mirror of https://github.com/qpdf/qpdf.git
Have QPDFObjectHandle notice when replaceObject was called
This results in a performance penalty of 1% to 2% when replaceObject and swapObjects are never called and a somewhat larger penalty if they are called, but it's worth it to avoid very confusing behavior as discussed in depth in qpdf#507.
This commit is contained in:
Jay Berkenbilt
parent
ec6719fd25
commit
a4d6589ff2
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@ -1,3 +1,10 @@
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2021-02-25 Jay Berkenbilt <ejb@ql.org>
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* Bug fix/behavior change: when QPDF::replaceObject or
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QPDF::swapObjects is called, existing QPDFObjectHandle instances
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will now notice the change. This removes a long-standing source of
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bugs and confusing behavior.
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2021-02-23 Jay Berkenbilt <ejb@ql.org>
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* The test for the input and output files being the same wasn't
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@ -278,34 +278,26 @@ class QPDF
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QPDFObjectHandle getObjectByID(int objid, int generation);
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// Replace the object with the given object id with the given
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// object. The object handle passed in must be a direct object,
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// object. The object handle passed in must be a direct object,
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// though it may contain references to other indirect objects
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// within it. Calling this method can have somewhat confusing
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// results. Any existing QPDFObjectHandle instances that point to
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// the old object and that have been resolved (which happens
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// automatically if you access them in any way) will continue to
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// point to the old object even though that object will no longer
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// be associated with the PDF file. Note that replacing an object
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// with QPDFObjectHandle::newNull() effectively removes the object
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// from the file since a non-existent object is treated as a null
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// object. To replace a reserved object, call replaceReserved
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// within it. Prior to qpdf 10.2.1, after calling this method,
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// existing QPDFObjectHandle instances that pointed to the
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// original object still pointed to the original object, resulting
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// in confusing and incorrect behavior. This was fixed in 10.2.1,
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// so existing QPDFObjectHandle objects will start pointing to the
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// newly replaced object. Note that replacing an object with
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// QPDFObjectHandle::newNull() effectively removes the object from
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// the file since a non-existent object is treated as a null
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// object. To replace a reserved object, call replaceReserved
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// instead.
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QPDF_DLL
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void replaceObject(QPDFObjGen const& og, QPDFObjectHandle);
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QPDF_DLL
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void replaceObject(int objid, int generation, QPDFObjectHandle);
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// Swap two objects given by ID. Calling this method can have
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// confusing results. After swapping two objects, existing
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// QPDFObjectHandle instances that reference them will still
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// reference the same underlying objects, at which point those
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// existing QPDFObjectHandle instances will have incorrect
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// information about the object and generation number of those
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// objects. While this does not necessarily cause a problem, it
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// can certainly be confusing. It is therefore recommended that
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// you replace any existing QPDFObjectHandle instances that point
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// to the swapped objects with new ones, possibly by calling
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// getObjectByID.
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// Swap two objects given by ID. Prior to qpdf 10.2.1, existing
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// QPDFObjectHandle instances that reference them objects not
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// notice the swap, but this was fixed in 10.2.1.
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QPDF_DLL
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void swapObjects(QPDFObjGen const& og1, QPDFObjGen const& og2);
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QPDF_DLL
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@ -697,6 +689,11 @@ class QPDF
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{
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return qpdf->resolve(objid, generation);
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}
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static bool objectChanged(
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QPDF* qpdf, QPDFObjGen const& og, PointerHolder<QPDFObject>& oph)
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{
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return qpdf->objectChanged(og, oph);
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}
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};
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friend class Resolver;
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@ -930,6 +927,7 @@ class QPDF
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qpdf_offset_t offset, std::string const& description,
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int exp_objid, int exp_generation,
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int& act_objid, int& act_generation);
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bool objectChanged(QPDFObjGen const& og, PointerHolder<QPDFObject>& oph);
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PointerHolder<QPDFObject> resolve(int objid, int generation);
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void resolveObjectsInStream(int obj_stream_number);
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void stopOnError(std::string const& message);
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@ -1441,6 +1439,7 @@ class QPDF
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bool in_parse;
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bool parsed;
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std::set<int> resolved_object_streams;
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bool ever_replaced_objects;
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// Linearization data
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qpdf_offset_t first_xref_item_offset; // actual value from file
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@ -210,6 +210,7 @@ QPDF::Members::Members() :
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immediate_copy_from(false),
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in_parse(false),
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parsed(false),
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ever_replaced_objects(false),
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first_xref_item_offset(0),
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uncompressed_after_compressed(false)
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{
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@ -2063,6 +2064,30 @@ QPDF::readObjectAtOffset(bool try_recovery,
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return oh;
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}
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bool
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QPDF::objectChanged(QPDFObjGen const& og, PointerHolder<QPDFObject>& oph)
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{
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// See if the object cached at og, if any, is the one passed in.
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// QPDFObjectHandle uses this to detect outdated handles to
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// replaced or swapped objects. This is a somewhat expensive check
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// because it happens with every dereference of a
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// QPDFObjectHandle. To reduce the hit somewhat, short-circuit the
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// check if we never called a function that replaces an object
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// already in cache. It is important for functions that do this to
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// set ever_replaced_objects = true.
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if (! this->m->ever_replaced_objects)
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{
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return false;
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}
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auto c = this->m->obj_cache.find(og);
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if (c == this->m->obj_cache.end())
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{
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return true;
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}
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return (c->second.object.getPointer() != oph.getPointer());
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}
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PointerHolder<QPDFObject>
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QPDF::resolve(int objid, int generation)
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{
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@ -2308,6 +2333,7 @@ QPDF::replaceObject(int objid, int generation, QPDFObjectHandle oh)
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// Replace the object in the object cache
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QPDFObjGen og(objid, generation);
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this->m->ever_replaced_objects = true;
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this->m->obj_cache[og] =
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ObjCache(QPDFObjectHandle::ObjAccessor::getObject(oh), -1, -1);
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}
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@ -2695,6 +2721,7 @@ QPDF::swapObjects(int objid1, int generation1, int objid2, int generation2)
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QPDFObjGen og1(objid1, generation1);
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QPDFObjGen og2(objid2, generation2);
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ObjCache t = this->m->obj_cache[og1];
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this->m->ever_replaced_objects = true;
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this->m->obj_cache[og1] = this->m->obj_cache[og2];
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this->m->obj_cache[og2] = t;
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}
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@ -3194,6 +3194,12 @@ QPDFObjectHandle::dereference()
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throw std::logic_error(
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"attempted to dereference an uninitialized QPDFObjectHandle");
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}
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if (this->obj.getPointer() && this->objid &&
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QPDF::Resolver::objectChanged(
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this->qpdf, QPDFObjGen(this->objid, this->generation), this->obj))
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{
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this->obj = nullptr;
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}
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if (this->obj.getPointer() == 0)
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{
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PointerHolder<QPDFObject> obj = QPDF::Resolver::resolve(
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@ -5060,6 +5060,32 @@ print "\n";
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</listitem>
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</varlistentry>
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-->
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<varlistentry>
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<term>XXX 10.2.1: Month dd, YYYY</term>
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<listitem>
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<itemizedlist>
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<listitem>
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<para>
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Bug Fixes
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</para>
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<itemizedlist>
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<listitem>
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<para>
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When <function>QPDF::replaceObject</function> or
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<function>QPDF::swapObjects</function> is called, existing
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<classname>QPDFObjectHandle</classname> instances no longer
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point to the old objects. The next time they are
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accessed, they automatically notice the change to the
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underlying object and update themselves. This resolves a
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very longstanding source of confusion, albeit in a very
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rarely used method call.
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</para>
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</listitem>
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</itemizedlist>
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</listitem>
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</itemizedlist>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>10.2.0: February 23, 2021</term>
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<listitem>
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@ -65,6 +65,7 @@ endobj
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612
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792
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]
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/OrigPage 2
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/Parent 4 0 R
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/Resources <<
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/Font <<
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@ -86,6 +87,7 @@ endobj
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612
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792
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]
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/OrigPage 3
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/Parent 4 0 R
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/Resources <<
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/Font <<
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@ -237,21 +239,21 @@ xref
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0000000140 00000 n
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0000000252 00000 n
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0000000456 00000 n
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0000000661 00000 n
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0000000866 00000 n
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0000001084 00000 n
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0000001186 00000 n
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0000001206 00000 n
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0000001325 00000 n
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0000001384 00000 n
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0000001487 00000 n
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0000001507 00000 n
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0000001566 00000 n
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0000001669 00000 n
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0000001689 00000 n
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0000001748 00000 n
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0000001851 00000 n
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0000001871 00000 n
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0000000675 00000 n
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0000000894 00000 n
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0000001112 00000 n
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0000001214 00000 n
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0000001234 00000 n
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0000001353 00000 n
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0000001412 00000 n
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0000001515 00000 n
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0000001535 00000 n
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0000001594 00000 n
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0000001697 00000 n
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0000001717 00000 n
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0000001776 00000 n
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0000001879 00000 n
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0000001899 00000 n
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trailer <<
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/QArray 2 0 R
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/QDict 3 0 R
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@ -260,5 +262,5 @@ trailer <<
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/ID [<20eb74876a3e8212c1b4fd43153860b0><1bb7a926da191c58f675435d77997d21>]
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>>
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startxref
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1907
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1935
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%%EOF
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@ -16,10 +16,10 @@ endobj
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<< /Contents 9 0 R /MediaBox [ 0 0 612 792 ] /Parent 4 0 R /Resources << /Font << /F1 10 0 R >> /ProcSet 11 0 R >> /Type /Page >>
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endobj
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6 0 obj
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<< /Contents 12 0 R /MediaBox [ 0 0 612 792 ] /Parent 4 0 R /Resources << /Font << /F1 10 0 R >> /ProcSet 13 0 R >> /Type /Page >>
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<< /Contents 12 0 R /MediaBox [ 0 0 612 792 ] /OrigPage 3 /Parent 4 0 R /Resources << /Font << /F1 10 0 R >> /ProcSet 13 0 R >> /Type /Page >>
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endobj
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7 0 obj
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<< /Contents 14 0 R /MediaBox [ 0 0 612 792 ] /Parent 4 0 R /Resources << /Font << /F1 10 0 R >> /ProcSet 15 0 R >> /Type /Page >>
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<< /Contents 14 0 R /MediaBox [ 0 0 612 792 ] /OrigPage 2 /Parent 4 0 R /Resources << /Font << /F1 10 0 R >> /ProcSet 15 0 R >> /Type /Page >>
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endobj
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8 0 obj
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<< /Contents 16 0 R /MediaBox [ 0 0 612 792 ] /Parent 4 0 R /Resources << /Font << /F1 10 0 R >> /ProcSet 17 0 R >> /Type /Page >>
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@ -88,18 +88,18 @@ xref
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0000000122 00000 n
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0000000199 00000 n
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0000000344 00000 n
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0000000490 00000 n
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0000000636 00000 n
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0000000782 00000 n
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0000000877 00000 n
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0000000985 00000 n
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0000001016 00000 n
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0000001112 00000 n
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0000001143 00000 n
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0000001239 00000 n
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0000001270 00000 n
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0000001366 00000 n
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0000000502 00000 n
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0000000660 00000 n
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0000000806 00000 n
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0000000901 00000 n
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0000001009 00000 n
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0000001040 00000 n
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0000001136 00000 n
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0000001167 00000 n
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0000001263 00000 n
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0000001294 00000 n
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0000001390 00000 n
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trailer << /QArray 2 0 R /QDict 3 0 R /Root 1 0 R /Size 18 /ID [<20eb74876a3e8212c1b4fd43153860b0><31415926535897932384626433832795>] >>
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startxref
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1397
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1421
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%%EOF
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@ -1,6 +1,6 @@
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caught logic error as expected
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old dict: 1
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old dict: 1
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old dict: 2
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swapped array: /Array
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new dict: 2
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swapped array: /Array
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array and dictionary contents are correct
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@ -740,7 +740,13 @@ void runtest(int n, char const* filename1, char const* arg2)
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" not called 4-page file");
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}
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// Swap pages 2 and 3
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pdf.swapObjects(pages.at(1).getObjGen(), pages.at(2).getObjGen());
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auto orig_page2 = pages.at(1);
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auto orig_page3 = pages.at(2);
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assert(orig_page2.getKey("/OrigPage").getIntValue() == 2);
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assert(orig_page3.getKey("/OrigPage").getIntValue() == 3);
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pdf.swapObjects(orig_page2.getObjGen(), orig_page3.getObjGen());
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assert(orig_page2.getKey("/OrigPage").getIntValue() == 3);
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assert(orig_page3.getKey("/OrigPage").getIntValue() == 2);
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// Replace object and swap objects
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QPDFObjectHandle trailer = pdf.getTrailer();
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QPDFObjectHandle qdict = trailer.getKey("/QDict");
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@ -759,18 +765,18 @@ void runtest(int n, char const* filename1, char const* arg2)
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std::cout << "caught logic error as expected" << std::endl;
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}
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pdf.replaceObject(qdict.getObjGen(), new_dict);
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// Now qdict still points to the old dictionary
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std::cout << "old dict: " << qdict.getKey("/Dict").getIntValue()
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// Now qdict points to the new dictionary
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std::cout << "old dict: " << qdict.getKey("/NewDict").getIntValue()
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<< std::endl;
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// Swap dict and array
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pdf.swapObjects(qdict.getObjGen(), qarray.getObjGen());
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// Now qarray will resolve to new object but qdict is still
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// the old object
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std::cout << "old dict: " << qdict.getKey("/Dict").getIntValue()
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// Now qarray will resolve to new object and qdict resolves to
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// the array
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std::cout << "swapped array: " << qdict.getArrayItem(0).getName()
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<< std::endl;
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std::cout << "new dict: " << qarray.getKey("/NewDict").getIntValue()
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<< std::endl;
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// Reread qdict, now pointing to an array
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// Reread qdict, still pointing to an array
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qdict = pdf.getObjectByObjGen(qdict.getObjGen());
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std::cout << "swapped array: " << qdict.getArrayItem(0).getName()
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<< std::endl;
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