d1bc89e30b
An XRef table usually starts with an object number of zero. While it could technically start at any other number, this is a tell-tale sign of a broken table. For the "broken" documents I encountered, this always meant that some objects must have been removed from the start of the table, without updating the following indices. When this is the case, the document is not able to be read normally. However, most other PDF parsers seem to know of this quirk and fix the XRef table automatically. Likewise, we now check for this exact case, and if it matches up with what we expect, we update the XRef table such that all object numbers match the actual objects found in the file again.
99 lines
3.7 KiB
C++
99 lines
3.7 KiB
C++
/*
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* Copyright (c) 2021-2022, Matthew Olsson <mattco@serenityos.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <LibPDF/Parser.h>
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namespace PDF {
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class DocumentParser final : public RefCounted<DocumentParser>
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, public Parser {
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public:
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DocumentParser(Document*, ReadonlyBytes);
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enum class LinearizationResult {
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NotLinearized,
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Linearized,
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};
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[[nodiscard]] ALWAYS_INLINE RefPtr<DictObject> const& trailer() const { return m_trailer; }
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// Parses the header and initializes the xref table and trailer
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PDFErrorOr<void> initialize();
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PDFErrorOr<Value> parse_object_with_index(u32 index);
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// Specialized version of parse_dict which aborts early if the dict being parsed
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// is not a page object
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PDFErrorOr<RefPtr<DictObject>> conditionally_parse_page_tree_node(u32 object_index);
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private:
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struct LinearizationDictionary {
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u32 length_of_file { 0 };
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u32 primary_hint_stream_offset { 0 };
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u32 primary_hint_stream_length { 0 };
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u32 overflow_hint_stream_offset { 0 };
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u32 overflow_hint_stream_length { 0 };
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u32 first_page_object_number { 0 };
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u32 offset_of_first_page_end { 0 };
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u16 number_of_pages { 0 };
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u32 offset_of_main_xref_table { 0 };
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u32 first_page { 0 }; // The page to initially open (I think, the spec isn't all that clear here)
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};
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struct PageOffsetHintTable {
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u32 least_number_of_objects_in_a_page { 0 };
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u32 location_of_first_page_object { 0 };
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u16 bits_required_for_object_number { 0 };
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u32 least_length_of_a_page { 0 };
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u16 bits_required_for_page_length { 0 };
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u32 least_offset_of_any_content_stream { 0 };
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u16 bits_required_for_content_stream_offsets { 0 };
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u32 least_content_stream_length { 0 };
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u16 bits_required_for_content_stream_length { 0 };
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u16 bits_required_for_number_of_shared_obj_refs { 0 };
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u16 bits_required_for_greatest_shared_obj_identifier { 0 };
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u16 bits_required_for_fraction_numerator { 0 };
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u16 shared_object_reference_fraction_denominator { 0 };
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};
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struct PageOffsetHintTableEntry {
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u32 objects_in_page_number { 0 };
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u32 page_length_number { 0 };
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u32 number_of_shared_objects { 0 };
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Vector<u32> shared_object_identifiers {};
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Vector<u32> shared_object_location_numerators {};
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u32 page_content_stream_offset_number { 0 };
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u32 page_content_stream_length_number { 0 };
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};
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friend struct AK::Formatter<LinearizationDictionary>;
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friend struct AK::Formatter<PageOffsetHintTable>;
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friend struct AK::Formatter<PageOffsetHintTableEntry>;
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PDFErrorOr<void> parse_header();
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PDFErrorOr<LinearizationResult> initialize_linearization_dict();
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PDFErrorOr<void> initialize_linearized_xref_table();
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PDFErrorOr<void> initialize_non_linearized_xref_table();
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PDFErrorOr<void> validate_xref_table_and_fix_if_necessary();
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PDFErrorOr<void> initialize_hint_tables();
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PDFErrorOr<PageOffsetHintTable> parse_page_offset_hint_table(ReadonlyBytes hint_stream_bytes);
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Vector<PageOffsetHintTableEntry> parse_all_page_offset_hint_table_entries(PageOffsetHintTable const&, ReadonlyBytes hint_stream_bytes);
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PDFErrorOr<NonnullRefPtr<XRefTable>> parse_xref_stream();
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PDFErrorOr<NonnullRefPtr<XRefTable>> parse_xref_table();
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PDFErrorOr<NonnullRefPtr<DictObject>> parse_file_trailer();
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PDFErrorOr<Value> parse_compressed_object_with_index(u32 index);
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bool navigate_to_before_eof_marker();
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bool navigate_to_after_startxref();
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RefPtr<XRefTable> m_xref_table;
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RefPtr<DictObject> m_trailer;
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Optional<LinearizationDictionary> m_linearization_dictionary;
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};
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}
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