From a8de9cf541174f80c433b363af6378ebf77a2ca1 Mon Sep 17 00:00:00 2001
From: Matthew Olsson <matthewcolsson@gmail.com>
Date: Mon, 21 Mar 2022 11:26:31 -0700
Subject: [PATCH] LibPDF: Keep track of the current object index/generation
 while Parsing

This information is required to decrypt encrypted strings/streams.
---
 Userland/Libraries/LibPDF/Parser.cpp | 18 +++++++++++++++---
 Userland/Libraries/LibPDF/Parser.h   |  6 +++++-
 2 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/Userland/Libraries/LibPDF/Parser.cpp b/Userland/Libraries/LibPDF/Parser.cpp
index 2a5bbddcf5..89b8109886 100644
--- a/Userland/Libraries/LibPDF/Parser.cpp
+++ b/Userland/Libraries/LibPDF/Parser.cpp
@@ -613,20 +613,26 @@ PDFErrorOr<Value> Parser::parse_possible_indirect_value_or_ref()
 
     if (m_reader.matches("obj")) {
         m_reader.discard();
-        return TRY(parse_indirect_value(first_number.get<int>(), second_number.value().get<int>()));
+        auto index = first_number.get<int>();
+        auto generation = second_number.value().get<int>();
+        VERIFY(index >= 0);
+        VERIFY(generation >= 0);
+        return TRY(parse_indirect_value(index, generation));
     }
 
     m_reader.load();
     return first_number;
 }
 
-PDFErrorOr<NonnullRefPtr<IndirectValue>> Parser::parse_indirect_value(int index, int generation)
+PDFErrorOr<NonnullRefPtr<IndirectValue>> Parser::parse_indirect_value(u32 index, u32 generation)
 {
     if (!m_reader.matches("obj"))
         return error("Expected \"obj\" at beginning of indirect value");
     m_reader.move_by(3);
     if (matches_eol())
         consume_eol();
+
+    push_reference({ index, generation });
     auto value = TRY(parse_value());
     if (!m_reader.matches("endobj"))
         return error("Expected \"endobj\" at end of indirect value");
@@ -634,6 +640,8 @@ PDFErrorOr<NonnullRefPtr<IndirectValue>> Parser::parse_indirect_value(int index,
     consume(6);
     consume_whitespace();
 
+    pop_reference();
+
     return make_object<IndirectValue>(index, generation, value);
 }
 
@@ -641,7 +649,11 @@ PDFErrorOr<NonnullRefPtr<IndirectValue>> Parser::parse_indirect_value()
 {
     auto first_number = TRY(parse_number());
     auto second_number = TRY(parse_number());
-    return parse_indirect_value(first_number.get<int>(), second_number.get<int>());
+    auto index = first_number.get<int>();
+    auto generation = second_number.get<int>();
+    VERIFY(index >= 0);
+    VERIFY(generation >= 0);
+    return parse_indirect_value(index, generation);
 }
 
 PDFErrorOr<Value> Parser::parse_number()
diff --git a/Userland/Libraries/LibPDF/Parser.h b/Userland/Libraries/LibPDF/Parser.h
index db2d49f404..0af0e2041b 100644
--- a/Userland/Libraries/LibPDF/Parser.h
+++ b/Userland/Libraries/LibPDF/Parser.h
@@ -104,7 +104,7 @@ private:
 
     PDFErrorOr<Value> parse_value();
     PDFErrorOr<Value> parse_possible_indirect_value_or_ref();
-    PDFErrorOr<NonnullRefPtr<IndirectValue>> parse_indirect_value(int index, int generation);
+    PDFErrorOr<NonnullRefPtr<IndirectValue>> parse_indirect_value(u32 index, u32 generation);
     PDFErrorOr<NonnullRefPtr<IndirectValue>> parse_indirect_value();
     PDFErrorOr<Value> parse_number();
     PDFErrorOr<NonnullRefPtr<NameObject>> parse_name();
@@ -117,6 +117,9 @@ private:
 
     PDFErrorOr<Vector<Command>> parse_graphics_commands();
 
+    void push_reference(Reference const& ref) { m_current_reference_stack.append(ref); }
+    void pop_reference() { m_current_reference_stack.take_last(); }
+
     bool matches_eol() const;
     bool matches_whitespace() const;
     bool matches_number() const;
@@ -142,6 +145,7 @@ private:
     RefPtr<XRefTable> m_xref_table;
     RefPtr<DictObject> m_trailer;
     Optional<LinearizationDictionary> m_linearization_dictionary;
+    Vector<Reference> m_current_reference_stack;
 };
 
 };