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Move xref table initialisation from QPDF::parse to QPDF::Xref_table

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This commit is contained in:
m-holger 2024-08-10 13:11:23 +01:00
parent a4db9b3149
commit db06e075ea
2 changed files with 53 additions and 42 deletions
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91
libqpdf/QPDF.cc
View File

@ -445,46 +445,8 @@ QPDF::parse(char const* password)
m->pdf_version = "1.2";
}
// PDF spec says %%EOF must be found within the last 1024 bytes of/ the file. We add an extra
// 30 characters to leave room for the startxref stuff.
m->file->seek(0, SEEK_END);
qpdf_offset_t end_offset = m->file->tell();
m->xref_table.max_offset = end_offset;
// Sanity check on object ids. All objects must appear in xref table / stream. In all realistic
// scenarios at least 3 bytes are required.
if (m->xref_table.max_id > m->xref_table.max_offset / 3) {
m->xref_table.max_id = static_cast<int>(m->xref_table.max_offset / 3);
}
qpdf_offset_t start_offset = (end_offset > 1054 ? end_offset - 1054 : 0);
PatternFinder sf(*this, &QPDF::findStartxref);
qpdf_offset_t xref_offset = 0;
if (m->file->findLast("startxref", start_offset, 0, sf)) {
xref_offset = QUtil::string_to_ll(readToken(*m->file).getValue().c_str());
}
try {
if (xref_offset == 0) {
QTC::TC("qpdf", "QPDF can't find startxref");
throw damagedPDF("", 0, "can't find startxref");
}
try {
m->xref_table.read(xref_offset);
} catch (QPDFExc&) {
throw;
} catch (std::exception& e) {
throw damagedPDF("", 0, std::string("error reading xref: ") + e.what());
}
} catch (QPDFExc& e) {
if (m->attempt_recovery) {
m->xref_table.reconstruct(e);
QTC::TC("qpdf", "QPDF reconstructed xref table");
} else {
throw;
}
}
m->xref_table.initialize();
initializeEncryption();
m->xref_table.parsed = true;
if (m->xref_table.size() > 0 && !getRoot().getKey("/Pages").isDictionary()) {
// QPDFs created from JSON have an empty xref table and no root object yet.
throw damagedPDF("", 0, "unable to find page tree");
@ -525,6 +487,52 @@ QPDF::warn(
warn(QPDFExc(error_code, getFilename(), object, offset, message));
}
void
QPDF::Xref_table::initialize()
{
auto* m = qpdf.m.get();
// PDF spec says %%EOF must be found within the last 1024 bytes of/ the file. We add an extra
// 30 characters to leave room for the startxref stuff.
m->file->seek(0, SEEK_END);
qpdf_offset_t end_offset = m->file->tell();
max_offset = end_offset;
// Sanity check on object ids. All objects must appear in xref table / stream. In all realistic
// scenarios at least 3 bytes are required.
if (max_id > max_offset / 3) {
max_id = static_cast<int>(max_offset / 3);
}
qpdf_offset_t start_offset = (end_offset > 1054 ? end_offset - 1054 : 0);
PatternFinder sf(qpdf, &QPDF::findStartxref);
qpdf_offset_t xref_offset = 0;
if (m->file->findLast("startxref", start_offset, 0, sf)) {
xref_offset = QUtil::string_to_ll(qpdf.readToken(*m->file).getValue().c_str());
}
try {
if (xref_offset == 0) {
QTC::TC("qpdf", "QPDF can't find startxref");
throw damaged_pdf("can't find startxref");
}
try {
read(xref_offset);
} catch (QPDFExc&) {
throw;
} catch (std::exception& e) {
throw damaged_pdf(std::string("error reading xref: ") + e.what());
}
} catch (QPDFExc& e) {
if (attempt_recovery) {
reconstruct(e);
QTC::TC("qpdf", "QPDF reconstructed xref table");
} else {
throw;
}
}
parsed = true;
}
void
QPDF::Xref_table::reconstruct(QPDFExc& e)
{
@ -739,8 +747,9 @@ QPDF::Xref_table::read(qpdf_offset_t xref_offset)
}
if ((size < 1) || (size - 1 != max_obj)) {
QTC::TC("qpdf", "QPDF xref size mismatch");
warn_damaged("reported number of objects (" + std::to_string(size) +
") is not one plus the highest object number (" + std::to_string(max_obj) + ")");
warn_damaged(
"reported number of objects (" + std::to_string(size) +
") is not one plus the highest object number (" + std::to_string(max_obj) + ")");
}
// We no longer need the deleted_objects table, so go ahead and clear it out to make sure we

4
libqpdf/qpdf/QPDF_private.hh
View File

@ -12,7 +12,7 @@ class QPDF::Xref_table: public std::map<QPDFObjGen, QPDFXRefEntry>
{
}
void read(qpdf_offset_t offset);
void initialize();
void reconstruct(QPDFExc& e);
QPDFObjectHandle trailer;
@ -30,6 +30,8 @@ class QPDF::Xref_table: public std::map<QPDFObjGen, QPDFXRefEntry>
qpdf_offset_t first_item_offset{0}; // actual value from file
private:
void read(qpdf_offset_t offset);
// Methods to parse tables
qpdf_offset_t read_table(qpdf_offset_t offset);
bool parse_first(std::string const& line, int& obj, int& num, int& bytes);