cpp/woff2.cc

// Copyright (c) 2012 Google Inc. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// This is the implementation of decompression of the proposed WOFF Ultra
// Condensed file format.

// For now, use of LZMA is conditional, because the build is trickier. When
// that gets all sorted out, we can get rid of these ifdefs.
#define USE_LZMA

#ifdef USE_LZMA
#include "third_party/lzma_sdk/LzmaLib.h"
#endif

#include <zlib.h>
#include <vector>
#include "opentype-sanitiser.h"
#include "ots-memory-stream.h"

#include "ots.h"
#include "woff2.h"

namespace {

// simple glyph flags
const int kGlyfOnCurve = 1 << 0;
const int kGlyfXShort = 1 << 1;
const int kGlyfYShort = 1 << 2;
const int kGlyfRepeat = 1 << 3;
const int kGlyfThisXIsSame = 1 << 4;
const int kGlyfThisYIsSame = 1 << 5;

// composite glyph flags
const int FLAG_ARG_1_AND_2_ARE_WORDS = 1 << 0;
const int FLAG_ARGS_ARE_XY_VALUES = 1 << 1;
const int FLAG_ROUND_XY_TO_GRID = 1 << 2;
const int FLAG_WE_HAVE_A_SCALE = 1 << 3;
const int FLAG_RESERVED = 1 << 4;
const int FLAG_MORE_COMPONENTS = 1 << 5;
const int FLAG_WE_HAVE_AN_X_AND_Y_SCALE = 1 << 6;
const int FLAG_WE_HAVE_A_TWO_BY_TWO = 1 << 7;
const int FLAG_WE_HAVE_INSTRUCTIONS = 1 << 8;
const int FLAG_USE_MY_METRICS = 1 << 9;
const int FLAG_OVERLAP_COMPOUND = 1 << 10;
const int FLAG_SCALED_COMPONENT_OFFSET = 1 << 11;
const int FLAG_UNSCALED_COMPONENT_OFFSET = 1 << 12;

const size_t kSfntHeaderSize = 12;
const size_t kSfntEntrySize = 16;
const size_t kCheckSumAdjustmentOffset = 8;

const size_t kEndPtsOfContoursOffset = 10;
const size_t kCompositeGlyphBegin = 10;

// Note that the byte order is big-endian, not the same as ots.cc
#define TAG(a, b, c, d) ((a << 24) | (b << 16) | (c << 8) | d)

const unsigned int kWoff2FlagsContinueStream = 1 << 4;
const unsigned int kWoff2FlagsTransform = 1 << 5;

const size_t kWoff2HeaderSize = 44;
const size_t kWoff2EntrySize = 20;

const size_t kLzmaHeaderSize = 13;

const uint32_t kCompressionTypeMask = 0xf;
const uint32_t kCompressionTypeNone = 0;
const uint32_t kCompressionTypeGzip = 1;
const uint32_t kCompressionTypeLzma = 2;


struct Point {
  int x;
  int y;
  bool on_curve;
};

struct Table {
  uint32_t tag;
  uint32_t flags;
  uint32_t src_offset;
  uint32_t src_length;

  uint32_t transform_length;

  uint32_t dst_offset;
  uint32_t dst_length;
};

// Based on section 6.1.1 of MicroType Express draft spec
bool Read255UShort(ots::Buffer *buf, unsigned int *value) {
  const int kWordCode = 253;
  const int kOneMoreByteCode2 = 254;
  const int kOneMoreByteCode1 = 255;
  const int kLowestUCode = 253;
  uint8_t code = 0;
  if (!buf->ReadU8(&code)) {
    return OTS_FAILURE();
  }
  if (code == kWordCode) {
    uint16_t result = 0;
    if (!buf->ReadU16(&result)) {
      return OTS_FAILURE();
    }
    *value = result;
    return true;
  } else if (code == kOneMoreByteCode1) {
    uint8_t result = 0;
    if (!buf->ReadU8(&result)) {
      return OTS_FAILURE();
    }
    *value = result + kLowestUCode;
    return true;
  } else if (code == kOneMoreByteCode2) {
    uint8_t result = 0;
    if (!buf->ReadU8(&result)) {
      return OTS_FAILURE();
    }
    *value = result + kLowestUCode * 2;
    return true;
  } else {
    *value = code;
    return true;
  }
}

bool ReadBase128(ots::Buffer *buf, uint32_t *value) {
  uint32_t result = 0;
  for (size_t i = 0; i < 5; ++i) {
    uint8_t code = 0;
    if (!buf->ReadU8(&code)) {
      return OTS_FAILURE();
    }
    result = (result << 7) | (code & 0x7f);
    if ((code & 0x80) == 0) {
      *value = result;
      return true;
    }
  }
  // Make sure not to exceed the size bound
  return OTS_FAILURE();
}

size_t StoreU32(uint8_t *dst, size_t offset, uint32_t x) {
  dst[offset] = x >> 24;
  dst[offset + 1] = (x >> 16) & 0xff;
  dst[offset + 2] = (x >> 8) & 0xff;
  dst[offset + 3] = x & 0xff;
  return offset + 4;
}

size_t Store16(uint8_t *dst, size_t offset, int x) {
  dst[offset] = x >> 8;
  dst[offset + 1] = x & 0xff;
  return offset + 2;
}

int WithSign(int flag, int baseval) {
  return (flag & 1) ? baseval : -baseval;
}

bool TripletDecode(const uint8_t *flags_in, const uint8_t *in, size_t in_size,
    unsigned int n_points, std::vector<Point> *result,
    size_t *in_bytes_consumed) {
  int x = 0;
  int y = 0;

  if (n_points > in_size) {
    return false;
  }
  unsigned int triplet_index = 0;

  for (unsigned int i = 0; i < n_points; ++i) {
    uint8_t flag = flags_in[i];
    bool on_curve = !(flag >> 7);
    flag &= 0x7f;
    int n_data_bytes;
    if (flag < 84) {
      n_data_bytes = 1;
    } else if (flag < 120) {
      n_data_bytes = 2;
    } else if (flag < 124) {
      n_data_bytes = 3;
    } else {
      n_data_bytes = 4;
    }
#if 0
    fprintf(stderr, "flag = %d:", flag);
    for (int j = 0; j < n_data_bytes; ++j) {
      fprintf(stderr, " %d", in[triplet_index + j]);
    }
    fprintf(stderr, "\n");
#endif
    if (triplet_index + n_data_bytes > in_size ||
        triplet_index + n_data_bytes < triplet_index) {
      return OTS_FAILURE();
    }
    int dx, dy;
    if (flag < 10) {
      dx = 0;
      dy = WithSign(flag, ((flag & 14) << 7) + in[triplet_index]);
    } else if (flag < 20) {
      dx = WithSign(flag, (((flag - 10) & 14) << 7) + in[triplet_index]);
      dy = 0;
    } else if (flag < 84) {
      int b0 = flag - 20;
      int b1 = in[triplet_index];
      dx = WithSign(flag, 1 + (b0 & 0x30) + (b1 >> 4));
      dy = WithSign(flag >> 1, 1 + ((b0 & 0x0c) << 2) + (b1 & 0x0f));
    } else if (flag < 120) {
      int b0 = flag - 84;
      dx = WithSign(flag, 1 + ((b0 / 12) << 8) + in[triplet_index]);
      dy = WithSign(flag >> 1,
                    1 + (((b0 % 12) >> 2) << 8) + in[triplet_index + 1]);
    } else if (flag < 124) {
      int b2 = in[triplet_index + 1];
      dx = WithSign(flag, (in[triplet_index] << 4) + (b2 >> 4));
      dy = WithSign(flag >> 1, ((b2 & 0x0f) << 8) + in[triplet_index + 2]);
    } else {
      dx = WithSign(flag, (in[triplet_index] << 8) + in[triplet_index + 1]);
      dy = WithSign(flag >> 1,
          (in[triplet_index + 2] << 8) + in[triplet_index + 3]);
    }
    triplet_index += n_data_bytes;
    x += dx;
    y += dy;
    result->push_back(Point());
    Point &back = result->back();
    back.x = x;
    back.y = y;
    back.on_curve = on_curve;
    // fprintf(stderr, "point %d: %d %d %s (delta %d %d)\n",
    //    i, x, y, on_curve ? "on" : "off", dx, dy);
  }
  *in_bytes_consumed = triplet_index;
  return true;
}

// This function stores just the point data. On entry, dst points to the
// beginning of a simple glyph. Returns true on success.
bool StorePoints(const std::vector<Point> &points, 
    unsigned int n_contours, unsigned int instruction_length,
    uint8_t *dst, size_t dst_size, size_t *glyph_size) {
  unsigned int flag_offset = kEndPtsOfContoursOffset + 2 * n_contours + 2 +
    instruction_length;
  int last_flag = -1;
  int repeat_count = 0;
  int last_x = 0;
  int last_y = 0;
  int x_bytes = 0;
  int y_bytes = 0;

  for (unsigned int i = 0; i < points.size(); ++i) {
    const Point &point = points[i];
    int flag = point.on_curve ? kGlyfOnCurve : 0;
    int dx = point.x - last_x;
    int dy = point.y - last_y;
    if (dx == 0) {
      flag |= kGlyfThisXIsSame;
    } else if (dx > -256 && dx < 256) {
      flag |= kGlyfXShort | (dx > 0 ? kGlyfThisXIsSame : 0);
      x_bytes += 1;
    } else {
      x_bytes += 2;
    }
    if (dy == 0) {
      flag |= kGlyfThisYIsSame;
    } else if (dy > -256 && dy < 256) {
      flag |= kGlyfYShort | (dy > 0 ? kGlyfThisYIsSame : 0);
      y_bytes += 1;
    } else {
      y_bytes += 2;
    }
    // fprintf(stderr, "nominal flag = %d\n", flag);
    if (flag == last_flag && repeat_count != 255) {
      dst[flag_offset - 1] |= kGlyfRepeat;
      repeat_count++;
    } else {
      if (repeat_count != 0) {
        if (flag_offset >= dst_size) return OTS_FAILURE();
        dst[flag_offset++] = repeat_count;
      }
      if (flag_offset >= dst_size) return OTS_FAILURE();
      dst[flag_offset++] = flag;
      repeat_count = 0;
    }
    last_x = point.x;
    last_y = point.y;
    last_flag = flag;
  }

  if (repeat_count != 0) {
    if (flag_offset >= dst_size) return OTS_FAILURE();
    dst[flag_offset++] = repeat_count;
  }
  if (flag_offset + x_bytes + y_bytes > dst_size ||
      flag_offset + x_bytes + y_bytes < flag_offset) {
    return OTS_FAILURE();
  }

  int x_offset = flag_offset;
  int y_offset = flag_offset + x_bytes;
  last_x = 0;
  last_y = 0;
  for (unsigned int i = 0; i < points.size(); ++i) {
    int dx = points[i].x - last_x;
    if (dx == 0) {
      // pass
    } else if (dx > -256 && dx < 256) {
      dst[x_offset++] = std::abs(dx);
    } else {
      x_offset = Store16(dst, x_offset, dx);
    }
    last_x += dx;
    int dy = points[i].y - last_y;
    if (dy == 0) {
      // pass
    } else if (dy > -256 && dy < 256) {
      dst[y_offset++] = std::abs(dy);
    } else {
      y_offset = Store16(dst, y_offset, dy);
    }
    last_y += dy;
  }
  *glyph_size = y_offset;
  return true;
}

// Compute the bounding box of the coordinates, and store into a glyf buffer.
// A precondition is that there are at least 10 bytes available.
void ComputeBbox(const std::vector<Point> &points, uint8_t *dst) {
  int x_min = 0;
  int y_min = 0;
  int x_max = 0;
  int y_max = 0;
  
  for (unsigned int i = 0; i < points.size(); ++i) {
    int x = points[i].x;
    int y = points[i].y;
    if (i == 0 || x < x_min) x_min = x;
    if (i == 0 || x > x_max) x_max = x;
    if (i == 0 || y < y_min) y_min = y;
    if (i == 0 || y > y_max) y_max = y;
  }
  size_t offset = 2;
  offset = Store16(dst, offset, x_min);
  offset = Store16(dst, offset, y_min);
  offset = Store16(dst, offset, x_max);
  offset = Store16(dst, offset, y_max);
}

// Process entire bbox stream. This is done as a separate pass to allow for
// composite bbox computations (an optional more aggressive transform).
bool ProcessBboxStream(ots::Buffer *bbox_stream, unsigned int n_glyphs,
    const std::vector<uint32_t> &loca_values, uint8_t *glyf_buf) {
  const uint8_t *buf = bbox_stream->buffer();
  unsigned int bitmap_length = ((n_glyphs + 31) >> 5) << 2;
  if (bbox_stream->length() < bitmap_length) {
    return OTS_FAILURE();
  }
  bbox_stream->Skip(bitmap_length);
  for (unsigned int i = 0; i < n_glyphs; ++i) {
    if (buf[i >> 3] & (0x80 >> (i & 7))) {
      uint32_t loca_offset = loca_values[i];
      if (loca_values[i + 1] - loca_offset < kEndPtsOfContoursOffset) {
        return OTS_FAILURE();
      }
      bbox_stream->Read(glyf_buf + loca_offset + 2, 8);
    }
  }
  return true;
}

bool ProcessComposite(ots::Buffer *composite_stream, uint8_t *dst,
    size_t dst_size, size_t *glyph_size, bool *have_instructions) {
  size_t start_offset = composite_stream->offset();
  bool we_have_instructions = false;

  uint16_t flags = FLAG_MORE_COMPONENTS;
  while (flags & FLAG_MORE_COMPONENTS) {
    if (!composite_stream->ReadU16(&flags)) {
      return OTS_FAILURE();
    }
    we_have_instructions |= (flags & FLAG_WE_HAVE_INSTRUCTIONS) != 0;
    size_t arg_size = 2;  // glyph index
    if (flags & FLAG_ARG_1_AND_2_ARE_WORDS) {
      arg_size += 4;
    } else {
      arg_size += 2;
    }
    if (flags & FLAG_WE_HAVE_A_SCALE) {
      arg_size += 2;
    } else if (flags & FLAG_WE_HAVE_AN_X_AND_Y_SCALE) {
      arg_size += 4;
    } else if (flags & FLAG_WE_HAVE_A_TWO_BY_TWO) {
      arg_size += 8;
    }
    if (!composite_stream->Skip(arg_size)) {
      return OTS_FAILURE();
    }
    //fprintf(stderr, "flags = %04x, arg_size = %d\n", flags, arg_size);
  }
  size_t composite_glyph_size = composite_stream->offset() - start_offset;
  if (composite_glyph_size + kCompositeGlyphBegin > dst_size) {
    return OTS_FAILURE();
  }
  Store16(dst, 0, 0xffff);  // nContours = -1 for composite glyph
  std::memcpy(dst + kCompositeGlyphBegin,
      composite_stream->buffer() + start_offset,
      composite_glyph_size);
  *glyph_size = kCompositeGlyphBegin + composite_glyph_size;
  *have_instructions = we_have_instructions;
  return true;
}

// Build TrueType loca table
bool StoreLoca(const std::vector<uint32_t> &loca_values, int index_format,
    uint8_t *dst, size_t dst_size) {
  size_t loca_size = loca_values.size();
  size_t offset_size = index_format ? 4 : 2;
  if (offset_size * loca_size > dst_size) {
    return OTS_FAILURE();
  }
  size_t offset = 0;
  for (size_t i = 0; i < loca_values.size(); ++i) {
    int value = loca_values[i];
    if (index_format) {
      offset = StoreU32(dst, offset, value);
    } else {
      offset = Store16(dst, offset, value >> 1);
    }
  }
  return true;
}

// Reconstruct entire glyf table based on transformed original
bool ReconstructGlyf(const uint8_t *data, size_t data_size,
    uint8_t *dst, size_t dst_size,
    uint8_t *loca_buf, size_t loca_size) {
  ots::Buffer file(data, data_size);
  uint32_t version;
  const int kNumSubStreams = 7;
  std::vector<std::pair<const uint8_t*, size_t> > substreams(kNumSubStreams);

  if (!file.ReadU32(&version)) {
    return OTS_FAILURE();
  }
  uint16_t num_glyphs = 0;
  uint16_t index_format = 0;
  if (!file.ReadU16(&num_glyphs) ||
      !file.ReadU16(&index_format)) {
    return OTS_FAILURE();
  }
  // fprintf(stderr, "num_glyphs = %d\n", num_glyphs);
  unsigned int offset = (2 + kNumSubStreams) * 4;
  for (int i = 0; i < kNumSubStreams; ++i) {
    uint32_t substream_size = 0;
    if (!file.ReadU32(&substream_size)) {
      return OTS_FAILURE();
    }
    if (substream_size > data_size - offset) {
      return OTS_FAILURE();
    }
    // fprintf(stderr, "substream size = %d\n", substream_size);
    substreams[i] = std::make_pair(data + offset, substream_size);
    offset += substream_size;
  }
  ots::Buffer n_contour_stream(substreams[0].first, substreams[0].second);
  ots::Buffer n_points_stream(substreams[1].first, substreams[1].second);
  ots::Buffer flag_stream(substreams[2].first, substreams[2].second);
  ots::Buffer glyph_stream(substreams[3].first, substreams[3].second);
  ots::Buffer composite_stream(substreams[4].first, substreams[4].second);
  ots::Buffer bbox_stream(substreams[5].first, substreams[5].second);
  ots::Buffer instruction_stream(substreams[6].first, substreams[6].second);
  
  std::vector<uint32_t> loca_values(num_glyphs + 1);
  std::vector<unsigned int> n_points_vec;
  std::vector<Point> points;
  uint32_t loca_offset = 0;
  for (unsigned int i = 0; i < num_glyphs; ++i) {
    size_t glyph_size = 0;
    uint16_t n_contours = 0;
    if (!n_contour_stream.ReadU16(&n_contours)) {
      return OTS_FAILURE();
    }
    // fprintf(stderr, "n_contours[%d] = %d\n", i, n_contours);
    uint8_t *glyf_dst = dst + loca_offset;
    size_t glyf_dst_size = dst_size - loca_offset;
    if (n_contours == 0xffff) {
      // composite glyph
      bool have_instructions = false;
      unsigned int instruction_size = 0;
      if (!ProcessComposite(&composite_stream, glyf_dst, glyf_dst_size,
            &glyph_size, &have_instructions)) {
        return OTS_FAILURE();
      }
      if (have_instructions) {
        if (!Read255UShort(&glyph_stream, &instruction_size)) {
          return OTS_FAILURE();
        }
        if (instruction_size + 2 > glyf_dst_size - glyph_size) {
          return OTS_FAILURE();
        }
        Store16(glyf_dst, glyph_size, instruction_size);
        if (!instruction_stream.Read(glyf_dst + glyph_size + 2,
              instruction_size)) {
          return OTS_FAILURE();
        }
        glyph_size += instruction_size + 2;
      }
    } else if (n_contours > 0) {
      // simple glyph
      n_points_vec.clear();
      points.clear();
      unsigned int total_n_points = 0;
      unsigned int n_points_contour;
      for (unsigned int j = 0; j < n_contours; ++j) {
        if (!Read255UShort(&n_points_stream, &n_points_contour)) {
          return OTS_FAILURE();
        }
        n_points_vec.push_back(n_points_contour);
        total_n_points += n_points_contour;
      }
      unsigned int flag_size = total_n_points;
      if (flag_size > flag_stream.length() - flag_stream.offset()) {
        return OTS_FAILURE();
      }
      const uint8_t *flags_buf = flag_stream.buffer() + flag_stream.offset();
      const uint8_t *triplet_buf = glyph_stream.buffer() +
        glyph_stream.offset();
      size_t triplet_size = glyph_stream.length() - glyph_stream.offset();
      size_t triplet_bytes_consumed = 0;
      if (!TripletDecode(flags_buf, triplet_buf, triplet_size, total_n_points,
            &points, &triplet_bytes_consumed)) {
        return OTS_FAILURE();
      }
      if (glyf_dst_size < kEndPtsOfContoursOffset + 2 * n_contours) {
        return OTS_FAILURE();
      }
      Store16(glyf_dst, 0, n_contours);
      ComputeBbox(points, glyf_dst);
      size_t offset = kEndPtsOfContoursOffset;
      int end_point = -1;
      for (unsigned int contour_ix = 0; contour_ix < n_contours; ++contour_ix) {
        end_point += n_points_vec[contour_ix];
        offset = Store16(glyf_dst, offset, end_point);
      }
      flag_stream.Skip(flag_size);
      glyph_stream.Skip(triplet_bytes_consumed);
      unsigned int instruction_size;
      if (!Read255UShort(&glyph_stream, &instruction_size)) {
        return OTS_FAILURE();
      }
      // fprintf(stderr, "%d: instruction size = %d\n", i, instruction_size);
      uint8_t *instruction_dst = glyf_dst + kEndPtsOfContoursOffset +
        2 * n_contours;
      Store16(instruction_dst, 0, instruction_size);
      if (!instruction_stream.Read(instruction_dst + 2, instruction_size)) {
        return OTS_FAILURE();
      }
      if (!StorePoints(points, n_contours, instruction_size,
            glyf_dst, glyf_dst_size, &glyph_size)) {
        return OTS_FAILURE();
      }
    } else {
      glyph_size = 0;
    }
    loca_values[i] = loca_offset;
    if (glyph_size + 3 < glyph_size) {
      return OTS_FAILURE();
    }
    // Round up to 4-byte alignment
    glyph_size = (glyph_size + 3) & -4;
    if (glyph_size > dst_size - loca_offset) {
      // This shouldn't happen, but this test defensively maintains the
      // invariant that loca_offset <= dst_size.
      return OTS_FAILURE();
    }
    loca_offset += glyph_size;
  }
  loca_values[num_glyphs] = loca_offset;
  if (!ProcessBboxStream(&bbox_stream, num_glyphs, loca_values, dst)) {
    return OTS_FAILURE();
  }
  return StoreLoca(loca_values, index_format, loca_buf, loca_size);
}

// This is linear search, but could be changed to binary because we
// do have a guarantee that the tables are sorted by tag. But the total
// cpu time is expected to be very small in any case.
const Table *FindTable(const std::vector<Table> &tables, uint32_t tag) {
  size_t n_tables = tables.size();
  for (size_t i = 0; i < n_tables; ++i) {
    if (tables[i].tag == tag) {
      return &tables[i];
    }
  }
  return NULL;
}

bool ReconstructTransformed(const std::vector<Table> &tables, uint32_t tag,
    const uint8_t *transformed_buf, size_t transformed_size,
    uint8_t *dst) {
  if (tag == TAG('g', 'l', 'y', 'f')) {
    const Table *glyf_table = FindTable(tables, tag);
    const Table *loca_table = FindTable(tables, TAG('l', 'o', 'c', 'a'));
    if (glyf_table == NULL || loca_table == NULL) {
      return OTS_FAILURE();
    }
    return ReconstructGlyf(transformed_buf, transformed_size,
        dst + glyf_table->dst_offset, glyf_table->dst_length,
        dst + loca_table->dst_offset, loca_table->dst_offset);
  } else if (tag == TAG('l', 'o', 'c', 'a')) {
    // processing was already done by glyf table, but validate
    if (!FindTable(tables, TAG('g', 'l', 'y', 'f'))) {
      return OTS_FAILURE();
    }
  } else {
    // transform for the tag is not known
    return OTS_FAILURE();
  }
  return true;
}

// TODO: copied from ots.cc, probably shouldn't be duplicated.
// Round a value up to the nearest multiple of 4. Don't round the value in the
// case that rounding up overflows.
template<typename T> T Round4(T value) {
  if (std::numeric_limits<T>::max() - value < 3) {
    return value;
  }
  return (value + 3) & ~3;
}

uint32_t ComputeChecksum(const uint8_t *buf, size_t size) {
  uint32_t checksum = 0;
  for (size_t i = 0; i < size; i += 4) {
    // We assume the addition is mod 2^32. This is a pretty safe assumption,
    // but technically it's undefined behavior.
    checksum += (buf[i] << 24) | (buf[i + 1] << 16) |
      (buf[i + 2] << 8) | buf[i + 3];
  }
  return checksum;
}

bool FixChecksums(const std::vector<Table> &tables, uint8_t *dst) {
  const Table *head_table = FindTable(tables, TAG('h', 'e', 'a', 'd'));
  if (head_table == NULL ||
      head_table->dst_length < kCheckSumAdjustmentOffset + 4) {
    return OTS_FAILURE();
  }
  size_t adjustment_offset = head_table->dst_offset + kCheckSumAdjustmentOffset;
  StoreU32(dst, adjustment_offset, 0);
  size_t n_tables = tables.size();
  uint32_t file_checksum = 0;
  for (size_t i = 0; i < n_tables; ++i) {
    const Table *table = &tables[i];
    size_t table_length = table->dst_length;
    uint8_t *table_data = dst + table->dst_offset;
    uint32_t checksum = ComputeChecksum(table_data, table_length);
    StoreU32(dst, kSfntHeaderSize + i * kSfntEntrySize + 4, checksum);
    file_checksum += checksum;
  }
  file_checksum += ComputeChecksum(dst,
      kSfntHeaderSize + kSfntEntrySize * n_tables);
  uint32_t checksum_adjustment = 0xb1b0afba - file_checksum;
  StoreU32(dst, adjustment_offset, checksum_adjustment);
  return true;
}

bool Woff2Uncompress(uint8_t *dst_buf, size_t dst_size,
    const uint8_t *src_buf, size_t src_size, uint32_t compression_type) {
  if (compression_type == kCompressionTypeGzip) {
    uLongf uncompressed_length = dst_size;
    int r = uncompress((Bytef *)dst_buf, &uncompressed_length,
        src_buf, src_size);
    if (r != Z_OK || uncompressed_length != src_size) {
      return OTS_FAILURE();
    }
    return true;
#ifdef USE_LZMA
  } else if (compression_type == kCompressionTypeLzma) {
    if (src_size < kLzmaHeaderSize) {
      // Make sure we have at least a full Lzma header
      return OTS_FAILURE();
    }
    // TODO: check that size matches (or elide size?)
    size_t uncompressed_size = dst_size;
    size_t compressed_size = src_size;
    int result = LzmaUncompress(dst_buf, &dst_size,
        src_buf + kLzmaHeaderSize, &compressed_size,
        src_buf, LZMA_PROPS_SIZE);
    if (result != SZ_OK || uncompressed_size != dst_size) {
      return OTS_FAILURE();
    }
    return true;
#endif
  }
  // Unknown compression type
  return OTS_FAILURE();
}

bool ReadLongDirectory(ots::Buffer *file, std::vector<Table> *tables,
    size_t num_tables) {
  for (size_t i = 0; i < num_tables; ++i) {
    Table *table = &(*tables)[i];
    if (!file->ReadU32(&table->tag) ||
        !file->ReadU32(&table->flags) ||
        !file->ReadU32(&table->src_length) ||
        !file->ReadU32(&table->transform_length) ||
        !file->ReadU32(&table->dst_length)) {
      return OTS_FAILURE();
    }
  }
  return true;
}

const uint32_t known_tags[29] = {
  TAG('c', 'm', 'a', 'p'),  // 0
  TAG('h', 'e', 'a', 'd'),  // 1
  TAG('h', 'h', 'e', 'a'),  // 2
  TAG('h', 'm', 't', 'x'),  // 3
  TAG('m', 'a', 'x', 'p'),  // 4
  TAG('n', 'a', 'm', 'e'),  // 5
  TAG('O', 'S', '/', '2'),  // 6
  TAG('p', 'o', 's', 't'),  // 7
  TAG('c', 'v', 't', ' '),  // 8
  TAG('f', 'p', 'g', 'm'),  // 9
  TAG('g', 'l', 'y', 'f'),  // 10
  TAG('l', 'o', 'c', 'a'),  // 11
  TAG('p', 'r', 'e', 'p'),  // 12
  TAG('C', 'F', 'F', ' '),  // 13
  TAG('V', 'O', 'R', 'G'),  // 14
  TAG('E', 'B', 'D', 'T'),  // 15
  TAG('E', 'B', 'L', 'C'),  // 16
  TAG('g', 'a', 's', 'p'),  // 17
  TAG('h', 'd', 'm', 'x'),  // 18
  TAG('k', 'e', 'r', 'n'),  // 19
  TAG('L', 'T', 'S', 'H'),  // 20
  TAG('P', 'C', 'L', 'T'),  // 21
  TAG('V', 'D', 'M', 'X'),  // 22
  TAG('v', 'h', 'e', 'a'),  // 23
  TAG('v', 'm', 't', 'x'),  // 24
  TAG('B', 'A', 'S', 'E'),  // 25
  TAG('G', 'D', 'E', 'F'),  // 26
  TAG('G', 'P', 'O', 'S'),  // 27
  TAG('G', 'S', 'U', 'B'),  // 28
};

bool ReadShortDirectory(ots::Buffer *file, std::vector<Table> *tables,
    size_t num_tables) {
  uint32_t last_compression_type = 0;
  for (size_t i = 0; i < num_tables; ++i) {
    Table *table = &(*tables)[i];
    uint8_t flag_byte = 0;
    if (!file->ReadU8(&flag_byte)) {
      return OTS_FAILURE();
    }
    uint32_t tag = 0;
    if ((flag_byte & 0x1f) == 0x1f) {
      if (!file->ReadU32(&tag)) {
        return OTS_FAILURE();
      }
    } else {
      tag = known_tags[flag_byte & 0x1f];
    }
    uint32_t flags = flag_byte >> 6;
    if (flags == 3) {
      flags = last_compression_type | kWoff2FlagsContinueStream;
    } else {
      last_compression_type = flags;
    }
    if ((flag_byte & 0x20) != 0) {
      flags |= kWoff2FlagsTransform;
    }
    uint32_t dst_length = 0;
    if (!ReadBase128(file, &dst_length)) {
      return OTS_FAILURE();
    }
    uint32_t transform_length = dst_length;
    if ((flags & kWoff2FlagsTransform) != 0) {
      if (!ReadBase128(file, &transform_length)) {
        return OTS_FAILURE();
      }
    }
    uint32_t src_length = transform_length;
    if ((flag_byte >> 6) == 1 | (flag_byte >> 6) == 2) {
      if (!ReadBase128(file, &src_length)) {
        return OTS_FAILURE();
      }
    }
    table->tag = tag;
    table->flags = flags;
    table->src_length = src_length;
    table->transform_length = transform_length;
    table->dst_length = dst_length;
  }
  return true;
}

}  // namespace

namespace ots {

size_t ComputeWOFF2FinalSize(const uint8_t *data, size_t length) {
  ots::Buffer file(data, length);

  file.Skip(16);
  uint32_t total_length = 0;
  if (!file.ReadU32(&total_length)) {
    return OTS_FAILURE();
  }
  return total_length;
}

bool ConvertWOFF2ToTTF(uint8_t *result, size_t result_length,
                       const uint8_t *data, size_t length) {
  ots::Buffer file(data, length);

  uint32_t signature = 0;
  uint32_t flavor = 0;
  if (!file.ReadU32(&signature) || signature != 0x774f4632 ||
      !file.ReadU32(&flavor)) {
    return OTS_FAILURE();
  }
  file.Skip(4);
  uint16_t num_tables = 0;
  if (!file.ReadU16(&num_tables)) {
    return OTS_FAILURE();
  }
  file.Skip(30);
  std::vector<Table> tables(num_tables);
  // Note: change below to ReadLongDirectory to enable long format.
  if (!ReadShortDirectory(&file, &tables, num_tables)) {
    return OTS_FAILURE();
  }
  size_t src_offset = file.offset();
  size_t dst_offset = kSfntHeaderSize + kSfntEntrySize * num_tables;
  size_t uncompressed_sum = 0;
  for (int i = 0; i < num_tables; ++i) {
    Table *table = &tables[i];
    table->src_offset = src_offset;
    if (src_offset + table->src_length < src_offset) {
      return OTS_FAILURE();
    }
    src_offset += table->src_length;
    src_offset = Round4(src_offset);  // TODO: reconsider
    table->dst_offset = dst_offset;
    if (dst_offset + table->dst_length < dst_offset) {
      return OTS_FAILURE();
    }
    dst_offset += table->dst_length;
    dst_offset = Round4(dst_offset);
    if ((table->flags & kCompressionTypeMask) != kCompressionTypeNone) {
      if (uncompressed_sum + table->src_length < uncompressed_sum) {
        return OTS_FAILURE();
      }
      uncompressed_sum += table->src_length;
    }
  }
  // Enforce same 30M limit on uncompressed tables as OTS
  if (uncompressed_sum > 30 * 1024 * 1024) {
    return OTS_FAILURE();
  }
  if (dst_offset > result_length) {
    return OTS_FAILURE();
  }

  // Start building the font
  size_t offset = 0;
  offset = StoreU32(result, offset, flavor);
  offset = Store16(result, offset, num_tables);
  unsigned max_pow2 = 0;
  while (1u << (max_pow2 + 1) <= num_tables) {
    max_pow2++;
  }
  const uint16_t output_search_range = (1u << max_pow2) << 4;
  offset = Store16(result, offset, output_search_range);
  offset = Store16(result, offset, max_pow2);
  offset = Store16(result, offset, (num_tables << 4) - output_search_range);
  for (int i = 0; i < num_tables; ++i) {
    const Table *table = &tables[i];
    offset = StoreU32(result, offset, table->tag);
    offset = StoreU32(result, offset, 0);  // checksum, to fill in later
    offset = StoreU32(result, offset, table->dst_offset);
    offset = StoreU32(result, offset, table->dst_length);
  }
  std::vector<uint8_t> uncompressed_buf;
  bool continue_valid = false;
  for (int i = 0; i < num_tables; ++i) {
    const Table *table = &tables[i];
    uint32_t flags = table->flags;
    const uint8_t *src_buf = data + table->src_offset;
    uint32_t compression_type = flags & kCompressionTypeMask;
    const uint8_t *transform_buf = NULL;
    size_t transform_length = table->transform_length;
    if ((flags & kWoff2FlagsContinueStream) != 0) {
      if (!continue_valid) {
        return OTS_FAILURE();
      }
    } else if (compression_type == kCompressionTypeNone) {
      if (transform_length != table->src_length) {
        return OTS_FAILURE();
      }
      transform_buf = src_buf;
      continue_valid = false;
    } else if ((flags & kWoff2FlagsContinueStream) == 0) {
      size_t total_size = transform_length;
      for (int j = i + 1; j < num_tables; ++j) {
        if ((tables[j].flags & kWoff2FlagsContinueStream) == 0) {
          break;
        }
        if (total_size + tables[j].transform_length < total_size) {
          return OTS_FAILURE();
        }
        total_size += tables[j].transform_length;
      }
      uncompressed_buf.resize(total_size);
      if (!Woff2Uncompress(&uncompressed_buf[0], total_size,
          src_buf, table->src_length, compression_type)) {
        return OTS_FAILURE();
      }
      transform_buf = &uncompressed_buf[0];
      continue_valid = true;
    } 

    if ((flags & kWoff2FlagsTransform) == 0) {
      if (transform_length != table->dst_length) {
        return OTS_FAILURE();
      }
      std::memcpy(result + table->dst_offset, transform_buf,
          transform_length);
    } else {
      if (!ReconstructTransformed(tables, table->tag,
            transform_buf, transform_length, result)) {
        return OTS_FAILURE();
      }
    }
    if (continue_valid) {
      transform_buf += transform_length;
    }
  }

  return FixChecksums(tables, result);
}

}  // namespace ots