From 1b8f73b6b3afd8d78172fcd30b95db67f259f58a Mon Sep 17 00:00:00 2001
From: Wesley Moret <wesmoret98@gmail.com>
Date: Wed, 14 Jul 2021 21:48:09 -0400
Subject: [PATCH] LibPDF: Fix treating not finding the linearized dict as a
 fatal error

We now try to parse the first indirect value and see
if it's the `Linearization Parameter Dictionary`. if it's not, we
fallback to reading the xref table from the end of the document
---
 Userland/Libraries/LibPDF/Parser.cpp | 31 +++++++++++++++++-----------
 Userland/Libraries/LibPDF/Parser.h   |  8 ++++++-
 2 files changed, 26 insertions(+), 13 deletions(-)

diff --git a/Userland/Libraries/LibPDF/Parser.cpp b/Userland/Libraries/LibPDF/Parser.cpp
index 51f59c99b61..263ea0a2700 100644
--- a/Userland/Libraries/LibPDF/Parser.cpp
+++ b/Userland/Libraries/LibPDF/Parser.cpp
@@ -45,14 +45,18 @@ bool Parser::initialize()
     if (!parse_header())
         return {};
 
-    if (!initialize_linearization_dict())
+    const auto result = initialize_linearization_dict();
+    if (result == LinearizationResult::Error)
         return {};
 
+    if (result == LinearizationResult::NotLinearized)
+        return initialize_non_linearized_xref_table();
+
     bool is_linearized = m_linearization_dictionary.has_value();
     if (is_linearized) {
         // The file may have been linearized at one point, but could have been updated afterwards,
         // which means it is no longer a linearized PDF file.
-        is_linearized = is_linearized && m_linearization_dictionary.value().length_of_file == m_reader.bytes().size();
+        is_linearized = m_linearization_dictionary.value().length_of_file == m_reader.bytes().size();
 
         if (!is_linearized) {
             // FIXME: The file shouldn't be treated as linearized, yet the xref tables are still
@@ -113,21 +117,24 @@ bool Parser::parse_header()
     return true;
 }
 
-bool Parser::initialize_linearization_dict()
+Parser::LinearizationResult Parser::initialize_linearization_dict()
 {
     // parse_header() is called immediately before this, so we are at the right location
     auto dict_value = m_document->resolve(parse_indirect_value());
     if (!dict_value || !dict_value.is_object())
-        return false;
+        return LinearizationResult::Error;
 
     auto dict_object = dict_value.as_object();
     if (!dict_object->is_dict())
-        return false;
+        return LinearizationResult::NotLinearized;
 
     auto dict = object_cast<DictObject>(dict_object);
 
+    if (!dict->contains(CommonNames::Linearized))
+        return LinearizationResult::NotLinearized;
+
     if (!dict->contains(CommonNames::L, CommonNames::H, CommonNames::O, CommonNames::E, CommonNames::N, CommonNames::T))
-        return true;
+        return LinearizationResult::Error;
 
     auto length_of_file = dict->get_value(CommonNames::L);
     auto hint_table = dict->get_value(CommonNames::H);
@@ -144,17 +151,17 @@ bool Parser::initialize_linearization_dict()
         || !number_of_pages.is_int_type<u16>()
         || !offset_of_main_xref_table.is_int_type<u32>()
         || (first_page && !first_page.is_int_type<u32>())) {
-        return true;
+        return LinearizationResult::Error;
     }
 
     auto hint_table_object = hint_table.as_object();
     if (!hint_table_object->is_array())
-        return true;
+        return LinearizationResult::Error;
 
     auto hint_table_array = object_cast<ArrayObject>(hint_table_object);
     auto hint_table_size = hint_table_array->size();
     if (hint_table_size != 2 && hint_table_size != 4)
-        return true;
+        return LinearizationResult::Error;
 
     auto primary_hint_stream_offset = hint_table_array->at(0);
     auto primary_hint_stream_length = hint_table_array->at(1);
@@ -170,7 +177,7 @@ bool Parser::initialize_linearization_dict()
         || !primary_hint_stream_length.is_int_type<u32>()
         || (overflow_hint_stream_offset && !overflow_hint_stream_offset.is_int_type<u32>())
         || (overflow_hint_stream_length && !overflow_hint_stream_length.is_int_type<u32>())) {
-        return true;
+        return LinearizationResult::Error;
     }
 
     m_linearization_dictionary = LinearizationDictionary {
@@ -186,7 +193,7 @@ bool Parser::initialize_linearization_dict()
         first_page ? first_page.as_int_type<u32>() : NumericLimits<u32>::max(),
     };
 
-    return true;
+    return LinearizationResult::Linearized;
 }
 
 bool Parser::initialize_linearized_xref_table()
@@ -1023,7 +1030,7 @@ RefPtr<StreamObject> Parser::parse_stream(NonnullRefPtr<DictObject> dict)
     ReadonlyBytes bytes;
 
     auto maybe_length = dict->get(CommonNames::Length);
-    if (maybe_length.has_value()) {
+    if (maybe_length.has_value() && (!maybe_length->is_ref() || m_xref_table)) {
         // The PDF writer has kindly provided us with the direct length of the stream
         m_reader.save();
         auto length = m_document->resolve_to<int>(maybe_length.value());
diff --git a/Userland/Libraries/LibPDF/Parser.h b/Userland/Libraries/LibPDF/Parser.h
index 6dbe3b2f5f8..2dba1a0515b 100644
--- a/Userland/Libraries/LibPDF/Parser.h
+++ b/Userland/Libraries/LibPDF/Parser.h
@@ -18,6 +18,12 @@ class Document;
 
 class Parser final : public RefCounted<Parser> {
 public:
+    enum class LinearizationResult {
+        Error,
+        NotLinearized,
+        Linearized,
+    };
+
     static Vector<Command> parse_graphics_commands(ReadonlyBytes const&);
 
     Parser(Badge<Document>, ReadonlyBytes const&);
@@ -83,7 +89,7 @@ private:
     explicit Parser(ReadonlyBytes const&);
 
     bool parse_header();
-    bool initialize_linearization_dict();
+    LinearizationResult initialize_linearization_dict();
     bool initialize_linearized_xref_table();
     bool initialize_non_linearized_xref_table();
     bool initialize_hint_tables();