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Refactor Xref_table::reconstruct
Split reconstruction into two passes - scanning of input for objects and insertion of objects into the xref table. This allows insertion to take place in the usual reverse order and removes the need for a separate insert_reconstructed method.
This commit is contained in:
m-holger
parent
39df5936fe
commit
91822ae6a1
@ -582,6 +582,9 @@ QPDF::Xref_table::reconstruct(QPDFExc& e)
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table.erase(iter);
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}
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std::vector<std::tuple<int, int, qpdf_offset_t>> objects;
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std::vector<qpdf_offset_t> trailers;
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file->seek(0, SEEK_END);
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qpdf_offset_t eof = file->tell();
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file->seek(0, SEEK_SET);
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@ -597,25 +600,37 @@ QPDF::Xref_table::reconstruct(QPDFExc& e)
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int obj = QUtil::string_to_int(t1.getValue().c_str());
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int gen = QUtil::string_to_int(t2.getValue().c_str());
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if (obj <= max_id_) {
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insert_reconstructed(obj, token_start, gen);
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objects.emplace_back(obj, gen, token_start);
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} else {
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warn_damaged("ignoring object with impossibly large id " + std::to_string(obj));
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}
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}
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file->seek(pos, SEEK_SET);
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} else if (!trailer_ && t1.isWord("trailer")) {
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auto pos = file->tell();
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QPDFObjectHandle t = read_trailer();
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if (!t.isDictionary()) {
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// Oh well. It was worth a try.
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} else {
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trailer_ = t;
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}
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file->seek(pos, SEEK_SET);
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trailers.emplace_back(file->tell());
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}
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check_warnings();
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file->findAndSkipNextEOL();
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}
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for (auto tr: trailers) {
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file->seek(tr, SEEK_SET);
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auto t = read_trailer();
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if (!t.isDictionary()) {
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// Oh well. It was worth a try.
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} else {
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trailer_ = t;
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break;
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}
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check_warnings();
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}
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auto rend = objects.rend();
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for (auto it = objects.rbegin(); it != rend; it++) {
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auto [obj, gen, token_start] = *it;
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insert(obj, 1, token_start, gen);
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check_warnings();
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}
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deleted_objects.clear();
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if (!trailer_) {
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@ -1321,8 +1336,13 @@ QPDF::Xref_table::insert(int obj, int f0, qpdf_offset_t f1, int f2)
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// If there is already an entry for this object and generation in the table, it means that a
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// later xref table has registered this object. Disregard this one.
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if (obj > max_id_) {
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// ignore impossibly large object ids or object ids > Size.
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int new_gen = f0 == 2 ? 0 : f2;
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if (!(obj > 0 && obj <= max_id_ && 0 <= f2 && new_gen < 65535)) {
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// We are ignoring invalid objgens. Most will arrive here from xref reconstruction. There
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// is probably no point having another warning but we could count invalid items in order to
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// decide when to give up.
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QTC::TC("qpdf", "QPDF xref overwrite invalid objgen");
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return;
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}
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@ -1337,7 +1357,7 @@ QPDF::Xref_table::insert(int obj, int f0, qpdf_offset_t f1, int f2)
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return;
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}
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auto [iter, created] = table.try_emplace(QPDFObjGen(obj, (f0 == 2 ? 0 : f2)));
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auto [iter, created] = table.try_emplace(QPDFObjGen(obj, new_gen));
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if (!created) {
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QTC::TC("qpdf", "QPDF xref reused object");
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return;
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@ -1369,25 +1389,6 @@ QPDF::Xref_table::insert_free(QPDFObjGen og)
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}
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}
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// Replace uncompressed object. This is used in xref recovery mode, which reads the file from
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// beginning to end.
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void
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QPDF::Xref_table::insert_reconstructed(int obj, qpdf_offset_t f1, int f2)
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{
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if (!(obj > 0 && obj <= max_id_ && 0 <= f2 && f2 < 65535)) {
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QTC::TC("qpdf", "QPDF xref overwrite invalid objgen");
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return;
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}
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QPDFObjGen og(obj, f2);
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if (!deleted_objects.count(obj)) {
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// deleted_objects stores the uncompressed objects removed from the xref table at the start
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// of recovery.
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QTC::TC("qpdf", "QPDF xref overwrite object");
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table.insert_or_assign(QPDFObjGen(obj, f2), QPDFXRefEntry(f1));
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}
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}
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void
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QPDF::showXRefTable()
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{
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@ -1698,7 +1698,6 @@ QPDFWriter::writeObjectStream(QPDFObjectHandle object)
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if (obj_to_write.isStream()) {
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// This condition occurred in a fuzz input. Ideally we should block it at parse
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// time, but it's not clear to me how to construct a case for this.
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QTC::TC("qpdf", "QPDFWriter stream in ostream");
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obj_to_write.warnIfPossible("stream found inside object stream; treating as null");
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obj_to_write = QPDFObjectHandle::newNull();
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}
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@ -105,7 +105,6 @@ QPDFWriter not recompressing /FlateDecode 0
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QPDF_encryption xref stream from encrypted file 0
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QPDFJob unable to filter 0
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QUtil non-trivial UTF-16 0
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QPDF xref overwrite object 0
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QPDF xref overwrite invalid objgen 0
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QPDF decoding error warning 0
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qpdf-c called qpdf_init 0
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@ -437,7 +436,6 @@ QPDF xref skipped space 0
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QPDF eof skipping spaces before xref 1
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QPDF_encryption user matches owner V < 5 0
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QPDF_encryption same password 1
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QPDFWriter stream in ostream 0
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QPDFParser duplicate dict key 0
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QPDFWriter no encryption sig contents 0
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QPDFPageObjectHelper colorspace lookup 0
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@ -11,11 +11,9 @@ WARNING: fuzz-16214.pdf (object 1 0, offset 7189): expected n n obj
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WARNING: fuzz-16214.pdf: Attempting to reconstruct cross-reference table
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WARNING: fuzz-16214.pdf (offset 7207): error decoding stream data for object 2 0: stream inflate: inflate: data: invalid code lengths set
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WARNING: fuzz-16214.pdf (offset 7207): getStreamData called on unfilterable stream
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WARNING: fuzz-16214.pdf (object 8 0, offset 7207): supposed object stream 5 has wrong type
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WARNING: fuzz-16214.pdf (object 8 0, offset 7207): object stream 5 has incorrect keys
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WARNING: fuzz-16214.pdf (object 7 0, offset 7207): supposed object stream 5 has wrong type
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WARNING: fuzz-16214.pdf (object 7 0, offset 7207): object stream 5 has incorrect keys
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WARNING: fuzz-16214.pdf (object 21 0, offset 3639): expected endstream
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WARNING: fuzz-16214.pdf (object 21 0, offset 3112): attempting to recover stream length
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WARNING: fuzz-16214.pdf (object 21 0, offset 3112): recovered stream length: 340
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WARNING: fuzz-16214.pdf, stream object 8 0: stream found inside object stream; treating as null
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WARNING: fuzz-16214.pdf, stream object 8 0: stream found inside object stream; treating as null
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qpdf: operation succeeded with warnings; resulting file may have some problems
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@ -2,6 +2,6 @@ WARNING: issue-147.pdf: can't find PDF header
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WARNING: issue-147.pdf: file is damaged
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WARNING: issue-147.pdf: can't find startxref
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WARNING: issue-147.pdf: Attempting to reconstruct cross-reference table
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WARNING: issue-147.pdf (trailer, offset 9): expected dictionary key but found non-name object; inserting key /QPDFFake1
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WARNING: issue-147.pdf: ignoring object with impossibly large id 62
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WARNING: issue-147.pdf (trailer, offset 9): expected dictionary key but found non-name object; inserting key /QPDFFake1
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qpdf: issue-147.pdf: unable to find objects while recovering damaged file
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