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Clarify intent in readObjectAtOffset

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Rather than using object id -1 to mean "don't care", use object ID 0,
and clarify the difference between that use and indication of a direct
object.
This commit is contained in:
Jay Berkenbilt 2022-07-24 09:40:11 -04:00
parent 9de29daba5
commit 6f1041afb8
2 changed files with 20 additions and 5 deletions
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23
libqpdf/QPDF.cc
View File

@ -1060,7 +1060,7 @@ QPDF::read_xrefStream(qpdf_offset_t xref_offset)
QPDFObjectHandle xref_obj;
try {
xref_obj = readObjectAtOffset(
false, xref_offset, "xref stream", -1, 0, xobj, xgen);
false, xref_offset, "xref stream", 0, 0, xobj, xgen);
} catch (QPDFExc&) {
// ignore -- report error below
}
@ -1782,10 +1782,25 @@ QPDF::readObjectAtOffset(
int& objid,
int& generation)
{
bool check_og = true;
if (exp_objid == 0) {
// This method uses an expect object ID of 0 to indicate that
// we don't know or don't care what the actual object ID is at
// this offset. This is true when we read the xref stream and
// linearization hint streams. In this case, we don't verify
// the expect object ID/generation against what was read from
// the file. There is also no reason to attempt xref recovery
// if we get a failure in this case since the read attempt was
// not triggered by an xref lookup.
check_og = false;
try_recovery = false;
} else {
setLastObjectDescription(description, exp_objid, exp_generation);
}
if (!this->m->attempt_recovery) {
try_recovery = false;
}
setLastObjectDescription(description, exp_objid, exp_generation);
// Special case: if offset is 0, just return null. Some PDF
// writers, in particular "Mac OS X 10.7.5 Quartz PDFContext", may
@ -1839,7 +1854,7 @@ QPDF::readObjectAtOffset(
"object with ID 0");
}
if ((exp_objid >= 0) &&
if (check_og &&
(!((objid == exp_objid) && (generation == exp_generation)))) {
QTC::TC("qpdf", "QPDF err wrong objid/generation");
QPDFExc e(
@ -1859,7 +1874,7 @@ QPDF::readObjectAtOffset(
}
}
} catch (QPDFExc& e) {
if ((exp_objid >= 0) && try_recovery) {
if (try_recovery) {
// Try again after reconstructing xref table
reconstruct_xref(e);
QPDFObjGen og(exp_objid, exp_generation);

2
libqpdf/QPDF_linearization.cc
View File

@ -328,7 +328,7 @@ QPDF::readHintStream(Pipeline& pl, qpdf_offset_t offset, size_t length)
int obj;
int gen;
QPDFObjectHandle H = readObjectAtOffset(
false, offset, "linearization hint stream", -1, 0, obj, gen);
false, offset, "linearization hint stream", 0, 0, obj, gen);
ObjCache& oc = this->m->obj_cache[QPDFObjGen(obj, gen)];
qpdf_offset_t min_end_offset = oc.end_before_space;
qpdf_offset_t max_end_offset = oc.end_after_space;