Updating OTS repo from https://github.com/khaledhosny/ots.git

third_party/ots/src/gpos.cc

+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "gpos.h"
+
+#include <limits>
+#include <vector>
+
+#include "layout.h"
+#include "maxp.h"
+
+// GPOS - The Glyph Positioning Table
+// http://www.microsoft.com/typography/otspec/gpos.htm
+
+#define TABLE_NAME "GPOS"
+
+namespace {
+
+enum GPOS_TYPE {
+  GPOS_TYPE_SINGLE_ADJUSTMENT = 1,
+  GPOS_TYPE_PAIR_ADJUSTMENT = 2,
+  GPOS_TYPE_CURSIVE_ATTACHMENT = 3,
+  GPOS_TYPE_MARK_TO_BASE_ATTACHMENT = 4,
+  GPOS_TYPE_MARK_TO_LIGATURE_ATTACHMENT = 5,
+  GPOS_TYPE_MARK_TO_MARK_ATTACHMENT = 6,
+  GPOS_TYPE_CONTEXT_POSITIONING = 7,
+  GPOS_TYPE_CHAINED_CONTEXT_POSITIONING = 8,
+  GPOS_TYPE_EXTENSION_POSITIONING = 9,
+  GPOS_TYPE_RESERVED = 10
+};
+
+// The size of gpos header.
+const unsigned kGposHeaderSize = 10;
+// The maximum format number for anchor tables.
+const uint16_t kMaxAnchorFormat = 3;
+// The maximum number of class value.
+const uint16_t kMaxClassDefValue = 0xFFFF;
+
+// Lookup type parsers.
+bool ParseSingleAdjustment(const ots::OpenTypeFile *file,
+                           const uint8_t *data, const size_t length);
+bool ParsePairAdjustment(const ots::OpenTypeFile *file,
+                         const uint8_t *data, const size_t length);
+bool ParseCursiveAttachment(const ots::OpenTypeFile *file,
+                            const uint8_t *data, const size_t length);
+bool ParseMarkToBaseAttachment(const ots::OpenTypeFile *file,
+                               const uint8_t *data, const size_t length);
+bool ParseMarkToLigatureAttachment(const ots::OpenTypeFile *file,
+                                   const uint8_t *data, const size_t length);
+bool ParseMarkToMarkAttachment(const ots::OpenTypeFile *file,
+                               const uint8_t *data, const size_t length);
+bool ParseContextPositioning(const ots::OpenTypeFile *file,
+                             const uint8_t *data, const size_t length);
+bool ParseChainedContextPositioning(const ots::OpenTypeFile *file,
+                                    const uint8_t *data, const size_t length);
+bool ParseExtensionPositioning(const ots::OpenTypeFile *file,
+                               const uint8_t *data, const size_t length);
+
+const ots::LookupSubtableParser::TypeParser kGposTypeParsers[] = {
+  {GPOS_TYPE_SINGLE_ADJUSTMENT, ParseSingleAdjustment},
+  {GPOS_TYPE_PAIR_ADJUSTMENT, ParsePairAdjustment},
+  {GPOS_TYPE_CURSIVE_ATTACHMENT, ParseCursiveAttachment},
+  {GPOS_TYPE_MARK_TO_BASE_ATTACHMENT, ParseMarkToBaseAttachment},
+  {GPOS_TYPE_MARK_TO_LIGATURE_ATTACHMENT, ParseMarkToLigatureAttachment},
+  {GPOS_TYPE_MARK_TO_MARK_ATTACHMENT, ParseMarkToMarkAttachment},
+  {GPOS_TYPE_CONTEXT_POSITIONING, ParseContextPositioning},
+  {GPOS_TYPE_CHAINED_CONTEXT_POSITIONING, ParseChainedContextPositioning},
+  {GPOS_TYPE_EXTENSION_POSITIONING, ParseExtensionPositioning}
+};
+
+const ots::LookupSubtableParser kGposLookupSubtableParser = {
+  arraysize(kGposTypeParsers),
+  GPOS_TYPE_EXTENSION_POSITIONING, kGposTypeParsers
+};
+
+// Shared Tables: ValueRecord, Anchor Table, and MarkArray
+
+bool ParseValueRecord(const ots::OpenTypeFile *file,
+                      ots::Buffer* subtable, const uint8_t *data,
+                      const size_t length, const uint16_t value_format) {
+  // Check existence of adjustment fields.
+  for (unsigned i = 0; i < 4; ++i) {
+    if ((value_format >> i) & 0x1) {
+      // Just read the field since these fileds could take an arbitrary values.
+      if (!subtable->Skip(2)) {
+        return OTS_FAILURE_MSG("Failed to read value reacord component");
+      }
+    }
+  }
+
+  // Check existence of offsets to device table.
+  for (unsigned i = 0; i < 4; ++i) {
+    if ((value_format >> (i + 4)) & 0x1) {
+      uint16_t offset = 0;
+      if (!subtable->ReadU16(&offset)) {
+        return OTS_FAILURE_MSG("Failed to read value record offset");
+      }
+      if (offset) {
+        // TODO(bashi): Is it possible that device tables locate before
+        // this record? No fonts contain such offset AKAIF.
+        if (offset >= length) {
+          return OTS_FAILURE_MSG("Value record offset too high %d >= %ld", offset, length);
+        }
+        if (!ots::ParseDeviceTable(file, data + offset, length - offset)) {
+          return OTS_FAILURE_MSG("Failed to parse device table in value record");
+        }
+      }
+    }
+  }
+  return true;
+}
+
+bool ParseAnchorTable(const ots::OpenTypeFile *file,
+                      const uint8_t *data, const size_t length) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t format = 0;
+  // Read format and skip 2 2-byte fields that could be arbitrary values.
+  if (!subtable.ReadU16(&format) ||
+      !subtable.Skip(4)) {
+    return OTS_FAILURE_MSG("Faled to read anchor table");
+  }
+
+  if (format == 0 || format > kMaxAnchorFormat) {
+    return OTS_FAILURE_MSG("Bad Anchor table format %d", format);
+  }
+
+  // Format 2 and 3 has additional fields.
+  if (format == 2) {
+    // Format 2 provides an index to a glyph contour point, which will take
+    // arbitrary value.
+    uint16_t anchor_point = 0;
+    if (!subtable.ReadU16(&anchor_point)) {
+      return OTS_FAILURE_MSG("Failed to read anchor point in format 2 Anchor Table");
+    }
+  } else if (format == 3) {
+    uint16_t offset_x_device = 0;
+    uint16_t offset_y_device = 0;
+    if (!subtable.ReadU16(&offset_x_device) ||
+        !subtable.ReadU16(&offset_y_device)) {
+      return OTS_FAILURE_MSG("Failed to read device table offsets in format 3 anchor table");
+    }
+    const unsigned format_end = static_cast<unsigned>(10);
+    if (offset_x_device) {
+      if (offset_x_device < format_end || offset_x_device >= length) {
+        return OTS_FAILURE_MSG("Bad x device table offset %d", offset_x_device);
+      }
+      if (!ots::ParseDeviceTable(file, data + offset_x_device,
+                                 length - offset_x_device)) {
+        return OTS_FAILURE_MSG("Failed to parse device table in anchor table");
+      }
+    }
+    if (offset_y_device) {
+      if (offset_y_device < format_end || offset_y_device >= length) {
+        return OTS_FAILURE_MSG("Bad y device table offset %d", offset_y_device);
+      }
+      if (!ots::ParseDeviceTable(file, data + offset_y_device,
+                                 length - offset_y_device)) {
+        return OTS_FAILURE_MSG("Failed to parse device table in anchor table");
+      }
+    }
+  }
+  return true;
+}
+
+bool ParseMarkArrayTable(const ots::OpenTypeFile *file,
+                         const uint8_t *data, const size_t length,
+                         const uint16_t class_count) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t mark_count = 0;
+  if (!subtable.ReadU16(&mark_count)) {
+    return OTS_FAILURE_MSG("Can't read mark table length");
+  }
+
+  // MarkRecord consists of 4-bytes.
+  const unsigned mark_records_end = 4 * static_cast<unsigned>(mark_count) + 2;
+  if (mark_records_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad mark table length");
+  }
+  for (unsigned i = 0; i < mark_count; ++i) {
+    uint16_t class_value = 0;
+    uint16_t offset_mark_anchor = 0;
+    if (!subtable.ReadU16(&class_value) ||
+        !subtable.ReadU16(&offset_mark_anchor)) {
+      return OTS_FAILURE_MSG("Can't read mark table %d", i);
+    }
+    // |class_value| may take arbitrary values including 0 here so we don't
+    // check the value.
+    if (offset_mark_anchor < mark_records_end ||
+        offset_mark_anchor >= length) {
+      return OTS_FAILURE_MSG("Bad mark anchor offset %d for mark table %d", offset_mark_anchor, i);
+    }
+    if (!ParseAnchorTable(file, data + offset_mark_anchor,
+                          length - offset_mark_anchor)) {
+      return OTS_FAILURE_MSG("Faled to parse anchor table for mark table %d", i);
+    }
+  }
+
+  return true;
+}
+
+// Lookup Type 1:
+// Single Adjustment Positioning Subtable
+bool ParseSingleAdjustment(const ots::OpenTypeFile *file, const uint8_t *data,
+                           const size_t length) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t format = 0;
+  uint16_t offset_coverage = 0;
+  uint16_t value_format = 0;
+  if (!subtable.ReadU16(&format) ||
+      !subtable.ReadU16(&offset_coverage) ||
+      !subtable.ReadU16(&value_format)) {
+    return OTS_FAILURE_MSG("Can't read single adjustment information");
+  }
+
+  if (format == 1) {
+    // Format 1 exactly one value record.
+    if (!ParseValueRecord(file, &subtable, data, length, value_format)) {
+      return OTS_FAILURE_MSG("Failed to parse format 1 single adjustment table");
+    }
+  } else if (format == 2) {
+    uint16_t value_count = 0;
+    if (!subtable.ReadU16(&value_count)) {
+      return OTS_FAILURE_MSG("Failed to parse format 2 single adjustment table");
+    }
+    for (unsigned i = 0; i < value_count; ++i) {
+      if (!ParseValueRecord(file, &subtable, data, length, value_format)) {
+        return OTS_FAILURE_MSG("Failed to parse value record %d in format 2 single adjustment table", i);
+      }
+    }
+  } else {
+    return OTS_FAILURE_MSG("Bad format %d in single adjustment table", format);
+  }
+
+  if (offset_coverage < subtable.offset() || offset_coverage >= length) {
+    return OTS_FAILURE_MSG("Bad coverage offset %d in single adjustment table", offset_coverage);
+  }
+
+  if (!ots::ParseCoverageTable(file, data + offset_coverage,
+                               length - offset_coverage,
+                               file->maxp->num_glyphs)) {
+    return OTS_FAILURE_MSG("Failed to parse coverage table in single adjustment table");
+  }
+
+  return true;
+}
+
+bool ParsePairSetTable(const ots::OpenTypeFile *file,
+                       const uint8_t *data, const size_t length,
+                       const uint16_t value_format1,
+                       const uint16_t value_format2,
+                       const uint16_t num_glyphs) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t value_count = 0;
+  if (!subtable.ReadU16(&value_count)) {
+    return OTS_FAILURE_MSG("Failed to read pair set table structure");
+  }
+  for (unsigned i = 0; i < value_count; ++i) {
+    // Check pair value record.
+    uint16_t glyph_id = 0;
+    if (!subtable.ReadU16(&glyph_id)) {
+      return OTS_FAILURE_MSG("Failed to read glyph in pair value record %d", i);
+    }
+    if (glyph_id >= num_glyphs) {
+      return OTS_FAILURE_MSG("glyph id %d too high >= %d", glyph_id, num_glyphs);
+    }
+    if (!ParseValueRecord(file, &subtable, data, length, value_format1)) {
+      return OTS_FAILURE_MSG("Failed to parse value record in format 1 pair set table");
+    }
+    if (!ParseValueRecord(file, &subtable, data, length, value_format2)) {
+      return OTS_FAILURE_MSG("Failed to parse value record in format 2 pair set table");
+    }
+  }
+  return true;
+}
+
+bool ParsePairPosFormat1(const ots::OpenTypeFile *file,
+                         const uint8_t *data, const size_t length,
+                         const uint16_t value_format1,
+                         const uint16_t value_format2,
+                         const uint16_t num_glyphs) {
+  ots::Buffer subtable(data, length);
+
+  // Skip 8 bytes that are already read before.
+  if (!subtable.Skip(8)) {
+    return OTS_FAILURE_MSG("Failed to read pair pos table structure");
+  }
+
+  uint16_t pair_set_count = 0;
+  if (!subtable.ReadU16(&pair_set_count)) {
+    return OTS_FAILURE_MSG("Failed to read pair pos set count");
+  }
+
+  const unsigned pair_pos_end = 2 * static_cast<unsigned>(pair_set_count) + 10;
+  if (pair_pos_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad pair set length %d", pair_pos_end);
+  }
+  for (unsigned i = 0; i < pair_set_count; ++i) {
+    uint16_t pair_set_offset = 0;
+    if (!subtable.ReadU16(&pair_set_offset)) {
+      return OTS_FAILURE_MSG("Failed to read pair set offset for pair set %d", i);
+    }
+    if (pair_set_offset < pair_pos_end || pair_set_offset >= length) {
+      return OTS_FAILURE_MSG("Bad pair set offset %d for pair set %d", pair_set_offset, i);
+    }
+    // Check pair set tables
+    if (!ParsePairSetTable(file, data + pair_set_offset, length - pair_set_offset,
+                           value_format1, value_format2,
+                           num_glyphs)) {
+      return OTS_FAILURE_MSG("Failed to parse pair set table %d", i);
+    }
+  }
+
+  return true;
+}
+
+bool ParsePairPosFormat2(const ots::OpenTypeFile *file,
+                         const uint8_t *data, const size_t length,
+                         const uint16_t value_format1,
+                         const uint16_t value_format2,
+                         const uint16_t num_glyphs) {
+  ots::Buffer subtable(data, length);
+
+  // Skip 8 bytes that are already read before.
+  if (!subtable.Skip(8)) {
+    return OTS_FAILURE_MSG("Failed to read pair pos format 2 structure");
+  }
+
+  uint16_t offset_class_def1 = 0;
+  uint16_t offset_class_def2 = 0;
+  uint16_t class1_count = 0;
+  uint16_t class2_count = 0;
+  if (!subtable.ReadU16(&offset_class_def1) ||
+      !subtable.ReadU16(&offset_class_def2) ||
+      !subtable.ReadU16(&class1_count) ||
+      !subtable.ReadU16(&class2_count)) {
+    return OTS_FAILURE_MSG("Failed to read pair pos format 2 data");
+  }
+
+  // Check class 1 records.
+  for (unsigned i = 0; i < class1_count; ++i) {
+    // Check class 2 records.
+    for (unsigned j = 0; j < class2_count; ++j) {
+      if (value_format1 && !ParseValueRecord(file, &subtable, data, length,
+                                             value_format1)) {
+        return OTS_FAILURE_MSG("Failed to parse value record 1 %d and %d", j, i);
+      }
+      if (value_format2 && !ParseValueRecord(file, &subtable, data, length,
+                                             value_format2)) {
+        return OTS_FAILURE_MSG("Falied to parse value record 2 %d and %d", j, i);
+      }
+    }
+  }
+
+  // Check class definition tables.
+  if (offset_class_def1 < subtable.offset() || offset_class_def1 >= length ||
+      offset_class_def2 < subtable.offset() || offset_class_def2 >= length) {
+    return OTS_FAILURE_MSG("Bad class definition table offsets %d or %d", offset_class_def1, offset_class_def2);
+  }
+  if (!ots::ParseClassDefTable(file, data + offset_class_def1,
+                               length - offset_class_def1,
+                               num_glyphs, kMaxClassDefValue)) {
+    return OTS_FAILURE_MSG("Failed to parse class definition table 1");
+  }
+  if (!ots::ParseClassDefTable(file, data + offset_class_def2,
+                               length - offset_class_def2,
+                               num_glyphs, kMaxClassDefValue)) {
+    return OTS_FAILURE_MSG("Failed to parse class definition table 2");
+  }
+
+  return true;
+}
+
+// Lookup Type 2:
+// Pair Adjustment Positioning Subtable
+bool ParsePairAdjustment(const ots::OpenTypeFile *file, const uint8_t *data,
+                         const size_t length) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t format = 0;
+  uint16_t offset_coverage = 0;
+  uint16_t value_format1 = 0;
+  uint16_t value_format2 = 0;
+  if (!subtable.ReadU16(&format) ||
+      !subtable.ReadU16(&offset_coverage) ||
+      !subtable.ReadU16(&value_format1) ||
+      !subtable.ReadU16(&value_format2)) {
+    return OTS_FAILURE_MSG("Failed to read pair adjustment structure");
+  }
+
+  if (format == 1) {
+    if (!ParsePairPosFormat1(file, data, length, value_format1, value_format2,
+                             file->maxp->num_glyphs)) {
+      return OTS_FAILURE_MSG("Failed to parse pair pos format 1");
+    }
+  } else if (format == 2) {
+    if (!ParsePairPosFormat2(file, data, length, value_format1, value_format2,
+                             file->maxp->num_glyphs)) {
+      return OTS_FAILURE_MSG("Failed to parse pair format 2");
+    }
+  } else {
+    return OTS_FAILURE_MSG("Bad pos pair format %d", format);
+  }
+
+  if (offset_coverage < subtable.offset() || offset_coverage >= length) {
+    return OTS_FAILURE_MSG("Bad pair pos offset coverage %d", offset_coverage);
+  }
+  if (!ots::ParseCoverageTable(file, data + offset_coverage,
+                               length - offset_coverage,
+                               file->maxp->num_glyphs)) {
+    return OTS_FAILURE_MSG("Failed to parse coverage table");
+  }
+
+  return true;
+}
+
+// Lookup Type 3
+// Cursive Attachment Positioning Subtable
+bool ParseCursiveAttachment(const ots::OpenTypeFile *file, const uint8_t *data,
+                            const size_t length) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t format = 0;
+  uint16_t offset_coverage = 0;
+  uint16_t entry_exit_count = 0;
+  if (!subtable.ReadU16(&format) ||
+      !subtable.ReadU16(&offset_coverage) ||
+      !subtable.ReadU16(&entry_exit_count)) {
+    return OTS_FAILURE_MSG("Failed to read cursive attachment structure");
+  }
+
+  if (format != 1) {
+    return OTS_FAILURE_MSG("Bad cursive attachment format %d", format);
+  }
+
+  // Check entry exit records.
+  const unsigned entry_exit_records_end =
+      2 * static_cast<unsigned>(entry_exit_count) + 6;
+  if (entry_exit_records_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad entry exit record end %d", entry_exit_records_end);
+  }
+  for (unsigned i = 0; i < entry_exit_count; ++i) {
+    uint16_t offset_entry_anchor = 0;
+    uint16_t offset_exit_anchor = 0;
+    if (!subtable.ReadU16(&offset_entry_anchor) ||
+        !subtable.ReadU16(&offset_exit_anchor)) {
+      return OTS_FAILURE_MSG("Can't read entry exit record %d", i);
+    }
+    // These offsets could be NULL.
+    if (offset_entry_anchor) {
+      if (offset_entry_anchor < entry_exit_records_end ||
+          offset_entry_anchor >= length) {
+        return OTS_FAILURE_MSG("Bad entry anchor offset %d in entry exit record %d", offset_entry_anchor, i);
+      }
+      if (!ParseAnchorTable(file, data + offset_entry_anchor,
+                            length - offset_entry_anchor)) {
+        return OTS_FAILURE_MSG("Failed to parse entry anchor table in entry exit record %d", i);
+      }
+    }
+    if (offset_exit_anchor) {
+      if (offset_exit_anchor < entry_exit_records_end ||
+         offset_exit_anchor >= length) {
+        return OTS_FAILURE_MSG("Bad exit anchor offset %d in entry exit record %d", offset_exit_anchor, i);
+      }
+      if (!ParseAnchorTable(file, data + offset_exit_anchor,
+                            length - offset_exit_anchor)) {
+        return OTS_FAILURE_MSG("Failed to parse exit anchor table in entry exit record %d", i);
+      }
+    }
+  }
+
+  if (offset_coverage < subtable.offset() || offset_coverage >= length) {
+    return OTS_FAILURE_MSG("Bad coverage offset in cursive attachment %d", offset_coverage);
+  }
+  if (!ots::ParseCoverageTable(file, data + offset_coverage,
+                               length - offset_coverage,
+                               file->maxp->num_glyphs)) {
+    return OTS_FAILURE_MSG("Failed to parse coverage table in cursive attachment");
+  }
+
+  return true;
+}
+
+bool ParseAnchorArrayTable(const ots::OpenTypeFile *file,
+                           const uint8_t *data, const size_t length,
+                           const uint16_t class_count) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t record_count = 0;
+  if (!subtable.ReadU16(&record_count)) {
+    return OTS_FAILURE_MSG("Can't read anchor array length");
+  }
+
+  const unsigned anchor_array_end = 2 * static_cast<unsigned>(record_count) *
+      static_cast<unsigned>(class_count) + 2;
+  if (anchor_array_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad end of anchor array %d", anchor_array_end);
+  }
+  for (unsigned i = 0; i < record_count; ++i) {
+    for (unsigned j = 0; j < class_count; ++j) {
+      uint16_t offset_record = 0;
+      if (!subtable.ReadU16(&offset_record)) {
+        return OTS_FAILURE_MSG("Can't read anchor array record offset for class %d and record %d", j, i);
+      }
+      // |offset_record| could be NULL.
+      if (offset_record) {
+        if (offset_record < anchor_array_end || offset_record >= length) {
+          return OTS_FAILURE_MSG("Bad record offset %d in class %d, record %d", offset_record, j, i);
+        }
+        if (!ParseAnchorTable(file, data + offset_record,
+                              length - offset_record)) {
+          return OTS_FAILURE_MSG("Failed to parse anchor table for class %d, record %d", j, i);
+        }
+      }
+    }
+  }
+  return true;
+}
+
+bool ParseLigatureArrayTable(const ots::OpenTypeFile *file,
+                             const uint8_t *data, const size_t length,
+                             const uint16_t class_count) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t ligature_count = 0;
+  if (!subtable.ReadU16(&ligature_count)) {
+    return OTS_FAILURE_MSG("Failed to read ligature count");
+  }
+  for (unsigned i = 0; i < ligature_count; ++i) {
+    uint16_t offset_ligature_attach = 0;
+    if (!subtable.ReadU16(&offset_ligature_attach)) {
+      return OTS_FAILURE_MSG("Can't read ligature offset %d", i);
+    }
+    if (offset_ligature_attach < 2 || offset_ligature_attach >= length) {
+      return OTS_FAILURE_MSG("Bad ligature attachment offset %d in ligature %d", offset_ligature_attach, i);
+    }
+    if (!ParseAnchorArrayTable(file, data + offset_ligature_attach,
+                               length - offset_ligature_attach, class_count)) {
+      return OTS_FAILURE_MSG("Failed to parse anchor table for ligature %d", i);
+    }
+  }
+  return true;
+}
+
+// Common parser for Lookup Type 4, 5 and 6.
+bool ParseMarkToAttachmentSubtables(const ots::OpenTypeFile *file,
+                                    const uint8_t *data, const size_t length,
+                                    const GPOS_TYPE type) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t format = 0;
+  uint16_t offset_coverage1 = 0;
+  uint16_t offset_coverage2 = 0;
+  uint16_t class_count = 0;
+  uint16_t offset_mark_array = 0;
+  uint16_t offset_type_specific_array = 0;
+  if (!subtable.ReadU16(&format) ||
+      !subtable.ReadU16(&offset_coverage1) ||
+      !subtable.ReadU16(&offset_coverage2) ||
+      !subtable.ReadU16(&class_count) ||
+      !subtable.ReadU16(&offset_mark_array) ||
+      !subtable.ReadU16(&offset_type_specific_array)) {
+    return OTS_FAILURE_MSG("Failed to read mark attachment subtable header");
+  }
+
+  if (format != 1) {
+    return OTS_FAILURE_MSG("bad mark attachment subtable format %d", format);
+  }
+
+  const unsigned header_end = static_cast<unsigned>(subtable.offset());
+  if (header_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad mark attachment subtable size ending at %d", header_end);
+  }
+  if (offset_coverage1 < header_end || offset_coverage1 >= length) {
+    return OTS_FAILURE_MSG("Bad coverage 1 offset %d", offset_coverage1);
+  }
+  if (!ots::ParseCoverageTable(file, data + offset_coverage1,
+                               length - offset_coverage1,
+                               file->maxp->num_glyphs)) {
+    return OTS_FAILURE_MSG("Failed to parse converge 1 table");
+  }
+  if (offset_coverage2 < header_end || offset_coverage2 >= length) {
+    return OTS_FAILURE_MSG("Bad coverage 2 offset %d", offset_coverage2);
+  }
+  if (!ots::ParseCoverageTable(file, data + offset_coverage2,
+                               length - offset_coverage2,
+                               file->maxp->num_glyphs)) {
+    return OTS_FAILURE_MSG("Failed to parse coverage table 2");
+  }
+
+  if (offset_mark_array < header_end || offset_mark_array >= length) {
+    return OTS_FAILURE_MSG("Bad mark array offset %d", offset_mark_array);
+  }
+  if (!ParseMarkArrayTable(file, data + offset_mark_array,
+                           length - offset_mark_array, class_count)) {
+    return OTS_FAILURE_MSG("Failed to parse mark array");
+  }
+
+  if (offset_type_specific_array < header_end ||
+      offset_type_specific_array >= length) {
+    return OTS_FAILURE_MSG("Bad type specific array offset %d", offset_type_specific_array);
+  }
+  if (type == GPOS_TYPE_MARK_TO_BASE_ATTACHMENT ||
+      type == GPOS_TYPE_MARK_TO_MARK_ATTACHMENT) {
+    if (!ParseAnchorArrayTable(file, data + offset_type_specific_array,
+                               length - offset_type_specific_array,
+                               class_count)) {
+      return OTS_FAILURE_MSG("Failed to parse anchor array");
+    }
+  } else if (type == GPOS_TYPE_MARK_TO_LIGATURE_ATTACHMENT) {
+    if (!ParseLigatureArrayTable(file, data + offset_type_specific_array,
+                                 length - offset_type_specific_array,
+                                 class_count)) {
+      return OTS_FAILURE_MSG("Failed to parse ligature array");
+    }
+  } else {
+    return OTS_FAILURE_MSG("Bad attachment type %d", type);
+  }
+
+  return true;
+}
+
+// Lookup Type 4:
+// MarkToBase Attachment Positioning Subtable
+bool ParseMarkToBaseAttachment(const ots::OpenTypeFile *file,
+                               const uint8_t *data, const size_t length) {
+  return ParseMarkToAttachmentSubtables(file, data, length,
+                                        GPOS_TYPE_MARK_TO_BASE_ATTACHMENT);
+}
+
+// Lookup Type 5:
+// MarkToLigature Attachment Positioning Subtable
+bool ParseMarkToLigatureAttachment(const ots::OpenTypeFile *file,
+                                   const uint8_t *data, const size_t length) {
+  return ParseMarkToAttachmentSubtables(file, data, length,
+                                        GPOS_TYPE_MARK_TO_LIGATURE_ATTACHMENT);
+}
+
+// Lookup Type 6:
+// MarkToMark Attachment Positioning Subtable
+bool ParseMarkToMarkAttachment(const ots::OpenTypeFile *file,
+                               const uint8_t *data, const size_t length) {
+  return ParseMarkToAttachmentSubtables(file, data, length,
+                                        GPOS_TYPE_MARK_TO_MARK_ATTACHMENT);
+}
+
+// Lookup Type 7:
+// Contextual Positioning Subtables
+bool ParseContextPositioning(const ots::OpenTypeFile *file,
+                             const uint8_t *data, const size_t length) {
+  return ots::ParseContextSubtable(file, data, length, file->maxp->num_glyphs,
+                                   file->gpos->num_lookups);
+}
+
+// Lookup Type 8:
+// Chaining Contexual Positioning Subtable
+bool ParseChainedContextPositioning(const ots::OpenTypeFile *file,
+                                    const uint8_t *data, const size_t length) {
+  return ots::ParseChainingContextSubtable(file, data, length,
+                                           file->maxp->num_glyphs,
+                                           file->gpos->num_lookups);
+}
+
+// Lookup Type 9:
+// Extension Positioning
+bool ParseExtensionPositioning(const ots::OpenTypeFile *file,
+                               const uint8_t *data, const size_t length) {
+  return ots::ParseExtensionSubtable(file, data, length,
+                                     &kGposLookupSubtableParser);
+}
+
+}  // namespace
+
+#define DROP_THIS_TABLE(msg_) \
+  do { \
+    OTS_FAILURE_MSG(msg_ ", table discarded"); \
+    file->gpos->data = 0; \
+    file->gpos->length = 0; \
+  } while (0)
+
+namespace ots {
+
+// As far as I checked, following fonts contain invalid GPOS table and
+// OTS will drop their GPOS table.
+//
+// # invalid delta format in device table
+// samanata.ttf
+//
+// # bad size range in device table
+// Sarai_07.ttf
+//
+// # bad offset to PairSetTable
+// chandas1-2.ttf
+//
+// # bad offset to FeatureTable
+// glrso12.ttf
+// gllr12.ttf
+// glbo12.ttf
+// glb12.ttf
+// glro12.ttf
+// glbso12.ttf
+// glrc12.ttf
+// glrsc12.ttf
+// glbs12.ttf
+// glrs12.ttf
+// glr12.ttf
+//
+// # ScriptRecords aren't sorted by tag
+// Garogier_unhinted.otf
+//
+// # bad start coverage index in CoverageFormat2
+// AndBasR.ttf
+// CharisSILB.ttf
+// CharisSILBI.ttf
+// CharisSILI.ttf
+// CharisSILR.ttf
+// DoulosSILR.ttf
+// GenBasBI.ttf
+// GenBasI.ttf
+// GenBkBasI.ttf
+// GenBkBasB.ttf
+// GenBkBasR.ttf
+// Padauk-Bold.ttf
+// Padauk.ttf
+//
+// # Contour point indexes aren't sorted
+// Arial Unicode.ttf
+
+bool ots_gpos_parse(OpenTypeFile *file, const uint8_t *data, size_t length) {
+  // Parsing GPOS table requires num_glyphs which is contained in maxp table.
+  if (!file->maxp) {
+    return OTS_FAILURE_MSG("missing maxp table needed in GPOS");
+  }
+
+  Buffer table(data, length);
+
+  OpenTypeGPOS *gpos = new OpenTypeGPOS;
+  file->gpos = gpos;
+
+  uint32_t version = 0;
+  uint16_t offset_script_list = 0;
+  uint16_t offset_feature_list = 0;
+  uint16_t offset_lookup_list = 0;
+  if (!table.ReadU32(&version) ||
+      !table.ReadU16(&offset_script_list) ||
+      !table.ReadU16(&offset_feature_list) ||
+      !table.ReadU16(&offset_lookup_list)) {
+    DROP_THIS_TABLE("Incomplete table");
+    return true;
+  }
+
+  if (version != 0x00010000) {
+    DROP_THIS_TABLE("Bad version");
+    return true;
+  }
+
+  if (offset_lookup_list) {
+    if (offset_lookup_list < kGposHeaderSize || offset_lookup_list >= length) {
+      DROP_THIS_TABLE("Bad lookup list offset in table header");
+      return true;
+    }
+
+    if (!ParseLookupListTable(file, data + offset_lookup_list,
+                              length - offset_lookup_list,
+                              &kGposLookupSubtableParser,
+                              &gpos->num_lookups)) {
+      DROP_THIS_TABLE("Failed to parse lookup list table");
+      return true;
+    }
+  }
+
+  uint16_t num_features = 0;
+  if (offset_feature_list) {
+    if (offset_feature_list < kGposHeaderSize || offset_feature_list >= length) {
+      DROP_THIS_TABLE("Bad feature list offset in table header");
+      return true;
+    }
+
+    if (!ParseFeatureListTable(file, data + offset_feature_list,
+                               length - offset_feature_list, gpos->num_lookups,
+                               &num_features)) {
+      DROP_THIS_TABLE("Failed to parse feature list table");
+      return true;
+    }
+  }
+
+  if (offset_script_list) {
+    if (offset_script_list < kGposHeaderSize || offset_script_list >= length) {
+      DROP_THIS_TABLE("Bad script list offset in table header");
+      return true;
+    }
+
+    if (!ParseScriptListTable(file, data + offset_script_list,
+                              length - offset_script_list, num_features)) {
+      DROP_THIS_TABLE("Failed to parse script list table");
+      return true;
+    }
+  }
+
+  gpos->data = data;
+  gpos->length = length;
+  return true;
+}
+
+bool ots_gpos_should_serialise(OpenTypeFile *file) {
+  return file->gpos != NULL && file->gpos->data != NULL;
+}
+
+bool ots_gpos_serialise(OTSStream *out, OpenTypeFile *file) {
+  if (!out->Write(file->gpos->data, file->gpos->length)) {
+    return OTS_FAILURE_MSG("Failed to write GPOS table");
+  }
+
+  return true;
+}
+
+void ots_gpos_free(OpenTypeFile *file) {
+  delete file->gpos;
+}
+
+}  // namespace ots
+
+#undef TABLE_NAME
+#undef DROP_THIS_TABLE