fix #1063: poor memory performance when duping DocumentFragment

CHANGELOG.md

@@ -10,6 +10,8 @@
 * `XML::Attr#value=` allows HTML node attribute values to be set to either a blank string or an empty boolean attribute. [#1800]
 * Introduce `XML::Node#wrap` which does what `XML::NodeSet#wrap` has always done, but for a single node. [#1531] (Thanks, @ethirajsrinivasan!)
 * [MRI] Improve installation experience on macOS High Sierra (Darwin). [#1812, #1813] (Thanks, @gpakosz and @nurse!)
+* [MRI] Node#dup supports copying a node directly to a new document. See the method documentation for details.
+* [MRI] DocumentFragment#dup is now more memory-efficient, avoiding making unnecessary copies. [#1063]
 * [JRuby] NodeSet has been rewritten to improve performance! [#1795]
 
 

ext/nokogiri/xml_node.c

@@ -113,7 +113,7 @@ static void relink_namespace(xmlNodePtr reparented)
         && ns != reparented->ns
         && xmlStrEqual(ns->prefix, reparented->ns->prefix)
         && xmlStrEqual(ns->href, reparented->ns->href)
-      ) {
+       ) {
       xmlSetNs(reparented, ns);
     }
   }
@@ -532,22 +532,39 @@ static VALUE internal_subset(VALUE self)
 /*
  * call-seq:
  *  dup
+ *  dup(depth)
+ *  dup(depth, new_parent_doc)
  *
- * Copy this node.  An optional depth may be passed in, but it defaults
- * to a deep copy.  0 is a shallow copy, 1 is a deep copy.
+ * Copy this node.
+ * An optional depth may be passed in. 0 is a shallow copy, 1 (the default) is a deep copy.
+ * An optional new_parent_doc may also be passed in, which will be the new
+ * node's parent document. Defaults to the current node's document.
+ * current document.
  */
 static VALUE duplicate_node(int argc, VALUE *argv, VALUE self)
 {
-  VALUE level;
+  VALUE r_level, r_new_parent_doc;
+  int level;
+  int n_args;
+  xmlDocPtr new_parent_doc;
   xmlNodePtr node, dup;
 
-  if(rb_scan_args(argc, argv, "01", &level) == 0) {
-    level = INT2NUM((long)1);
+  Data_Get_Struct(self, xmlNode, node);
+
+  n_args = rb_scan_args(argc, argv, "02", &r_level, &r_new_parent_doc);
+
+  if (n_args < 1) {
+    r_level = INT2NUM((long)1);
   }
+  level = (int)NUM2INT(r_level);
 
-  Data_Get_Struct(self, xmlNode, node);
+  if (n_args < 2) {
+    new_parent_doc = node->doc;
+  } else {
+    Data_Get_Struct(r_new_parent_doc, xmlDoc, new_parent_doc);
+  }
 
-  dup = xmlDocCopyNode(node, node->doc, (int)NUM2INT(level));
+  dup = xmlDocCopyNode(node, new_parent_doc, level);
   if(dup == NULL) { return Qnil; }
 
   nokogiri_root_node(dup);

lib/nokogiri/xml/document_fragment.rb

@@ -25,6 +25,17 @@ def initialize document, tags = nil, ctx = nil
         children.each { |child| child.parent = self }
       end
 
+      if Nokogiri.uses_libxml?
+        def dup
+          new_document = document.dup
+          new_fragment = XML::DocumentFragment.new(new_document)
+          children.each do |child|
+            child.dup(1, new_document).parent = new_fragment
+          end
+          new_fragment
+        end
+      end
+
       ###
       # return the name for DocumentFragment
       def name

test/xml/test_document_fragment.rb

@@ -263,6 +263,20 @@ def test_issue_1077_parsing_of_frozen_strings
         Nokogiri::XML::DocumentFragment.parse(input) # assert_nothing_raised
       end
 
+      def test_dup_creates_tree_with_identical_structure
+        original = Nokogiri::XML::DocumentFragment.parse("<div><p>hello</p></div>")
+        duplicate = original.dup
+        assert_equal original.to_html, duplicate.to_html
+      end
+
+      def test_dup_creates_mutable_tree
+        original = Nokogiri::XML::DocumentFragment.parse("<div><p>hello</p></div>")
+        duplicate = original.dup
+        duplicate.at_css("div").add_child("<b>hello there</b>")
+        assert_nil original.at_css("b")
+        assert_not_nil duplicate.at_css("b")
+      end
+
       if Nokogiri.uses_libxml?
         def test_for_libxml_in_context_fragment_parsing_bug_workaround
           10.times do

test/xml/test_node.rb

@@ -165,6 +165,44 @@ def test_parse_with_unparented_html_fragment_text_context_node
         assert_equal x.first.name, "span"
       end
 
+      def test_dup_is_deep_copy_by_default
+        doc = XML::Document.parse "<root><div><p>hello</p></div></root>"
+        div = doc.at_css "div"
+        node = div.dup
+        assert_equal 1, node.children.length
+        assert_equal "<p>hello</p>", node.children.first.to_html
+      end
+
+      def test_dup_deep_copy
+        doc = XML::Document.parse "<root><div><p>hello</p></div></root>"
+        div = doc.at_css "div"
+        node = div.dup(1)
+        assert_equal 1, node.children.length
+        assert_equal "<p>hello</p>", node.children.first.to_html
+      end
+
+      def test_dup_shallow_copy
+        doc = XML::Document.parse "<root><div><p>hello</p></div></root>"
+        div = doc.at_css "div"
+        node = div.dup(0)
+        assert_equal 0, node.children.length
+      end
+
+      if Nokogiri.uses_libxml?
+        def test_dup_to_another_document
+          doc1 = HTML::Document.parse "<root><div><p>hello</p></div></root>"
+          doc2 = HTML::Document.parse "<div></div>"
+
+          div = doc1.at_css "div"
+          duplicate_div = div.dup(1, doc2)
+
+          assert_not_nil doc1.at_css("div")
+          assert_equal doc2, duplicate_div.document
+          assert_equal 1, duplicate_div.children.length
+          assert_equal "<p>hello</p>", duplicate_div.children.first.to_html
+        end
+      end
+
       def test_subclass_dup
         subclass = Class.new(Nokogiri::XML::Node)
         node = subclass.new('foo', @xml).dup