pdfkit: UTF-16BE text strings so accented titles are not mojibake

document.go

@@ -363,7 +363,7 @@ func outlineCount(ns []*outlineNode) int {
 func (d *Document) fillOutline(bd *builder, pageRefs []objRef, ns []*outlineNode, parent objRef) {
 	for i, n := range ns {
 		od := newDict()
-		od.set("Title", pdfString(n.item.title))
+		od.set("Title", pdfTextString(n.item.title))
 		od.set("Parent", parent)
 		od.set("Dest", pdfArray{pageRefs[n.item.pageIndex], pdfName("Fit")})
 		if i > 0 {
@@ -394,10 +394,10 @@ func (d *Document) producer() string {
 func (d *Document) infoDict() *pdfDict {
 	info := newDict()
 	if d.opts.Title != "" {
-		info.set("Title", pdfString(d.opts.Title))
+		info.set("Title", pdfTextString(d.opts.Title))
 	}
 	if d.opts.Author != "" {
-		info.set("Author", pdfString(d.opts.Author))
+		info.set("Author", pdfTextString(d.opts.Author))
 	}
 	if p := d.producer(); p != "" {
 		info.set("Producer", pdfString(p))

objects.go

@@ -82,6 +82,42 @@ func (s pdfString) encodePDF(b *bytes.Buffer) {
 	b.WriteByte(')')
 }
 
+// pdfTextString is a PDF "text string" — metadata and UI text such as a document
+// title, an author, or a bookmark label. Pure-ASCII text is written as a literal
+// (…) string; text with any non-ASCII rune is written UTF-16BE with a leading BOM as
+// a hex <FEFF…> string, so accented and other non-Latin titles display correctly
+// instead of as mojibake.
+type pdfTextString string
+
+func (s pdfTextString) encodePDF(b *bytes.Buffer) {
+	for _, r := range s {
+		if r > 0x7f {
+			b.WriteString("<FEFF")
+			for _, r := range s {
+				if r > 0xFFFF {
+					r -= 0x10000
+					textHex16(b, 0xD800+int(r>>10))
+					textHex16(b, 0xDC00+int(r&0x3FF))
+				} else {
+					textHex16(b, int(r))
+				}
+			}
+			b.WriteByte('>')
+			return
+		}
+	}
+	pdfString(s).encodePDF(b) // all-ASCII: a literal (…) string with the usual escaping
+}
+
+// textHex16 writes v as four uppercase hex digits (one UTF-16 code unit).
+func textHex16(b *bytes.Buffer, v int) {
+	const hexd = "0123456789ABCDEF"
+	b.WriteByte(hexd[(v>>12)&0xF])
+	b.WriteByte(hexd[(v>>8)&0xF])
+	b.WriteByte(hexd[(v>>4)&0xF])
+	b.WriteByte(hexd[v&0xF])
+}
+
 // pdfHexString is a PDF hexadecimal string, written between angle brackets. It
 // is used for the trailer /ID and other binary payloads.
 type pdfHexString []byte

pdftextstring_test.go

@@ -0,0 +1,51 @@
+// Copyright (c) the go-pdfkit authors.
+// SPDX-License-Identifier: BSD-3-Clause
+
+package pdfkit
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+)
+
+// A PDF text string (document title, author, bookmark label) is a literal (…) string
+// when pure ASCII and a UTF-16BE <FEFF…> hex string when it carries any non-ASCII
+// rune, so accented and astral text displays correctly instead of as mojibake.
+func TestPDFTextString(t *testing.T) {
+	enc := func(s string) string {
+		var b bytes.Buffer
+		pdfTextString(s).encodePDF(&b)
+		return b.String()
+	}
+	if got := enc("Hi (x)"); got != `(Hi \(x\))` {
+		t.Errorf("ASCII = %q, want a literal escaped string", got)
+	}
+	// café: c=0063 a=0061 f=0066 é=00E9, prefixed by the BOM FEFF.
+	if got := enc("café"); got != "<FEFF00630061006600E9>" {
+		t.Errorf("accented = %q, want UTF-16BE hex", got)
+	}
+	// 😀 = U+1F600 encodes as the surrogate pair D83D DE00.
+	if got := enc("😀"); got != "<FEFFD83DDE00>" {
+		t.Errorf("astral = %q, want a UTF-16 surrogate pair", got)
+	}
+}
+
+// A document's accented title, author and bookmark are UTF-16BE-encoded in the PDF,
+// so a viewer shows them correctly rather than the raw UTF-8 bytes.
+func TestAccentedMetadataAndOutline(t *testing.T) {
+	doc := New(Options{Title: "Résumé", Author: "Frédéric"})
+	doc.AddPage(A4)
+	doc.AddOutlineItem("Méthode", 1, 0)
+	var b bytes.Buffer
+	if err := doc.Write(&b); err != nil {
+		t.Fatal(err)
+	}
+	out := b.String()
+	if !strings.Contains(out, "<FEFF") {
+		t.Error("accented metadata was not written as a UTF-16BE string")
+	}
+	if strings.Contains(out, "Résumé") || strings.Contains(out, "Méthode") {
+		t.Error("accented text leaked as raw UTF-8 bytes instead of UTF-16BE")
+	}
+}