 fn extend<T>(&mut self, iter: T)
1368 where
1369 T: IntoIterator<Item = u8>,
1370 {
1371 let iter: ::IntoIter = iter.into_iter();
1372
1373 let (lower: usize, _) = iter.size_hint();
1374 self.reserve(additional:lower);
1375
1376 // TODO: optimize
1377 // 1. If self.kind() == KIND_VEC, use Vec::extend
1378 for b: u8 in iter {
1379 self.put_u8(b);
1380 }
1381 }
1382}
1383
1384impl<'a> Extend<&'a u8> for BytesMut {
1385 fn extend<T>(&mut self, iter: T)
1386 where
1387 T: IntoIterator<Item = &'a u8>,
1388 {
1389 self.extend(iter.into_iter().copied())
1390 }
1391}
1392
1393impl Extend<Bytes> for BytesMut {
1394 fn extend<T>(&mut self, iter: T)
1395 where
1396 T: IntoIterator<Item = Bytes>,
1397 {
1398 for bytes: Bytes in iter {
1399 self.extend_from_slice(&bytes)
1400 }
1401 }
1402}
1403
1404impl FromIterator<u8> for BytesMut {
1405 fn from_iter<T: IntoIterator<Item = u8>>(into_iter: T) -> Self {
1406 BytesMut::from_vec(Vec::from_iter(into_iter))
1407 }
1408}
1409
1410impl<'a> FromIterator<&'a u8> for BytesMut {
1411 fn from_iter<T: IntoIterator<Item = &'a u8>>(into_iter: T) -> Self {
1412 BytesMut::from_iter(into_iter.into_iter().copied())
1413 }
1414}
1415
1416/*
1417 *
1418 * ===== Inner =====
1419 *
1420 */
1421
1422unsafe fn increment_shared(ptr: *mut Shared) {
1423 let old_size: usize = (*ptr).ref_count.fetch_add(val:1, order:Ordering::Relaxed);
1424
1425 if old_size > isize::MAX as usize {
1426 crate::abort();
1427 }
1428}
1429
1430unsafe fn release_shared(ptr: *mut Shared) {
1431 // `Shared` storage... follow the drop steps from Arc.
1432 if (*ptr).ref_count.fetch_sub(1, Ordering::Release) != 1 {
1433 return;
1434 }
1435
1436 // This fence is needed to prevent reordering of use of the data and
1437 // deletion of the data. Because it is marked `Release`, the decreasing
1438 // of the reference count synchronizes with this `Acquire` fence. This
1439 // means that use of the data happens before decreasing the reference
1440 // count, which happens before this fence, which happens before the
1441 // deletion of the data.
1442 //
1443 // As explained in the [Boost documentation][1],
1444 //
1445 // > It is important to enforce any possible access to the object in one
1446 // > thread (through an existing reference) to *happen before* deleting
1447 // > the object in a different thread. This is achieved by a "release"
1448 // > operation after dropping a reference (any access to the object
1449 // > through this reference must obviously happened before), and an
1450 // > "acquire" operation before deleting the object.
1451 //
1452 // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
1453 //
1454 // Thread sanitizer does not support atomic fences. Use an atomic load
1455 // instead.
1456 (*ptr).ref_count.load(Ordering::Acquire);
1457
1458 // Drop the data
1459 drop(Box::from_raw(ptr));
1460}
1461
1462impl Shared {
1463 fn is_unique(&self) -> bool {
1464 // The goal is to check if the current handle is the only handle
1465 // that currently has access to the buffer. This is done by
1466 // checking if the `ref_count` is currently 1.
1467 //
1468 // The `Acquire` ordering synchronizes with the `Release` as
1469 // part of the `fetch_sub` in `release_shared`. The `fetch_sub`
1470 // operation guarantees that any mutations done in other threads
1471 // are ordered before the `ref_count` is decremented. As such,
1472 // this `Acquire` will guarantee that those mutations are
1473 // visible to the current thread.
1474 self.ref_count.load(order:Ordering::Acquire) == 1
1475 }
1476}
1477
1478#[inline]
1479fn original_capacity_to_repr(cap: usize) -> usize {
1480 let width: usize = PTR_WIDTH - ((cap >> MIN_ORIGINAL_CAPACITY_WIDTH).leading_zeros() as usize);
1481 cmp::min(
1482 v1:width,
1483 MAX_ORIGINAL_CAPACITY_WIDTH - MIN_ORIGINAL_CAPACITY_WIDTH,
1484 )
1485}
1486
1487fn original_capacity_from_repr(repr: usize) -> usize {
1488 if repr == 0 {
1489 return 0;
1490 }
1491
1492 1 << (repr + (MIN_ORIGINAL_CAPACITY_WIDTH - 1))
1493}
1494
1495#[cfg(test)]
1496mod tests {
1497 use super::*;
1498
1499 #[test]
1500 fn test_original_capacity_to_repr() {
1501 assert_eq!(original_capacity_to_repr(0), 0);
1502
1503 let max_width = 32;
1504
1505 for width in 1..(max_width + 1) {
1506 let cap = 1 << width - 1;
1507
1508 let expected = if width < MIN_ORIGINAL_CAPACITY_WIDTH {
1509 0
1510 } else if width < MAX_ORIGINAL_CAPACITY_WIDTH {
1511 width - MIN_ORIGINAL_CAPACITY_WIDTH
1512 } else {
1513 MAX_ORIGINAL_CAPACITY_WIDTH - MIN_ORIGINAL_CAPACITY_WIDTH
1514 };
1515
1516 assert_eq!(original_capacity_to_repr(cap), expected);
1517
1518 if width > 1 {
1519 assert_eq!(original_capacity_to_repr(cap + 1), expected);
1520 }
1521
1522 // MIN_ORIGINAL_CAPACITY_WIDTH must be bigger than 7 to pass tests below
1523 if width == MIN_ORIGINAL_CAPACITY_WIDTH + 1 {
1524 assert_eq!(original_capacity_to_repr(cap - 24), expected - 1);
1525 assert_eq!(original_capacity_to_repr(cap + 76), expected);
1526 } else if width == MIN_ORIGINAL_CAPACITY_WIDTH + 2 {
1527 assert_eq!(original_capacity_to_repr(cap - 1), expected - 1);
1528 assert_eq!(original_capacity_to_repr(cap - 48), expected - 1);
1529 }
1530 }
1531 }
1532
1533 #[test]
1534 fn test_original_capacity_from_repr() {
1535 assert_eq!(0, original_capacity_from_repr(0));
1536
1537 let min_cap = 1 << MIN_ORIGINAL_CAPACITY_WIDTH;
1538
1539 assert_eq!(min_cap, original_capacity_from_repr(1));
1540 assert_eq!(min_cap * 2, original_capacity_from_repr(2));
1541 assert_eq!(min_cap * 4, original_capacity_from_repr(3));
1542 assert_eq!(min_cap * 8, original_capacity_from_repr(4));
1543 assert_eq!(min_cap * 16, original_capacity_from_repr(5));
1544 assert_eq!(min_cap * 32, original_capacity_from_repr(6));
1545 assert_eq!(min_cap * 64, original_capacity_from_repr(7));
1546 }
1547}
1548
1549unsafe impl Send for BytesMut {}
1550unsafe impl Sync for BytesMut {}
1551
1552/*
1553 *
1554 * ===== PartialEq / PartialOrd =====
1555 *
1556 */
1557
1558impl PartialEq<[u8]> for BytesMut {
1559 fn eq(&self, other: &[u8]) -> bool {
1560 &**self == other
1561 }
1562}
1563
1564impl PartialOrd<[u8]> for BytesMut {
1565 fn partial_cmp(&self, other: &[u8]) -> Option<cmp::Ordering> {
1566 (**self).partial_cmp(other)
1567 }
1568}
1569
1570impl PartialEq<BytesMut> for [u8] {
1571 fn eq(&self, other: &BytesMut) -> bool {
1572 *other == *self
1573 }
1574}
1575
1576impl PartialOrd<BytesMut> for [u8] {
1577 fn partial_cmp(&self, other: &BytesMut) -> Option<cmp::Ordering> {
1578 <[u8] as PartialOrd<[u8]>>::partial_cmp(self, other)
1579 }
1580}
1581
1582impl PartialEq<str> for BytesMut {
1583 fn eq(&self, other: &str) -> bool {
1584 &**self == other.as_bytes()
1585 }
1586}
1587
1588impl PartialOrd<str> for BytesMut {
1589 fn partial_cmp(&self, other: &str) -> Option<cmp::Ordering> {
1590 (**self).partial_cmp(other.as_bytes())
1591 }
1592}
1593
1594impl PartialEq<BytesMut> for str {
1595 fn eq(&self, other: &BytesMut) -> bool {
1596 *other == *self
1597 }
1598}
1599
1600impl PartialOrd<BytesMut> for str {
1601 fn partial_cmp(&self, other: &BytesMut) -> Option<cmp::Ordering> {
1602 <[u8] as PartialOrd<[u8]>>::partial_cmp(self.as_bytes(), other)
1603 }
1604}
1605
1606impl PartialEq<Vec<u8>> for BytesMut {
1607 fn eq(&self, other: &Vec<u8>) -> bool {
1608 *self == other[..]
1609 }
1610}
1611
1612impl PartialOrd<Vec<u8>> for BytesMut {
1613 fn partial_cmp(&self, other: &Vec<u8>) -> Option<cmp::Ordering> {
1614 (**self).partial_cmp(&other[..])
1615 }
1616}
1617
1618impl PartialEq<BytesMut> for Vec<u8> {
1619 fn eq(&self, other: &BytesMut) -> bool {
1620 *other == *self
1621 }
1622}
1623
1624impl PartialOrd<BytesMut> for Vec<u8> {
1625 fn partial_cmp(&self, other: &BytesMut) -> Option<cmp::Ordering> {
1626 other.partial_cmp(self)
1627 }
1628}
1629
1630impl PartialEq<String> for BytesMut {
1631 fn eq(&self, other: &String) -> bool {
1632 *self == other[..]
1633 }
1634}
1635
1636impl PartialOrd<String> for BytesMut {
1637 fn partial_cmp(&self, other: &String) -> Option<cmp::Ordering> {
1638 (**self).partial_cmp(other.as_bytes())
1639 }
1640}
1641
1642impl PartialEq<BytesMut> for String {
1643 fn eq(&self, other: &BytesMut) -> bool {
1644 *other == *self
1645 }
1646}
1647
1648impl PartialOrd<BytesMut> for String {
1649 fn partial_cmp(&self, other: &BytesMut) -> Option<cmp::Ordering> {
1650 <[u8] as PartialOrd<[u8]>>::partial_cmp(self.as_bytes(), other)
1651 }
1652}
1653
1654impl<'a, T: ?Sized> PartialEq<&'a T> for BytesMut
1655where
1656 BytesMut: PartialEq<T>,
1657{
1658 fn eq(&self, other: &&'a T) -> bool {
1659 *self == **other
1660 }
1661}
1662
1663impl<'a, T: ?Sized> PartialOrd<&'a T> for BytesMut
1664where
1665 BytesMut: PartialOrd<T>,
1666{
1667 fn partial_cmp(&self, other: &&'a T) -> Option<cmp::Ordering> {
1668 self.partial_cmp(*other)
1669 }
1670}
1671
1672impl PartialEq<BytesMut> for &[u8] {
1673 fn eq(&self, other: &BytesMut) -> bool {
1674 *other == *self
1675 }
1676}
1677
1678impl PartialOrd<BytesMut> for &[u8] {
1679 fn partial_cmp(&self, other: &BytesMut) -> Option<cmp::Ordering> {
1680 <[u8] as PartialOrd<[u8]>>::partial_cmp(self, other)
1681 }
1682}
1683
1684impl PartialEq<BytesMut> for &str {
1685 fn eq(&self, other: &BytesMut) -> bool {
1686 *other == *self
1687 }
1688}
1689
1690impl PartialOrd<BytesMut> for &str {
1691 fn partial_cmp(&self, other: &BytesMut) -> Option<cmp::Ordering> {
1692 other.partial_cmp(self)
1693 }
1694}
1695
1696impl PartialEq<BytesMut> for Bytes {
1697 fn eq(&self, other: &BytesMut) -> bool {
1698 other[..] == self[..]
1699 }
1700}
1701
1702impl PartialEq<Bytes> for BytesMut {
1703 fn eq(&self, other: &Bytes) -> bool {
1704 other[..] == self[..]
1705 }
1706}
1707
1708impl From<BytesMut> for Vec<u8> {
1709 fn from(bytes: BytesMut) -> Self {
1710 let kind = bytes.kind();
1711 let bytes = ManuallyDrop::new(bytes);
1712
1713 let mut vec = if kind == KIND_VEC {
1714 unsafe {
1715 let off = bytes.get_vec_pos();
1716 rebuild_vec(bytes.ptr.as_ptr(), bytes.len, bytes.cap, off)
1717 }
1718 } else {
1719 let shared = bytes.data as *mut Shared;
1720
1721 if unsafe { (*shared).is_unique() } {
1722 let vec = mem::replace(unsafe { &mut (*shared).vec }, Vec::new());
1723
1724 unsafe { release_shared(shared) };
1725
1726 vec
1727 } else {
1728 return ManuallyDrop::into_inner(bytes).deref().to_vec();
1729 }
1730 };
1731
1732 let len = bytes.len;
1733
1734 unsafe {
1735 ptr::copy(bytes.ptr.as_ptr(), vec.as_mut_ptr(), len);
1736 vec.set_len(len);
1737 }
1738
1739 vec
1740 }
1741}
1742
1743#[inline]
1744fn vptr(ptr: *mut u8) -> NonNull<u8> {
1745 if cfg!(debug_assertions) {
1746 NonNull::new(ptr).expect(msg:"Vec pointer should be non-null")
1747 } else {
1748 unsafe { NonNull::new_unchecked(ptr) }
1749 }
1750}
1751
1752/// Returns a dangling pointer with the given address. This is used to store
1753/// integer data in pointer fields.
1754///
1755/// It is equivalent to `addr as *mut T`, but this fails on miri when strict
1756/// provenance checking is enabled.
1757#[inline]
1758fn invalid_ptr<T>(addr: usize) -> *mut T {
1759 let ptr: *mut u8 = core::ptr::null_mut::<u8>().wrapping_add(count:addr);
1760 debug_assert_eq!(ptr as usize, addr);
1761 ptr.cast::<T>()
1762}
1763
1764unsafe fn rebuild_vec(ptr: *mut u8, mut len: usize, mut cap: usize, off: usize) -> Vec<u8> {
1765 let ptr: *mut u8 = ptr.sub(count:off);
1766 len += off;
1767 cap += off;
1768
1769 Vec::from_raw_parts(ptr, length:len, capacity:cap)
1770}
1771
1772// ===== impl SharedVtable =====
1773
1774static SHARED_VTABLE: Vtable = Vtable {
1775 clone: shared_v_clone,
1776 to_vec: shared_v_to_vec,
1777 to_mut: shared_v_to_mut,
1778 is_unique: shared_v_is_unique,
1779 drop: shared_v_drop,
1780};
1781
1782unsafe fn shared_v_clone(data: &AtomicPtr<()>, ptr: *const u8, len: usize) -> Bytes {
1783 let shared: *mut Shared = data.load(order:Ordering::Relaxed) as *mut Shared;
1784 increment_shared(ptr:shared);
1785
1786 let data: AtomicPtr<()> = AtomicPtr::new(shared as *mut ());
1787 Bytes::with_vtable(ptr, len, data, &SHARED_VTABLE)
1788}
1789
1790unsafe fn shared_v_to_vec(data: &AtomicPtr<()>, ptr: *const u8, len: usize) -> Vec<u8> {
1791 let shared: *mut Shared = data.load(order:Ordering::Relaxed).cast();
1792
1793 if (*shared).is_unique() {
1794 let shared: &mut Shared = &mut *shared;
1795
1796 // Drop shared
1797 let mut vec: Vec = mem::replace(&mut shared.vec, src:Vec::new());
1798 release_shared(ptr:shared);
1799
1800 // Copy back buffer
1801 ptr::copy(src:ptr, dst:vec.as_mut_ptr(), count:len);
1802 vec.set_len(len);
1803
1804 vec
1805 } else {
1806 let v: Vec = slice::from_raw_parts(data:ptr, len).to_vec();
1807 release_shared(ptr:shared);
1808 v
1809 }
1810}
1811
1812unsafe fn shared_v_to_mut(data: &AtomicPtr<()>, ptr: *const u8, len: usize) -> BytesMut {
1813 let shared: *mut Shared = data.load(Ordering::Relaxed).cast();
1814
1815 if (*shared).is_unique() {
1816 let shared = &mut *shared;
1817
1818 // The capacity is always the original capacity of the buffer
1819 // minus the offset from the start of the buffer
1820 let v = &mut shared.vec;
1821 let v_capacity = v.capacity();
1822 let v_ptr = v.as_mut_ptr();
1823 let offset = offset_from(ptr as *mut u8, v_ptr);
1824 let cap = v_capacity - offset;
1825
1826 let ptr = vptr(ptr as *mut u8);
1827
1828 BytesMut {
1829 ptr,
1830 len,
1831 cap,
1832 data: shared,
1833 }
1834 } else {
1835 let v = slice::from_raw_parts(ptr, len).to_vec();
1836 release_shared(shared);
1837 BytesMut::from_vec(v)
1838 }
1839}
1840
1841unsafe fn shared_v_is_unique(data: &AtomicPtr<()>) -> bool {
1842 let shared: *mut () = data.load(order:Ordering::Acquire);
1843 let ref_count: usize = (*shared.cast::<Shared>()).ref_count.load(order:Ordering::Relaxed);
1844 ref_count == 1
1845}
1846
1847unsafe fn shared_v_drop(data: &mut AtomicPtr<()>, _ptr: *const u8, _len: usize) {
1848 data.with_mut(|shared: &mut *mut ()| {
1849 release_shared(*shared as *mut Shared);
1850 });
1851}
1852
1853// compile-fails
1854
1855/// ```compile_fail
1856/// use bytes::BytesMut;
1857/// #[deny(unused_must_use)]
1858/// {
1859/// let mut b1 = BytesMut::from("hello world");
1860/// b1.split_to(6);
1861/// }
1862/// ```
1863fn _split_to_must_use() {}
1864
1865/// ```compile_fail
1866/// use bytes::BytesMut;
1867/// #[deny(unused_must_use)]
1868/// {
1869/// let mut b1 = BytesMut::from("hello world");
1870/// b1.split_off(6);
1871/// }
1872/// ```
1873fn _split_off_must_use() {}
1874
1875/// ```compile_fail
1876/// use bytes::BytesMut;
1877/// #[deny(unused_must_use)]
1878/// {
1879/// let mut b1 = BytesMut::from("hello world");
1880/// b1.split();
1881/// }
1882/// ```
1883fn _split_must_use() {}
1884
1885// fuzz tests
1886#[cfg(all(test, loom))]
1887mod fuzz {
1888 use loom::sync::Arc;
1889 use loom::thread;
1890
1891 use super::BytesMut;
1892 use crate::Bytes;
1893
1894 #[test]
1895 fn bytes_mut_cloning_frozen() {
1896 loom::model(|| {
1897 let a = BytesMut::from(&b"abcdefgh"[..]).split().freeze();
1898 let addr = a.as_ptr() as usize;
1899
1900 // test the Bytes::clone is Sync by putting it in an Arc
1901 let a1 = Arc::new(a);
1902 let a2 = a1.clone();
1903
1904 let t1 = thread::spawn(move || {
1905 let b: Bytes = (*a1).clone();
1906 assert_eq!(b.as_ptr() as usize, addr);
1907 });
1908
1909 let t2 = thread::spawn(move || {
1910 let b: Bytes = (*a2).clone();
1911 assert_eq!(b.as_ptr() as usize, addr);
1912 });
1913
1914 t1.join().unwrap();
1915 t2.join().unwrap();
1916 });
1917 }
1918}
1919