tor-browser

Buffer.h (5908B)

---

/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef mozilla_Buffer_h
#define mozilla_Buffer_h

#include "mozilla/Assertions.h"
#include "mozilla/Maybe.h"
#include "mozilla/Span.h"
#include "mozilla/UniquePtr.h"
#include "mozilla/UniquePtrExtensions.h"

#include <cstddef>
#include <iterator>
#include <utility>

namespace mozilla {

/**
* A move-only type that wraps a mozilla::UniquePtr<T[]> and the length of
* the T[].
*
* Unlike mozilla::Array, the length is a run-time property.
* Unlike mozilla::Vector and nsTArray, does not have capacity and
* assocatiated growth functionality.
* Unlike mozilla::Span, mozilla::Buffer owns the allocation it points to.
*/
template <typename T>
class Buffer final {
private:
 mozilla::UniquePtr<T[]> mData;
 size_t mLength;

public:
 Buffer(const Buffer<T>& aOther) = delete;
 Buffer<T>& operator=(const Buffer<T>& aOther) = delete;

 /**
  * Construct zero-lenth Buffer (without actually pointing to a heap
  * allocation).
  */
 Buffer() : mData(nullptr), mLength(0) {};

 /**
  * Construct from raw parts.
  *
  * aLength must not be greater than the actual length of the buffer pointed
  * to by aData.
  */
 Buffer(mozilla::UniquePtr<T[]>&& aData, size_t aLength)
     : mData(std::move(aData)), mLength(aLength) {}

 /**
  * Move constructor. Sets the moved-from Buffer to zero-length
  * state.
  */
 Buffer(Buffer<T>&& aOther)
     : mData(std::move(aOther.mData)), mLength(aOther.mLength) {
   aOther.mLength = 0;
 }

 /**
  * Move assignment. Sets the moved-from Buffer to zero-length
  * state.
  */
 Buffer<T>& operator=(Buffer<T>&& aOther) {
   mData = std::move(aOther.mData);
   mLength = aOther.mLength;
   aOther.mLength = 0;
   return *this;
 }

 /**
  * Construct by copying the elements of a Span.
  *
  * Allocates the internal buffer infallibly. Use CopyFrom for fallible
  * allocation.
  */
 explicit Buffer(mozilla::Span<const T> aSpan)
     : mData(mozilla::MakeUniqueForOverwrite<T[]>(aSpan.Length())),
       mLength(aSpan.Length()) {
   std::copy(aSpan.cbegin(), aSpan.cend(), mData.get());
 }

 /**
  * Create a new Buffer by copying the elements of a Span.
  *
  * Allocates the internal buffer fallibly.
  */
 static mozilla::Maybe<Buffer<T>> CopyFrom(mozilla::Span<const T> aSpan) {
   if (aSpan.IsEmpty()) {
     return Some(Buffer());
   }

   auto data = mozilla::MakeUniqueForOverwriteFallible<T[]>(aSpan.Length());
   if (!data) {
     return mozilla::Nothing();
   }
   std::copy(aSpan.cbegin(), aSpan.cend(), data.get());
   return mozilla::Some(Buffer(std::move(data), aSpan.Length()));
 }

 /**
  * Construct a buffer of requested length.
  *
  * The contents will be initialized or uninitialized according
  * to the behavior of mozilla::MakeUnique<T[]>(aLength) for T.
  *
  * Allocates the internal buffer infallibly. Use Alloc for fallible
  * allocation.
  */
 explicit Buffer(size_t aLength)
     : mData(mozilla::MakeUnique<T[]>(aLength)), mLength(aLength) {}

 /**
  * Create a new Buffer with an internal buffer of requested length.
  *
  * The contents will be initialized or uninitialized according to the
  * behavior of mozilla::MakeUnique<T[]>(aLength) for T.
  *
  * Allocates the internal buffer fallibly.
  */
 static mozilla::Maybe<Buffer<T>> Alloc(size_t aLength) {
   auto data = mozilla::MakeUniqueFallible<T[]>(aLength);
   if (!data) {
     return mozilla::Nothing();
   }
   return mozilla::Some(Buffer(std::move(data), aLength));
 }

 /**
  * Create a new Buffer with an internal buffer of requested length.
  *
  * This uses MakeUniqueFallibleForOverwrite so the contents will be
  * default-initialized.
  *
  * Allocates the internal buffer fallibly.
  */
 static Maybe<Buffer<T>> AllocForOverwrite(size_t aLength) {
   auto data = MakeUniqueForOverwriteFallible<T[]>(aLength);
   if (!data) {
     return Nothing();
   }
   return Some(Buffer(std::move(data), aLength));
 }

 auto AsSpan() const { return mozilla::Span<const T>{mData.get(), mLength}; }
 auto AsWritableSpan() { return mozilla::Span<T>{mData.get(), mLength}; }
 operator mozilla::Span<const T>() const { return AsSpan(); }
 operator mozilla::Span<T>() { return AsWritableSpan(); }

 /**
  * Guarantees a non-null and aligned pointer
  * even for the zero-length case.
  */
 T* Elements() { return AsWritableSpan().Elements(); }
 size_t Length() const { return mLength; }

 T& operator[](size_t aIndex) {
   MOZ_ASSERT(aIndex < mLength);
   return mData.get()[aIndex];
 }

 const T& operator[](size_t aIndex) const {
   MOZ_ASSERT(aIndex < mLength);
   return mData.get()[aIndex];
 }

 typedef T* iterator;
 typedef const T* const_iterator;
 typedef std::reverse_iterator<T*> reverse_iterator;
 typedef std::reverse_iterator<const T*> const_reverse_iterator;

 // Methods for range-based for loops.
 iterator begin() { return mData.get(); }
 const_iterator begin() const { return mData.get(); }
 const_iterator cbegin() const { return begin(); }
 iterator end() { return mData.get() + mLength; }
 const_iterator end() const { return mData.get() + mLength; }
 const_iterator cend() const { return end(); }

 // Methods for reverse iterating.
 reverse_iterator rbegin() { return reverse_iterator(end()); }
 const_reverse_iterator rbegin() const {
   return const_reverse_iterator(end());
 }
 const_reverse_iterator crbegin() const { return rbegin(); }
 reverse_iterator rend() { return reverse_iterator(begin()); }
 const_reverse_iterator rend() const {
   return const_reverse_iterator(begin());
 }
 const_reverse_iterator crend() const { return rend(); }
};

} /* namespace mozilla */

#endif /* mozilla_Buffer_h */