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https://github.com/RGBCube/serenity
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LibPDF: Parse linearized PDF files
This is a big step, as most PDFs which are downloaded online will be linearized. Pretty much the only difference is that the xref structure is slightly different.
This commit is contained in:
Matthew Olsson
Ali Mohammad Pur
parent
be1be47613
commit
e23bfd7252
8 changed files with 270 additions and 45 deletions
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@ -43,37 +43,33 @@ bool Parser::initialize()
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if (!parse_header())
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return {};
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m_reader.move_to(m_reader.bytes().size() - 1);
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if (!navigate_to_before_eof_marker())
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return false;
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if (!navigate_to_after_startxref())
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return false;
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if (m_reader.done())
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return false;
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if (!initialize_linearization_dict())
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return {};
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m_reader.set_reading_forwards();
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auto xref_offset_value = parse_number();
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if (!xref_offset_value.is_int())
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return false;
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auto xref_offset = xref_offset_value.as_int();
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bool is_linearized = m_linearization_dictionary.has_value();
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if (is_linearized) {
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// The file may have been linearized at one point, but could have been updated afterwards,
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// which means it is no longer a linearized PDF file.
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is_linearized = is_linearized && m_linearization_dictionary.value().length_of_file == m_reader.bytes().size();
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m_reader.move_to(xref_offset);
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auto xref_table = parse_xref_table();
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if (!xref_table.has_value())
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return false;
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auto trailer = parse_file_trailer();
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if (!trailer)
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return false;
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if (!is_linearized) {
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// FIXME: The file shouldn't be treated as linearized, yet the xref tables are still
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// split. This might take some tweaking to ensure correct behavior, which can be
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// implemented later.
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TODO();
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}
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}
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m_xref_table = xref_table.value();
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m_trailer = trailer;
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return true;
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if (is_linearized)
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return initialize_linearized_xref_table();
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return initialize_non_linearized_xref_table();
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}
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Value Parser::parse_object_with_index(u32 index)
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{
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VERIFY(m_xref_table.has_object(index));
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auto byte_offset = m_xref_table.byte_offset_for_object(index);
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VERIFY(m_xref_table->has_object(index));
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auto byte_offset = m_xref_table->byte_offset_for_object(index);
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m_reader.move_to(byte_offset);
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auto indirect_value = parse_indirect_value();
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VERIFY(indirect_value);
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@ -115,7 +111,135 @@ bool Parser::parse_header()
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return true;
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}
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Optional<XRefTable> Parser::parse_xref_table()
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bool Parser::initialize_linearization_dict()
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{
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// parse_header() is called immediately before this, so we are at the right location
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auto dict_value = m_document->resolve(parse_indirect_value());
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if (!dict_value || !dict_value.is_object())
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return false;
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auto dict_object = dict_value.as_object();
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if (!dict_object->is_dict())
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return false;
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auto dict = object_cast<DictObject>(dict_object);
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if (!dict->contains(CommonNames::L, CommonNames::H, CommonNames::O, CommonNames::E, CommonNames::N, CommonNames::T))
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return true;
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auto length_of_file = dict->get_value(CommonNames::L);
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auto hint_table = dict->get_value(CommonNames::H);
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auto first_page_object_number = dict->get_value(CommonNames::O);
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auto offset_of_first_page_end = dict->get_value(CommonNames::E);
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auto number_of_pages = dict->get_value(CommonNames::N);
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auto offset_of_main_xref_table = dict->get_value(CommonNames::T);
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auto first_page = dict->get(CommonNames::P).value_or({});
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// Validation
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if (!length_of_file.is_int_type<u32>()
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|| !hint_table.is_object()
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|| !first_page_object_number.is_int_type<u32>()
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|| !number_of_pages.is_int_type<u16>()
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|| !offset_of_main_xref_table.is_int_type<u32>()
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|| (first_page && !first_page.is_int_type<u32>())) {
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return true;
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}
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auto hint_table_object = hint_table.as_object();
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if (!hint_table_object->is_array())
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return true;
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auto hint_table_array = object_cast<ArrayObject>(hint_table_object);
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auto hint_table_size = hint_table_array->size();
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if (hint_table_size != 2 && hint_table_size != 4)
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return true;
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auto primary_hint_stream_offset = hint_table_array->at(0);
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auto primary_hint_stream_length = hint_table_array->at(1);
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Value overflow_hint_stream_offset;
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Value overflow_hint_stream_length;
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if (hint_table_size == 4) {
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overflow_hint_stream_offset = hint_table_array->at(2);
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overflow_hint_stream_length = hint_table_array->at(3);
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}
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if (!primary_hint_stream_offset.is_int_type<u32>()
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|| !primary_hint_stream_length.is_int_type<u32>()
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|| (overflow_hint_stream_offset && !overflow_hint_stream_offset.is_int_type<u32>())
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|| (overflow_hint_stream_length && !overflow_hint_stream_length.is_int_type<u32>())) {
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return true;
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}
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m_linearization_dictionary = LinearizationDictionary {
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length_of_file.as_int_type<u32>(),
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primary_hint_stream_offset.as_int_type<u32>(),
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primary_hint_stream_length.as_int_type<u32>(),
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overflow_hint_stream_offset ? overflow_hint_stream_offset.as_int_type<u32>() : NumericLimits<u32>::max(),
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overflow_hint_stream_length ? overflow_hint_stream_length.as_int_type<u32>() : NumericLimits<u32>::max(),
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first_page_object_number.as_int_type<u32>(),
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offset_of_first_page_end.as_int_type<u32>(),
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number_of_pages.as_int_type<u16>(),
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offset_of_main_xref_table.as_int_type<u32>(),
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first_page ? first_page.as_int_type<u32>() : NumericLimits<u32>::max(),
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};
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return true;
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}
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bool Parser::initialize_linearized_xref_table()
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{
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// The linearization parameter dictionary has just been parsed, and the xref table
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// comes immediately after it. We are in the correct spot.
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if (!m_reader.matches("xref"))
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return false;
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m_xref_table = parse_xref_table();
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if (!m_xref_table)
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return false;
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m_trailer = parse_file_trailer();
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if (!m_trailer)
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return false;
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// Also parse the main xref table and merge into the first-page xref table. Note
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// that we don't use the main xref table offset from the linearization dict because
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// for some reason, it specified the offset of the whitespace after the object
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// index start and length? So it's much easier to do it this way.
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auto main_xref_table_offset = m_trailer->get_value(CommonNames::Prev).to_int();
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m_reader.move_to(main_xref_table_offset);
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auto main_xref_table = parse_xref_table();
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if (!main_xref_table)
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return false;
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return m_xref_table->merge(move(*main_xref_table));
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}
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bool Parser::initialize_non_linearized_xref_table()
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{
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m_reader.move_to(m_reader.bytes().size() - 1);
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if (!navigate_to_before_eof_marker())
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return false;
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if (!navigate_to_after_startxref())
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return false;
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if (m_reader.done())
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return false;
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m_reader.set_reading_forwards();
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auto xref_offset_value = parse_number();
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if (!xref_offset_value.is_int())
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return false;
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auto xref_offset = xref_offset_value.as_int();
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m_reader.move_to(xref_offset);
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m_xref_table = parse_xref_table();
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if (!m_xref_table)
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return false;
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m_trailer = parse_file_trailer();
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return m_trailer;
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}
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RefPtr<XRefTable> Parser::parse_xref_table()
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{
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if (!m_reader.matches("xref"))
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return {};
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@ -123,11 +247,11 @@ Optional<XRefTable> Parser::parse_xref_table()
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if (!consume_eol())
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return {};
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XRefTable table;
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auto table = adopt_ref(*new XRefTable());
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while (true) {
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if (m_reader.matches("trailer"))
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break;
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return table;
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Vector<XRefEntry> entries;
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@ -170,10 +294,8 @@ Optional<XRefTable> Parser::parse_xref_table()
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entries.append({ offset, static_cast<u16>(generation), letter == 'n' });
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}
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table.add_section({ starting_index, object_count, entries });
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table->add_section({ starting_index, object_count, entries });
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}
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return table;
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}
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RefPtr<DictObject> Parser::parse_file_trailer()
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@ -195,9 +317,9 @@ RefPtr<DictObject> Parser::parse_file_trailer()
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VERIFY(consume_eol());
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if (!m_reader.matches("%%EOF"))
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return {};
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m_reader.move_by(5);
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consume_whitespace();
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return dict;
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}
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@ -658,8 +780,8 @@ RefPtr<DictObject> Parser::conditionally_parse_page_tree_node(u32 object_index,
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{
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ok = true;
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VERIFY(m_xref_table.has_object(object_index));
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auto byte_offset = m_xref_table.byte_offset_for_object(object_index);
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VERIFY(m_xref_table->has_object(object_index));
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auto byte_offset = m_xref_table->byte_offset_for_object(object_index);
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m_reader.move_to(byte_offset);
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parse_number();
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@ -866,3 +988,28 @@ bool Parser::consume(char ch)
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}
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}
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namespace AK {
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template<>
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struct Formatter<PDF::Parser::LinearizationDictionary> : Formatter<StringView> {
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void format(FormatBuilder& format_builder, const PDF::Parser::LinearizationDictionary& dict)
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{
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StringBuilder builder;
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builder.append("{\n");
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builder.appendff(" length_of_file={}\n", dict.length_of_file);
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builder.appendff(" primary_hint_stream_offset={}\n", dict.primary_hint_stream_offset);
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builder.appendff(" primary_hint_stream_length={}\n", dict.primary_hint_stream_length);
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builder.appendff(" overflow_hint_stream_offset={}\n", dict.overflow_hint_stream_offset);
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builder.appendff(" overflow_hint_stream_length={}\n", dict.overflow_hint_stream_length);
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builder.appendff(" first_page_object_number={}\n", dict.first_page_object_number);
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builder.appendff(" offset_of_first_page_end={}\n", dict.offset_of_first_page_end);
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builder.appendff(" number_of_pages={}\n", dict.number_of_pages);
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builder.appendff(" offset_of_main_xref_table={}\n", dict.offset_of_main_xref_table);
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builder.appendff(" first_page={}\n", dict.first_page);
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builder.append('}');
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Formatter<StringView>::format(format_builder, builder.to_string());
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}
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};
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}
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