HADOOP-18575: followup: try to avoid repeatedly hitting exceptions when transformer factories do not support attributes (#5253)

Part of HADOOP-18469 and the hardening of XML/XSL parsers.
Followup to the main HADOOP-18575 patch, to improve performance when
working with xml/xsl engines which don't support the relevant attributes.

Include this change when backporting.

Contributed by PJ Fanning.

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/XMLUtils.java

@@ -34,6 +34,7 @@
 import org.xml.sax.SAXException;
 
 import java.io.*;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 /**
  * General xml utilities.
@@ -59,6 +60,11 @@ public class XMLUtils {
   public static final String VALIDATION =
       "http://xml.org/sax/features/validation";
 
+  private static final AtomicBoolean CAN_SET_TRANSFORMER_ACCESS_EXTERNAL_DTD =
+          new AtomicBoolean(true);
+  private static final AtomicBoolean CAN_SET_TRANSFORMER_ACCESS_EXTERNAL_STYLESHEET =
+          new AtomicBoolean(true);
+
   /**
    * Transform input xml given a stylesheet.
    * 
@@ -143,8 +149,7 @@ public static TransformerFactory newSecureTransformerFactory()
           throws TransformerConfigurationException {
     TransformerFactory trfactory = TransformerFactory.newInstance();
     trfactory.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, true);
-    bestEffortSetAttribute(trfactory, XMLConstants.ACCESS_EXTERNAL_DTD, "");
+    setOptionalSecureTransformerAttributes(trfactory);
-    bestEffortSetAttribute(trfactory, XMLConstants.ACCESS_EXTERNAL_STYLESHEET, "");
     return trfactory;
   }
 
@@ -161,29 +166,45 @@ public static SAXTransformerFactory newSecureSAXTransformerFactory()
           throws TransformerConfigurationException {
     SAXTransformerFactory trfactory = (SAXTransformerFactory) SAXTransformerFactory.newInstance();
     trfactory.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, true);
-    bestEffortSetAttribute(trfactory, XMLConstants.ACCESS_EXTERNAL_DTD, "");
+    setOptionalSecureTransformerAttributes(trfactory);
-    bestEffortSetAttribute(trfactory, XMLConstants.ACCESS_EXTERNAL_STYLESHEET, "");
     return trfactory;
   }
 
+  /**
+   * These attributes are recommended for maximum security but some JAXP transformers do
+   * not support them. If at any stage, we fail to set these attributes, then we won't try again
+   * for subsequent transformers.
+   *
+   * @param transformerFactory to update
+   */
+  private static void setOptionalSecureTransformerAttributes(
+          TransformerFactory transformerFactory) {
+    bestEffortSetAttribute(transformerFactory, CAN_SET_TRANSFORMER_ACCESS_EXTERNAL_DTD,
+            XMLConstants.ACCESS_EXTERNAL_DTD, "");
+    bestEffortSetAttribute(transformerFactory, CAN_SET_TRANSFORMER_ACCESS_EXTERNAL_STYLESHEET,
+            XMLConstants.ACCESS_EXTERNAL_STYLESHEET, "");
+  }
+
   /**
    * Set an attribute value on a {@link TransformerFactory}. If the TransformerFactory
    * does not support the attribute, the method just returns <code>false</code> and
    * logs the issue at debug level.
    *
    * @param transformerFactory to update
+   * @param flag that indicates whether to do the update and the flag can be set to
+   *             <code>false</code> if an update fails
    * @param name of the attribute to set
    * @param value to set on the attribute
-   * @return whether the attribute was successfully set
    */
-  static boolean bestEffortSetAttribute(TransformerFactory transformerFactory,
+  static void bestEffortSetAttribute(TransformerFactory transformerFactory, AtomicBoolean flag,
                                      String name, Object value) {
+    if (flag.get()) {
       try {
         transformerFactory.setAttribute(name, value);
-      return true;
       } catch (Throwable t) {
+        flag.set(false);
         LOG.debug("Issue setting TransformerFactory attribute {}: {}", name, t.toString());
       }
-    return false;
+    }
   }
 }

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/util/TestXMLUtils.java

@@ -20,6 +20,7 @@
 import java.io.InputStream;
 import java.io.StringReader;
 import java.io.StringWriter;
+import java.util.concurrent.atomic.AtomicBoolean;
 import javax.xml.XMLConstants;
 import javax.xml.parsers.DocumentBuilder;
 import javax.xml.parsers.SAXParser;
@@ -134,10 +135,16 @@ public void testExternalDtdWithSecureSAXTransformerFactory() throws Exception {
   @Test
   public void testBestEffortSetAttribute() throws Exception {
     TransformerFactory factory = TransformerFactory.newInstance();
-    Assert.assertFalse("unexpected attribute results in return of false",
+    AtomicBoolean flag1 = new AtomicBoolean(true);
-            XMLUtils.bestEffortSetAttribute(factory, "unsupportedAttribute false", "abc"));
+    XMLUtils.bestEffortSetAttribute(factory, flag1, "unsupportedAttribute false", "abc");
-    Assert.assertTrue("expected attribute results in return of false",
+    Assert.assertFalse("unexpected attribute results in return of false?", flag1.get());
-            XMLUtils.bestEffortSetAttribute(factory, XMLConstants.ACCESS_EXTERNAL_DTD, ""));
+    AtomicBoolean flag2 = new AtomicBoolean(true);
+    XMLUtils.bestEffortSetAttribute(factory, flag2, XMLConstants.ACCESS_EXTERNAL_DTD, "");
+    Assert.assertTrue("expected attribute results in return of true?", flag2.get());
+    AtomicBoolean flag3 = new AtomicBoolean(false);
+    XMLUtils.bestEffortSetAttribute(factory, flag3, XMLConstants.ACCESS_EXTERNAL_DTD, "");
+    Assert.assertFalse("expected attribute results in return of false if input flag is false?",
+            flag3.get());
   }
 
   private static InputStream getResourceStream(final String filename) {