fix(pdf): do not embed a CFF font of only .notdef

CHANGELOG.md

@@ -16,6 +16,9 @@ The release run heads these entries with the version and opens a fresh
 
 ## Unreleased
 
+- **Fix**: a pdf CFF font with no glyph but `.notdef` is no longer embedded,
+  because browsers reject it. Its text uses a substitute font.
+
 - **Fix**: a pdf whose zlib streams declare a smaller window than they use
   failed to open with "Inflator: error in compressed block". It opens now.
 

src/odr/internal/font/cff_transform.cpp

@@ -136,6 +136,10 @@ namespace odr::internal::font {
 std::string cff::wrap_to_otf(const CffFont &font,
                              const std::map<char32_t, std::uint16_t> &extra) {
   const std::uint16_t glyphs = font.glyph_count();
+  if (glyphs < 2) {
+    // OTS rejects a `CFF ` table whose CharStrings hold only `.notdef`.
+    throw std::runtime_error("cff: no glyph besides .notdef");
+  }
 
   // Glyphs past the 6400-slot BMP PUA overflow into Supplementary PUA-A, which
   // serialize_cmap covers with a format-12 subtable.

src/odr/internal/font/cff_transform.hpp

@@ -18,7 +18,7 @@ class CffFont;
 ///
 /// The `cmap` is `pua_cmap(glyph_count, extra)`, so the font renders every
 /// glyph — including charset-unreachable ones — at the PUA code points the PDF
-/// HTML layer emits.
+/// HTML layer emits. Throws for a font with no glyph besides `.notdef`.
 [[nodiscard]] std::string
 wrap_to_otf(const CffFont &font,
             const std::map<char32_t, std::uint16_t> &extra = {});

test/data.cmake

@@ -17,9 +17,9 @@ odr_test_data(
 odr_test_data(
         PATH "reference-output/odr-public"
         URL "https://github.com/opendocument-app/OpenDocument.test.output.git"
-        REVISION "542037eec472235ed0ada025fb41de76f082ea6e")
+        REVISION "055e7ec00193112b0759c1189463ef17ca892201")
 
 odr_test_data(
         PATH "reference-output/odr-private"
         URL "https://github.com/opendocument-app/OpenDocument.test-private.output.git"
-        REVISION "78502f22a1c2631825476daa3351843f9f6c60ae")
+        REVISION "509b8191ac4ef3be1d5e14c0f69647d586dbe6c5")

test/src/internal/font/cff_font.cpp

@@ -10,6 +10,7 @@
 #include <gtest/gtest.h>
 
 #include <cstdint>
+#include <stdexcept>
 #include <string>
 #include <string_view>
 #include <vector>
@@ -491,6 +492,16 @@ TEST(CffFontTest, WrapSanitizesTheFontName) {
   EXPECT_EQ(patched.advance_width(1), cff.advance_width(1));
 }
 
+TEST(CffFontTest, WrapRejectsAFontOfOnlyNotdef) {
+  using namespace odr::internal::font;
+  const std::vector<cff::BuilderGlyph> glyphs = {
+      {".notdef", std::string("\x0e", 1)}};
+  const cff::CffFont font{
+      cff::build_cff("Hidden", glyphs, 0, 0, FontBBox{0, 0, 1000, 1000})};
+  ASSERT_EQ(font.glyph_count(), 1);
+  EXPECT_THROW((void)cff::wrap_to_otf(font), std::runtime_error);
+}
+
 TEST(CffFontTest, WrapDropsExtraEntriesPastGlyphCount) {
   using namespace odr::internal::font;
   const CffFont cff{build_cff()}; // 2 glyphs: valid ids 0..1