rtc_base/copy_on_write_buffer.h - src - Git at Google

 /*
  *  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_
	/*
	* 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_