path: root/dom/base/nsTextFragment.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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/. */

/*
 * A class which represents a fragment of text (eg inside a text
 * node); if only codepoints below 256 are used, the text is stored as
 * a char*; otherwise the text is stored as a char16_t*
 */

#ifndef nsTextFragment_h___
#define nsTextFragment_h___

#include "mozilla/Attributes.h"
#include "mozilla/MemoryReporting.h"

#include "nsString.h"
#include "nsReadableUtils.h"
#include "nsISupportsImpl.h"

class nsString;

#define NS_MAX_TEXT_FRAGMENT_LENGTH (static_cast<uint32_t>(0x1FFFFFFF))

// XXX should this normalize the code to keep a \u0000 at the end?

// XXX nsTextFragmentPool?

/**
 * A fragment of text. If mIs2b is 1 then the m2b pointer is valid
 * otherwise the m1b pointer is valid. If m1b is used then each byte
 * of data represents a single ucs2 character with the high byte being
 * zero.
 *
 * This class does not have a virtual destructor therefore it is not
 * meant to be subclassed.
 */
class nsTextFragment final {
public:
  static nsresult Init();
  static void Shutdown();

  /**
   * Default constructor. Initialize the fragment to be empty.
   */
  nsTextFragment()
    : m1b(nullptr), mAllBits(0)
  {
    MOZ_COUNT_CTOR(nsTextFragment);
    NS_ASSERTION(sizeof(FragmentBits) == 4, "Bad field packing!");
  }

  ~nsTextFragment();

  /**
   * Change the contents of this fragment to be a copy of the
   * the argument fragment, or to "" if unable to allocate enough memory.
   */
  nsTextFragment& operator=(const nsTextFragment& aOther);

  /**
   * Return true if this fragment is represented by char16_t data
   */
  bool Is2b() const
  {
    return mState.mIs2b;
  }

  /**
   * Return true if this fragment contains Bidi text
   * For performance reasons this flag is only set if explicitely requested (by
   * setting the aUpdateBidi argument on SetTo or Append to true).
   */
  bool IsBidi() const
  {
    return mState.mIsBidi;
  }

  /**
   * Get a pointer to constant char16_t data.
   */
  const char16_t *Get2b() const
  {
    NS_ASSERTION(Is2b(), "not 2b text"); 
    return m2b;
  }

  /**
   * Get a pointer to constant char data.
   */
  const char *Get1b() const
  {
    NS_ASSERTION(!Is2b(), "not 1b text"); 
    return (const char *)m1b;
  }

  /**
   * Get the length of the fragment. The length is the number of logical
   * characters, not the number of bytes to store the characters.
   */
  uint32_t GetLength() const
  {
    return mState.mLength;
  }

  bool CanGrowBy(size_t n) const
  {
    return n < (1 << 29) && mState.mLength + n < (1 << 29);
  }

  /**
   * Change the contents of this fragment to be a copy of the given
   * buffer. If aUpdateBidi is true, contents of the fragment will be scanned,
   * and mState.mIsBidi will be turned on if it includes any Bidi characters.
   */
  bool SetTo(const char16_t* aBuffer, int32_t aLength, bool aUpdateBidi);

  /**
   * Append aData to the end of this fragment. If aUpdateBidi is true, contents
   * of the fragment will be scanned, and mState.mIsBidi will be turned on if
   * it includes any Bidi characters.
   */
  bool Append(const char16_t* aBuffer, uint32_t aLength, bool aUpdateBidi);

  /**
   * Append the contents of this string fragment to aString
   */
  void AppendTo(nsAString& aString) const {
    if (!AppendTo(aString, mozilla::fallible)) {
      aString.AllocFailed(aString.Length() + GetLength());
    }
  }

  /**
   * Append the contents of this string fragment to aString
   * @return false if an out of memory condition is detected, true otherwise
   */
  MOZ_MUST_USE
  bool AppendTo(nsAString& aString,
                const mozilla::fallible_t& aFallible) const {
    if (mState.mIs2b) {
      bool ok = aString.Append(m2b, mState.mLength, aFallible);
      if (!ok) {
        return false;
      }

      return true;
    } else {
      return AppendASCIItoUTF16(Substring(m1b, mState.mLength), aString,
                                aFallible);
    }
  }

  /**
   * Append a substring of the contents of this string fragment to aString.
   * @param aOffset where to start the substring in this text fragment
   * @param aLength the length of the substring
   */
  void AppendTo(nsAString& aString, int32_t aOffset, int32_t aLength) const {
    if (!AppendTo(aString, aOffset, aLength, mozilla::fallible)) {
      aString.AllocFailed(aString.Length() + aLength);
    }
  }

  /**
   * Append a substring of the contents of this string fragment to aString.
   * @param aString the string in which to append
   * @param aOffset where to start the substring in this text fragment
   * @param aLength the length of the substring
   * @return false if an out of memory condition is detected, true otherwise
   */
  MOZ_MUST_USE
  bool AppendTo(nsAString& aString, int32_t aOffset, int32_t aLength,
                const mozilla::fallible_t& aFallible) const
  {
    if (mState.mIs2b) {
      bool ok = aString.Append(m2b + aOffset, aLength, aFallible);
      if (!ok) {
        return false;
      }

      return true;
    } else {
      return AppendASCIItoUTF16(Substring(m1b + aOffset, aLength), aString,
                                aFallible);
    }
  }

  /**
   * Make a copy of the fragments contents starting at offset for
   * count characters. The offset and count will be adjusted to
   * lie within the fragments data. The fragments data is converted if
   * necessary.
   */
  void CopyTo(char16_t *aDest, int32_t aOffset, int32_t aCount);

  /**
   * Return the character in the text-fragment at the given
   * index. This always returns a char16_t.
   */
  char16_t CharAt(int32_t aIndex) const
  {
    NS_ASSERTION(uint32_t(aIndex) < mState.mLength, "bad index");
    return mState.mIs2b ? m2b[aIndex] : static_cast<unsigned char>(m1b[aIndex]);
  }

  // Packed 32-bit data structure:
  // [InHeap(1)][Is2b(1)][IsBidi(1)][Data(29)]
  struct FragmentBits {
    // uint32_t to ensure that the values are unsigned, because we
    // want 0/1, not 0/-1!
    // Making these bool causes Windows to not actually pack them,
    // which causes crashes because we assume this structure is no more than
    // 32 bits!
    uint32_t mInHeap : 1;
    uint32_t mIs2b : 1;
    uint32_t mIsBidi : 1;
    // Note: If you change the number of bits of mLength, you also need to
    // change NS_MAX_TEXT_FRAGMENT_LENGTH (see top of file).
    uint32_t mLength : 29;
  };

  size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;

private:
  void ReleaseText();

  /**
   * Scan the contents of the fragment and turn on mState.mIsBidi if it
   * includes any Bidi characters.
   */
  void UpdateBidiFlag(const char16_t* aBuffer, uint32_t aLength);
 
  union {
    char16_t *m2b;
    const char *m1b; // This is const since it can point to shared data
  };

  union {
    uint32_t mAllBits;
    FragmentBits mState;
  };
};

#endif /* nsTextFragment_h___ */