fix: emit valid PDF binary marker and omit empty /Contents

gopdf.go

@@ -1048,7 +1048,7 @@ func (gp *GoPdf) compilePdf(w io.Writer) (n int64, err error) {
 	}
 	max := len(gp.pdfObjs)
 	writer := newCountingWriter(w)
-	fmt.Fprint(writer, "%PDF-1.7\n%����\n\n")
+	fmt.Fprint(writer, "%PDF-1.7\n%\xe2\xe3\xcf\xd3\n\n")
 	linelens := make([]int64, max)
 	i := 0
 

gopdf_test.go

@@ -818,6 +818,45 @@ func TestAddHeaderFooter(t *testing.T) {
 	}
 }
 
+// TestPdfBinaryHeader verifies that the compiled PDF starts with the correct
+// "%PDF-1.7" version header followed by the 4-byte binary marker
+// (0xE2 0xE3 0xCF 0xD3). Per the PDF spec, this binary marker must contain
+// at least four bytes >= 128 so that file-transfer tools treat the file as
+// binary instead of text.
+func TestPdfBinaryHeader(t *testing.T) {
+	if err := initTesting(); err != nil {
+		t.Fatal(err)
+	}
+
+	pdf := GoPdf{}
+	pdf.Start(Config{PageSize: *PageSizeA4})
+	pdf.AddPage()
+
+	got, err := pdf.GetBytesPdfReturnErr()
+	if err != nil {
+		t.Fatalf("GetBytesPdfReturnErr() error = %v", err)
+	}
+
+	want := []byte("%PDF-1.7\n%\xe2\xe3\xcf\xd3\n\n")
+	if len(got) < len(want) {
+		t.Fatalf("compiled pdf too short: got %d bytes, want at least %d", len(got), len(want))
+	}
+	if !bytes.Equal(got[:len(want)], want) {
+		t.Fatalf("pdf header mismatch:\n got: % x\nwant: % x", got[:len(want)], want)
+	}
+
+	binaryMarker := got[10:14]
+	expectedMarker := []byte{0xE2, 0xE3, 0xCF, 0xD3}
+	if !bytes.Equal(binaryMarker, expectedMarker) {
+		t.Fatalf("binary marker mismatch:\n got: % x\nwant: % x", binaryMarker, expectedMarker)
+	}
+	for i, b := range binaryMarker {
+		if b < 128 {
+			t.Fatalf("binary marker byte %d (0x%02x) must be >= 128 to satisfy PDF spec", i, b)
+		}
+	}
+}
+
 func initTesting() error {
 	err := os.MkdirAll("./test/out", 0777)
 	if err != nil {

page_obj.go

@@ -52,7 +52,9 @@ func (p *PageObj) write(w io.Writer, objID int) error {
 	}
 	me.buffer.WriteString("    >>\n")*/
 	//me.buffer.WriteString("  >>\n")
-	fmt.Fprintf(w, "  /Contents %s\n", p.Contents) //sample  Contents 8 0 R
+	if p.Contents != "" {
+		fmt.Fprintf(w, "  /Contents %s\n", p.Contents) //sample  Contents 8 0 R
+	}
 	if !p.pageOption.isEmpty() {
 		fmt.Fprintf(w, " /MediaBox [ 0 0 %0.2f %0.2f ]\n", p.pageOption.PageSize.W, p.pageOption.PageSize.H)
 	}

page_obj_test.go

@@ -0,0 +1,52 @@
+package gopdf
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+)
+
+// TestPageObjWriteOmitsContentsWhenEmpty verifies that PageObj.write does not
+// emit a "/Contents" entry when PageObj.Contents is empty.
+//
+// Previously the write method always wrote "  /Contents %s\n", which produced
+// a malformed "  /Contents \n" line in the PDF when no content stream was
+// attached (e.g. when importing pages from an existing source).
+func TestPageObjWriteOmitsContentsWhenEmpty(t *testing.T) {
+	p := &PageObj{
+		ResourcesRelate: "5 0 R",
+	}
+
+	var buf bytes.Buffer
+	if err := p.write(&buf, 1); err != nil {
+		t.Fatalf("PageObj.write error = %v", err)
+	}
+
+	out := buf.String()
+	if strings.Contains(out, "/Contents") {
+		t.Fatalf("PageObj.write emitted /Contents for empty Contents; output:\n%s", out)
+	}
+	if !strings.HasPrefix(out, "<<\n") || !strings.HasSuffix(out, ">>\n") {
+		t.Fatalf("PageObj.write produced malformed dictionary:\n%s", out)
+	}
+}
+
+// TestPageObjWriteIncludesContentsWhenSet verifies that PageObj.write emits the
+// "/Contents" entry with the correct indirect reference when PageObj.Contents
+// is populated.
+func TestPageObjWriteIncludesContentsWhenSet(t *testing.T) {
+	p := &PageObj{
+		Contents:        "8 0 R",
+		ResourcesRelate: "5 0 R",
+	}
+
+	var buf bytes.Buffer
+	if err := p.write(&buf, 1); err != nil {
+		t.Fatalf("PageObj.write error = %v", err)
+	}
+
+	want := "  /Contents 8 0 R\n"
+	if !strings.Contains(buf.String(), want) {
+		t.Fatalf("PageObj.write missing %q in:\n%s", want, buf.String())
+	}
+}