fix: implement Copilot PR review suggestions

- Fix test assertion for remove_namespaces feature
- Use StandardCharsets.UTF_8 instead of string literal
- Replace string reference comparison with isEmpty()
- Move regex pattern to static final field for performance

Author: marc-gr

modules/ingest-common/src/main/java/org/elasticsearch/ingest/common/XmlProcessor.java

@@ -15,12 +15,14 @@
 import org.elasticsearch.ingest.IngestDocument;
 import org.elasticsearch.ingest.Processor;
 
+import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.regex.Pattern;
 
 import javax.xml.namespace.NamespaceContext;
 import javax.xml.parsers.DocumentBuilder;
@@ -52,6 +54,9 @@ public final class XmlProcessor extends AbstractProcessor {
 
     private static final XPathFactory XPATH_FACTORY = XPathFactory.newInstance();
 
+    // Pre-compiled pattern to detect namespace prefixes
+    private static final Pattern NAMESPACE_PATTERN = Pattern.compile(".*\\b[a-zA-Z][a-zA-Z0-9_-]*:[a-zA-Z][a-zA-Z0-9_-]*.*");
+    
     // Pre-configured SAX parser factories for secure XML parsing
     private static final javax.xml.parsers.SAXParserFactory SAX_PARSER_FACTORY = createSecureSaxParserFactory();
     private static final javax.xml.parsers.SAXParserFactory SAX_PARSER_FACTORY_NS = createSecureSaxParserFactoryNamespaceAware();
@@ -383,16 +388,14 @@ public Iterator<String> getPrefixes(String namespaceURI) {
             });
         }
 
-        // Pre-compiled pattern to detect namespace prefixes
-        java.util.regex.Pattern namespacePattern = 
-            java.util.regex.Pattern.compile(".*\\b[a-zA-Z][a-zA-Z0-9_-]*:[a-zA-Z][a-zA-Z0-9_-]*.*");
+        // Use pre-compiled pattern to detect namespace prefixes
 
         for (Map.Entry<String, String> entry : xpathExpressions.entrySet()) {
             String xpathExpression = entry.getKey();
             String targetFieldName = entry.getValue();
 
             // Validate namespace prefixes if no namespaces are configured
-            if (!hasNamespaces && namespacePattern.matcher(xpathExpression).matches()) {
+            if (!hasNamespaces && NAMESPACE_PATTERN.matcher(xpathExpression).matches()) {
                 throw new IllegalArgumentException(
                     "Invalid XPath expression [" + xpathExpression + "]: contains namespace prefixes but no namespace configuration provided"
                 );
@@ -476,7 +479,7 @@ public XmlProcessor create(
 
             // Parse parse_options parameter
             String parseOptions = ConfigurationUtils.readStringProperty(TYPE, processorTag, config, "parse_options", "");
-            if (parseOptions != null && parseOptions != "" && !"strict".equals(parseOptions)) {
+            if (parseOptions != null && !parseOptions.isEmpty() && !"strict".equals(parseOptions)) {
                 throw new IllegalArgumentException("Invalid parse_options [" + parseOptions + "]. Only 'strict' is supported.");
             }
 
@@ -528,7 +531,7 @@ public void fatalError(org.xml.sax.SAXParseException exception) throws org.xml.s
         // Use enhanced handler that can build DOM during streaming when needed
         XmlStreamingWithDomHandler handler = new XmlStreamingWithDomHandler(needsDom);
 
-        parser.parse(new java.io.ByteArrayInputStream(xmlString.getBytes("UTF-8")), handler);
+        parser.parse(new java.io.ByteArrayInputStream(xmlString.getBytes(StandardCharsets.UTF_8)), handler);
 
         // Store structured result if needed
         if (storeXml) {
@@ -926,10 +929,11 @@ private static DocumentBuilderFactory createSecureDocumentBuilderFactory() {
      * @return the appropriate SAX parser factory for the current configuration
      */
     private javax.xml.parsers.SAXParserFactory selectSaxParserFactory() {
+        boolean needsNamespaceAware = hasNamespaces() || removeNamespaces;
         if (isStrict()) {
-            return hasNamespaces() ? SAX_PARSER_FACTORY_NS_STRICT : SAX_PARSER_FACTORY_STRICT;
+            return needsNamespaceAware ? SAX_PARSER_FACTORY_NS_STRICT : SAX_PARSER_FACTORY_STRICT;
         } else {
-            return hasNamespaces() ? SAX_PARSER_FACTORY_NS : SAX_PARSER_FACTORY;
+            return needsNamespaceAware ? SAX_PARSER_FACTORY_NS : SAX_PARSER_FACTORY;
         }
     }
 }

modules/ingest-common/src/test/java/org/elasticsearch/ingest/common/XmlProcessorTests.java

@@ -583,8 +583,8 @@ public void testRemoveNamespaces() {
         Map<String, Object> data = ingestDocument.getFieldValue(TARGET_FIELD, Map.class);
         Map<String, Object> foo = (Map<String, Object>) data.get("foo");
 
-        assertTrue("Element with namespace should be present", foo.containsKey("ns:bar"));
-        assertThat(foo.get("ns:bar"), equalTo("value"));
+        assertTrue("Element without namespace should be present", foo.containsKey("bar"));
+        assertThat(foo.get("bar"), equalTo("value"));
 
         // Now test with removeNamespaces=false
         IngestDocument ingestDocument2 = createTestIngestDocument(xml);