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https://github.com/RGBCube/serenity
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LibPDF: Parse hint tables
This code isn't _actually_ used as of right now, but I wrote it at the same time as all of the code in the previous commit. I realized after I wrote it that these hint tables aren't super useful if the parser already has access to the full file. However, this will be useful if we ever want to stream PDFs from the web (and possibly view them in the browser).
This commit is contained in:
Matthew Olsson
Ali Mohammad Pur
parent
e23bfd7252
commit
ea3abb14fe
2 changed files with 253 additions and 0 deletions
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@ -4,6 +4,8 @@
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <AK/BitStream.h>
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#include <AK/MemoryStream.h>
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#include <AK/ScopeGuard.h>
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#include <AK/TypeCasts.h>
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#include <LibPDF/CommonNames.h>
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@ -215,6 +217,71 @@ bool Parser::initialize_linearized_xref_table()
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return m_xref_table->merge(move(*main_xref_table));
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}
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bool Parser::initialize_hint_tables()
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{
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auto linearization_dict = m_linearization_dictionary.value();
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auto primary_offset = linearization_dict.primary_hint_stream_offset;
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auto overflow_offset = linearization_dict.overflow_hint_stream_offset;
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auto parse_hint_table = [&](size_t offset) -> RefPtr<StreamObject> {
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m_reader.move_to(offset);
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auto stream_indirect_value = parse_indirect_value();
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if (!stream_indirect_value)
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return {};
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auto stream_value = stream_indirect_value->value();
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if (!stream_value.is_object())
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return {};
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auto stream_object = stream_value.as_object();
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if (!stream_object->is_stream())
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return {};
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return object_cast<StreamObject>(stream_object);
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};
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auto primary_hint_stream = parse_hint_table(primary_offset);
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if (!primary_hint_stream)
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return false;
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RefPtr<StreamObject> overflow_hint_stream;
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if (overflow_offset != NumericLimits<u32>::max())
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overflow_hint_stream = parse_hint_table(overflow_offset);
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ByteBuffer possible_merged_stream_buffer;
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ReadonlyBytes hint_stream_bytes;
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if (overflow_hint_stream) {
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auto primary_size = primary_hint_stream->bytes().size();
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auto overflow_size = overflow_hint_stream->bytes().size();
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auto total_size = primary_size + overflow_size;
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possible_merged_stream_buffer = ByteBuffer::create_uninitialized(total_size);
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possible_merged_stream_buffer.append(primary_hint_stream->bytes());
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possible_merged_stream_buffer.append(overflow_hint_stream->bytes());
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hint_stream_bytes = possible_merged_stream_buffer.bytes();
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} else {
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hint_stream_bytes = primary_hint_stream->bytes();
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}
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auto hint_table = parse_page_offset_hint_table(hint_stream_bytes);
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if (!hint_table.has_value())
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return false;
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dbgln("hint table: {}", hint_table.value());
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auto hint_table_entries = parse_all_page_offset_hint_table_entries(hint_table.value(), hint_stream_bytes);
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if (!hint_table_entries.has_value())
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return false;
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auto entries = hint_table_entries.value();
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dbgln("hint table entries size: {}", entries.size());
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for (auto& entry : entries)
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dbgln("{}", entry);
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return true;
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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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@ -323,6 +390,113 @@ RefPtr<DictObject> Parser::parse_file_trailer()
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return dict;
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}
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Optional<Parser::PageOffsetHintTable> Parser::parse_page_offset_hint_table(const ReadonlyBytes& hint_stream_bytes)
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{
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if (hint_stream_bytes.size() < sizeof(PageOffsetHintTable))
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return {};
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size_t offset = 0;
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auto read_u32 = [&] {
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u32 data = reinterpret_cast<const u32*>(hint_stream_bytes.data() + offset)[0];
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offset += 4;
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return AK::convert_between_host_and_big_endian(data);
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};
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auto read_u16 = [&] {
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u16 data = reinterpret_cast<const u16*>(hint_stream_bytes.data() + offset)[0];
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offset += 2;
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return AK::convert_between_host_and_big_endian(data);
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};
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PageOffsetHintTable hint_table {
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read_u32(),
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read_u32(),
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read_u16(),
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read_u32(),
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read_u16(),
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read_u32(),
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read_u16(),
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read_u32(),
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read_u16(),
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read_u16(),
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read_u16(),
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read_u16(),
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read_u16(),
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};
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// Verify that all of the bits_required_for_xyz fields are <= 32, since all of the numeric
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// fields in PageOffsetHintTableEntry are u32
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VERIFY(hint_table.bits_required_for_object_number <= 32);
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VERIFY(hint_table.bits_required_for_page_length <= 32);
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VERIFY(hint_table.bits_required_for_content_stream_offsets <= 32);
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VERIFY(hint_table.bits_required_for_content_stream_length <= 32);
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VERIFY(hint_table.bits_required_for_number_of_shared_obj_refs <= 32);
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VERIFY(hint_table.bits_required_for_greatest_shared_obj_identifier <= 32);
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VERIFY(hint_table.bits_required_for_fraction_numerator <= 32);
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return hint_table;
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}
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Optional<Vector<Parser::PageOffsetHintTableEntry>> Parser::parse_all_page_offset_hint_table_entries(const PageOffsetHintTable& hint_table, const ReadonlyBytes& hint_stream_bytes)
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{
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InputMemoryStream input_stream(hint_stream_bytes);
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input_stream.seek(sizeof(PageOffsetHintTable));
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if (input_stream.has_any_error())
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return {};
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InputBitStream bit_stream(input_stream);
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auto number_of_pages = m_linearization_dictionary.value().number_of_pages;
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Vector<PageOffsetHintTableEntry> entries;
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for (size_t i = 0; i < number_of_pages; i++)
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entries.append(PageOffsetHintTableEntry {});
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auto bits_required_for_object_number = hint_table.bits_required_for_object_number;
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auto bits_required_for_page_length = hint_table.bits_required_for_page_length;
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auto bits_required_for_content_stream_offsets = hint_table.bits_required_for_content_stream_offsets;
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auto bits_required_for_content_stream_length = hint_table.bits_required_for_content_stream_length;
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auto bits_required_for_number_of_shared_obj_refs = hint_table.bits_required_for_number_of_shared_obj_refs;
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auto bits_required_for_greatest_shared_obj_identifier = hint_table.bits_required_for_greatest_shared_obj_identifier;
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auto bits_required_for_fraction_numerator = hint_table.bits_required_for_fraction_numerator;
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auto parse_int_entry = [&](u32 PageOffsetHintTableEntry::*field, u32 bit_size) {
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if (bit_size <= 0)
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return;
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for (int i = 0; i < number_of_pages; i++) {
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auto& entry = entries[i];
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entry.*field = bit_stream.read_bits(bit_size);
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}
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};
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auto parse_vector_entry = [&](Vector<u32> PageOffsetHintTableEntry::*field, u32 bit_size) {
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if (bit_size <= 0)
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return;
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for (int page = 1; page < number_of_pages; page++) {
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auto number_of_shared_objects = entries[page].number_of_shared_objects;
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Vector<u32> items;
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items.ensure_capacity(number_of_shared_objects);
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for (size_t i = 0; i < number_of_shared_objects; i++)
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items.unchecked_append(bit_stream.read_bits(bit_size));
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entries[page].*field = move(items);
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}
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};
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parse_int_entry(&PageOffsetHintTableEntry::objects_in_page_number, bits_required_for_object_number);
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parse_int_entry(&PageOffsetHintTableEntry::page_length_number, bits_required_for_page_length);
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parse_int_entry(&PageOffsetHintTableEntry::number_of_shared_objects, bits_required_for_number_of_shared_obj_refs);
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parse_vector_entry(&PageOffsetHintTableEntry::shared_object_identifiers, bits_required_for_greatest_shared_obj_identifier);
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parse_vector_entry(&PageOffsetHintTableEntry::shared_object_location_numerators, bits_required_for_fraction_numerator);
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parse_int_entry(&PageOffsetHintTableEntry::page_content_stream_offset_number, bits_required_for_content_stream_offsets);
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parse_int_entry(&PageOffsetHintTableEntry::page_content_stream_length_number, bits_required_for_content_stream_length);
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return entries;
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}
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bool Parser::navigate_to_before_eof_marker()
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{
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m_reader.set_reading_backwards();
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@ -1012,4 +1186,52 @@ struct Formatter<PDF::Parser::LinearizationDictionary> : Formatter<StringView> {
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}
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};
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template<>
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struct Formatter<PDF::Parser::PageOffsetHintTable> : Formatter<StringView> {
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void format(FormatBuilder& format_builder, const PDF::Parser::PageOffsetHintTable& table)
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{
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StringBuilder builder;
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builder.append("{\n");
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builder.appendff(" least_number_of_objects_in_a_page={}\n", table.least_number_of_objects_in_a_page);
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builder.appendff(" location_of_first_page_object={}\n", table.location_of_first_page_object);
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builder.appendff(" bits_required_for_object_number={}\n", table.bits_required_for_object_number);
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builder.appendff(" least_length_of_a_page={}\n", table.least_length_of_a_page);
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builder.appendff(" bits_required_for_page_length={}\n", table.bits_required_for_page_length);
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builder.appendff(" least_offset_of_any_content_stream={}\n", table.least_offset_of_any_content_stream);
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builder.appendff(" bits_required_for_content_stream_offsets={}\n", table.bits_required_for_content_stream_offsets);
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builder.appendff(" least_content_stream_length={}\n", table.least_content_stream_length);
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builder.appendff(" bits_required_for_content_stream_length={}\n", table.bits_required_for_content_stream_length);
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builder.appendff(" bits_required_for_number_of_shared_obj_refs={}\n", table.bits_required_for_number_of_shared_obj_refs);
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builder.appendff(" bits_required_for_greatest_shared_obj_identifier={}\n", table.bits_required_for_greatest_shared_obj_identifier);
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builder.appendff(" bits_required_for_fraction_numerator={}\n", table.bits_required_for_fraction_numerator);
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builder.appendff(" shared_object_reference_fraction_denominator={}\n", table.shared_object_reference_fraction_denominator);
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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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template<>
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struct Formatter<PDF::Parser::PageOffsetHintTableEntry> : Formatter<StringView> {
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void format(FormatBuilder& format_builder, const PDF::Parser::PageOffsetHintTableEntry& entry)
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{
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StringBuilder builder;
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builder.append("{\n");
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builder.appendff(" objects_in_page_number={}\n", entry.objects_in_page_number);
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builder.appendff(" page_length_number={}\n", entry.page_length_number);
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builder.appendff(" number_of_shared_objects={}\n", entry.number_of_shared_objects);
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builder.append(" shared_object_identifiers=[");
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for (auto& identifier : entry.shared_object_identifiers)
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builder.appendff(" {}", identifier);
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builder.append(" ]\n");
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builder.append(" shared_object_location_numerators=[");
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for (auto& numerator : entry.shared_object_location_numerators)
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builder.appendff(" {}", numerator);
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builder.append(" ]\n");
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builder.appendff(" page_content_stream_offset_number={}\n", entry.page_content_stream_offset_number);
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builder.appendff(" page_content_stream_length_number={}\n", entry.page_content_stream_length_number);
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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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