backend/pdf: separate the font-file key from its object number

backend/pdf/font.go

@@ -109,7 +109,7 @@ func (e *embedded) write(d *document, compress bool) error {
 		// CFF outlines are embedded whole and described as OpenType, because
 		// this package does not cut charstrings up — see internal/sfnt.
 		dict = "/Subtype /CIDFontType0"
-		fileKey = "/FontFile3 "
+		fileKey = "/FontFile3"
 	}
 
 	stream := fmt.Sprintf("/Length1 %d", len(prog))
@@ -121,7 +121,7 @@ func (e *embedded) write(d *document, compress bool) error {
 	xMin, yMin, xMax, yMax := f.BBox()
 	desc := d.add([]byte(fmt.Sprintf(
 		"<< /Type /FontDescriptor /FontName /%s /Flags 4 /FontBBox [%d %d %d %d] "+
-			"/ItalicAngle %s /Ascent %d /Descent %d /CapHeight %d /StemV %d %s%d 0 R >>",
+			"/ItalicAngle %s /Ascent %d /Descent %d /CapHeight %d /StemV %d %s %d 0 R >>",
 		name, k(xMin), k(yMin), k(xMax), k(yMax),
 		fmtNum(f.ItalicAngle()), k(f.Ascent()), k(f.Descent()), k(f.CapHeight()),
 		stemV(f.WeightClass()), fileKey, file)))

backend/pdf/font_test.go

@@ -1,6 +1,7 @@
 package pdf_test
 
 import (
+	"regexp"
 	"strings"
 	"testing"
 
@@ -58,6 +59,35 @@ func TestAnEmbeddedFontIsACIDFont(t *testing.T) {
 	}
 }
 
+// The descriptor points at the font program by reference. A key run into the
+// object number ("/FontFile22 0 R") is a different name followed by a stray
+// "0 R": readers then treat the font as not embedded, and a PDF importer that
+// re-serialises the dictionary scrambles it.
+func TestTheDescriptorReferencesTheFontProgram(t *testing.T) {
+	for _, tc := range []struct {
+		name, key string
+		font      []byte
+	}{
+		{"TrueType", "/FontFile2", testTTF()},
+		{"CFF", "/FontFile3", sfnttest.CFFFont()},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			doc := drawLabel(t, "AB", pdf.WithFont(tc.font, nil, nil), pdf.Uncompressed())
+			m := regexp.MustCompile(regexp.QuoteMeta(tc.key) + ` (\d+) 0 R`).FindStringSubmatch(doc)
+			if m == nil {
+				t.Fatalf("the descriptor carries no %s reference", tc.key)
+			}
+			obj := regexp.MustCompile(`(?s)\n` + m[1] + ` 0 obj\n<<(.*?)>>\nstream`).FindStringSubmatch(doc)
+			if obj == nil {
+				t.Fatalf("%s points at object %s, which is not a stream", tc.key, m[1])
+			}
+			if tc.key == "/FontFile2" && !strings.Contains(obj[1], "/Length1") {
+				t.Errorf("object %s is not the font program: %s", m[1], obj[1])
+			}
+		})
+	}
+}
+
 // The glyphs are numbered as they are first met, which is what makes writing
 // a PDF one pass: the content stream names an id before the subset that
 // defines it exists.