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Refactor QPDF::processXRefStream

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Tune processing of subsections.
This commit is contained in:
m-holger 2024-05-21 19:46:13 +01:00
parent f1c774f13f
commit 1737902a5e
1 changed files with 44 additions and 48 deletions
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92
libqpdf/QPDF.cc
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@ -1071,63 +1071,59 @@ QPDF::processXRefStream(qpdf_offset_t xref_offset, QPDFObjectHandle& xref_obj)
}
}
size_t cur_chunk = 0;
int chunk_count = 0;
bool saw_first_compressed_object = false;
// Actual size vs. expected size check above ensures that we will not overflow any buffers here.
// We know that entry_size * num_entries is less or equal to the size of the buffer.
auto p = bp->getBuffer();
for (size_t i = 0; i < num_entries; ++i) {
// Read this entry
qpdf_offset_t fields[3];
for (int j = 0; j < 3; ++j) {
fields[j] = 0;
if ((j == 0) && (W[0] == 0)) {
QTC::TC("qpdf", "QPDF default for xref stream field 0");
fields[0] = 1;
for (auto iter = indx.cbegin(); iter < indx.cend(); ++iter) {
// Process a subsection.
// Get the object number. The object number is based on /Index.
int obj = toI(*iter++);
size_t sec_entries = toS(*iter);
for (size_t i = 0; i < sec_entries; ++i) {
if (obj < 0 || obj >= (std::numeric_limits<int>::max() - 1)) {
std::ostringstream msg;
msg.imbue(std::locale::classic());
msg << "adding 1 to " << obj
<< " while computing index in xref stream would cause an integer overflow";
throw std::range_error(msg.str());
}
for (int k = 0; k < W[j]; ++k) {
fields[j] <<= 8;
fields[j] |= *p++;
// Read this entry
qpdf_offset_t fields[3];
for (int j = 0; j < 3; ++j) {
fields[j] = 0;
if ((j == 0) && (W[0] == 0)) {
QTC::TC("qpdf", "QPDF default for xref stream field 0");
fields[0] = 1;
}
for (int k = 0; k < W[j]; ++k) {
fields[j] <<= 8;
fields[j] |= *p++;
}
}
}
// Get the object and generation number. The object number is based on /Index. The
// generation number is 0 unless this is an uncompressed object record, in which case the
// generation number appears as the third field.
int obj = toI(indx.at(cur_chunk));
if ((obj < 0) || ((std::numeric_limits<int>::max() - obj) < chunk_count)) {
std::ostringstream msg;
msg.imbue(std::locale::classic());
msg << "adding " << chunk_count << " to " << obj
<< " while computing index in xref stream would cause an integer overflow";
throw std::range_error(msg.str());
}
obj += chunk_count;
++chunk_count;
if (chunk_count >= indx.at(cur_chunk + 1)) {
cur_chunk += 2;
chunk_count = 0;
}
if (saw_first_compressed_object) {
if (fields[0] != 2) {
m->uncompressed_after_compressed = true;
// Get the generation number. The generation number is 0 unless this is an uncompressed
// object record, in which case the generation number appears as the third field.
if (saw_first_compressed_object) {
if (fields[0] != 2) {
m->uncompressed_after_compressed = true;
}
} else if (fields[0] == 2) {
saw_first_compressed_object = true;
}
} else if (fields[0] == 2) {
saw_first_compressed_object = true;
}
if (obj == 0) {
// This is needed by checkLinearization()
m->first_xref_item_offset = xref_offset;
} else if (fields[0] == 0) {
// Ignore fields[2], which we don't care about in this case. This works around the issue
// of some PDF files that put invalid values, like -1, here for deleted objects.
insertFreeXrefEntry(QPDFObjGen(obj, 0));
} else {
insertXrefEntry(obj, toI(fields[0]), fields[1], toI(fields[2]));
if (obj == 0) {
// This is needed by checkLinearization()
m->first_xref_item_offset = xref_offset;
} else if (fields[0] == 0) {
// Ignore fields[2], which we don't care about in this case. This works around the
// issue of some PDF files that put invalid values, like -1, here for deleted
// objects.
insertFreeXrefEntry(QPDFObjGen(obj, 0));
} else {
insertXrefEntry(obj, toI(fields[0]), fields[1], toI(fields[2]));
}
++obj;
}
}