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/*
* Copyright 2016 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_COPY_ON_WRITE_BUFFER_H_
#define RTC_BASE_COPY_ON_WRITE_BUFFER_H_
#include <stdint.h>
#include <algorithm>
#include <cstring>
#include <string>
#include <type_traits>
#include <utility>
#include "absl/strings/string_view.h"
#include "api/scoped_refptr.h"
#include "rtc_base/buffer.h"
#include "rtc_base/checks.h"
#include "rtc_base/ref_counted_object.h"
#include "rtc_base/system/rtc_export.h"
#include "rtc_base/type_traits.h"
namespace rtc {
class RTC_EXPORT CopyOnWriteBuffer {
public:
// An empty buffer.
CopyOnWriteBuffer();
// Share the data with an existing buffer.
CopyOnWriteBuffer(const CopyOnWriteBuffer& buf);
// Move contents from an existing buffer.
CopyOnWriteBuffer(CopyOnWriteBuffer&& buf) noexcept;
// Construct a buffer from a string, convenient for unittests.
explicit CopyOnWriteBuffer(absl::string_view s);
// Construct a buffer with the specified number of uninitialized bytes.
explicit CopyOnWriteBuffer(size_t size);
CopyOnWriteBuffer(size_t size, size_t capacity);
// Construct a buffer and copy the specified number of bytes into it. The
// source array may be (const) uint8_t*, int8_t*, or char*.
template <typename T,
typename std::enable_if<
internal::BufferCompat<uint8_t, T>::value>::type* = nullptr>
CopyOnWriteBuffer(const T* data, size_t size)
: CopyOnWriteBuffer(data, size, size) {}
template <typename T,
typename std::enable_if<
internal::BufferCompat<uint8_t, T>::value>::type* = nullptr>
CopyOnWriteBuffer(const T* data, size_t size, size_t capacity)
: CopyOnWriteBuffer(size, capacity) {
if (buffer_) {
std::memcpy(buffer_->data(), data, size);
offset_ = 0;
size_ = size;
}
}
// Construct a buffer from the contents of an array.
template <typename T,
size_t N,
typename std::enable_if<
internal::BufferCompat<uint8_t, T>::value>::type* = nullptr>
CopyOnWriteBuffer(const T (&array)[N]) // NOLINT: runtime/explicit
: CopyOnWriteBuffer(array, N) {}
// Construct a buffer from a vector like type.
template <typename VecT,
typename ElemT = typename std::remove_pointer_t<
decltype(std::declval<VecT>().data())>,
typename std::enable_if_t<
!std::is_same<VecT, CopyOnWriteBuffer>::value &&
HasDataAndSize<VecT, ElemT>::value &&
internal::BufferCompat<uint8_t, ElemT>::value>* = nullptr>
explicit CopyOnWriteBuffer(const VecT& v)
: CopyOnWriteBuffer(v.data(), v.size()) {}
~CopyOnWriteBuffer();
// Get a pointer to the data. Just .data() will give you a (const) uint8_t*,
// but you may also use .data<int8_t>() and .data<char>().
template <typename T = uint8_t,
typename std::enable_if<
internal::BufferCompat<uint8_t, T>::value>::type* = nullptr>
const T* data() const {
return cdata<T>();
}
// Get writable pointer to the data. This will create a copy of the underlying
// data if it is shared with other buffers.
template <typename T = uint8_t,
typename std::enable_if<
internal::BufferCompat<uint8_t, T>::value>::type* = nullptr>
T* MutableData() {
RTC_DCHECK(IsConsistent());
if (!buffer_) {
return nullptr;
}
UnshareAndEnsureCapacity(capacity());
return buffer_->data<T>() + offset_;
}
// Get const pointer to the data. This will not create a copy of the
// underlying data if it is shared with other buffers.
template <typename T = uint8_t,
typename std::enable_if<
internal::BufferCompat<uint8_t, T>::value>::type* = nullptr>
const T* cdata() const {
RTC_DCHECK(IsConsistent());
if (!buffer_) {
return nullptr;
}
return buffer_->data<T>() + offset_;
}
size_t size() const {
RTC_DCHECK(IsConsistent());
return size_;
}
size_t capacity() const {
RTC_DCHECK(IsConsistent());
return buffer_ ? buffer_->capacity() - offset_ : 0;
}
CopyOnWriteBuffer& operator=(const CopyOnWriteBuffer& buf) {
RTC_DCHECK(IsConsistent());
RTC_DCHECK(buf.IsConsistent());
if (&buf != this) {
buffer_ = buf.buffer_;
offset_ = buf.offset_;
size_ = buf.size_;
}
return *this;
}
CopyOnWriteBuffer& operator=(CopyOnWriteBuffer&& buf) {
RTC_DCHECK(IsConsistent());
RTC_DCHECK(buf.IsConsistent());
buffer_ = std::move(buf.buffer_);
offset_ = buf.offset_;
size_ = buf.size_;
buf.offset_ = 0;
buf.size_ = 0;
return *this;
}
bool operator==(const CopyOnWriteBuffer& buf) const;
bool operator!=(const CopyOnWriteBuffer& buf) const {
return !(*this == buf);
}
uint8_t operator[](size_t index) const {
RTC_DCHECK_LT(index, size());
return cdata()[index];
}
// Replace the contents of the buffer. Accepts the same types as the
// constructors.
template <typename T,
typename std::enable_if<
internal::BufferCompat<uint8_t, T>::value>::type* = nullptr>
void SetData(const T* data, size_t size) {
RTC_DCHECK(IsConsistent());
if (!buffer_) {
buffer_ = size > 0 ? new RefCountedBuffer(data, size) : nullptr;
} else if (!buffer_->HasOneRef()) {
buffer_ = new RefCountedBuffer(data, size, capacity());
} else {
buffer_->SetData(data, size);
}
offset_ = 0;
size_ = size;
RTC_DCHECK(IsConsistent());
}
template <typename T,
size_t N,
typename std::enable_if<
internal::BufferCompat<uint8_t, T>::value>::type* = nullptr>
void SetData(const T (&array)[N]) {
SetData(array, N);
}
void SetData(const CopyOnWriteBuffer& buf) {
RTC_DCHECK(IsConsistent());
RTC_DCHECK(buf.IsConsistent());
if (&buf != this) {
buffer_ = buf.buffer_;
offset_ = buf.offset_;
size_ = buf.size_;
}
}
// Append data to the buffer. Accepts the same types as the constructors.
template <typename T,
typename std::enable_if<
internal::BufferCompat<uint8_t, T>::value>::type* = nullptr>
void AppendData(const T* data, size_t size) {
RTC_DCHECK(IsConsistent());
if (!buffer_) {
buffer_ = new RefCountedBuffer(data, size);
offset_ = 0;
size_ = size;
RTC_DCHECK(IsConsistent());
return;
}
UnshareAndEnsureCapacity(std::max(capacity(), size_ + size));
buffer_->SetSize(offset_ +
size_); // Remove data to the right of the slice.
buffer_->AppendData(data, size);
size_ += size;
RTC_DCHECK(IsConsistent());
}
template <typename T,
size_t N,
typename std::enable_if<
internal::BufferCompat<uint8_t, T>::value>::type* = nullptr>
void AppendData(const T (&array)[N]) {
AppendData(array, N);
}
template <typename VecT,
typename ElemT = typename std::remove_pointer_t<
decltype(std::declval<VecT>().data())>,
typename std::enable_if_t<
HasDataAndSize<VecT, ElemT>::value &&
internal::BufferCompat<uint8_t, ElemT>::value>* = nullptr>
void AppendData(const VecT& v) {
AppendData(v.data(), v.size());
}
// 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);
// 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);
// Resets the buffer to zero size without altering capacity. Works even if the
// buffer has been moved from.
void Clear();
// Swaps two buffers.
friend void swap(CopyOnWriteBuffer& a, CopyOnWriteBuffer& b) {
a.buffer_.swap(b.buffer_);
std::swap(a.offset_, b.offset_);
std::swap(a.size_, b.size_);
}
CopyOnWriteBuffer Slice(size_t offset, size_t length) const {
CopyOnWriteBuffer slice(*this);
RTC_DCHECK_LE(offset, size_);
RTC_DCHECK_LE(length + offset, size_);
slice.offset_ += offset;
slice.size_ = length;
return slice;
}
private:
using RefCountedBuffer = FinalRefCountedObject<Buffer>;
// Create a copy of the underlying data if it is referenced from other Buffer
// objects or there is not enough capacity.
void UnshareAndEnsureCapacity(size_t new_capacity);
// Pre- and postcondition of all methods.
bool IsConsistent() const {
if (buffer_) {
return buffer_->capacity() > 0 && offset_ <= buffer_->size() &&
offset_ + size_ <= buffer_->size();
} else {
return size_ == 0 && offset_ == 0;
}
}
// buffer_ is either null, or points to an rtc::Buffer with capacity > 0.
scoped_refptr<RefCountedBuffer> buffer_;
// This buffer may represent a slice of a original data.
size_t offset_; // Offset of a current slice in the original data in buffer_.
// Should be 0 if the buffer_ is empty.
size_t size_; // Size of a current slice in the original data in buffer_.
// Should be 0 if the buffer_ is empty.
};
} // namespace rtc
#endif // RTC_BASE_COPY_ON_WRITE_BUFFER_H_