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

third_party/ots/src/layout.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 "layout.h"
+
+#include <limits>
+#include <vector>
+
+#include "gdef.h"
+
+// OpenType Layout Common Table Formats
+// http://www.microsoft.com/typography/otspec/chapter2.htm
+
+#define TABLE_NAME "Layout" // XXX: use individual table names
+
+namespace {
+
+// The 'DFLT' tag of script table.
+const uint32_t kScriptTableTagDflt = 0x44464c54;
+// The value which represents there is no required feature index.
+const uint16_t kNoRequiredFeatureIndexDefined = 0xFFFF;
+// The lookup flag bit which indicates existence of MarkFilteringSet.
+const uint16_t kUseMarkFilteringSetBit = 0x0010;
+// The lookup flags which require GDEF table.
+const uint16_t kGdefRequiredFlags = 0x0002 | 0x0004 | 0x0008;
+// The mask for MarkAttachmentType.
+const uint16_t kMarkAttachmentTypeMask = 0xFF00;
+// The maximum type number of format for device tables.
+const uint16_t kMaxDeltaFormatType = 3;
+// The maximum number of class value.
+const uint16_t kMaxClassDefValue = 0xFFFF;
+
+struct ScriptRecord {
+  uint32_t tag;
+  uint16_t offset;
+};
+
+struct LangSysRecord {
+  uint32_t tag;
+  uint16_t offset;
+};
+
+struct FeatureRecord {
+  uint32_t tag;
+  uint16_t offset;
+};
+
+bool ParseLangSysTable(const ots::OpenTypeFile *file,
+                       ots::Buffer *subtable, const uint32_t tag,
+                       const uint16_t num_features) {
+  uint16_t offset_lookup_order = 0;
+  uint16_t req_feature_index = 0;
+  uint16_t feature_count = 0;
+  if (!subtable->ReadU16(&offset_lookup_order) ||
+      !subtable->ReadU16(&req_feature_index) ||
+      !subtable->ReadU16(&feature_count)) {
+    return OTS_FAILURE_MSG("Failed to read langsys header for tag %4.4s", (char *)&tag);
+  }
+  // |offset_lookup_order| is reserved and should be NULL.
+  if (offset_lookup_order != 0) {
+    return OTS_FAILURE_MSG("Bad lookup offset order %d for langsys tag %4.4s", offset_lookup_order, (char *)&tag);
+  }
+  if (req_feature_index != kNoRequiredFeatureIndexDefined &&
+      req_feature_index >= num_features) {
+    return OTS_FAILURE_MSG("Bad required features index %d for langsys tag %4.4s", req_feature_index, (char *)&tag);
+  }
+  if (feature_count > num_features) {
+    return OTS_FAILURE_MSG("Bad feature count %d for langsys tag %4.4s", feature_count, (char *)&tag);
+  }
+
+  for (unsigned i = 0; i < feature_count; ++i) {
+    uint16_t feature_index = 0;
+    if (!subtable->ReadU16(&feature_index)) {
+      return OTS_FAILURE_MSG("Failed to read feature index %d for langsys tag %4.4s", i, (char *)&tag);
+    }
+    if (feature_index >= num_features) {
+      return OTS_FAILURE_MSG("Bad feature index %d for feature %d for langsys tag %4.4s", feature_index, i, (char *)&tag);
+    }
+  }
+  return true;
+}
+
+bool ParseScriptTable(const ots::OpenTypeFile *file,
+                      const uint8_t *data, const size_t length,
+                      const uint32_t tag, const uint16_t num_features) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t offset_default_lang_sys = 0;
+  uint16_t lang_sys_count = 0;
+  if (!subtable.ReadU16(&offset_default_lang_sys) ||
+      !subtable.ReadU16(&lang_sys_count)) {
+    return OTS_FAILURE_MSG("Failed to read script header for script tag %4.4s", (char *)&tag);
+  }
+
+  // The spec requires a script table for 'DFLT' tag must contain non-NULL
+  // |offset_default_lang_sys| and |lang_sys_count| == 0
+  if (tag == kScriptTableTagDflt &&
+      (offset_default_lang_sys == 0 || lang_sys_count != 0)) {
+    return OTS_FAILURE_MSG("DFLT table doesn't satisfy the spec. for script tag %4.4s", (char *)&tag);
+  }
+
+  const unsigned lang_sys_record_end =
+      6 * static_cast<unsigned>(lang_sys_count) + 4;
+  if (lang_sys_record_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad end of langsys record %d for script tag %4.4s", lang_sys_record_end, (char *)&tag);
+  }
+
+  std::vector<LangSysRecord> lang_sys_records;
+  lang_sys_records.resize(lang_sys_count);
+  uint32_t last_tag = 0;
+  for (unsigned i = 0; i < lang_sys_count; ++i) {
+    if (!subtable.ReadU32(&lang_sys_records[i].tag) ||
+        !subtable.ReadU16(&lang_sys_records[i].offset)) {
+      return OTS_FAILURE_MSG("Failed to read langsys record header %d for script tag %4.4s", i, (char *)&tag);
+    }
+    // The record array must store the records alphabetically by tag
+    if (last_tag != 0 && last_tag > lang_sys_records[i].tag) {
+      return OTS_FAILURE_MSG("Bad last tag %d for langsys record %d for script tag %4.4s", last_tag, i, (char *)&tag);
+    }
+    if (lang_sys_records[i].offset < lang_sys_record_end ||
+        lang_sys_records[i].offset >= length) {
+      return OTS_FAILURE_MSG("bad offset to lang sys table: %x",
+                  lang_sys_records[i].offset);
+    }
+    last_tag = lang_sys_records[i].tag;
+  }
+
+  // Check lang sys tables
+  for (unsigned i = 0; i < lang_sys_count; ++i) {
+    subtable.set_offset(lang_sys_records[i].offset);
+    if (!ParseLangSysTable(file, &subtable, lang_sys_records[i].tag, num_features)) {
+      return OTS_FAILURE_MSG("Failed to parse langsys table %d (%4.4s) for script tag %4.4s", i, (char *)&lang_sys_records[i].tag, (char *)&tag);
+    }
+  }
+
+  return true;
+}
+
+bool ParseFeatureTable(const ots::OpenTypeFile *file,
+                       const uint8_t *data, const size_t length,
+                       const uint16_t num_lookups) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t offset_feature_params = 0;
+  uint16_t lookup_count = 0;
+  if (!subtable.ReadU16(&offset_feature_params) ||
+      !subtable.ReadU16(&lookup_count)) {
+    return OTS_FAILURE_MSG("Failed to read feature table header");
+  }
+
+  const unsigned feature_table_end =
+      2 * static_cast<unsigned>(lookup_count) + 4;
+  if (feature_table_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad end of feature table %d", feature_table_end);
+  }
+  // |offset_feature_params| is generally set to NULL.
+  if (offset_feature_params != 0 &&
+      (offset_feature_params < feature_table_end ||
+       offset_feature_params >= length)) {
+    return OTS_FAILURE_MSG("Bad feature params offset %d", offset_feature_params);
+  }
+
+  for (unsigned i = 0; i < lookup_count; ++i) {
+    uint16_t lookup_index = 0;
+    if (!subtable.ReadU16(&lookup_index)) {
+      return OTS_FAILURE_MSG("Failed to read lookup index for lookup %d", i);
+    }
+    // lookup index starts with 0.
+    if (lookup_index >= num_lookups) {
+      return OTS_FAILURE_MSG("Bad lookup index %d for lookup %d", lookup_index, i);
+    }
+  }
+  return true;
+}
+
+bool ParseLookupTable(ots::OpenTypeFile *file, const uint8_t *data,
+                      const size_t length,
+                      const ots::LookupSubtableParser* parser) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t lookup_type = 0;
+  uint16_t lookup_flag = 0;
+  uint16_t subtable_count = 0;
+  if (!subtable.ReadU16(&lookup_type) ||
+      !subtable.ReadU16(&lookup_flag) ||
+      !subtable.ReadU16(&subtable_count)) {
+    return OTS_FAILURE_MSG("Failed to read lookup table header");
+  }
+
+  if (lookup_type == 0 || lookup_type > parser->num_types) {
+    return OTS_FAILURE_MSG("Bad lookup type %d", lookup_type);
+  }
+
+  // Check lookup flags.
+  if ((lookup_flag & kGdefRequiredFlags) &&
+      (!file->gdef || !file->gdef->has_glyph_class_def)) {
+    return OTS_FAILURE_MSG("Bad lookup flags %d", lookup_flag);
+  }
+  if ((lookup_flag & kMarkAttachmentTypeMask) &&
+      (!file->gdef || !file->gdef->has_mark_attachment_class_def)) {
+    return OTS_FAILURE_MSG("lookup flag asks for mark attachment that is bad %d", lookup_flag);
+  }
+  bool use_mark_filtering_set = false;
+  if (lookup_flag & kUseMarkFilteringSetBit) {
+    if (!file->gdef || !file->gdef->has_mark_glyph_sets_def) {
+      return OTS_FAILURE_MSG("lookup flag asks for mark filtering that is bad %d", lookup_flag);
+    }
+    use_mark_filtering_set = true;
+  }
+
+  std::vector<uint16_t> subtables;
+  subtables.reserve(subtable_count);
+  // If the |kUseMarkFilteringSetBit| of |lookup_flag| is set,
+  // extra 2 bytes will follow after subtable offset array.
+  const unsigned lookup_table_end = 2 * static_cast<unsigned>(subtable_count) +
+      (use_mark_filtering_set ? 8 : 6);
+  if (lookup_table_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad end of lookup %d", lookup_table_end);
+  }
+  for (unsigned i = 0; i < subtable_count; ++i) {
+    uint16_t offset_subtable = 0;
+    if (!subtable.ReadU16(&offset_subtable)) {
+      return OTS_FAILURE_MSG("Failed to read subtable offset %d", i);
+    }
+    if (offset_subtable < lookup_table_end ||
+        offset_subtable >= length) {
+      return OTS_FAILURE_MSG("Bad subtable offset %d for subtable %d", offset_subtable, i);
+    }
+    subtables.push_back(offset_subtable);
+  }
+  if (subtables.size() != subtable_count) {
+    return OTS_FAILURE_MSG("Bad subtable size %ld", subtables.size());
+  }
+
+  if (use_mark_filtering_set) {
+    uint16_t mark_filtering_set = 0;
+    if (!subtable.ReadU16(&mark_filtering_set)) {
+      return OTS_FAILURE_MSG("Failed to read mark filtering set");
+    }
+    if (file->gdef->num_mark_glyph_sets == 0 ||
+        mark_filtering_set >= file->gdef->num_mark_glyph_sets) {
+      return OTS_FAILURE_MSG("Bad mark filtering set %d", mark_filtering_set);
+    }
+  }
+
+  // Parse lookup subtables for this lookup type.
+  for (unsigned i = 0; i < subtable_count; ++i) {
+    if (!parser->Parse(file, data + subtables[i], length - subtables[i],
+                       lookup_type)) {
+      return OTS_FAILURE_MSG("Failed to parse subtable %d", i);
+    }
+  }
+  return true;
+}
+
+bool ParseClassDefFormat1(const ots::OpenTypeFile *file,
+                          const uint8_t *data, size_t length,
+                          const uint16_t num_glyphs,
+                          const uint16_t num_classes) {
+  ots::Buffer subtable(data, length);
+
+  // Skip format field.
+  if (!subtable.Skip(2)) {
+    return OTS_FAILURE_MSG("Failed to skip class definition header");
+  }
+
+  uint16_t start_glyph = 0;
+  if (!subtable.ReadU16(&start_glyph)) {
+    return OTS_FAILURE_MSG("Failed to read starting glyph of class definition");
+  }
+  if (start_glyph > num_glyphs) {
+    return OTS_FAILURE_MSG("Bad starting glyph %d in class definition", start_glyph);
+  }
+
+  uint16_t glyph_count = 0;
+  if (!subtable.ReadU16(&glyph_count)) {
+    return OTS_FAILURE_MSG("Failed to read glyph count in class definition");
+  }
+  if (glyph_count > num_glyphs) {
+    return OTS_FAILURE_MSG("bad glyph count: %u", glyph_count);
+  }
+  for (unsigned i = 0; i < glyph_count; ++i) {
+    uint16_t class_value = 0;
+    if (!subtable.ReadU16(&class_value)) {
+      return OTS_FAILURE_MSG("Failed to read class value for glyph %d in class definition", i);
+    }
+    if (class_value > num_classes) {
+      return OTS_FAILURE_MSG("Bad class value %d for glyph %d in class definition", class_value, i);
+    }
+  }
+
+  return true;
+}
+
+bool ParseClassDefFormat2(const ots::OpenTypeFile *file,
+                          const uint8_t *data, size_t length,
+                          const uint16_t num_glyphs,
+                          const uint16_t num_classes) {
+  ots::Buffer subtable(data, length);
+
+  // Skip format field.
+  if (!subtable.Skip(2)) {
+    return OTS_FAILURE_MSG("Failed to skip format of class defintion header");
+  }
+
+  uint16_t range_count = 0;
+  if (!subtable.ReadU16(&range_count)) {
+    return OTS_FAILURE_MSG("Failed to read range count in class definition");
+  }
+  if (range_count > num_glyphs) {
+    return OTS_FAILURE_MSG("bad range count: %u", range_count);
+  }
+
+  uint16_t last_end = 0;
+  for (unsigned i = 0; i < range_count; ++i) {
+    uint16_t start = 0;
+    uint16_t end = 0;
+    uint16_t class_value = 0;
+    if (!subtable.ReadU16(&start) ||
+        !subtable.ReadU16(&end) ||
+        !subtable.ReadU16(&class_value)) {
+      return OTS_FAILURE_MSG("Failed to read class definition reange %d", i);
+    }
+    if (start > end || (last_end && start <= last_end)) {
+      return OTS_FAILURE_MSG("glyph range is overlapping.in range %d", i);
+    }
+    if (class_value > num_classes) {
+      return OTS_FAILURE_MSG("bad class value: %u", class_value);
+    }
+    last_end = end;
+  }
+
+  return true;
+}
+
+bool ParseCoverageFormat1(const ots::OpenTypeFile *file,
+                          const uint8_t *data, size_t length,
+                          const uint16_t num_glyphs,
+                          const uint16_t expected_num_glyphs) {
+  ots::Buffer subtable(data, length);
+
+  // Skip format field.
+  if (!subtable.Skip(2)) {
+    return OTS_FAILURE_MSG("Failed to skip coverage format");
+  }
+
+  uint16_t glyph_count = 0;
+  if (!subtable.ReadU16(&glyph_count)) {
+    return OTS_FAILURE_MSG("Failed to read glyph count in coverage");
+  }
+  if (glyph_count > num_glyphs) {
+    return OTS_FAILURE_MSG("bad glyph count: %u", glyph_count);
+  }
+  for (unsigned i = 0; i < glyph_count; ++i) {
+    uint16_t glyph = 0;
+    if (!subtable.ReadU16(&glyph)) {
+      return OTS_FAILURE_MSG("Failed to read glyph %d in coverage", i);
+    }
+    if (glyph > num_glyphs) {
+      return OTS_FAILURE_MSG("bad glyph ID: %u", glyph);
+    }
+  }
+
+  if (expected_num_glyphs && expected_num_glyphs != glyph_count) {
+      return OTS_FAILURE_MSG("unexpected number of glyphs: %u", glyph_count);
+  }
+
+  return true;
+}
+
+bool ParseCoverageFormat2(const ots::OpenTypeFile *file,
+                          const uint8_t *data, size_t length,
+                          const uint16_t num_glyphs,
+                          const uint16_t expected_num_glyphs) {
+  ots::Buffer subtable(data, length);
+
+  // Skip format field.
+  if (!subtable.Skip(2)) {
+    return OTS_FAILURE_MSG("Failed to skip format of coverage type 2");
+  }
+
+  uint16_t range_count = 0;
+  if (!subtable.ReadU16(&range_count)) {
+    return OTS_FAILURE_MSG("Failed to read range count in coverage");
+  }
+  if (range_count > num_glyphs) {
+    return OTS_FAILURE_MSG("bad range count: %u", range_count);
+  }
+  uint16_t last_end = 0;
+  uint16_t last_start_coverage_index = 0;
+  for (unsigned i = 0; i < range_count; ++i) {
+    uint16_t start = 0;
+    uint16_t end = 0;
+    uint16_t start_coverage_index = 0;
+    if (!subtable.ReadU16(&start) ||
+        !subtable.ReadU16(&end) ||
+        !subtable.ReadU16(&start_coverage_index)) {
+      return OTS_FAILURE_MSG("Failed to read range %d in coverage", i);
+    }
+
+    // Some of the Adobe Pro fonts have ranges that overlap by one element: the
+    // start of one range is equal to the end of the previous range. Therefore
+    // the < in the following condition should be <= were it not for this.
+    // See crbug.com/134135.
+    if (start > end || (last_end && start < last_end)) {
+      return OTS_FAILURE_MSG("glyph range is overlapping.");
+    }
+    if (start_coverage_index != last_start_coverage_index) {
+      return OTS_FAILURE_MSG("bad start coverage index.");
+    }
+    last_end = end;
+    last_start_coverage_index += end - start + 1;
+  }
+
+  if (expected_num_glyphs &&
+      expected_num_glyphs != last_start_coverage_index) {
+      return OTS_FAILURE_MSG("unexpected number of glyphs: %u", last_start_coverage_index);
+  }
+
+  return true;
+}
+
+// Parsers for Contextual subtables in GSUB/GPOS tables.
+
+bool ParseLookupRecord(const ots::OpenTypeFile *file,
+                       ots::Buffer *subtable, const uint16_t num_glyphs,
+                       const uint16_t num_lookups) {
+  uint16_t sequence_index = 0;
+  uint16_t lookup_list_index = 0;
+  if (!subtable->ReadU16(&sequence_index) ||
+      !subtable->ReadU16(&lookup_list_index)) {
+    return OTS_FAILURE_MSG("Failed to read header for lookup record");
+  }
+  if (sequence_index >= num_glyphs) {
+    return OTS_FAILURE_MSG("Bad sequence index %d in lookup record", sequence_index);
+  }
+  if (lookup_list_index >= num_lookups) {
+    return OTS_FAILURE_MSG("Bad lookup list index %d in lookup record", lookup_list_index);
+  }
+  return true;
+}
+
+bool ParseRuleSubtable(const ots::OpenTypeFile *file,
+                       const uint8_t *data, const size_t length,
+                       const uint16_t num_glyphs,
+                       const uint16_t num_lookups) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t glyph_count = 0;
+  uint16_t lookup_count = 0;
+  if (!subtable.ReadU16(&glyph_count) ||
+      !subtable.ReadU16(&lookup_count)) {
+    return OTS_FAILURE_MSG("Failed to read rule subtable header");
+  }
+
+  if (glyph_count == 0 || glyph_count >= num_glyphs) {
+    return OTS_FAILURE_MSG("Bad glyph count %d in rule subtable", glyph_count);
+  }
+  for (unsigned i = 0; i < glyph_count - static_cast<unsigned>(1); ++i) {
+    uint16_t glyph_id = 0;
+    if (!subtable.ReadU16(&glyph_id)) {
+      return OTS_FAILURE_MSG("Failed to read glyph %d", i);
+    }
+    if (glyph_id > num_glyphs) {
+      return OTS_FAILURE_MSG("Bad glyph %d for entry %d", glyph_id, i);
+    }
+  }
+
+  for (unsigned i = 0; i < lookup_count; ++i) {
+    if (!ParseLookupRecord(file, &subtable, num_glyphs, num_lookups)) {
+      return OTS_FAILURE_MSG("Failed to parse lookup record %d", i);
+    }
+  }
+  return true;
+}
+
+bool ParseRuleSetTable(const ots::OpenTypeFile *file,
+                       const uint8_t *data, const size_t length,
+                       const uint16_t num_glyphs,
+                       const uint16_t num_lookups) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t rule_count = 0;
+  if (!subtable.ReadU16(&rule_count)) {
+    return OTS_FAILURE_MSG("Failed to read rule count in rule set");
+  }
+  const unsigned rule_end = 2 * static_cast<unsigned>(rule_count) + 2;
+  if (rule_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad end of rule %d in rule set", rule_end);
+  }
+
+  for (unsigned i = 0; i < rule_count; ++i) {
+    uint16_t offset_rule = 0;
+    if (!subtable.ReadU16(&offset_rule)) {
+      return OTS_FAILURE_MSG("Failed to read rule offset for rule set %d", i);
+    }
+    if (offset_rule < rule_end || offset_rule >= length) {
+      return OTS_FAILURE_MSG("Bad rule offset %d in set %d", offset_rule, i);
+    }
+    if (!ParseRuleSubtable(file, data + offset_rule, length - offset_rule,
+                           num_glyphs, num_lookups)) {
+      return OTS_FAILURE_MSG("Failed to parse rule set %d", i);
+    }
+  }
+
+  return true;
+}
+
+bool ParseContextFormat1(const ots::OpenTypeFile *file,
+                         const uint8_t *data, const size_t length,
+                         const uint16_t num_glyphs,
+                         const uint16_t num_lookups) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t offset_coverage = 0;
+  uint16_t rule_set_count = 0;
+  // Skip format field.
+  if (!subtable.Skip(2) ||
+      !subtable.ReadU16(&offset_coverage) ||
+      !subtable.ReadU16(&rule_set_count)) {
+    return OTS_FAILURE_MSG("Failed to read header of context format 1");
+  }
+
+  const unsigned rule_set_end = static_cast<unsigned>(6) +
+      rule_set_count * 2;
+  if (rule_set_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad end of rule set %d of context format 1", rule_set_end);
+  }
+  if (offset_coverage < rule_set_end || offset_coverage >= length) {
+    return OTS_FAILURE_MSG("Bad coverage offset %d in context format 1", offset_coverage);
+  }
+  if (!ots::ParseCoverageTable(file, data + offset_coverage,
+                               length - offset_coverage, num_glyphs)) {
+    return OTS_FAILURE_MSG("Failed to parse coverage table in context format 1");
+  }
+
+  for (unsigned i = 0; i < rule_set_count; ++i) {
+    uint16_t offset_rule = 0;
+    if (!subtable.ReadU16(&offset_rule)) {
+      return OTS_FAILURE_MSG("Failed to read rule offset %d in context format 1", i);
+    }
+    if (offset_rule < rule_set_end || offset_rule >= length) {
+      return OTS_FAILURE_MSG("Bad rule offset %d in rule %d in context format 1", offset_rule, i);
+    }
+    if (!ParseRuleSetTable(file, data + offset_rule, length - offset_rule,
+                           num_glyphs, num_lookups)) {
+      return OTS_FAILURE_MSG("Failed to parse rule set %d in context format 1", i);
+    }
+  }
+
+  return true;
+}
+
+bool ParseClassRuleTable(const ots::OpenTypeFile *file,
+                         const uint8_t *data, const size_t length,
+                         const uint16_t num_glyphs,
+                         const uint16_t num_lookups) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t glyph_count = 0;
+  uint16_t lookup_count = 0;
+  if (!subtable.ReadU16(&glyph_count) ||
+      !subtable.ReadU16(&lookup_count)) {
+    return OTS_FAILURE_MSG("Failed to read header of class rule table");
+  }
+
+  if (glyph_count == 0 || glyph_count >= num_glyphs) {
+    return OTS_FAILURE_MSG("Bad glyph count %d in class rule table", glyph_count);
+  }
+
+  // ClassRule table contains an array of classes. Each value of classes
+  // could take arbitrary values including zero so we don't check these value.
+  const unsigned num_classes = glyph_count - static_cast<unsigned>(1);
+  if (!subtable.Skip(2 * num_classes)) {
+    return OTS_FAILURE_MSG("Failed to skip classes in class rule table");
+  }
+
+  for (unsigned i = 0; i < lookup_count; ++i) {
+    if (!ParseLookupRecord(file, &subtable, num_glyphs, num_lookups)) {
+      return OTS_FAILURE_MSG("Failed to parse lookup record %d in class rule table", i);
+    }
+  }
+  return true;
+}
+
+bool ParseClassSetTable(const ots::OpenTypeFile *file,
+                        const uint8_t *data, const size_t length,
+                        const uint16_t num_glyphs,
+                        const uint16_t num_lookups) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t class_rule_count = 0;
+  if (!subtable.ReadU16(&class_rule_count)) {
+    return OTS_FAILURE_MSG("Failed to read class rule count in class set table");
+  }
+  const unsigned class_rule_end =
+      2 * static_cast<unsigned>(class_rule_count) + 2;
+  if (class_rule_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("bad class rule end %d in class set table", class_rule_end);
+  }
+  for (unsigned i = 0; i < class_rule_count; ++i) {
+    uint16_t offset_class_rule = 0;
+    if (!subtable.ReadU16(&offset_class_rule)) {
+      return OTS_FAILURE_MSG("Failed to read class rule offset %d in class set table", i);
+    }
+    if (offset_class_rule < class_rule_end || offset_class_rule >= length) {
+      return OTS_FAILURE_MSG("Bad class rule offset %d in class %d", offset_class_rule, i);
+    }
+    if (!ParseClassRuleTable(file, data + offset_class_rule,
+                             length - offset_class_rule, num_glyphs,
+                             num_lookups)) {
+      return OTS_FAILURE_MSG("Failed to parse class rule table %d", i);
+    }
+  }
+
+  return true;
+}
+
+bool ParseContextFormat2(const ots::OpenTypeFile *file,
+                         const uint8_t *data, const size_t length,
+                         const uint16_t num_glyphs,
+                         const uint16_t num_lookups) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t offset_coverage = 0;
+  uint16_t offset_class_def = 0;
+  uint16_t class_set_cnt = 0;
+  // Skip format field.
+  if (!subtable.Skip(2) ||
+      !subtable.ReadU16(&offset_coverage) ||
+      !subtable.ReadU16(&offset_class_def) ||
+      !subtable.ReadU16(&class_set_cnt)) {
+    return OTS_FAILURE_MSG("Failed to read header for context format 2");
+  }
+
+  const unsigned class_set_end = 2 * static_cast<unsigned>(class_set_cnt) + 8;
+  if (class_set_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad end of class set %d for context format 2", class_set_end);
+  }
+  if (offset_coverage < class_set_end || offset_coverage >= length) {
+    return OTS_FAILURE_MSG("Bad coverage offset %d in context format 2", offset_coverage);
+  }
+  if (!ots::ParseCoverageTable(file, data + offset_coverage,
+                               length - offset_coverage, num_glyphs)) {
+    return OTS_FAILURE_MSG("Failed to parse coverage table in context format 2");
+  }
+
+  if (offset_class_def < class_set_end || offset_class_def >= length) {
+    return OTS_FAILURE_MSG("bad class definition offset %d in context format 2", offset_class_def);
+  }
+  if (!ots::ParseClassDefTable(file, data + offset_class_def,
+                               length - offset_class_def,
+                               num_glyphs, kMaxClassDefValue)) {
+    return OTS_FAILURE_MSG("Failed to parse class definition table in context format 2");
+  }
+
+  for (unsigned i = 0; i < class_set_cnt; ++i) {
+    uint16_t offset_class_rule = 0;
+    if (!subtable.ReadU16(&offset_class_rule)) {
+      return OTS_FAILURE_MSG("Failed to read class rule offset %d in context format 2", i);
+    }
+    if (offset_class_rule) {
+      if (offset_class_rule < class_set_end || offset_class_rule >= length) {
+        return OTS_FAILURE_MSG("Bad class rule offset %d for rule %d in context format 2", offset_class_rule, i);
+      }
+      if (!ParseClassSetTable(file, data + offset_class_rule,
+                              length - offset_class_rule, num_glyphs,
+                              num_lookups)) {
+        return OTS_FAILURE_MSG("Failed to parse class set %d in context format 2", i);
+      }
+    }
+  }
+
+  return true;
+}
+
+bool ParseContextFormat3(const ots::OpenTypeFile *file,
+                         const uint8_t *data, const size_t length,
+                         const uint16_t num_glyphs,
+                         const uint16_t num_lookups) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t glyph_count = 0;
+  uint16_t lookup_count = 0;
+  // Skip format field.
+  if (!subtable.Skip(2) ||
+      !subtable.ReadU16(&glyph_count) ||
+      !subtable.ReadU16(&lookup_count)) {
+    return OTS_FAILURE_MSG("Failed to read header in context format 3");
+  }
+
+  if (glyph_count >= num_glyphs) {
+    return OTS_FAILURE_MSG("Bad glyph count %d in context format 3", glyph_count);
+  }
+  const unsigned lookup_record_end = 2 * static_cast<unsigned>(glyph_count) +
+      4 * static_cast<unsigned>(lookup_count) + 6;
+  if (lookup_record_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad end of lookup %d in context format 3", lookup_record_end);
+  }
+  for (unsigned i = 0; i < glyph_count; ++i) {
+    uint16_t offset_coverage = 0;
+    if (!subtable.ReadU16(&offset_coverage)) {
+      return OTS_FAILURE_MSG("Failed to read coverage offset %d in conxtext format 3", i);
+    }
+    if (offset_coverage < lookup_record_end || offset_coverage >= length) {
+      return OTS_FAILURE_MSG("Bad coverage offset %d for glyph %d in context format 3", offset_coverage, i);
+    }
+    if (!ots::ParseCoverageTable(file, data + offset_coverage,
+                                 length - offset_coverage, num_glyphs)) {
+      return OTS_FAILURE_MSG("Failed to parse coverage table for glyph %d in context format 3", i);
+    }
+  }
+
+  for (unsigned i = 0; i < lookup_count; ++i) {
+    if (!ParseLookupRecord(file, &subtable, num_glyphs, num_lookups)) {
+      return OTS_FAILURE_MSG("Failed to parse lookup record %d in context format 3", i);
+    }
+  }
+
+  return true;
+}
+
+// Parsers for Chaning Contextual subtables in GSUB/GPOS tables.
+
+bool ParseChainRuleSubtable(const ots::OpenTypeFile *file,
+                            const uint8_t *data, const size_t length,
+                            const uint16_t num_glyphs,
+                            const uint16_t num_lookups) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t backtrack_count = 0;
+  if (!subtable.ReadU16(&backtrack_count)) {
+    return OTS_FAILURE_MSG("Failed to read backtrack count in chain rule subtable");
+  }
+  if (backtrack_count >= num_glyphs) {
+    return OTS_FAILURE_MSG("Bad backtrack count %d in chain rule subtable", backtrack_count);
+  }
+  for (unsigned i = 0; i < backtrack_count; ++i) {
+    uint16_t glyph_id = 0;
+    if (!subtable.ReadU16(&glyph_id)) {
+      return OTS_FAILURE_MSG("Failed to read backtrack glyph %d in chain rule subtable", i);
+    }
+    if (glyph_id > num_glyphs) {
+      return OTS_FAILURE_MSG("Bad glyph id %d for bactrack glyph %d in chain rule subtable", glyph_id, i);
+    }
+  }
+
+  uint16_t input_count = 0;
+  if (!subtable.ReadU16(&input_count)) {
+    return OTS_FAILURE_MSG("Failed to read input count in chain rule subtable");
+  }
+  if (input_count == 0 || input_count >= num_glyphs) {
+    return OTS_FAILURE_MSG("Bad input count %d in chain rule subtable", input_count);
+  }
+  for (unsigned i = 0; i < input_count - static_cast<unsigned>(1); ++i) {
+    uint16_t glyph_id = 0;
+    if (!subtable.ReadU16(&glyph_id)) {
+      return OTS_FAILURE_MSG("Failed to read input glyph %d in chain rule subtable", i);
+    }
+    if (glyph_id > num_glyphs) {
+      return OTS_FAILURE_MSG("Bad glyph id %d for input glyph %d in chain rule subtable", glyph_id, i);
+    }
+  }
+
+  uint16_t lookahead_count = 0;
+  if (!subtable.ReadU16(&lookahead_count)) {
+    return OTS_FAILURE_MSG("Failed to read lookahead count in chain rule subtable");
+  }
+  if (lookahead_count >= num_glyphs) {
+    return OTS_FAILURE_MSG("Bad lookahead count %d in chain rule subtable", lookahead_count);
+  }
+  for (unsigned i = 0; i < lookahead_count; ++i) {
+    uint16_t glyph_id = 0;
+    if (!subtable.ReadU16(&glyph_id)) {
+      return OTS_FAILURE_MSG("Failed to read lookahead glyph %d in chain rule subtable", i);
+    }
+    if (glyph_id > num_glyphs) {
+      return OTS_FAILURE_MSG("Bad glyph id %d for lookadhead glyph %d in chain rule subtable", glyph_id, i);
+    }
+  }
+
+  uint16_t lookup_count = 0;
+  if (!subtable.ReadU16(&lookup_count)) {
+    return OTS_FAILURE_MSG("Failed to read lookup count in chain rule subtable");
+  }
+  for (unsigned i = 0; i < lookup_count; ++i) {
+    if (!ParseLookupRecord(file, &subtable, num_glyphs, num_lookups)) {
+      return OTS_FAILURE_MSG("Failed to parse lookup record %d in chain rule subtable", i);
+    }
+  }
+
+  return true;
+}
+
+bool ParseChainRuleSetTable(const ots::OpenTypeFile *file,
+                            const uint8_t *data, const size_t length,
+                            const uint16_t num_glyphs,
+                            const uint16_t num_lookups) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t chain_rule_count = 0;
+  if (!subtable.ReadU16(&chain_rule_count)) {
+    return OTS_FAILURE_MSG("Failed to read rule count in chain rule set");
+  }
+  const unsigned chain_rule_end =
+      2 * static_cast<unsigned>(chain_rule_count) + 2;
+  if (chain_rule_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad end of chain rule %d in chain rule set", chain_rule_end);
+  }
+  for (unsigned i = 0; i < chain_rule_count; ++i) {
+    uint16_t offset_chain_rule = 0;
+    if (!subtable.ReadU16(&offset_chain_rule)) {
+      return OTS_FAILURE_MSG("Failed to read chain rule offset %d in chain rule set", i);
+    }
+    if (offset_chain_rule < chain_rule_end || offset_chain_rule >= length) {
+      return OTS_FAILURE_MSG("Bad chain rule offset %d for chain rule %d in chain rule set", offset_chain_rule, i);
+    }
+    if (!ParseChainRuleSubtable(file, data + offset_chain_rule,
+                                length - offset_chain_rule,
+                                num_glyphs, num_lookups)) {
+      return OTS_FAILURE_MSG("Failed to parse chain rule %d in chain rule set", i);
+    }
+  }
+
+  return true;
+}
+
+bool ParseChainContextFormat1(const ots::OpenTypeFile *file,
+                              const uint8_t *data, const size_t length,
+                              const uint16_t num_glyphs,
+                              const uint16_t num_lookups) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t offset_coverage = 0;
+  uint16_t chain_rule_set_count = 0;
+  // Skip format field.
+  if (!subtable.Skip(2) ||
+      !subtable.ReadU16(&offset_coverage) ||
+      !subtable.ReadU16(&chain_rule_set_count)) {
+    return OTS_FAILURE_MSG("Failed to read header of chain context format 1");
+  }
+
+  const unsigned chain_rule_set_end =
+      2 * static_cast<unsigned>(chain_rule_set_count) + 6;
+  if (chain_rule_set_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad chain rule end %d in chain context format 1", chain_rule_set_end);
+  }
+  if (offset_coverage < chain_rule_set_end || offset_coverage >= length) {
+    return OTS_FAILURE_MSG("Bad coverage offset %d in chain context format 1", chain_rule_set_end);
+  }
+  if (!ots::ParseCoverageTable(file, data + offset_coverage,
+                               length - offset_coverage, num_glyphs)) {
+    return OTS_FAILURE_MSG("Failed to parse coverage table for chain context format 1");
+  }
+
+  for (unsigned i = 0; i < chain_rule_set_count; ++i) {
+    uint16_t offset_chain_rule_set = 0;
+    if (!subtable.ReadU16(&offset_chain_rule_set)) {
+      return OTS_FAILURE_MSG("Failed to read chain rule offset %d in chain context format 1", i);
+    }
+    if (offset_chain_rule_set < chain_rule_set_end ||
+        offset_chain_rule_set >= length) {
+      return OTS_FAILURE_MSG("Bad chain rule set offset %d for chain rule set %d in chain context format 1", offset_chain_rule_set, i);
+    }
+    if (!ParseChainRuleSetTable(file, data + offset_chain_rule_set,
+                                   length - offset_chain_rule_set,
+                                   num_glyphs, num_lookups)) {
+      return OTS_FAILURE_MSG("Failed to parse chain rule set %d in chain context format 1", i);
+    }
+  }
+
+  return true;
+}
+
+bool ParseChainClassRuleSubtable(const ots::OpenTypeFile *file,
+                                 const uint8_t *data, const size_t length,
+                                 const uint16_t num_glyphs,
+                                 const uint16_t num_lookups) {
+  ots::Buffer subtable(data, length);
+
+  // In this subtable, we don't check the value of classes for now since
+  // these could take arbitrary values.
+
+  uint16_t backtrack_count = 0;
+  if (!subtable.ReadU16(&backtrack_count)) {
+    return OTS_FAILURE_MSG("Failed to read backtrack count in chain class rule subtable");
+  }
+  if (backtrack_count >= num_glyphs) {
+    return OTS_FAILURE_MSG("Bad backtrack count %d in chain class rule subtable", backtrack_count);
+  }
+  if (!subtable.Skip(2 * backtrack_count)) {
+    return OTS_FAILURE_MSG("Failed to skip backtrack offsets in chain class rule subtable");
+  }
+
+  uint16_t input_count = 0;
+  if (!subtable.ReadU16(&input_count)) {
+    return OTS_FAILURE_MSG("Failed to read input count in chain class rule subtable");
+  }
+  if (input_count == 0 || input_count >= num_glyphs) {
+    return OTS_FAILURE_MSG("Bad input count %d in chain class rule subtable", input_count);
+  }
+  if (!subtable.Skip(2 * (input_count - 1))) {
+    return OTS_FAILURE_MSG("Failed to skip input offsets in chain class rule subtable");
+  }
+
+  uint16_t lookahead_count = 0;
+  if (!subtable.ReadU16(&lookahead_count)) {
+    return OTS_FAILURE_MSG("Failed to read lookahead count in chain class rule subtable");
+  }
+  if (lookahead_count >= num_glyphs) {
+    return OTS_FAILURE_MSG("Bad lookahead count %d in chain class rule subtable", lookahead_count);
+  }
+  if (!subtable.Skip(2 * lookahead_count)) {
+    return OTS_FAILURE_MSG("Failed to skip lookahead offsets in chain class rule subtable");
+  }
+
+  uint16_t lookup_count = 0;
+  if (!subtable.ReadU16(&lookup_count)) {
+    return OTS_FAILURE_MSG("Failed to read lookup count in chain class rule subtable");
+  }
+  for (unsigned i = 0; i < lookup_count; ++i) {
+    if (!ParseLookupRecord(file, &subtable, num_glyphs, num_lookups)) {
+      return OTS_FAILURE_MSG("Failed to parse lookup record %d in chain class rule subtable", i);
+    }
+  }
+
+  return true;
+}
+
+bool ParseChainClassSetTable(const ots::OpenTypeFile *file,
+                             const uint8_t *data, const size_t length,
+                             const uint16_t num_glyphs,
+                             const uint16_t num_lookups) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t chain_class_rule_count = 0;
+  if (!subtable.ReadU16(&chain_class_rule_count)) {
+    return OTS_FAILURE_MSG("Failed to read rule count in chain class set");
+  }
+  const unsigned chain_class_rule_end =
+      2 * static_cast<unsigned>(chain_class_rule_count) + 2;
+  if (chain_class_rule_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad end of chain class set %d in chain class set", chain_class_rule_end);
+  }
+  for (unsigned i = 0; i < chain_class_rule_count; ++i) {
+    uint16_t offset_chain_class_rule = 0;
+    if (!subtable.ReadU16(&offset_chain_class_rule)) {
+      return OTS_FAILURE_MSG("Failed to read chain class rule offset %d in chain class set", i);
+    }
+    if (offset_chain_class_rule < chain_class_rule_end ||
+        offset_chain_class_rule >= length) {
+      return OTS_FAILURE_MSG("Bad chain class rule offset %d for chain class %d in chain class set", offset_chain_class_rule, i);
+    }
+    if (!ParseChainClassRuleSubtable(file, data + offset_chain_class_rule,
+                                     length - offset_chain_class_rule,
+                                     num_glyphs, num_lookups)) {
+      return OTS_FAILURE_MSG("Failed to parse chain class rule %d in chain class set", i);
+    }
+  }
+
+  return true;
+}
+
+bool ParseChainContextFormat2(const ots::OpenTypeFile *file,
+                              const uint8_t *data, const size_t length,
+                              const uint16_t num_glyphs,
+                              const uint16_t num_lookups) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t offset_coverage = 0;
+  uint16_t offset_backtrack_class_def = 0;
+  uint16_t offset_input_class_def = 0;
+  uint16_t offset_lookahead_class_def = 0;
+  uint16_t chain_class_set_count = 0;
+  // Skip format field.
+  if (!subtable.Skip(2) ||
+      !subtable.ReadU16(&offset_coverage) ||
+      !subtable.ReadU16(&offset_backtrack_class_def) ||
+      !subtable.ReadU16(&offset_input_class_def) ||
+      !subtable.ReadU16(&offset_lookahead_class_def) ||
+      !subtable.ReadU16(&chain_class_set_count)) {
+    return OTS_FAILURE_MSG("Failed to read header of chain context format 2");
+  }
+
+  const unsigned chain_class_set_end =
+      2 * static_cast<unsigned>(chain_class_set_count) + 12;
+  if (chain_class_set_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad chain class set end %d in chain context format 2", chain_class_set_end);
+  }
+  if (offset_coverage < chain_class_set_end || offset_coverage >= length) {
+    return OTS_FAILURE_MSG("Bad coverage offset %d in chain context format 2", offset_coverage);
+  }
+  if (!ots::ParseCoverageTable(file, data + offset_coverage,
+                               length - offset_coverage, num_glyphs)) {
+    return OTS_FAILURE_MSG("Failed to parse coverage table in chain context format 2");
+  }
+
+  // Classes for backtrack/lookahead sequences might not be defined.
+  if (offset_backtrack_class_def) {
+    if (offset_backtrack_class_def < chain_class_set_end ||
+        offset_backtrack_class_def >= length) {
+      return OTS_FAILURE_MSG("Bad backtrack class offset %d in chain context format 2", offset_backtrack_class_def);
+    }
+    if (!ots::ParseClassDefTable(file, data + offset_backtrack_class_def,
+                                 length - offset_backtrack_class_def,
+                                 num_glyphs, kMaxClassDefValue)) {
+      return OTS_FAILURE_MSG("Failed to parse backtrack class defn table in chain context format 2");
+    }
+  }
+
+  if (offset_input_class_def < chain_class_set_end ||
+      offset_input_class_def >= length) {
+    return OTS_FAILURE_MSG("Bad input class defn offset %d in chain context format 2", offset_input_class_def);
+  }
+  if (!ots::ParseClassDefTable(file, data + offset_input_class_def,
+                               length - offset_input_class_def,
+                               num_glyphs, kMaxClassDefValue)) {
+    return OTS_FAILURE_MSG("Failed to parse input class defn in chain context format 2");
+  }
+
+  if (offset_lookahead_class_def) {
+    if (offset_lookahead_class_def < chain_class_set_end ||
+        offset_lookahead_class_def >= length) {
+      return OTS_FAILURE_MSG("Bad lookahead class defn offset %d in chain context format 2", offset_lookahead_class_def);
+    }
+    if (!ots::ParseClassDefTable(file, data + offset_lookahead_class_def,
+                                 length - offset_lookahead_class_def,
+                                 num_glyphs, kMaxClassDefValue)) {
+      return OTS_FAILURE_MSG("Failed to parse lookahead class defn in chain context format 2");
+    }
+  }
+
+  for (unsigned i = 0; i < chain_class_set_count; ++i) {
+    uint16_t offset_chain_class_set = 0;
+    if (!subtable.ReadU16(&offset_chain_class_set)) {
+      return OTS_FAILURE_MSG("Failed to read chain class set offset %d", i);
+    }
+    // |offset_chain_class_set| could be NULL.
+    if (offset_chain_class_set) {
+      if (offset_chain_class_set < chain_class_set_end ||
+          offset_chain_class_set >= length) {
+        return OTS_FAILURE_MSG("Bad chain set class offset %d for chain set %d in chain context format 2", offset_chain_class_set, i);
+      }
+      if (!ParseChainClassSetTable(file, data + offset_chain_class_set,
+                                   length - offset_chain_class_set,
+                                   num_glyphs, num_lookups)) {
+        return OTS_FAILURE_MSG("Failed to parse chain class set table %d in chain context format 2", i);
+      }
+    }
+  }
+
+  return true;
+}
+
+bool ParseChainContextFormat3(const ots::OpenTypeFile *file,
+                              const uint8_t *data, const size_t length,
+                              const uint16_t num_glyphs,
+                              const uint16_t num_lookups) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t backtrack_count = 0;
+  // Skip format field.
+  if (!subtable.Skip(2) ||
+      !subtable.ReadU16(&backtrack_count)) {
+    return OTS_FAILURE_MSG("Failed to read backtrack count in chain context format 3");
+  }
+
+  if (backtrack_count >= num_glyphs) {
+    return OTS_FAILURE_MSG("Bad backtrack count %d in chain context format 3", backtrack_count);
+  }
+  std::vector<uint16_t> offsets_backtrack;
+  offsets_backtrack.reserve(backtrack_count);
+  for (unsigned i = 0; i < backtrack_count; ++i) {
+    uint16_t offset = 0;
+    if (!subtable.ReadU16(&offset)) {
+      return OTS_FAILURE_MSG("Failed to read backtrack offset %d in chain context format 3", i);
+    }
+    offsets_backtrack.push_back(offset);
+  }
+  if (offsets_backtrack.size() != backtrack_count) {
+    return OTS_FAILURE_MSG("Bad backtrack offsets size %ld in chain context format 3", offsets_backtrack.size());
+  }
+
+  uint16_t input_count = 0;
+  if (!subtable.ReadU16(&input_count)) {
+    return OTS_FAILURE_MSG("Failed to read input count in chain context format 3");
+  }
+  if (input_count >= num_glyphs) {
+    return OTS_FAILURE_MSG("Bad input count %d in chain context format 3", input_count);
+  }
+  std::vector<uint16_t> offsets_input;
+  offsets_input.reserve(input_count);
+  for (unsigned i = 0; i < input_count; ++i) {
+    uint16_t offset = 0;
+    if (!subtable.ReadU16(&offset)) {
+      return OTS_FAILURE_MSG("Failed to read input offset %d in chain context format 3", i);
+    }
+    offsets_input.push_back(offset);
+  }
+  if (offsets_input.size() != input_count) {
+    return OTS_FAILURE_MSG("Bad input offsets size %ld in chain context format 3", offsets_input.size());
+  }
+
+  uint16_t lookahead_count = 0;
+  if (!subtable.ReadU16(&lookahead_count)) {
+    return OTS_FAILURE_MSG("Failed ot read lookahead count in chain context format 3");
+  }
+  if (lookahead_count >= num_glyphs) {
+    return OTS_FAILURE_MSG("Bad lookahead count %d in chain context format 3", lookahead_count);
+  }
+  std::vector<uint16_t> offsets_lookahead;
+  offsets_lookahead.reserve(lookahead_count);
+  for (unsigned i = 0; i < lookahead_count; ++i) {
+    uint16_t offset = 0;
+    if (!subtable.ReadU16(&offset)) {
+      return OTS_FAILURE_MSG("Failed to read lookahead offset %d in chain context format 3", i);
+    }
+    offsets_lookahead.push_back(offset);
+  }
+  if (offsets_lookahead.size() != lookahead_count) {
+    return OTS_FAILURE_MSG("Bad lookahead offsets size %ld in chain context format 3", offsets_lookahead.size());
+  }
+
+  uint16_t lookup_count = 0;
+  if (!subtable.ReadU16(&lookup_count)) {
+    return OTS_FAILURE_MSG("Failed to read lookup count in chain context format 3");
+  }
+  for (unsigned i = 0; i < lookup_count; ++i) {
+    if (!ParseLookupRecord(file, &subtable, num_glyphs, num_lookups)) {
+      return OTS_FAILURE_MSG("Failed to parse lookup %d in chain context format 3", i);
+    }
+  }
+
+  const unsigned lookup_record_end =
+      2 * (static_cast<unsigned>(backtrack_count) +
+           static_cast<unsigned>(input_count) +
+           static_cast<unsigned>(lookahead_count)) +
+      4 * static_cast<unsigned>(lookup_count) + 10;
+  if (lookup_record_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad end of lookup record %d in chain context format 3", lookup_record_end);
+  }
+  for (unsigned i = 0; i < backtrack_count; ++i) {
+    if (offsets_backtrack[i] < lookup_record_end ||
+        offsets_backtrack[i] >= length) {
+      return OTS_FAILURE_MSG("Bad backtrack offset of %d for backtrack %d in chain context format 3", offsets_backtrack[i], i);
+    }
+    if (!ots::ParseCoverageTable(file, data + offsets_backtrack[i],
+                                 length - offsets_backtrack[i], num_glyphs)) {
+      return OTS_FAILURE_MSG("Failed to parse backtrack coverage %d in chain context format 3", i);
+    }
+  }
+  for (unsigned i = 0; i < input_count; ++i) {
+    if (offsets_input[i] < lookup_record_end || offsets_input[i] >= length) {
+      return OTS_FAILURE_MSG("Bad input offset %d for input %d in chain context format 3", offsets_input[i], i);
+    }
+    if (!ots::ParseCoverageTable(file, data + offsets_input[i],
+                                 length - offsets_input[i], num_glyphs)) {
+      return OTS_FAILURE_MSG("Failed to parse input coverage table %d in chain context format 3", i);
+    }
+  }
+  for (unsigned i = 0; i < lookahead_count; ++i) {
+    if (offsets_lookahead[i] < lookup_record_end ||
+        offsets_lookahead[i] >= length) {
+      return OTS_FAILURE_MSG("Bad lookadhead offset %d for lookahead %d in chain context format 3", offsets_lookahead[i], i);
+    }
+    if (!ots::ParseCoverageTable(file, data + offsets_lookahead[i],
+                                 length - offsets_lookahead[i], num_glyphs)) {
+      return OTS_FAILURE_MSG("Failed to parse lookahead coverage table %d in chain context format 3", i);
+    }
+  }
+
+  return true;
+}
+
+}  // namespace
+
+namespace ots {
+
+bool LookupSubtableParser::Parse(const OpenTypeFile *file, const uint8_t *data,
+                                 const size_t length,
+                                 const uint16_t lookup_type) const {
+  for (unsigned i = 0; i < num_types; ++i) {
+    if (parsers[i].type == lookup_type && parsers[i].parse) {
+      if (!parsers[i].parse(file, data, length)) {
+        return OTS_FAILURE_MSG("Failed to parse lookup subtable %d", i);
+      }
+      return true;
+    }
+  }
+  return OTS_FAILURE_MSG("No lookup subtables to parse");
+}
+
+// Parsing ScriptListTable requires number of features so we need to
+// parse FeatureListTable before calling this function.
+bool ParseScriptListTable(const ots::OpenTypeFile *file,
+                          const uint8_t *data, const size_t length,
+                          const uint16_t num_features) {
+  Buffer subtable(data, length);
+
+  uint16_t script_count = 0;
+  if (!subtable.ReadU16(&script_count)) {
+    return OTS_FAILURE_MSG("Failed to read script count in script list table");
+  }
+
+  const unsigned script_record_end =
+      6 * static_cast<unsigned>(script_count) + 2;
+  if (script_record_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad end of script record %d in script list table", script_record_end);
+  }
+  std::vector<ScriptRecord> script_list;
+  script_list.reserve(script_count);
+  uint32_t last_tag = 0;
+  for (unsigned i = 0; i < script_count; ++i) {
+    ScriptRecord record;
+    if (!subtable.ReadU32(&record.tag) ||
+        !subtable.ReadU16(&record.offset)) {
+      return OTS_FAILURE_MSG("Failed to read script record %d in script list table", i);
+    }
+    // Script tags should be arranged alphabetically by tag
+    if (last_tag != 0 && last_tag > record.tag) {
+      // Several fonts don't arrange tags alphabetically.
+      // It seems that the order of tags might not be a security issue
+      // so we just warn it.
+      OTS_WARNING("tags aren't arranged alphabetically.");
+    }
+    last_tag = record.tag;
+    if (record.offset < script_record_end || record.offset >= length) {
+      return OTS_FAILURE_MSG("Bad record offset %d for script %4.4s entry %d in script list table", record.offset, (char *)&record.tag, i);
+    }
+    script_list.push_back(record);
+  }
+  if (script_list.size() != script_count) {
+    return OTS_FAILURE_MSG("Bad script list size %ld in script list table", script_list.size());
+  }
+
+  // Check script records.
+  for (unsigned i = 0; i < script_count; ++i) {
+    if (!ParseScriptTable(file, data + script_list[i].offset,
+                          length - script_list[i].offset,
+                          script_list[i].tag, num_features)) {
+      return OTS_FAILURE_MSG("Failed to parse script table %d", i);
+    }
+  }
+
+  return true;
+}
+
+// Parsing FeatureListTable requires number of lookups so we need to parse
+// LookupListTable before calling this function.
+bool ParseFeatureListTable(const ots::OpenTypeFile *file,
+                           const uint8_t *data, const size_t length,
+                           const uint16_t num_lookups,
+                           uint16_t* num_features) {
+  Buffer subtable(data, length);
+
+  uint16_t feature_count = 0;
+  if (!subtable.ReadU16(&feature_count)) {
+    return OTS_FAILURE_MSG("Failed to read feature count");
+  }
+
+  std::vector<FeatureRecord> feature_records;
+  feature_records.resize(feature_count);
+  const unsigned feature_record_end =
+      6 * static_cast<unsigned>(feature_count) + 2;
+  if (feature_record_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad end of feature record %d", feature_record_end);
+  }
+  uint32_t last_tag = 0;
+  for (unsigned i = 0; i < feature_count; ++i) {
+    if (!subtable.ReadU32(&feature_records[i].tag) ||
+        !subtable.ReadU16(&feature_records[i].offset)) {
+      return OTS_FAILURE_MSG("Failed to read feature header %d", i);
+    }
+    // Feature record array should be arranged alphabetically by tag
+    if (last_tag != 0 && last_tag > feature_records[i].tag) {
+      // Several fonts don't arrange tags alphabetically.
+      // It seems that the order of tags might not be a security issue
+      // so we just warn it.
+      OTS_WARNING("tags aren't arranged alphabetically.");
+    }
+    last_tag = feature_records[i].tag;
+    if (feature_records[i].offset < feature_record_end ||
+        feature_records[i].offset >= length) {
+      return OTS_FAILURE_MSG("Bad feature offset %d for feature %d %4.4s", feature_records[i].offset, i, (char *)&feature_records[i].tag);
+    }
+  }
+
+  for (unsigned i = 0; i < feature_count; ++i) {
+    if (!ParseFeatureTable(file, data + feature_records[i].offset,
+                           length - feature_records[i].offset, num_lookups)) {
+      return OTS_FAILURE_MSG("Failed to parse feature table %d", i);
+    }
+  }
+  *num_features = feature_count;
+  return true;
+}
+
+// For parsing GPOS/GSUB tables, this function should be called at first to
+// obtain the number of lookups because parsing FeatureTableList requires
+// the number.
+bool ParseLookupListTable(OpenTypeFile *file, const uint8_t *data,
+                          const size_t length,
+                          const LookupSubtableParser* parser,
+                          uint16_t *num_lookups) {
+  Buffer subtable(data, length);
+
+  if (!subtable.ReadU16(num_lookups)) {
+    return OTS_FAILURE_MSG("Failed to read number of lookups");
+  }
+
+  std::vector<uint16_t> lookups;
+  lookups.reserve(*num_lookups);
+  const unsigned lookup_end =
+      2 * static_cast<unsigned>(*num_lookups) + 2;
+  if (lookup_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad end of lookups %d", lookup_end);
+  }
+  for (unsigned i = 0; i < *num_lookups; ++i) {
+    uint16_t offset = 0;
+    if (!subtable.ReadU16(&offset)) {
+      return OTS_FAILURE_MSG("Failed to read lookup offset %d", i);
+    }
+    if (offset < lookup_end || offset >= length) {
+      return OTS_FAILURE_MSG("Bad lookup offset %d for lookup %d", offset, i);
+    }
+    lookups.push_back(offset);
+  }
+  if (lookups.size() != *num_lookups) {
+    return OTS_FAILURE_MSG("Bad lookup offsets list size %ld", lookups.size());
+  }
+
+  for (unsigned i = 0; i < *num_lookups; ++i) {
+    if (!ParseLookupTable(file, data + lookups[i], length - lookups[i],
+                          parser)) {
+      return OTS_FAILURE_MSG("Failed to parse lookup %d", i);
+    }
+  }
+
+  return true;
+}
+
+bool ParseClassDefTable(const ots::OpenTypeFile *file,
+                        const uint8_t *data, size_t length,
+                        const uint16_t num_glyphs,
+                        const uint16_t num_classes) {
+  Buffer subtable(data, length);
+
+  uint16_t format = 0;
+  if (!subtable.ReadU16(&format)) {
+    return OTS_FAILURE_MSG("Failed to read class defn format");
+  }
+  if (format == 1) {
+    return ParseClassDefFormat1(file, data, length, num_glyphs, num_classes);
+  } else if (format == 2) {
+    return ParseClassDefFormat2(file, data, length, num_glyphs, num_classes);
+  }
+
+  return OTS_FAILURE_MSG("Bad class defn format %d", format);
+}
+
+bool ParseCoverageTable(const ots::OpenTypeFile *file,
+                        const uint8_t *data, size_t length,
+                        const uint16_t num_glyphs,
+                        const uint16_t expected_num_glyphs) {
+  Buffer subtable(data, length);
+
+  uint16_t format = 0;
+  if (!subtable.ReadU16(&format)) {
+    return OTS_FAILURE_MSG("Failed to read coverage table format");
+  }
+  if (format == 1) {
+    return ParseCoverageFormat1(file, data, length, num_glyphs, expected_num_glyphs);
+  } else if (format == 2) {
+    return ParseCoverageFormat2(file, data, length, num_glyphs, expected_num_glyphs);
+  }
+
+  return OTS_FAILURE_MSG("Bad coverage table format %d", format);
+}
+
+bool ParseDeviceTable(const ots::OpenTypeFile *file,
+                      const uint8_t *data, size_t length) {
+  Buffer subtable(data, length);
+
+  uint16_t start_size = 0;
+  uint16_t end_size = 0;
+  uint16_t delta_format = 0;
+  if (!subtable.ReadU16(&start_size) ||
+      !subtable.ReadU16(&end_size) ||
+      !subtable.ReadU16(&delta_format)) {
+    return OTS_FAILURE_MSG("Failed to read device table header");
+  }
+  if (start_size > end_size) {
+    return OTS_FAILURE_MSG("bad size range: %u > %u", start_size, end_size);
+  }
+  if (delta_format == 0 || delta_format > kMaxDeltaFormatType) {
+    return OTS_FAILURE_MSG("bad delta format: %u", delta_format);
+  }
+  // The number of delta values per uint16. The device table should contain
+  // at least |num_units| * 2 bytes compressed data.
+  const unsigned num_units = (end_size - start_size) /
+      (1 << (4 - delta_format)) + 1;
+  // Just skip |num_units| * 2 bytes since the compressed data could take
+  // arbitrary values.
+  if (!subtable.Skip(num_units * 2)) {
+    return OTS_FAILURE_MSG("Failed to skip data in device table");
+  }
+  return true;
+}
+
+bool ParseContextSubtable(const ots::OpenTypeFile *file,
+                          const uint8_t *data, const size_t length,
+                          const uint16_t num_glyphs,
+                          const uint16_t num_lookups) {
+  Buffer subtable(data, length);
+
+  uint16_t format = 0;
+  if (!subtable.ReadU16(&format)) {
+    return OTS_FAILURE_MSG("Failed to read context subtable format");
+  }
+
+  if (format == 1) {
+    if (!ParseContextFormat1(file, data, length, num_glyphs, num_lookups)) {
+      return OTS_FAILURE_MSG("Failed to parse context format 1 subtable");
+    }
+  } else if (format == 2) {
+    if (!ParseContextFormat2(file, data, length, num_glyphs, num_lookups)) {
+      return OTS_FAILURE_MSG("Failed to parse context format 2 subtable");
+    }
+  } else if (format == 3) {
+    if (!ParseContextFormat3(file, data, length, num_glyphs, num_lookups)) {
+      return OTS_FAILURE_MSG("Failed to parse context format 3 subtable");
+    }
+  } else {
+    return OTS_FAILURE_MSG("Bad context subtable format %d", format);
+  }
+
+  return true;
+}
+
+bool ParseChainingContextSubtable(const ots::OpenTypeFile *file,
+                                  const uint8_t *data, const size_t length,
+                                  const uint16_t num_glyphs,
+                                  const uint16_t num_lookups) {
+  Buffer subtable(data, length);
+
+  uint16_t format = 0;
+  if (!subtable.ReadU16(&format)) {
+    return OTS_FAILURE_MSG("Failed to read chaining context subtable format");
+  }
+
+  if (format == 1) {
+    if (!ParseChainContextFormat1(file, data, length, num_glyphs, num_lookups)) {
+      return OTS_FAILURE_MSG("Failed to parse chaining context format 1 subtable");
+    }
+  } else if (format == 2) {
+    if (!ParseChainContextFormat2(file, data, length, num_glyphs, num_lookups)) {
+      return OTS_FAILURE_MSG("Failed to parse chaining context format 2 subtable");
+    }
+  } else if (format == 3) {
+    if (!ParseChainContextFormat3(file, data, length, num_glyphs, num_lookups)) {
+      return OTS_FAILURE_MSG("Failed to parse chaining context format 3 subtable");
+    }
+  } else {
+    return OTS_FAILURE_MSG("Bad chaining context subtable format %d", format);
+  }
+
+  return true;
+}
+
+bool ParseExtensionSubtable(const OpenTypeFile *file,
+                            const uint8_t *data, const size_t length,
+                            const LookupSubtableParser* parser) {
+  Buffer subtable(data, length);
+
+  uint16_t format = 0;
+  uint16_t lookup_type = 0;
+  uint32_t offset_extension = 0;
+  if (!subtable.ReadU16(&format) ||
+      !subtable.ReadU16(&lookup_type) ||
+      !subtable.ReadU32(&offset_extension)) {
+    return OTS_FAILURE_MSG("Failed to read extension table header");
+  }
+
+  if (format != 1) {
+    return OTS_FAILURE_MSG("Bad extension table format %d", format);
+  }
+  // |lookup_type| should be other than |parser->extension_type|.
+  if (lookup_type < 1 || lookup_type > parser->num_types ||
+      lookup_type == parser->extension_type) {
+    return OTS_FAILURE_MSG("Bad lookup type %d in extension table", lookup_type);
+  }
+
+  const unsigned format_end = static_cast<unsigned>(8);
+  if (offset_extension < format_end ||
+      offset_extension >= length) {
+    return OTS_FAILURE_MSG("Bad extension offset %d", offset_extension);
+  }
+
+  // Parse the extension subtable of |lookup_type|.
+  if (!parser->Parse(file, data + offset_extension, length - offset_extension,
+                     lookup_type)) {
+    return OTS_FAILURE_MSG("Failed to parse lookup from extension lookup");
+  }
+
+  return true;
+}
+
+}  // namespace ots
+
+#undef TABLE_NAME