LibGfx: Read OpenType table directory using structs and streams

Userland/Libraries/LibGfx/Font/OpenType/Font.cpp

@@ -3,6 +3,7 @@
  * Copyright (c) 2021-2023, Andreas Kling <kling@serenityos.org>
  * Copyright (c) 2022, Jelle Raaijmakers <jelle@gmta.nl>
  * Copyright (c) 2023, Lukas Affolter <git@lukasach.dev>
+ * Copyright (c) 2023, Sam Atkins <atkinssj@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -111,11 +112,9 @@ ErrorOr<NonnullRefPtr<Font>> Font::try_load_from_externally_owned_memory(Readonl
 // FIXME: "loca" and "glyf" are not available for CFF fonts.
 ErrorOr<NonnullRefPtr<Font>> Font::try_load_from_offset(ReadonlyBytes buffer, u32 offset)
 {
-    if (Checked<u32>::addition_would_overflow(offset, (u32)Sizes::OffsetTable))
+    FixedMemoryStream stream { buffer };
-        return Error::from_string_literal("Invalid offset in font header");
+    TRY(stream.seek(offset, AK::SeekMode::SetPosition));
-
+    auto& table_directory = *TRY(stream.read_in_place<TableDirectory const>());
-    if (buffer.size() <= offset + (u32)Sizes::OffsetTable)
-        return Error::from_string_literal("Font file too small");
 
     Optional<ReadonlyBytes> opt_head_slice = {};
     Optional<ReadonlyBytes> opt_name_slice = {};
@@ -144,54 +143,47 @@ ErrorOr<NonnullRefPtr<Font>> Font::try_load_from_offset(ReadonlyBytes buffer, u3
     Optional<CBDT> cbdt;
     Optional<GPOS> gpos;
 
-    auto num_tables = be_u16(buffer.offset(offset + (u32)Offsets::NumTables));
+    for (auto i = 0; i < table_directory.num_tables; i++) {
-    if (buffer.size() <= offset + (u32)Sizes::OffsetTable + num_tables * (u32)Sizes::TableRecord)
+        auto& table_record = *TRY(stream.read_in_place<TableRecord const>());
-        return Error::from_string_literal("Font file too small");
 
-    for (auto i = 0; i < num_tables; i++) {
+        if (table_record.length == 0 || Checked<u32>::addition_would_overflow(static_cast<u32>(table_record.offset), static_cast<u32>(table_record.length)))
-        u32 record_offset = offset + (u32)Sizes::OffsetTable + i * (u32)Sizes::TableRecord;
-        u32 tag = be_u32(buffer.offset(record_offset));
-        u32 table_offset = be_u32(buffer.offset(record_offset + (u32)Offsets::TableRecord_Offset));
-        u32 table_length = be_u32(buffer.offset(record_offset + (u32)Offsets::TableRecord_Length));
-
-        if (table_length == 0 || Checked<u32>::addition_would_overflow(table_offset, table_length))
             return Error::from_string_literal("Invalid table offset or length in font");
 
-        if (buffer.size() < table_offset + table_length)
+        if (buffer.size() < table_record.offset + table_record.length)
             return Error::from_string_literal("Font file too small");
 
-        auto buffer_here = ReadonlyBytes(buffer.offset(table_offset), table_length);
+        auto buffer_here = buffer.slice(table_record.offset, table_record.length);
 
         // Get the table offsets we need.
-        if (tag == tag_from_str("head")) {
+        if (table_record.table_tag == tag_from_str("head")) {
             opt_head_slice = buffer_here;
-        } else if (tag == tag_from_str("name")) {
+        } else if (table_record.table_tag == tag_from_str("name")) {
             opt_name_slice = buffer_here;
-        } else if (tag == tag_from_str("hhea")) {
+        } else if (table_record.table_tag == tag_from_str("hhea")) {
             opt_hhea_slice = buffer_here;
-        } else if (tag == tag_from_str("maxp")) {
+        } else if (table_record.table_tag == tag_from_str("maxp")) {
             opt_maxp_slice = buffer_here;
-        } else if (tag == tag_from_str("hmtx")) {
+        } else if (table_record.table_tag == tag_from_str("hmtx")) {
             opt_hmtx_slice = buffer_here;
-        } else if (tag == tag_from_str("cmap")) {
+        } else if (table_record.table_tag == tag_from_str("cmap")) {
             opt_cmap_slice = buffer_here;
-        } else if (tag == tag_from_str("loca")) {
+        } else if (table_record.table_tag == tag_from_str("loca")) {
             opt_loca_slice = buffer_here;
-        } else if (tag == tag_from_str("glyf")) {
+        } else if (table_record.table_tag == tag_from_str("glyf")) {
             opt_glyf_slice = buffer_here;
-        } else if (tag == tag_from_str("OS/2")) {
+        } else if (table_record.table_tag == tag_from_str("OS/2")) {
             opt_os2_slice = buffer_here;
-        } else if (tag == tag_from_str("kern")) {
+        } else if (table_record.table_tag == tag_from_str("kern")) {
             opt_kern_slice = buffer_here;
-        } else if (tag == tag_from_str("fpgm")) {
+        } else if (table_record.table_tag == tag_from_str("fpgm")) {
             opt_fpgm_slice = buffer_here;
-        } else if (tag == tag_from_str("prep")) {
+        } else if (table_record.table_tag == tag_from_str("prep")) {
             opt_prep_slice = buffer_here;
-        } else if (tag == tag_from_str("CBLC")) {
+        } else if (table_record.table_tag == tag_from_str("CBLC")) {
             cblc = TRY(CBLC::from_slice(buffer_here));
-        } else if (tag == tag_from_str("CBDT")) {
+        } else if (table_record.table_tag == tag_from_str("CBDT")) {
             cbdt = TRY(CBDT::from_slice(buffer_here));
-        } else if (tag == tag_from_str("GPOS")) {
+        } else if (table_record.table_tag == tag_from_str("GPOS")) {
             gpos = TRY(GPOS::from_slice(buffer_here));
         }
     }

Userland/Libraries/LibGfx/Font/OpenType/Font.h

@@ -68,17 +68,6 @@ private:
 
     EmbeddedBitmapData embedded_bitmap_data_for_glyph(u32 glyph_id) const;
 
-    enum class Offsets {
-        NumTables = 4,
-        TableRecord_Offset = 8,
-        TableRecord_Length = 12,
-    };
-    enum class Sizes {
-        TTCHeaderV1 = 12,
-        OffsetTable = 12,
-        TableRecord = 16,
-    };
-
     static ErrorOr<NonnullRefPtr<Font>> try_load_from_offset(ReadonlyBytes, unsigned index = 0);
 
     Font(

Userland/Libraries/LibGfx/Font/OpenType/Tables.h

@@ -67,6 +67,22 @@ struct [[gnu::packed]] TableRecord {
 };
 static_assert(AssertSize<TableRecord, 16>());
 
+}
+
+template<>
+class AK::Traits<OpenType::TableDirectory const> : public GenericTraits<OpenType::TableDirectory const> {
+public:
+    static constexpr bool is_trivially_serializable() { return true; }
+};
+
+template<>
+class AK::Traits<OpenType::TableRecord const> : public GenericTraits<OpenType::TableRecord const> {
+public:
+    static constexpr bool is_trivially_serializable() { return true; }
+};
+
+namespace OpenType {
+
 // https://learn.microsoft.com/en-us/typography/opentype/spec/head
 // head: Font Header Table
 class Head {