Speed improvement: cap number of cloned active formatting elements

Also saves on memory allocations for empty attribute lists.

Fixes #1613

CHANGES

@@ -77,6 +77,11 @@ jsoup changelog
   * Bugfix [Fuzz]: Fix an IOOB when the HTML root was cleared from the stack and then attributes were merged onto it.
     <https://github.com/jhy/jsoup/issues/1611>
 
+  * Bugfix [Fuzz]: Improved the speed of parsing when crafted HTML contains hundreds of active formatting elements
+    that were copied for all new elements (similar to an amplification attack). The number of considered active
+    formatting elements that will be cloned when mis-nested is now capped to 12.
+    <https://github.com/jhy/jsoup/issues/1613>
+
 *** Release 1.14.1 [2021-Jul-10]
   * Change: updated the minimum supported Java version from Java 7 to Java 8.
 

src/main/java/org/jsoup/nodes/Attributes.java

@@ -275,7 +275,6 @@ public void addAll(Attributes incoming) {
             // todo - should this be case insensitive?
             put(attr);
         }
-
     }
 
     public Iterator<Attribute> iterator() {

src/main/java/org/jsoup/nodes/Node.java

@@ -86,6 +86,16 @@ else if (attributeKey.startsWith("abs:"))
      */
     public abstract Attributes attributes();
 
+    /**
+     Get the number of attributes that this Node has.
+     @return the number of attributes
+     @since 1.14.2
+     */
+    public int attributesSize() {
+        // added so that we can test how many attributes exist without implicitly creating the Attributes object
+        return hasAttributes() ? attributes().size() : 0;
+    }
+
     /**
      * Set an attribute (key=value). If the attribute already exists, it is replaced. The attribute key comparison is
      * <b>case insensitive</b>. The key will be set with case sensitivity as set in the parser settings.
@@ -100,7 +110,7 @@ public Node attr(String attributeKey, String attributeValue) {
     }
 
     /**
-     * Test if this element has an attribute. <b>Case insensitive</b>
+     * Test if this Node has an attribute. <b>Case insensitive</b>.
      * @param attributeKey The attribute key to check.
      * @return true if the attribute exists, false if not.
      */

src/main/java/org/jsoup/parser/HtmlTreeBuilder.java

@@ -690,10 +690,11 @@ void reconstructFormattingElements() {
 
         Element entry = last;
         int size = formattingElements.size();
+        int ceil = size - maxUsedFormattingElements; if (ceil <0) ceil = 0;
         int pos = size - 1;
         boolean skip = false;
         while (true) {
-            if (pos == 0) { // step 4. if none before, skip to 8
+            if (pos == ceil) { // step 4. if none before, skip to 8
                 skip = true;
                 break;
             }
@@ -710,7 +711,8 @@ void reconstructFormattingElements() {
             skip = false; // can only skip increment from 4.
             Element newEl = insertStartTag(entry.normalName()); // todo: avoid fostering here?
             // newEl.namespace(entry.namespace()); // todo: namespaces
-            newEl.attributes().addAll(entry.attributes());
+            if (entry.attributesSize() > 0)
+                newEl.attributes().addAll(entry.attributes());
 
             // 10. replace entry with new entry
             formattingElements.set(pos, newEl);
@@ -720,6 +722,7 @@ void reconstructFormattingElements() {
                 break;
         }
     }
+    private static final int maxUsedFormattingElements = 12; // limit how many elements get recreated
 
     void clearFormattingElementsToLastMarker() {
         while (!formattingElements.isEmpty()) {

src/main/java/org/jsoup/parser/HtmlTreeBuilderState.java

@@ -815,8 +815,7 @@ else if (!tb.onStack(formatEl)) {
                 Element furthestBlock = null;
                 Element commonAncestor = null;
                 boolean seenFormattingElement = false;
-                // the spec doesn't limit to < 64, but in degenerate cases (9000+ stack depth) this prevents
-                // run-aways
+                // the spec doesn't limit to < 64, but in degenerate cases (9000+ stack depth) this prevents run-aways
                 final int stackSize = stack.size();
                 int bookmark = -1;
                 for (int si = 1; si < stackSize && si < 64; si++) {

src/test/java/org/jsoup/integration/FuzzFixesTest.java

@@ -220,4 +220,13 @@ public void unconsume() throws IOException {
         Document docXml = Jsoup.parse(new FileInputStream(in), "UTF-8", "https://example.com", Parser.xmlParser());
         assertNotNull(docXml);
     }
+
+    @Test
+    public void test36916() throws IOException {
+        // https://github.com/jhy/jsoup/issues/1613
+        File in = ParseTest.getFile("/fuzztests/1613.html.gz");
+
+        Document doc = Jsoup.parse(in, "UTF-8");
+        assertNotNull(doc);
+    }
 }

src/test/java/org/jsoup/nodes/ElementTest.java

@@ -2039,4 +2039,20 @@ public void childNodesAccessorDoesNotVivify() {
         els.add(new Element("a"));
         assertEquals(1, els.size());
     }
+
+    @Test public void attributeSizeDoesNotAutoVivify() {
+        Document doc = Jsoup.parse("<p></p>");
+        Element p = doc.selectFirst("p");
+        assertNotNull(p);
+        assertFalse(p.hasAttributes());
+        assertEquals(0, p.attributesSize());
+        assertFalse(p.hasAttributes());
+
+        p.attr("foo", "bar");
+        assertEquals(1, p.attributesSize());
+        assertTrue(p.hasAttributes());
+
+        p.removeAttr("foo");
+        assertEquals(0, p.attributesSize());
+    }
 }