Fix TTC detection, based on findings by libFuzzer

src/font.cc

@@ -181,15 +181,14 @@ bool ReadFontCollection(const uint8_t* data, size_t len,
                         FontCollection* font_collection) {
   Buffer file(data, len);
 
-  uint32_t flavor;
-  if (!file.ReadU32(&flavor)) {
+  if (!file.ReadU32(&font_collection->flavor)) {
     return FONT_COMPRESSION_FAILURE();
   }
 
-  if (flavor != kTtcFontFlavor) {
+  if (font_collection->flavor != kTtcFontFlavor) {
     font_collection->fonts.resize(1);
     Font& font = font_collection->fonts[0];
-    font.flavor = flavor;
+    font.flavor = font_collection->flavor;
     return ReadTrueTypeFont(&file, data, len, &font);
   }
   return ReadTrueTypeCollection(&file, data, len, font_collection);
@@ -286,7 +285,7 @@ bool WriteFontCollection(const FontCollection& font_collection, uint8_t* dst,
   size_t offset = 0;
 
   // It's simpler if this just a simple sfnt
-  if (font_collection.fonts.size() == 1) {
+  if (font_collection.flavor != kTtcFontFlavor) {
     return WriteFont(font_collection.fonts[0], &offset, dst, dst_size);
   }
 

src/font.h

@@ -61,6 +61,7 @@ struct Font {
 
 // Accomodates both singular (OTF, TTF) and collection (TTC) fonts
 struct FontCollection {
+  uint32_t flavor;
   uint32_t header_version;
   // (offset, first use of table*) pairs
   std::map<uint32_t, Font::Table*> tables;

src/woff2_enc.cc

@@ -121,7 +121,7 @@ size_t ComputeWoff2Length(const FontCollection& font_collection,
   }
 
   // for collections only, collection tables
-  if (font_collection.fonts.size() > 1) {
+  if (font_collection.flavor == kTtcFontFlavor) {
     size += 4;  // UInt32 Version of TTC Header
     size += Size255UShort(font_collection.fonts.size());  // 255UInt16 numFonts
 
@@ -161,7 +161,7 @@ size_t ComputeUncompressedLength(const Font& font) {
 }
 
 size_t ComputeUncompressedLength(const FontCollection& font_collection) {
-  if (font_collection.fonts.size() == 1) {
+  if (font_collection.flavor != kTtcFontFlavor) {
     return ComputeUncompressedLength(font_collection.fonts[0]);
   }
   size_t size = CollectionHeaderSize(font_collection.header_version,
@@ -372,13 +372,12 @@ bool ConvertTTFToWOFF2(const uint8_t *data, size_t length,
   }
   *result_length = woff2_length;
 
-  const Font& first_font = font_collection.fonts[0];
   size_t offset = 0;
 
   // start of woff2 header (http://www.w3.org/TR/WOFF2/#woff20Header)
   StoreU32(kWoff2Signature, &offset, result);
-  if (font_collection.fonts.size() == 1) {
-    StoreU32(first_font.flavor, &offset, result);
+  if (font_collection.flavor != kTtcFontFlavor) {
+    StoreU32(font_collection.fonts[0].flavor, &offset, result);
   } else {
     StoreU32(kTtcFontFlavor, &offset, result);
   }
@@ -389,9 +388,9 @@ bool ConvertTTFToWOFF2(const uint8_t *data, size_t length,
   StoreU32(ComputeUncompressedLength(font_collection), &offset, result);
   StoreU32(total_compressed_length, &offset, result);  // totalCompressedSize
 
-  // TODO(user): is always taking this from the first tables head OK?
-  // font revision
-  StoreBytes(first_font.FindTable(kHeadTableTag)->data + 4, 4, &offset, result);
+  // Let's just all be v1.0
+  Store16(1, &offset, result);  // majorVersion
+  Store16(0, &offset, result);  // minorVersion
   if (compressed_metadata_buf_length > 0) {
     StoreU32(woff2_length - compressed_metadata_buf_length,
              &offset, result);  // metaOffset
@@ -413,7 +412,7 @@ bool ConvertTTFToWOFF2(const uint8_t *data, size_t length,
   }
 
   // for collections only, collection table directory
-  if (font_collection.fonts.size() > 1) {
+  if (font_collection.flavor == kTtcFontFlavor) {
     StoreU32(font_collection.header_version, &offset, result);
     Store255UShort(font_collection.fonts.size(), &offset, result);
     for (const Font& font : font_collection.fonts) {