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/*
* Copyright 2004 The WebRTC Project Authors. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#ifndef RTC_BASE_BUFFER_H_
#define RTC_BASE_BUFFER_H_
#include <stdint.h>
#include <algorithm>
#include <cstring>
#include <memory>
#include <type_traits>
#include <utility>
#include "absl/strings/string_view.h"
#include "api/array_view.h"
#include "rtc_base/checks.h"
#include "rtc_base/type_traits.h"
#include "rtc_base/zero_memory.h"
namespace rtc {
namespace internal {
// (Internal; please don't use outside this file.) Determines if elements of
// type U are compatible with a BufferT<T>. For most types, we just ignore
// top-level const and forbid top-level volatile and require T and U to be
// otherwise equal, but all byte-sized integers (notably char, int8_t, and
// uint8_t) are compatible with each other. (Note: We aim to get rid of this
// behavior, and treat all types the same.)
template <typename T, typename U>
struct BufferCompat {
static constexpr bool value =
!std::is_volatile<U>::value &&
((std::is_integral<T>::value && sizeof(T) == 1)
? (std::is_integral<U>::value && sizeof(U) == 1)
: (std::is_same<T, typename std::remove_const<U>::type>::value));
};
} // namespace internal
// Basic buffer class, can be grown and shrunk dynamically.
// Unlike std::string/vector, does not initialize data when increasing size.
// If "ZeroOnFree" is true, any memory is explicitly cleared before releasing.
// The type alias "ZeroOnFreeBuffer" below should be used instead of setting
// "ZeroOnFree" in the template manually to "true".
template <typename T, bool ZeroOnFree = false>
class BufferT {
// We want T's destructor and default constructor to be trivial, i.e. perform
// no action, so that we don't have to touch the memory we allocate and
// deallocate. And we want T to be trivially copyable, so that we can copy T
// instances with std::memcpy. This is precisely the definition of a trivial
// type.
static_assert(std::is_trivial<T>::value, "T must be a trivial type.");
// This class relies heavily on being able to mutate its data.
static_assert(!std::is_const<T>::value, "T may not be const");
public:
using value_type = T;
using const_iterator = const T*;
// An empty BufferT.
BufferT() : size_(0), capacity_(0), data_(nullptr) {
RTC_DCHECK(IsConsistent());
}
// Disable copy construction and copy assignment, since copying a buffer is
// expensive enough that we want to force the user to be explicit about it.
BufferT(const BufferT&) = delete;
BufferT& operator=(const BufferT&) = delete;
BufferT(BufferT&& buf)
: size_(buf.size()),
capacity_(buf.capacity()),
data_(std::move(buf.data_)) {
RTC_DCHECK(IsConsistent());
buf.OnMovedFrom();
}
// Construct a buffer with the specified number of uninitialized elements.
explicit BufferT(size_t size) : BufferT(size, size) {}
BufferT(size_t size, size_t capacity)
: size_(size),
capacity_(std::max(size, capacity)),
data_(capacity_ > 0 ? new T[capacity_] : nullptr) {
RTC_DCHECK(IsConsistent());
}
// Construct a buffer and copy the specified number of elements into it.
template <typename U,
typename std::enable_if<
internal::BufferCompat<T, U>::value>::type* = nullptr>
BufferT(const U* data, size_t size) : BufferT(data, size, size) {}
template <typename U,
typename std::enable_if<
internal::BufferCompat<T, U>::value>::type* = nullptr>
BufferT(U* data, size_t size, size_t capacity) : BufferT(size, capacity) {
static_assert(sizeof(T) == sizeof(U), "");
if (size > 0) {
RTC_DCHECK(data);
std::memcpy(data_.get(), data, size * sizeof(U));
}
}
// Construct a buffer from the contents of an array.
template <typename U,
size_t N,
typename std::enable_if<
internal::BufferCompat<T, U>::value>::type* = nullptr>
BufferT(U (&array)[N]) : BufferT(array, N) {}
~BufferT() { MaybeZeroCompleteBuffer(); }
// Implicit conversion to absl::string_view if T is compatible with char.
template <typename U = T>
operator typename std::enable_if<internal::BufferCompat<U, char>::value,
absl::string_view>::type() const {
return absl::string_view(data<char>(), size());
}
// Get a pointer to the data. Just .data() will give you a (const) T*, but if
// T is a byte-sized integer, you may also use .data<U>() for any other
// byte-sized integer U.
template <typename U = T,
typename std::enable_if<
internal::BufferCompat<T, U>::value>::type* = nullptr>
const U* data() const {
RTC_DCHECK(IsConsistent());
return reinterpret_cast<U*>(data_.get());
}
template <typename U = T,
typename std::enable_if<
internal::BufferCompat<T, U>::value>::type* = nullptr>
U* data() {
RTC_DCHECK(IsConsistent());
return reinterpret_cast<U*>(data_.get());
}
bool empty() const {
RTC_DCHECK(IsConsistent());
return size_ == 0;
}
size_t size() const {
RTC_DCHECK(IsConsistent());
return size_;
}
size_t capacity() const {
RTC_DCHECK(IsConsistent());
return capacity_;
}
BufferT& operator=(BufferT&& buf) {
RTC_DCHECK(buf.IsConsistent());
MaybeZeroCompleteBuffer();
size_ = buf.size_;
capacity_ = buf.capacity_;
using std::swap;
swap(data_, buf.data_);
buf.data_.reset();
buf.OnMovedFrom();
return *this;
}
bool operator==(const BufferT& buf) const {
RTC_DCHECK(IsConsistent());
if (size_ != buf.size_) {
return false;
}
if (std::is_integral<T>::value) {
// Optimization.
return std::memcmp(data_.get(), buf.data_.get(), size_ * sizeof(T)) == 0;
}
for (size_t i = 0; i < size_; ++i) {
if (data_[i] != buf.data_[i]) {
return false;
}
}
return true;
}
bool operator!=(const BufferT& buf) const { return !(*this == buf); }
T& operator[](size_t index) {
RTC_DCHECK_LT(index, size_);
return data()[index];
}
T operator[](size_t index) const {
RTC_DCHECK_LT(index, size_);
return data()[index];
}
T* begin() { return data(); }
T* end() { return data() + size(); }
const T* begin() const { return data(); }
const T* end() const { return data() + size(); }
const T* cbegin() const { return data(); }
const T* cend() const { return data() + size(); }
// The SetData functions replace the contents of the buffer. They accept the
// same input types as the constructors.
template <typename U,
typename std::enable_if<
internal::BufferCompat<T, U>::value>::type* = nullptr>
void SetData(const U* data, size_t size) {
RTC_DCHECK(IsConsistent());
const size_t old_size = size_;
size_ = 0;
AppendData(data, size);
if (ZeroOnFree && size_ < old_size) {
ZeroTrailingData(old_size - size_);
}
}
template <typename U,
size_t N,
typename std::enable_if<
internal::BufferCompat<T, U>::value>::type* = nullptr>
void SetData(const U (&array)[N]) {
SetData(array, N);
}
template <typename W,
typename std::enable_if<
HasDataAndSize<const W, const T>::value>::type* = nullptr>
void SetData(const W& w) {
SetData(w.data(), w.size());
}
// Replaces the data in the buffer with at most `max_elements` of data, using
// the function `setter`, which should have the following signature:
//
// size_t setter(ArrayView<U> view)
//
// `setter` is given an appropriately typed ArrayView of length exactly
// `max_elements` that describes the area where it should write the data; it
// should return the number of elements actually written. (If it doesn't fill
// the whole ArrayView, it should leave the unused space at the end.)
template <typename U = T,
typename F,
typename std::enable_if<
internal::BufferCompat<T, U>::value>::type* = nullptr>
size_t SetData(size_t max_elements, F&& setter) {
RTC_DCHECK(IsConsistent());
const size_t old_size = size_;
size_ = 0;
const size_t written = AppendData<U>(max_elements, std::forward<F>(setter));
if (ZeroOnFree && size_ < old_size) {
ZeroTrailingData(old_size - size_);
}
return written;
}
// The AppendData functions add data to the end of the buffer. They accept
// the same input types as the constructors.
template <typename U,
typename std::enable_if<
internal::BufferCompat<T, U>::value>::type* = nullptr>
void AppendData(const U* data, size_t size) {
if (size == 0) {
return;
}
RTC_DCHECK(data);
RTC_DCHECK(IsConsistent());
const size_t new_size = size_ + size;
EnsureCapacityWithHeadroom(new_size, true);
static_assert(sizeof(T) == sizeof(U), "");
std::memcpy(data_.get() + size_, data, size * sizeof(U));
size_ = new_size;
RTC_DCHECK(IsConsistent());
}
template <typename U,
size_t N,
typename std::enable_if<
internal::BufferCompat<T, U>::value>::type* = nullptr>
void AppendData(const U (&array)[N]) {
AppendData(array, N);
}
template <typename W,
typename std::enable_if<
HasDataAndSize<const W, const T>::value>::type* = nullptr>
void AppendData(const W& w) {
AppendData(w.data(), w.size());
}
template <typename U,
typename std::enable_if<
internal::BufferCompat<T, U>::value>::type* = nullptr>
void AppendData(const U& item) {
AppendData(&item, 1);
}
// Appends at most `max_elements` to the end of the buffer, using the function
// `setter`, which should have the following signature:
//
// size_t setter(ArrayView<U> view)
//
// `setter` is given an appropriately typed ArrayView of length exactly
// `max_elements` that describes the area where it should write the data; it
// should return the number of elements actually written. (If it doesn't fill
// the whole ArrayView, it should leave the unused space at the end.)
template <typename U = T,
typename F,
typename std::enable_if<
internal::BufferCompat<T, U>::value>::type* = nullptr>
size_t AppendData(size_t max_elements, F&& setter) {
RTC_DCHECK(IsConsistent());
const size_t old_size = size_;
SetSize(old_size + max_elements);
U* base_ptr = data<U>() + old_size;
size_t written_elements = setter(rtc::ArrayView<U>(base_ptr, max_elements));
RTC_CHECK_LE(written_elements, max_elements);
size_ = old_size + written_elements;
RTC_DCHECK(IsConsistent());
return written_elements;
}
// Sets the size of the buffer. If the new size is smaller than the old, the
// buffer contents will be kept but truncated; if the new size is greater,
// the existing contents will be kept and the new space will be
// uninitialized.
void SetSize(size_t size) {
const size_t old_size = size_;
EnsureCapacityWithHeadroom(size, true);
size_ = size;
if (ZeroOnFree && size_ < old_size) {
ZeroTrailingData(old_size - size_);
}
}
// Ensure that the buffer size can be increased to at least capacity without
// further reallocation. (Of course, this operation might need to reallocate
// the buffer.)
void EnsureCapacity(size_t capacity) {
// Don't allocate extra headroom, since the user is asking for a specific
// capacity.
EnsureCapacityWithHeadroom(capacity, false);
}
// Resets the buffer to zero size without altering capacity. Works even if the
// buffer has been moved from.
void Clear() {
MaybeZeroCompleteBuffer();
size_ = 0;
RTC_DCHECK(IsConsistent());
}
// Swaps two buffers. Also works for buffers that have been moved from.
friend void swap(BufferT& a, BufferT& b) {
using std::swap;
swap(a.size_, b.size_);
swap(a.capacity_, b.capacity_);
swap(a.data_, b.data_);
}
private:
void EnsureCapacityWithHeadroom(size_t capacity, bool extra_headroom) {
RTC_DCHECK(IsConsistent());
if (capacity <= capacity_)
return;
// If the caller asks for extra headroom, ensure that the new capacity is
// >= 1.5 times the old capacity. Any constant > 1 is sufficient to prevent
// quadratic behavior; as to why we pick 1.5 in particular, see
// https://github.com/facebook/folly/blob/master/folly/docs/FBVector.md and
// http://www.gahcep.com/cpp-internals-stl-vector-part-1/.
const size_t new_capacity =
extra_headroom ? std::max(capacity, capacity_ + capacity_ / 2)
: capacity;
std::unique_ptr<T[]> new_data(new T[new_capacity]);
if (data_ != nullptr) {
std::memcpy(new_data.get(), data_.get(), size_ * sizeof(T));
}
MaybeZeroCompleteBuffer();
data_ = std::move(new_data);
capacity_ = new_capacity;
RTC_DCHECK(IsConsistent());
}
// Zero the complete buffer if template argument "ZeroOnFree" is true.
void MaybeZeroCompleteBuffer() {
if (ZeroOnFree && capacity_ > 0) {
// It would be sufficient to only zero "size_" elements, as all other
// methods already ensure that the unused capacity contains no sensitive
// data---but better safe than sorry.
ExplicitZeroMemory(data_.get(), capacity_ * sizeof(T));
}
}
// Zero the first "count" elements of unused capacity.
void ZeroTrailingData(size_t count) {
RTC_DCHECK(IsConsistent());
RTC_DCHECK_LE(count, capacity_ - size_);
ExplicitZeroMemory(data_.get() + size_, count * sizeof(T));
}
// Precondition for all methods except Clear, operator= and the destructor.
// Postcondition for all methods except move construction and move
// assignment, which leave the moved-from object in a possibly inconsistent
// state.
bool IsConsistent() const {
return (data_ || capacity_ == 0) && capacity_ >= size_;
}
// Called when *this has been moved from. Conceptually it's a no-op, but we
// can mutate the state slightly to help subsequent sanity checks catch bugs.
void OnMovedFrom() {
RTC_DCHECK(!data_); // Our heap block should have been stolen.
#if RTC_DCHECK_IS_ON
// Ensure that *this is always inconsistent, to provoke bugs.
size_ = 1;
capacity_ = 0;
#else
// Make *this consistent and empty. Shouldn't be necessary, but better safe
// than sorry.
size_ = 0;
capacity_ = 0;
#endif
}
size_t size_;
size_t capacity_;
std::unique_ptr<T[]> data_;
};
// By far the most common sort of buffer.
using Buffer = BufferT<uint8_t>;
// A buffer that zeros memory before releasing it.
template <typename T>
using ZeroOnFreeBuffer = BufferT<T, true>;
} // namespace rtc
#endif // RTC_BASE_BUFFER_H_