Restructure optimize to allow skipping parameters of filtered streams

include/qpdf/QPDF.hh

@@ -564,16 +564,28 @@ class QPDF
     // QPDF_optimization.cc
 
     // The object_stream_data map maps from a "compressed" object to
-    // the object stream that contains it.  This enables optimize to
+    // the object stream that contains it. This enables optimize to
     // populate the object <-> user maps with only uncompressed
-    // objects.  If allow_changes is false, an exception will be
-    // thrown if any changes are made during the optimization process.
-    // This is available so that the test suite can make sure that a
-    // linearized file is already optimized.  When called in this way,
-    // optimize() still populates the object <-> user maps
+    // objects. If allow_changes is false, an exception will be thrown
+    // if any changes are made during the optimization process. This
+    // is available so that the test suite can make sure that a
+    // linearized file is already optimized. When called in this way,
+    // optimize() still populates the object <-> user maps. The
+    // optional skip_stream_parameters parameter, if present, is
+    // called for each stream object. The function should return 2 if
+    // optimization should discard /Length, /Filter, and /DecodeParms;
+    // 1 if it should discard /Length, and 0 if it should preserve all
+    // keys. This is used by QPDFWriter to avoid creation of dangling
+    // objects for stream dictionary keys it will be regenerating.
     QPDF_DLL
     void optimize(std::map<int, int> const& object_stream_data,
 		  bool allow_changes = true);
+    // ABI: make function optional and merge overloaded versions
+    QPDF_DLL
+    void optimize(
+        std::map<int, int> const& object_stream_data,
+        bool allow_changes,
+        std::function<int(QPDFObjectHandle&)> skip_stream_parameters);
 
     // Traverse page tree return all /Page objects. It also detects
     // and resolves cases in which the same /Page object is
@@ -1356,10 +1368,14 @@ class QPDF
 	std::vector<QPDFObjectHandle>& all_pages,
 	bool allow_changes, bool warn_skipped_keys,
         std::set<QPDFObjGen>& visited);
-    void updateObjectMaps(ObjUser const& ou, QPDFObjectHandle oh);
-    void updateObjectMapsInternal(ObjUser const& ou, QPDFObjectHandle oh,
-				  std::set<QPDFObjGen>& visited, bool top,
-                                  int depth);
+    void updateObjectMaps(
+        ObjUser const& ou, QPDFObjectHandle oh,
+        std::function<int(QPDFObjectHandle&)> skip_stream_parameters);
+    void updateObjectMapsInternal(
+        ObjUser const& ou, QPDFObjectHandle oh,
+        std::function<int(QPDFObjectHandle&)> skip_stream_parameters,
+        std::set<QPDFObjGen>& visited, bool top,
+        int depth);
     void filterCompressedObjects(std::map<int, int> const& object_stream_data);
 
     // Type conversion helper methods

libqpdf/QPDF_optimization.cc

@@ -61,6 +61,14 @@ QPDF::ObjUser::operator<(ObjUser const& rhs) const
 void
 QPDF::optimize(std::map<int, int> const& object_stream_data,
 	       bool allow_changes)
+{
+    optimize(object_stream_data, allow_changes, nullptr);
+}
+
+void
+QPDF::optimize(std::map<int, int> const& object_stream_data,
+	       bool allow_changes,
+               std::function<int(QPDFObjectHandle&)> skip_stream_parameters)
 {
     if (! this->m->obj_user_to_objects.empty())
     {
@@ -91,7 +99,8 @@ QPDF::optimize(std::map<int, int> const& object_stream_data,
     for (int pageno = 0; pageno < n; ++pageno)
     {
         updateObjectMaps(ObjUser(ObjUser::ou_page, pageno),
-                         this->m->all_pages.at(toS(pageno)));
+                         this->m->all_pages.at(toS(pageno)),
+                         skip_stream_parameters);
     }
 
     // Traverse document-level items
@@ -107,7 +116,8 @@ QPDF::optimize(std::map<int, int> const& object_stream_data,
 	else
 	{
 	    updateObjectMaps(ObjUser(ObjUser::ou_trailer_key, key),
-			     this->m->trailer.getKey(key));
+			     this->m->trailer.getKey(key),
+                             skip_stream_parameters);
 	}
     }
 
@@ -124,7 +134,8 @@ QPDF::optimize(std::map<int, int> const& object_stream_data,
 
 	std::string const& key = *iter;
 	updateObjectMaps(ObjUser(ObjUser::ou_root_key, key),
-			 root.getKey(key));
+			 root.getKey(key),
+                         skip_stream_parameters);
     }
 
     ObjUser root_ou = ObjUser(ObjUser::ou_root);
@@ -351,16 +362,20 @@ QPDF::pushInheritedAttributesToPageInternal(
 }
 
 void
-QPDF::updateObjectMaps(ObjUser const& ou, QPDFObjectHandle oh)
+QPDF::updateObjectMaps(
+    ObjUser const& ou, QPDFObjectHandle oh,
+    std::function<int(QPDFObjectHandle&)> skip_stream_parameters)
 {
     std::set<QPDFObjGen> visited;
-    updateObjectMapsInternal(ou, oh, visited, true, 0);
+    updateObjectMapsInternal(ou, oh, skip_stream_parameters, visited, true, 0);
 }
 
 void
-QPDF::updateObjectMapsInternal(ObjUser const& ou, QPDFObjectHandle oh,
-			       std::set<QPDFObjGen>& visited, bool top,
-                               int depth)
+QPDF::updateObjectMapsInternal(
+    ObjUser const& ou, QPDFObjectHandle oh,
+    std::function<int(QPDFObjectHandle&)> skip_stream_parameters,
+    std::set<QPDFObjGen>& visited, bool top,
+    int depth)
 {
     // Traverse the object tree from this point taking care to avoid
     // crossing page boundaries.
@@ -399,15 +414,22 @@ QPDF::updateObjectMapsInternal(ObjUser const& ou, QPDFObjectHandle oh,
 	for (int i = 0; i < n; ++i)
 	{
 	    updateObjectMapsInternal(
-                ou, oh.getArrayItem(i), visited, false, 1 + depth);
+                ou, oh.getArrayItem(i), skip_stream_parameters,
+                visited, false, 1 + depth);
 	}
     }
     else if (oh.isDictionary() || oh.isStream())
     {
 	QPDFObjectHandle dict = oh;
-	if (oh.isStream())
+        bool is_stream = oh.isStream();
+        int ssp = 0;
+	if (is_stream)
 	{
 	    dict = oh.getDict();
+            if (skip_stream_parameters)
+            {
+                ssp = skip_stream_parameters(oh);
+            }
 	}
 
 	std::set<std::string> keys = dict.getKeys();
@@ -421,16 +443,25 @@ QPDF::updateObjectMapsInternal(ObjUser const& ou, QPDFObjectHandle oh,
 		// case.
 		updateObjectMapsInternal(
                     ObjUser(ObjUser::ou_thumb, ou.pageno),
-                    dict.getKey(key), visited, false, 1 + depth);
+                    dict.getKey(key), skip_stream_parameters,
+                    visited, false, 1 + depth);
 	    }
 	    else if (is_page_node && (key == "/Parent"))
 	    {
 		// Don't traverse back up the page tree
 	    }
+            else if (((ssp >= 1) && (key == "/Length")) ||
+                     ((ssp >= 2) && ((key == "/Filter") ||
+                                     (key == "/DecodeParms"))))
+            {
+                // Don't traverse into stream parameters that we are
+                // not going to write.
+            }
 	    else
 	    {
 		updateObjectMapsInternal(
-                    ou, dict.getKey(key), visited, false, 1 + depth);
+                    ou, dict.getKey(key), skip_stream_parameters,
+                    visited, false, 1 + depth);
 	    }
 	}
     }