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Merge pull request #1002 from m-holger/ixe

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Add new private method QPDF::insertReconstructedXrefEntry
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Jay Berkenbilt 2023-07-08 09:55:51 -04:00 committed by GitHub
commit ddd78ac7c6
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2 changed files with 49 additions and 40 deletions
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4
include/qpdf/QPDF.hh
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@ -1002,7 +1002,9 @@ class QPDF
qpdf_offset_t read_xrefTable(qpdf_offset_t offset);
qpdf_offset_t read_xrefStream(qpdf_offset_t offset);
qpdf_offset_t processXRefStream(qpdf_offset_t offset, QPDFObjectHandle& xref_stream);
void insertXrefEntry(int obj, int f0, qpdf_offset_t f1, int f2, bool overwrite = false);
void insertXrefEntry(int obj, int f0, qpdf_offset_t f1, int f2);
void insertFreeXrefEntry(QPDFObjGen);
void insertReconstructedXrefEntry(int obj, qpdf_offset_t f1, int f2);
void setLastObjectDescription(std::string const& description, QPDFObjGen const& og);
QPDFObjectHandle readObject(
std::shared_ptr<InputSource>,

85
libqpdf/QPDF.cc
View File

@ -564,7 +564,7 @@ QPDF::reconstruct_xref(QPDFExc& e)
if ((t2.isInteger()) && (readToken(m->file, MAX_LEN).isWord("obj"))) {
int obj = QUtil::string_to_int(t1.getValue().c_str());
int gen = QUtil::string_to_int(t2.getValue().c_str());
insertXrefEntry(obj, 1, token_start, gen, true);
insertReconstructedXrefEntry(obj, token_start, gen);
}
} else if (!m->trailer.isInitialized() && t1.isWord("trailer")) {
QPDFObjectHandle t = readObject(m->file, "trailer", QPDFObjGen(), false);
@ -577,6 +577,7 @@ QPDF::reconstruct_xref(QPDFExc& e)
m->file->seek(next_line_start, SEEK_SET);
line_start = next_line_start;
}
m->deleted_objects.clear();
if (!m->trailer.isInitialized()) {
// We could check the last encountered object to see if it was an xref stream. If so, we
@ -889,7 +890,7 @@ QPDF::read_xrefTable(qpdf_offset_t xref_offset)
// Handle any deleted items now that we've read the /XRefStm.
for (auto const& og: deleted_items) {
insertXrefEntry(og.getObj(), 0, 0, og.getGen());
insertFreeXrefEntry(og);
}
if (cur_trailer.hasKey("/Prev")) {
@ -909,7 +910,6 @@ QPDF::read_xrefTable(qpdf_offset_t xref_offset)
qpdf_offset_t
QPDF::read_xrefStream(qpdf_offset_t xref_offset)
{
bool found = false;
if (!m->ignore_xref_streams) {
QPDFObjGen x_og;
QPDFObjectHandle xref_obj;
@ -921,17 +921,13 @@ QPDF::read_xrefStream(qpdf_offset_t xref_offset)
}
if (xref_obj.isStreamOfType("/XRef")) {
QTC::TC("qpdf", "QPDF found xref stream");
found = true;
xref_offset = processXRefStream(xref_offset, xref_obj);
return processXRefStream(xref_offset, xref_obj);
}
}
if (!found) {
QTC::TC("qpdf", "QPDF can't find xref");
throw damagedPDF("", xref_offset, "xref not found");
}
return xref_offset;
QTC::TC("qpdf", "QPDF can't find xref");
throw damagedPDF("", xref_offset, "xref not found");
return 0; // unreachable
}
qpdf_offset_t
@ -1087,9 +1083,10 @@ QPDF::processXRefStream(qpdf_offset_t xref_offset, QPDFObjectHandle& xref_obj)
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.
fields[2] = 0;
insertFreeXrefEntry(QPDFObjGen(obj, 0));
} else {
insertXrefEntry(obj, toI(fields[0]), fields[1], toI(fields[2]));
}
insertXrefEntry(obj, toI(fields[0]), fields[1], toI(fields[2]));
}
if (!m->trailer.isInitialized()) {
@ -1111,47 +1108,35 @@ QPDF::processXRefStream(qpdf_offset_t xref_offset, QPDFObjectHandle& xref_obj)
}
void
QPDF::insertXrefEntry(int obj, int f0, qpdf_offset_t f1, int f2, bool overwrite)
QPDF::insertXrefEntry(int obj, int f0, qpdf_offset_t f1, int f2)
{
// Populate the xref table in such a way that the first reference to an object that we see,
// which is the one in the latest xref table in which it appears, is the one that gets stored.
// This works because we are reading more recent appends before older ones. Exception: if
// overwrite is true, then replace any existing object. This is used in xref recovery mode,
// which reads the file from beginning to end.
// This works because we are reading more recent appends before older ones.
// If there is already an entry for this object and generation in the table, it means that a
// later xref table has registered this object. Disregard this one.
{ // private scope
int gen = (f0 == 2 ? 0 : f2);
QPDFObjGen og(obj, gen);
if (m->xref_table.count(og)) {
if (overwrite) {
QTC::TC("qpdf", "QPDF xref overwrite object");
m->xref_table.erase(og);
} else {
QTC::TC("qpdf", "QPDF xref reused object");
return;
}
}
if (m->deleted_objects.count(obj)) {
QTC::TC("qpdf", "QPDF xref deleted object");
return;
}
if (m->deleted_objects.count(obj)) {
QTC::TC("qpdf", "QPDF xref deleted object");
return;
}
auto [iter, created] = m->xref_table.try_emplace(QPDFObjGen(obj, (f0 == 2 ? 0 : f2)));
if (!created) {
QTC::TC("qpdf", "QPDF xref reused object");
return;
}
switch (f0) {
case 0:
m->deleted_objects.insert(obj);
break;
case 1:
// f2 is generation
QTC::TC("qpdf", "QPDF xref gen > 0", ((f2 > 0) ? 1 : 0));
m->xref_table[QPDFObjGen(obj, f2)] = QPDFXRefEntry(f1);
iter->second = QPDFXRefEntry(f1);
break;
case 2:
m->xref_table[QPDFObjGen(obj, 0)] = QPDFXRefEntry(toI(f1), f2);
iter->second = QPDFXRefEntry(toI(f1), f2);
break;
default:
@ -1160,6 +1145,28 @@ QPDF::insertXrefEntry(int obj, int f0, qpdf_offset_t f1, int f2, bool overwrite)
}
}
void
QPDF::insertFreeXrefEntry(QPDFObjGen og)
{
if (!m->xref_table.count(og)) {
m->deleted_objects.insert(og.getObj());
}
}
// Replace uncompressed object. This is used in xref recovery mode, which reads the file from
// beginning to end.
void
QPDF::insertReconstructedXrefEntry(int obj, qpdf_offset_t f1, int f2)
{
QPDFObjGen og(obj, f2);
if (!m->deleted_objects.count(obj)) {
// deleted_objects stores the uncompressed objects removed from the xref table at the start
// of recovery.
QTC::TC("qpdf", "QPDF xref overwrite object");
m->xref_table[QPDFObjGen(obj, f2)] = QPDFXRefEntry(f1);
}
}
void
QPDF::showXRefTable()
{