Prevent destruction of shared null objects

#863 uses a single null object for nulls that were previously implicit. In certain circumstances this shared null object gets destroyed (i.e changed to a QPDF_Destroyed object) when a QPDF object is destroyed. Modify the QPDF destructor so that null objects get disconnected from the dying QPDF object but not destroyed to prevent this from happening.

Prevent destruction of shared null objects
#863 uses a single null object for nulls that were previously implicit. In certain circumstances this shared null object gets destroyed (i.e changed to a QPDF_Destroyed object) when a QPDF object is destroyed. Modify the QPDF destructor so that null objects get disconnected from the dying QPDF object but not destroyed to prevent this from happening.
m-holger
1 parent 7e77af35
Showing 1 changed file with 3 additions and 2 deletions
libqpdf/QPDF.cc
@@ -247,10 +247,11 @@ QPDF::~QPDF()
     // but we'll explicitly clear the xref table anyway just to
     // prevent any possibility of resolve() succeeding.
     this->m->xref_table.clear();
-    auto null_obj = QPDF_Null::create();
     for (auto const& iter: this->m->obj_cache) {
         iter.second.object->disconnect();
-        iter.second.object->destroy();
+        if (iter.second.object->getTypeCode() != ::ot_null) {
+            iter.second.object->destroy();
+        }
     }
 }