nsUTF8Utils.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=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/. */
#ifndef nsUTF8Utils_h_
#define nsUTF8Utils_h_

// This file may be used in two ways: if MOZILLA_INTERNAL_API is defined, this
// file will provide signatures for the Mozilla abstract string types. It will
// use XPCOM assertion/debugging macros, etc.

#include "nscore.h"
#include "mozilla/Assertions.h"
#include "mozilla/SSE.h"
#include "mozilla/TypeTraits.h"

#include "nsCharTraits.h"

#ifdef MOZILLA_INTERNAL_API
#define UTF8UTILS_WARNING(msg) NS_WARNING(msg)
#else
#define UTF8UTILS_WARNING(msg)
#endif

class UTF8traits
{
public:
  static bool isASCII(char aChar)
  {
    return (aChar & 0x80) == 0x00;
  }
  static bool isInSeq(char aChar)
  {
    return (aChar & 0xC0) == 0x80;
  }
  static bool is2byte(char aChar)
  {
    return (aChar & 0xE0) == 0xC0;
  }
  static bool is3byte(char aChar)
  {
    return (aChar & 0xF0) == 0xE0;
  }
  static bool is4byte(char aChar)
  {
    return (aChar & 0xF8) == 0xF0;
  }
  static bool is5byte(char aChar)
  {
    return (aChar & 0xFC) == 0xF8;
  }
  static bool is6byte(char aChar)
  {
    return (aChar & 0xFE) == 0xFC;
  }
};

/**
 * Extract the next UCS-4 character from the buffer and return it.  The
 * pointer passed in is advanced to the start of the next character in the
 * buffer.  If non-null, the parameters err and overlong are filled in to
 * indicate that the character was represented by an overlong sequence, or
 * that an error occurred.
 */

class UTF8CharEnumerator
{
public:
  static uint32_t NextChar(const char** aBuffer, const char* aEnd, bool* aErr)
  {
    NS_ASSERTION(aBuffer && *aBuffer, "null buffer!");

    const char* p = *aBuffer;
    *aErr = false;

    if (p >= aEnd) {
      *aErr = true;

      return 0;
    }

    char c = *p++;

    if (UTF8traits::isASCII(c)) {
      *aBuffer = p;
      return c;
    }

    uint32_t ucs4;
    uint32_t minUcs4;
    int32_t state = 0;

    if (!CalcState(c, ucs4, minUcs4, state)) {
      NS_ERROR("Not a UTF-8 string. This code should only be used for converting from known UTF-8 strings.");
      *aErr = true;

      return 0;
    }

    while (state--) {
      if (p == aEnd) {
        *aErr = true;

        return 0;
      }

      c = *p++;

      if (!AddByte(c, state, ucs4)) {
        *aErr = true;

        return 0;
      }
    }

    if (ucs4 < minUcs4) {
      // Overlong sequence
      ucs4 = UCS2_REPLACEMENT_CHAR;
    } else if (ucs4 >= 0xD800 &&
               (ucs4 <= 0xDFFF || ucs4 >= UCS_END)) {
      // Surrogates and code points outside the Unicode range.
      ucs4 = UCS2_REPLACEMENT_CHAR;
    }

    *aBuffer = p;
    return ucs4;
  }

private:
  static bool CalcState(char aChar, uint32_t& aUcs4, uint32_t& aMinUcs4,
                        int32_t& aState)
  {
    if (UTF8traits::is2byte(aChar)) {
      aUcs4 = (uint32_t(aChar) << 6) & 0x000007C0L;
      aState = 1;
      aMinUcs4 = 0x00000080;
    } else if (UTF8traits::is3byte(aChar)) {
      aUcs4 = (uint32_t(aChar) << 12) & 0x0000F000L;
      aState = 2;
      aMinUcs4 = 0x00000800;
    } else if (UTF8traits::is4byte(aChar)) {
      aUcs4 = (uint32_t(aChar) << 18) & 0x001F0000L;
      aState = 3;
      aMinUcs4 = 0x00010000;
    } else if (UTF8traits::is5byte(aChar)) {
      aUcs4 = (uint32_t(aChar) << 24) & 0x03000000L;
      aState = 4;
      aMinUcs4 = 0x00200000;
    } else if (UTF8traits::is6byte(aChar)) {
      aUcs4 = (uint32_t(aChar) << 30) & 0x40000000L;
      aState = 5;
      aMinUcs4 = 0x04000000;
    } else {
      return false;
    }

    return true;
  }

  static bool AddByte(char aChar, int32_t aState, uint32_t& aUcs4)
  {
    if (UTF8traits::isInSeq(aChar)) {
      int32_t shift = aState * 6;
      aUcs4 |= (uint32_t(aChar) & 0x3F) << shift;
      return true;
    }

    return false;
  }
};


/**
 * Extract the next UCS-4 character from the buffer and return it.  The
 * pointer passed in is advanced to the start of the next character in the
 * buffer.  If non-null, the err parameter is filled in if an error occurs.
 *
 * If an error occurs that causes UCS2_REPLACEMENT_CHAR to be returned, then
 * the buffer will be updated to move only a single UCS-2 character.
 *
 * Any other error returns 0 and does not move the buffer position.
 */


class UTF16CharEnumerator
{
public:
  static uint32_t NextChar(const char16_t** aBuffer, const char16_t* aEnd,
                           bool* aErr = nullptr)
  {
    NS_ASSERTION(aBuffer && *aBuffer, "null buffer!");

    const char16_t* p = *aBuffer;

    if (p >= aEnd) {
      NS_ERROR("No input to work with");
      if (aErr) {
        *aErr = true;
      }

      return 0;
    }

    char16_t c = *p++;

    if (!IS_SURROGATE(c)) { // U+0000 - U+D7FF,U+E000 - U+FFFF
      if (aErr) {
        *aErr = false;
      }
      *aBuffer = p;
      return c;
    } else if (NS_IS_HIGH_SURROGATE(c)) { // U+D800 - U+DBFF
      if (p == aEnd) {
        // Found a high surrogate at the end of the buffer. Flag this
        // as an error and return the Unicode replacement
        // character 0xFFFD.

        UTF8UTILS_WARNING("Unexpected end of buffer after high surrogate");

        if (aErr) {
          *aErr = true;
        }
        *aBuffer = p;
        return 0xFFFD;
      }

      // D800- DBFF - High Surrogate
      char16_t h = c;

      c = *p++;

      if (NS_IS_LOW_SURROGATE(c)) {
        // DC00- DFFF - Low Surrogate
        // N = (H - D800) *400 + 10000 + (L - DC00)
        uint32_t ucs4 = SURROGATE_TO_UCS4(h, c);
        if (aErr) {
          *aErr = false;
        }
        *aBuffer = p;
        return ucs4;
      } else {
        // Found a high surrogate followed by something other than
        // a low surrogate. Flag this as an error and return the
        // Unicode replacement character 0xFFFD.  Note that the
        // pointer to the next character points to the second 16-bit
        // value, not beyond it, as per Unicode 5.0.0 Chapter 3 C10,
        // only the first code unit of an illegal sequence must be
        // treated as an illegally terminated code unit sequence
        // (also Chapter 3 D91, "isolated [not paired and ill-formed]
        // UTF-16 code units in the range D800..DFFF are ill-formed").
        UTF8UTILS_WARNING("got a High Surrogate but no low surrogate");

        if (aErr) {
          *aErr = true;
        }
        *aBuffer = p - 1;
        return 0xFFFD;
      }
    } else { // U+DC00 - U+DFFF
      // DC00- DFFF - Low Surrogate

      // Found a low surrogate w/o a preceding high surrogate. Flag
      // this as an error and return the Unicode replacement
      // character 0xFFFD.

      UTF8UTILS_WARNING("got a low Surrogate but no high surrogate");
      if (aErr) {
        *aErr = true;
      }
      *aBuffer = p;
      return 0xFFFD;
    }

    MOZ_ASSERT_UNREACHABLE("Impossible UCS-2 character value.");
  }
};


/**
 * A character sink (see |copy_string| in nsAlgorithm.h) for converting
 * UTF-8 to UTF-16
 */
class ConvertUTF8toUTF16
{
public:
  typedef char value_type;
  typedef char16_t buffer_type;

  explicit ConvertUTF8toUTF16(buffer_type* aBuffer)
    : mStart(aBuffer), mBuffer(aBuffer), mErrorEncountered(false)
  {
  }

  size_t Length() const
  {
    return mBuffer - mStart;
  }

  bool ErrorEncountered() const
  {
    return mErrorEncountered;
  }

  void write(const value_type* aStart, uint32_t aN)
  {
    if (mErrorEncountered) {
      return;
    }

    // algorithm assumes utf8 units won't
    // be spread across fragments
    const value_type* p = aStart;
    const value_type* end = aStart + aN;
    buffer_type* out = mBuffer;
    for (; p != end /* && *p */;) {
      bool err;
      uint32_t ucs4 = UTF8CharEnumerator::NextChar(&p, end, &err);

      if (err) {
        mErrorEncountered = true;
        mBuffer = out;
        return;
      }

      if (ucs4 >= PLANE1_BASE) {
        *out++ = (buffer_type)H_SURROGATE(ucs4);
        *out++ = (buffer_type)L_SURROGATE(ucs4);
      } else {
        *out++ = ucs4;
      }
    }
    mBuffer = out;
  }

  void write_terminator()
  {
    *mBuffer = buffer_type(0);
  }

private:
  buffer_type* const mStart;
  buffer_type* mBuffer;
  bool mErrorEncountered;
};

/**
 * A character sink (see |copy_string| in nsAlgorithm.h) for computing
 * the length of the UTF-16 string equivalent to a UTF-8 string.
 */
class CalculateUTF8Length
{
public:
  typedef char value_type;

  CalculateUTF8Length()
    : mLength(0), mErrorEncountered(false)
  {
  }

  size_t Length() const
  {
    return mLength;
  }

  void write(const value_type* aStart, uint32_t aN)
  {
    // ignore any further requests
    if (mErrorEncountered) {
      return;
    }

    // algorithm assumes utf8 units won't
    // be spread across fragments
    const value_type* p = aStart;
    const value_type* end = aStart + aN;
    for (; p < end /* && *p */; ++mLength) {
      if (UTF8traits::isASCII(*p)) {
        p += 1;
      } else if (UTF8traits::is2byte(*p)) {
        p += 2;
      } else if (UTF8traits::is3byte(*p)) {
        p += 3;
      } else if (UTF8traits::is4byte(*p)) {
        // Because a UTF-8 sequence of 4 bytes represents a codepoint
        // greater than 0xFFFF, it will become a surrogate pair in the
        // UTF-16 string, so add 1 more to mLength.
        // This doesn't happen with is5byte and is6byte because they
        // are illegal UTF-8 sequences (greater than 0x10FFFF) so get
        // converted to a single replacement character.

        // However, there is one case when a 4 byte UTF-8 sequence will
        // only generate 2 UTF-16 bytes. If we have a properly encoded
        // sequence, but with an invalid value (too small or too big),
        // that will result in a replacement character being written
        // This replacement character is encoded as just 1 single
        // UTF-16 character, which is 2 bytes.

        // The below code therefore only adds 1 to mLength if the UTF8
        // data will produce a decoded character which is greater than
        // or equal to 0x010000 and less than 0x0110000.

        // A 4byte UTF8 character is encoded as
        // 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
        // Bit 1-3 on the first byte, and bit 5-6 on the second byte,
        // map to bit 17-21 in the final result. If these bits are
        // between 0x01 and 0x11, that means that the final result is
        // between 0x010000 and 0x110000. The below code reads these
        // bits out and assigns them to c, but shifted up 4 bits to
        // avoid having to shift twice.

        // It doesn't matter what to do in the case where p + 4 > end
        // since no UTF16 characters will be written in that case by
        // ConvertUTF8toUTF16. Likewise it doesn't matter what we do if
        // any of the surrogate bits are wrong since no UTF16
        // characters will be written in that case either.

        if (p + 4 <= end) {
          uint32_t c = ((uint32_t)(p[0] & 0x07)) << 6 |
                       ((uint32_t)(p[1] & 0x30));
          if (c >= 0x010 && c < 0x110) {
            ++mLength;
          }
        }

        p += 4;
      } else if (UTF8traits::is5byte(*p)) {
        p += 5;
      } else if (UTF8traits::is6byte(*p)) {
        p += 6;
      } else { // error
        ++mLength; // to account for the decrement below
        break;
      }
    }
    if (p != end) {
      NS_ERROR("Not a UTF-8 string. This code should only be used for converting from known UTF-8 strings.");
      --mLength; // The last multi-byte char wasn't complete, discard it.
      mErrorEncountered = true;
    }
  }

private:
  size_t mLength;
  bool mErrorEncountered;
};

/**
 * A character sink (see |copy_string| in nsAlgorithm.h) for
 * converting UTF-16 to UTF-8. Treats invalid UTF-16 data as 0xFFFD
 * (0xEFBFBD in UTF-8).
 */
class ConvertUTF16toUTF8
{
public:
  typedef char16_t value_type;
  typedef char buffer_type;

  // The error handling here is more lenient than that in
  // |ConvertUTF8toUTF16|, but it's that way for backwards
  // compatibility.

  explicit ConvertUTF16toUTF8(buffer_type* aBuffer)
    : mStart(aBuffer), mBuffer(aBuffer)
  {
  }

  size_t Size() const
  {
    return mBuffer - mStart;
  }

  void write(const value_type* aStart, uint32_t aN)
  {
    buffer_type* out = mBuffer; // gcc isn't smart enough to do this!

    for (const value_type* p = aStart, *end = aStart + aN; p < end; ++p) {
      value_type c = *p;
      if (!(c & 0xFF80)) { // U+0000 - U+007F
        *out++ = (char)c;
      } else if (!(c & 0xF800)) { // U+0100 - U+07FF
        *out++ = 0xC0 | (char)(c >> 6);
        *out++ = 0x80 | (char)(0x003F & c);
      } else if (!IS_SURROGATE(c)) { // U+0800 - U+D7FF,U+E000 - U+FFFF
        *out++ = 0xE0 | (char)(c >> 12);
        *out++ = 0x80 | (char)(0x003F & (c >> 6));
        *out++ = 0x80 | (char)(0x003F & c);
      } else if (NS_IS_HIGH_SURROGATE(c)) { // U+D800 - U+DBFF
        // D800- DBFF - High Surrogate
        value_type h = c;

        ++p;
        if (p == end) {
          // Treat broken characters as the Unicode
          // replacement character 0xFFFD (0xEFBFBD in
          // UTF-8)
          *out++ = '\xEF';
          *out++ = '\xBF';
          *out++ = '\xBD';

          UTF8UTILS_WARNING("String ending in half a surrogate pair!");

          break;
        }
        c = *p;

        if (NS_IS_LOW_SURROGATE(c)) {
          // DC00- DFFF - Low Surrogate
          // N = (H - D800) *400 + 10000 + ( L - DC00 )
          uint32_t ucs4 = SURROGATE_TO_UCS4(h, c);

          // 0001 0000-001F FFFF
          *out++ = 0xF0 | (char)(ucs4 >> 18);
          *out++ = 0x80 | (char)(0x003F & (ucs4 >> 12));
          *out++ = 0x80 | (char)(0x003F & (ucs4 >> 6));
          *out++ = 0x80 | (char)(0x003F & ucs4);
        } else {
          // Treat broken characters as the Unicode
          // replacement character 0xFFFD (0xEFBFBD in
          // UTF-8)
          *out++ = '\xEF';
          *out++ = '\xBF';
          *out++ = '\xBD';

          // The pointer to the next character points to the second
          // 16-bit value, not beyond it, as per Unicode 5.0.0
          // Chapter 3 C10, only the first code unit of an illegal
          // sequence must be treated as an illegally terminated
          // code unit sequence (also Chapter 3 D91, "isolated [not
          // paired and ill-formed] UTF-16 code units in the range
          // D800..DFFF are ill-formed").
          p--;

          UTF8UTILS_WARNING("got a High Surrogate but no low surrogate");
        }
      } else { // U+DC00 - U+DFFF
        // Treat broken characters as the Unicode replacement
        // character 0xFFFD (0xEFBFBD in UTF-8)
        *out++ = '\xEF';
        *out++ = '\xBF';
        *out++ = '\xBD';

        // DC00- DFFF - Low Surrogate
        UTF8UTILS_WARNING("got a low Surrogate but no high surrogate");
      }
    }

    mBuffer = out;
  }

  void write_terminator()
  {
    *mBuffer = buffer_type(0);
  }

private:
  buffer_type* const mStart;
  buffer_type* mBuffer;
};

/**
 * A character sink (see |copy_string| in nsAlgorithm.h) for computing
 * the number of bytes a UTF-16 would occupy in UTF-8. Treats invalid
 * UTF-16 data as 0xFFFD (0xEFBFBD in UTF-8).
 */
class CalculateUTF8Size
{
public:
  typedef char16_t value_type;

  CalculateUTF8Size()
    : mSize(0)
  {
  }

  size_t Size() const
  {
    return mSize;
  }

  void write(const value_type* aStart, uint32_t aN)
  {
    // Assume UCS2 surrogate pairs won't be spread across fragments.
    for (const value_type* p = aStart, *end = aStart + aN; p < end; ++p) {
      value_type c = *p;
      if (!(c & 0xFF80)) { // U+0000 - U+007F
        mSize += 1;
      } else if (!(c & 0xF800)) { // U+0100 - U+07FF
        mSize += 2;
      } else if (0xD800 != (0xF800 & c)) { // U+0800 - U+D7FF,U+E000 - U+FFFF
        mSize += 3;
      } else if (0xD800 == (0xFC00 & c)) { // U+D800 - U+DBFF
        ++p;
        if (p == end) {
          // Treat broken characters as the Unicode
          // replacement character 0xFFFD (0xEFBFBD in
          // UTF-8)
          mSize += 3;

          UTF8UTILS_WARNING("String ending in half a surrogate pair!");

          break;
        }
        c = *p;

        if (0xDC00 == (0xFC00 & c)) {
          mSize += 4;
        } else {
          // Treat broken characters as the Unicode
          // replacement character 0xFFFD (0xEFBFBD in
          // UTF-8)
          mSize += 3;

          // The next code unit is the second 16-bit value, not
          // the one beyond it, as per Unicode 5.0.0 Chapter 3 C10,
          // only the first code unit of an illegal sequence must
          // be treated as an illegally terminated code unit
          // sequence (also Chapter 3 D91, "isolated [not paired and
          // ill-formed] UTF-16 code units in the range D800..DFFF
          // are ill-formed").
          p--;

          UTF8UTILS_WARNING("got a high Surrogate but no low surrogate");
        }
      } else { // U+DC00 - U+DFFF
        // Treat broken characters as the Unicode replacement
        // character 0xFFFD (0xEFBFBD in UTF-8)
        mSize += 3;

        UTF8UTILS_WARNING("got a low Surrogate but no high surrogate");
      }
    }
  }

private:
  size_t mSize;
};

#ifdef MOZILLA_INTERNAL_API
/**
 * A character sink that performs a |reinterpret_cast|-style conversion
 * from char to char16_t.
 */
class LossyConvertEncoding8to16
{
public:
  typedef char value_type;
  typedef char input_type;
  typedef char16_t output_type;

public:
  explicit LossyConvertEncoding8to16(char16_t* aDestination) :
    mDestination(aDestination)
  {
  }

  void
  write(const char* aSource, uint32_t aSourceLength)
  {
#ifdef MOZILLA_MAY_SUPPORT_SSE2
    if (mozilla::supports_sse2()) {
      write_sse2(aSource, aSourceLength);
      return;
    }
#endif
    const char* done_writing = aSource + aSourceLength;
    while (aSource < done_writing) {
      *mDestination++ = (char16_t)(unsigned char)(*aSource++);
    }
  }

  void
  write_sse2(const char* aSource, uint32_t aSourceLength);

  void
  write_terminator()
  {
    *mDestination = (char16_t)(0);
  }

private:
  char16_t* mDestination;
};

/**
 * A character sink that performs a |reinterpret_cast|-style conversion
 * from char16_t to char.
 */
class LossyConvertEncoding16to8
{
public:
  typedef char16_t value_type;
  typedef char16_t input_type;
  typedef char output_type;

  explicit LossyConvertEncoding16to8(char* aDestination)
    : mDestination(aDestination)
  {
  }

  void
  write(const char16_t* aSource, uint32_t aSourceLength)
  {
#ifdef MOZILLA_MAY_SUPPORT_SSE2
    if (mozilla::supports_sse2()) {
      write_sse2(aSource, aSourceLength);
      return;
    }
#endif
    const char16_t* done_writing = aSource + aSourceLength;
    while (aSource < done_writing) {
      *mDestination++ = (char)(*aSource++);
    }
  }

#ifdef MOZILLA_MAY_SUPPORT_SSE2
  void
  write_sse2(const char16_t* aSource, uint32_t aSourceLength);
#endif

  void
  write_terminator()
  {
    *mDestination = '\0';
  }

private:
  char* mDestination;
};
#endif // MOZILLA_INTERNAL_API


template<typename Char, typename UnsignedT>
inline UnsignedT
RewindToPriorUTF8Codepoint(const Char* utf8Chars, UnsignedT index)
{
  static_assert(mozilla::IsSame<Char, char>::value ||
                mozilla::IsSame<Char, unsigned char>::value ||
                mozilla::IsSame<Char, signed char>::value,
                "UTF-8 data must be in 8-bit units");
  static_assert(mozilla::IsUnsigned<UnsignedT>::value, "index type must be unsigned");
  while (index > 0 && (utf8Chars[index] & 0xC0) == 0x80)
    --index;

  return index;
}

#undef UTF8UTILS_WARNING

#endif /* !defined(nsUTF8Utils_h_) */