Add FontHelper::Cff2GetCharstrings.

Author: garretrieger

MODULE.bazel

@@ -37,9 +37,9 @@ http_archive(
 http_archive(
     name = "harfbuzz",
     build_file = "//third_party:harfbuzz.BUILD",
-    integrity = "sha256-7+uXin3Ov76LIARwi104FtmjW3ZIB0DlFiHnliAGVJ8=",
-    strip_prefix = "harfbuzz-0752e5852be6f98f2a9e8d0f8020db3654739860",
-    urls = ["https://github.com/harfbuzz/harfbuzz/archive/0752e5852be6f98f2a9e8d0f8020db3654739860.zip"],
+    integrity = "sha256-yNAzHL3p++Giyd3IKGYH/8Gn5YGbh2j2h/uyeWD/GtE=",
+    strip_prefix = "harfbuzz-a1e587b75acfa91b8756c21e5305af53fb2114af",
+    urls = ["https://github.com/harfbuzz/harfbuzz/archive/a1e587b75acfa91b8756c21e5305af53fb2114af.zip"],
 )
 
 # URI Templates

common/font_helper.cc

@@ -15,6 +15,7 @@
 
 using absl::btree_set;
 using absl::flat_hash_map;
+using absl::Status;
 using absl::StatusOr;
 using absl::StrCat;
 using absl::string_view;
@@ -122,6 +123,33 @@ FontData FontHelper::Cff2Data(hb_face_t* face, uint32_t gid) {
   return data;
 }
 
+Status FontHelper::Cff2GetCharstrings(hb_face_t* face,
+                                      FontData& non_charstrings,
+                                      FontData& charstrings) {
+  FontData cff2_data = FontHelper::TableData(face, FontHelper::kCFF2);
+  hb_blob_unique_ptr cff2_data_blob = cff2_data.blob();
+
+  hb_blob_unique_ptr charstrings_index_blob =
+      make_hb_blob(hb_subset_cff2_get_charstrings_index(face));
+  charstrings.set(charstrings_index_blob.get());
+
+  const char* cff2_start = cff2_data.data();
+  const char* charstrings_start = charstrings.data();
+  if (charstrings_start < cff2_start) {
+    return absl::InternalError("CharStrings is not after CFF2 start.");
+  }
+  uint64_t non_charstrings_length = (uint64_t)(charstrings_start - cff2_start);
+  if (non_charstrings_length > cff2_data.size()) {
+    return absl::InternalError("Non CharStrings data is too large.");
+  }
+
+  hb_blob_unique_ptr non_charstrings_blob = make_hb_blob(
+      hb_blob_create_sub_blob(cff2_data_blob.get(), 0, non_charstrings_length));
+  non_charstrings.set(non_charstrings_blob.get());
+
+  return absl::OkStatus();
+}
+
 StatusOr<uint32_t> FontHelper::GvarSharedTupleCount(const hb_face_t* face) {
   auto gvar = TableData(face, kGvar);
   if (gvar.empty()) {

common/font_helper.h

@@ -144,6 +144,10 @@ class FontHelper {
 
   static FontData Cff2Data(hb_face_t* face, uint32_t gid);
 
+  static absl::Status Cff2GetCharstrings(hb_face_t* face,
+                                         FontData& non_charstrings,
+                                         FontData& charstrings);
+
   static absl::StatusOr<uint32_t> GvarSharedTupleCount(const hb_face_t* face);
 
   static absl::StatusOr<absl::string_view> Loca(const hb_face_t* face) {

common/font_helper_test.cc

@@ -404,6 +404,23 @@ TEST_F(FontHelperTest, Cff2Data) {
   ASSERT_EQ(data.size(), 0);
 }
 
+TEST_F(FontHelperTest, Cff2GetCharstrings) {
+  FontData noncharstrings;
+  FontData charstrings;
+  auto status = FontHelper::Cff2GetCharstrings(noto_sans_vf_jp_otf.get(),
+                                               noncharstrings, charstrings);
+  ASSERT_TRUE(status.ok()) << status;
+
+  uint32_t charstrings_offset = 0x8f;  // pulled manually from the font file.
+  auto cff2 =
+      FontHelper::TableData(noto_sans_vf_jp_otf.get(), FontHelper::kCFF2);
+  auto expected_noncharstrings = cff2.str(0, charstrings_offset);
+  auto expected_charstrings = cff2.str(charstrings_offset);
+
+  ASSERT_EQ(expected_noncharstrings, noncharstrings.str());
+  ASSERT_EQ(expected_charstrings, charstrings.str());
+}
+
 TEST_F(FontHelperTest, GvarSharedTupleCount) {
   auto count = FontHelper::GvarSharedTupleCount(roboto_vf.get());
   ASSERT_TRUE(count.ok()) << count.status();