Clear owning QPDF information for all objects, not just indirect

Jay Berkenbilt
1 parent a6159858
Showing 16 changed files with 141 additions and 15 deletions
TODO
include/qpdf/QPDFObjectHandle.hh
libqpdf/QPDF.cc
libqpdf/QPDFObjectHandle.cc
libqpdf/QPDFWriter.cc
libqpdf/QPDF_Array.cc
libqpdf/QPDF_Dictionary.cc
libqpdf/QPDF_Stream.cc
libqpdf/SparseOHArray.cc
libqpdf/qpdf/QPDFValue.hh
libqpdf/qpdf/QPDFValueProxy.hh
libqpdf/qpdf/QPDF_Array.hh
libqpdf/qpdf/QPDF_Dictionary.hh
libqpdf/qpdf/QPDF_Stream.hh
libqpdf/qpdf/SparseOHArray.hh
qpdf/test_driver.cc
@@ -811,3 +811,10 @@ Rejected Ideas
   Note that arrays and dictionaries still need to contain
   QPDFObjectHandle because of indirect objects. This only pertains to
   direct objects, which are always "resolved" in QPDFObjectHandle.
+
+  If this is addressed, read comments in QPDFWriter.cc::enqueueObject
+  near the call to getOwningQPDF, comments in QPDFValueProxy::reset,
+  and comments in QPDF::~QPDF() near the line that assigns to null.
+  This will also affect test 92 in test_driver.cc. All these
+  references were from the release of qpdf 11 (in case they have moved
+  by such time as this might be resurrected).
@@ -1534,6 +1534,23 @@ class QPDFObjectHandle
     };
     friend class ObjAccessor;
  
+    // Provide access to specific classes for recursive
+    // reset().
+    class Resetter
+    {
+        friend class QPDF_Dictionary;
+        friend class QPDF_Stream;
+        friend class SparseOHArray;
+
+      private:
+        static void
+        reset(QPDFObjectHandle& o)
+        {
+            o.reset();
+        }
+    };
+    friend class Resetter;
+
     // Convenience routine: Throws if the assumption is violated. Your
     // code will be better if you call one of the isType methods and
     // handle the case of the type being wrong, but these can be
@@ -1631,6 +1648,7 @@ class QPDFObjectHandle
         bool first_level_only,
         bool stop_at_streams);
     void shallowCopyInternal(QPDFObjectHandle& oh, bool first_level_only);
+    void reset();
     void setParsedOffset(qpdf_offset_t offset);
     void parseContentStream_internal(
         std::string const& description, ParserCallbacks* callbacks);
@@ -247,19 +247,24 @@ QPDF::~QPDF()
     // having an array or dictionary that contains an indirect
     // reference to the other), the circular references in the
     // std::shared_ptr objects will prevent the objects from being
-    // deleted.  Walk through all objects in the object cache, which
-    // is those objects that we read from the file, and break all
-    // resolved indirect references by replacing them with direct
-    // null objects.  At this point, obviously no one is still
-    // using the QPDF object, but we'll explicitly clear the xref
-    // table anyway just to prevent any possibility of resolve()
-    // succeeding.  Note that we can't break references like this at
-    // any time when the QPDF object is active.
+    // deleted. Walk through all objects in the object cache, which is
+    // those objects that we read from the file, and break all
+    // resolved indirect references by replacing them with direct null
+    // objects. At this point, obviously no one is still using the
+    // QPDF object, but we'll explicitly clear the xref table anyway
+    // just to prevent any possibility of resolve() succeeding. Note
+    // that we can't break references like this at any time when the
+    // QPDF object is active. This also causes all QPDFObjectHandle
+    // objects that are reachable from this object to become nulls and
+    // release their association with this QPDF.
     this->m->xref_table.clear();
     auto null_obj = QPDF_Null::create();
     for (auto const& iter: this->m->obj_cache) {
+        iter.second.object->reset();
+        // If the issue discussed in QPDFValueProxy::reset were
+        // resolved, then this assignment to null_obj could be
+        // removed.
         iter.second.object->assign(null_obj);
-        iter.second.object->resetObjGen();
     }
 }
  
@@ -248,6 +248,17 @@ QPDFObjectHandle::operator!=(QPDFObjectHandle const&amp; rhs) const
     return this->obj != rhs.obj;
 }
  
+void
+QPDFObjectHandle::reset()
+{
+    // Recursively remove association with any QPDF object. This
+    // method may only be called during final destruction. See
+    // comments in QPDF::~QPDF().
+    if (!isIndirect()) {
+        this->obj->reset();
+    }
+}
+
 qpdf_object_type_e
 QPDFObjectHandle::getTypeCode()
 {
@@ -1198,6 +1198,14 @@ void
 QPDFWriter::enqueueObject(QPDFObjectHandle object)
 {
     if (object.isIndirect()) {
+        // This owner check should really be done for all objects, not
+        // just indirect objects. As of the time of the release of
+        // qpdf 11, it is known that there are cases of direct objects
+        // from other files getting copied into multiple QPDF objects.
+        // This definitely happens in the page splitting code. If we
+        // were to implement strong checks to prevent objects from
+        // having multiple owners, once that was complete phased in,
+        // this check could be moved outside the if statement.
         if (object.getOwningQPDF() != &(this->m->pdf)) {
             QTC::TC("qpdf", "QPDFWriter foreign object");
             throw std::logic_error(
@@ -34,6 +34,12 @@ QPDF_Array::shallowCopy()
     return create(elements);
 }
  
+void
+QPDF_Array::reset()
+{
+    elements.reset();
+}
+
 std::string
 QPDF_Array::unparse()
 {
@@ -21,6 +21,14 @@ QPDF_Dictionary::shallowCopy()
     return create(items);
 }
  
+void
+QPDF_Dictionary::reset()
+{
+    for (auto& iter: this->items) {
+        QPDFObjectHandle::Resetter::reset(iter.second);
+    }
+}
+
 std::string
 QPDF_Dictionary::unparse()
 {
@@ -168,6 +168,13 @@ QPDF_Stream::getFilterOnWrite() const
 }
  
 void
+QPDF_Stream::reset()
+{
+    this->stream_provider = nullptr;
+    QPDFObjectHandle::Resetter::reset(this->stream_dict);
+}
+
+void
 QPDF_Stream::setObjGen(QPDFObjGen const& og)
 {
     if (this->og.isIndirect()) {
@@ -49,6 +49,14 @@ SparseOHArray::remove_last()
 }
  
 void
+SparseOHArray::reset()
+{
+    for (auto& iter: this->elements) {
+        QPDFObjectHandle::Resetter::reset(iter.second);
+    }
+}
+
+void
 SparseOHArray::setAt(size_t idx, QPDFObjectHandle oh)
 {
     if (idx >= this->n_elements) {
@@ -63,6 +63,10 @@ class QPDFValue
     {
         return og;
     }
+    virtual void
+    reset()
+    {
+    }
  
   protected:
     QPDFValue() :
@@ -110,8 +110,21 @@ class QPDFValueProxy
         value->og = og;
     }
     void
-    resetObjGen()
-    {
+    reset()
+    {
+        value->reset();
+        // It would be better if, rather than clearing value->qpdf and
+        // value->og, we completely replaced value with a null object.
+        // However, at the time of the release of qpdf 11, this causes
+        // test failures and would likely break a lot of code since it
+        // possible for a direct object that recursively contains no
+        // indirect objects to be copied into multiple QPDF objects.
+        // For that reason, we have to break the association with the
+        // owning QPDF but not otherwise mutate the object. For
+        // indirect objects, QPDF::~QPDF replaces the object with
+        // null, which clears circular references. If this code were
+        // able to do the null replacement, that code would not have
+        // to.
         value->qpdf = nullptr;
         value->og = QPDFObjGen();
     }
@@ -17,6 +17,7 @@ class QPDF_Array: public QPDFValue
     virtual std::shared_ptr<QPDFValueProxy> shallowCopy();
     virtual std::string unparse();
     virtual JSON getJSON(int json_version);
+    virtual void reset();
  
     int getNItems() const;
     QPDFObjectHandle getItem(int n) const;
@@ -17,6 +17,7 @@ class QPDF_Dictionary: public QPDFValue
     virtual std::shared_ptr<QPDFValueProxy> shallowCopy();
     virtual std::string unparse();
     virtual JSON getJSON(int json_version);
+    virtual void reset();
  
     // hasKey() and getKeys() treat keys with null values as if they
     // aren't there.  getKey() returns null for the value of a
@@ -27,6 +27,7 @@ class QPDF_Stream: public QPDFValue
     virtual std::string unparse();
     virtual JSON getJSON(int json_version);
     virtual void setDescription(QPDF*, std::string const&);
+    virtual void reset();
     QPDFObjectHandle getDict() const;
     bool isDataModified() const;
     void setFilterOnWrite(bool);
@@ -15,6 +15,7 @@ class SparseOHArray
     void setAt(size_t idx, QPDFObjectHandle oh);
     void erase(size_t idx);
     void insert(size_t idx, QPDFObjectHandle oh);
+    void reset();
  
     typedef std::unordered_map<size_t, QPDFObjectHandle>::const_iterator
         const_iterator;
@@ -3274,13 +3274,40 @@ test_92(QPDF&amp; pdf, char const* arg2)
 {
     // Exercise indirect objects owned by destroyed QPDF object.
     auto qpdf = QPDF::create();
-    qpdf->emptyPDF();
+    qpdf->processFile("minimal.pdf");
     auto root = qpdf->getRoot();
-    assert(root.getOwningQPDF() != nullptr);
+    assert(root.getOwningQPDF() == qpdf.get());
     assert(root.isIndirect());
+    assert(root.isDictionary());
+    auto page1 = root.getKey("/Pages").getKey("/Kids").getArrayItem(0);
+    assert(page1.getOwningQPDF() == qpdf.get());
+    assert(page1.isIndirect());
+    assert(page1.isDictionary());
+    auto resources = page1.getKey("/Resources");
+    assert(resources.getOwningQPDF() == qpdf.get());
+    assert(resources.isDictionary());
+    assert(!resources.isIndirect());
+    auto contents = page1.getKey("/Contents");
+    auto contents_dict = contents.getDict();
     qpdf = nullptr;
-    assert(root.getOwningQPDF() == nullptr);
-    assert(!root.isIndirect());
+    auto check = [](QPDFObjectHandle& oh) {
+        assert(oh.getOwningQPDF() == nullptr);
+        assert(!oh.isIndirect());
+    };
+    // All objects should no longer have an owning QPDF or be indirect.
+    check(root);
+    check(page1);
+    check(resources);
+    check(contents);
+    check(contents_dict);
+    // Objects that were originally indirect should be null.
+    // Otherwise, they should have retained their old values. See
+    // comments in QPDFValueProxy::reset for why this is the case.
+    assert(root.isNull());
+    assert(page1.isNull());
+    assert(contents.isNull());
+    assert(!resources.isNull());
+    assert(!contents_dict.isNull());
 }
  
 static void