From 6e98469ef723960ce4fcf37b27416cf2ebfca263 Mon Sep 17 00:00:00 2001
From: Přemysl Eric Janouch <p@janouch.name>
Date: Thu, 29 Jun 2023 05:01:23 +0200
Subject: WIP: PDF 1.5 cross-reference stream support

Perhaps only for Go.
---
 pdf/pdf.go | 40 +++++++++++++++++++++++++++++++++++++++-
 test.sh    |  3 +--
 2 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/pdf/pdf.go b/pdf/pdf.go
index 92d18e9..e9f42a7 100644
--- a/pdf/pdf.go
+++ b/pdf/pdf.go
@@ -671,11 +671,49 @@ func (u *Updater) parse(lex *Lexer, stack *[]Object) (Object, error) {
 	}
 }
 
+// TODO: ISO 32000-2:2020 7.5.8.2 Cross-reference stream dictionary
+//   - How to update this kind of file? Hybrid-reference file?
+//     ⋄ XRefStm could point to this old-new xref. But it's actually a /Prev.
+func (u *Updater) loadXrefStream(
+	lex *Lexer, loadedEntries map[uint]struct{}) error {
+	var stack []Object
+	for {
+		object, err := u.parse(lex, &stack)
+		if err != nil {
+			return fmt.Errorf("invalid xref table: %s", err)
+		} else if object.Kind == End {
+			return errors.New("invalid xref table")
+		}
+
+		// For the sake of simplicity, keep stacking until we find an object.
+		if object.Kind != Indirect {
+			stack = append(stack, object)
+			continue
+		}
+
+		object = object.Array[0]
+		if object.Kind != Stream {
+			return errors.New("invalid xref table")
+		}
+		if typ, ok := object.Dict["Type"]; !ok || typ.String != "XRef" {
+			return errors.New("invalid xref stream")
+		}
+		if filter, ok := object.Dict["Filter"]; !ok ||
+			filter.String != "FlateDecode" {
+			return errors.New("invalid xref stream")
+		}
+
+		return errors.New("unimplemented")
+	}
+}
+
+// TODO: Also return the trailer dictionary, but remove any XRef/stream fields,
+// perhaps as per Table 17 + /Filter, /Length.
 func (u *Updater) loadXref(lex *Lexer, loadedEntries map[uint]struct{}) error {
 	var throwawayStack []Object
 	if keyword, _ := u.parse(lex,
 		&throwawayStack); keyword.Kind != Keyword || keyword.String != "xref" {
-		return errors.New("invalid xref table")
+		return u.loadXrefStream(lex, loadedEntries)
 	}
 	for {
 		object, _ := u.parse(lex, &throwawayStack)
diff --git a/test.sh b/test.sh
index 831a15e..9d3ab60 100755
--- a/test.sh
+++ b/test.sh
@@ -11,8 +11,7 @@ mkdir tmp
 
 # Create documents in various tools
 log "Creating source documents"
-inkscape --pipe --export-filename=tmp/cairo.pdf --export-pdf-version=1.4 \
-<<'EOF' 2>/dev/null || :
+inkscape --pipe --export-filename=tmp/cairo.pdf <<'EOF' 2>/dev/null || :
 <svg xmlns="http://www.w3.org/2000/svg"><text x="5" y="10">Hello</text></svg>
 EOF
 
-- 
cgit v1.2.3-70-g09d2