Perf: limit attribute count per element to 512

Prevents runaway situations

Should improve #1578

CHANGES

@@ -23,6 +23,10 @@ jsoup changelog
   * Bugfix [Fuzz]: malformed deeply nested table elements could create a stack overflow.
     <https://github.com/jhy/jsoup/issues/1577>
 
+  * Bugfix [Fuzz]: Speed optimized malformed HTML creating elements with thousands of elements - limit the attribute
+    count per element when parsing to 512 (in real-world HTML, P99 is ~ 8).
+    <https://github.com/jhy/jsoup/issues/1578>
+
 *** 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/parser/Token.java

@@ -97,11 +97,16 @@ Tag reset() {
             return this;
         }
 
+        /* Limits runaway crafted HTML from spewing attributes and getting a little sluggish in ensureCapacity.
+        Real-world HTML will P99 around 8 attributes, so plenty of headroom. Implemented here and not in the Attributes
+        object so that API users can add more if ever required. */
+        private static final int MaxAttributes = 512;
+
         final void newAttribute() {
             if (attributes == null)
                 attributes = new Attributes();
 
-            if (pendingAttributeName != null) {
+            if (pendingAttributeName != null && attributes.size() < MaxAttributes) {
                 // the tokeniser has skipped whitespace control chars, but trimming could collapse to empty for other control codes, so verify here
                 pendingAttributeName = pendingAttributeName.trim();
                 if (pendingAttributeName.length() > 0) {