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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=2 et sw=2 tw=80: */
/* 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/. */
#include <glib.h>
#include <cstdint>
#include "mozilla/a11y/HyperTextAccessibleBase.h"
#include "nsCharTraits.h"
#include "nsString.h"
/**
* ATK offsets are counted in unicode codepoints, while DOM offsets are counted
* in UTF-16 code units. That makes a difference for non-BMP characters,
* which need two UTF-16 code units to be represented (a pair of surrogates),
* while they are just one unicode character.
*
* To keep synchronization between ATK offsets (unicode codepoints) and DOM
* offsets (UTF-16 code units), after translation from UTF-16 to UTF-8 we add a
* BOM after each non-BMP character (which would otherwise use 2 UTF-16
* code units for only 1 unicode codepoint).
*
* BOMs (Byte Order Marks, U+FEFF, also known as ZERO WIDTH NO-BREAK SPACE, but
* that usage is deprecated) normally only appear at the beginning of unicode
* files, but their occurrence within text (notably after cut&paste) is not
* uncommon, and are thus considered as non-text.
*
* Since the selection requested through ATK may not contain both surrogates
* at the ends of the selection, we need to fetch one UTF-16 code point more
* on both side, and get rid of it before returning the string to ATK. The
* ATKStringConverterHelper class maintains this, NewATKString should be used
* to call it properly.
*
* In the end,
* - if the start is between the high and low surrogates, the UTF-8 result
* includes a BOM from it but not the character
* - if the end is between the high and low surrogates, the UTF-8 result
* includes the character but *not* the BOM
* - all non-BMP characters that are fully in the string are in the UTF-8 result
* as character followed by BOM
*/
namespace mozilla {
namespace a11y {
namespace DOMtoATK {
/**
* Converts a string of accessible text into ATK gchar* string (by adding
* BOMs). This can be used when offsets do not need to be adjusted because
* ends of the string can not fall between surrogates.
*/
gchar* Convert(const nsAString& aStr);
/**
* Add a BOM after each non-BMP character.
*/
void AddBOMs(nsACString& aDest, const nsACString& aSource);
class ATKStringConverterHelper {
public:
ATKStringConverterHelper(void)
:
#ifdef DEBUG
mAdjusted(false),
#endif
mStartShifted(false),
mEndShifted(false) {
}
/**
* In order to properly get non-BMP values, offsets need to be changed
* to get one character more on each end, so that ConvertUTF16toUTF8 can
* convert surrogates even if the originally requested offsets fall between
* them.
*/
void AdjustOffsets(gint* aStartOffset, gint* aEndOffset, gint count);
/**
* Converts a string of accessible text with adjusted offsets into ATK
* gchar* string (by adding BOMs). Note, AdjustOffsets has to be called
* before getting the text passed to this.
*/
gchar* ConvertAdjusted(const nsAString& aStr);
private:
/**
* Remove the additional characters requested by PrepareUTF16toUTF8.
*/
gchar* FinishUTF16toUTF8(nsCString& aStr);
#ifdef DEBUG
bool mAdjusted;
#endif
bool mStartShifted;
bool mEndShifted;
};
/**
* Get text from aAccessible, using ATKStringConverterHelper to properly
* introduce appropriate BOMs.
*/
inline gchar* NewATKString(HyperTextAccessibleBase* aAccessible,
gint aStartOffset, gint aEndOffset) {
gint startOffset = aStartOffset, endOffset = aEndOffset;
ATKStringConverterHelper converter;
converter.AdjustOffsets(&startOffset, &endOffset,
gint(aAccessible->CharacterCount()));
nsAutoString str;
aAccessible->TextSubstring(startOffset, endOffset, str);
if (str.Length() == 0) {
// Bogus offsets, or empty string, either way we do not need conversion.
return g_strdup("");
}
return converter.ConvertAdjusted(str);
}
/**
* Get a character from aAccessible, fetching more data as appropriate to
* properly get non-BMP characters or a BOM as appropriate.
*/
inline gunichar ATKCharacter(HyperTextAccessibleBase* aAccessible,
gint aOffset) {
// char16_t is unsigned short in Mozilla, gnuichar is guint32 in glib.
gunichar character = static_cast<gunichar>(aAccessible->CharAt(aOffset));
if (NS_IS_LOW_SURROGATE(character)) {
// Trailing surrogate, return BOM instead.
return 0xFEFF;
}
if (NS_IS_HIGH_SURROGATE(character)) {
// Heading surrogate, get the trailing surrogate and combine them.
gunichar characterLow =
static_cast<gunichar>(aAccessible->CharAt(aOffset + 1));
if (!NS_IS_LOW_SURROGATE(characterLow)) {
// It should have been a trailing surrogate... Flag the error.
return 0xFFFD;
}
return SURROGATE_TO_UCS4(character, characterLow);
}
return character;
}
} // namespace DOMtoATK
} // namespace a11y
} // namespace mozilla
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