Fixes #114 in 2.x: support STRICT_DUPLICATE_DETECTION

src/main/java/com/fasterxml/jackson/dataformat/xml/deser/FromXmlParser.java

@@ -18,6 +18,7 @@
 import com.fasterxml.jackson.core.exc.StreamConstraintsException;
 import com.fasterxml.jackson.core.io.IOContext;
 import com.fasterxml.jackson.core.io.NumberInput;
+import com.fasterxml.jackson.core.json.DupDetector;
 import com.fasterxml.jackson.core.util.ByteArrayBuilder;
 import com.fasterxml.jackson.core.util.JacksonFeatureSet;
 
@@ -284,18 +285,21 @@ public FromXmlParser(IOContext ctxt, int genericParserFeatures, int xmlFeatures,
      * This constructor initializes the parser with the given I/O context, parser features,
      * and object codec for deserializing XML content into Java objects.
      *
-     * @since 2.20
      * @param ctxt I/O context used for handling low-level I/O operations and buffering
      * @param genericParserFeatures set of bitmasked parser features to control parsing behavior
      * @param codec object codec used for converting between JSON-like structures and Java objects
      * @param xmlTokenStream the pre-processed XML token stream to parse from
      * @throws IOException if an I/O error occurs during initialization or parsing setup
+     *
+     * @since 2.20
      */
     public FromXmlParser(IOContext ctxt, int genericParserFeatures, ObjectCodec codec, XmlTokenStream xmlTokenStream) throws IOException {
         super(genericParserFeatures, ctxt.streamReadConstraints());
         _ioContext = ctxt;
         _objectCodec = codec;
-        _parsingContext = XmlReadContext.createRootContext(-1, -1);
+        DupDetector dups = JsonParser.Feature.STRICT_DUPLICATE_DETECTION.enabledIn(genericParserFeatures)
+                ? DupDetector.rootDetector(this) : null;
+        _parsingContext = XmlReadContext.createRootContext(dups, -1, -1);
         _xmlTokens = Objects.requireNonNull(xmlTokenStream, "xmlTokenStream cannot be null");
         _formatFeatures = xmlTokenStream.getFormatFeatures();
         final int firstToken;
@@ -526,7 +530,12 @@ public void overrideCurrentName(String name)
         if (_currToken == JsonToken.START_OBJECT || _currToken == JsonToken.START_ARRAY) {
             ctxt = ctxt.getParent();
         }
-        ctxt.setCurrentName(name);
+        // Unfortunate, but since we did not expose exceptions, need to wrap
+        try {
+            ctxt.setCurrentName(name);
+        } catch (IOException e) {
+            throw new IllegalStateException(e);
+        }
     }
 
     @Override
@@ -1050,7 +1059,7 @@ public String nextTextValue() throws IOException
     }
 
 
-    private void _updateState(JsonToken t)
+    private void _updateState(JsonToken t) throws JsonProcessingException
     {
         switch (t) {
         case START_OBJECT:

src/main/java/com/fasterxml/jackson/dataformat/xml/deser/XmlReadContext.java

@@ -5,6 +5,7 @@
 import com.fasterxml.jackson.core.*;
 import com.fasterxml.jackson.core.io.CharTypes;
 import com.fasterxml.jackson.core.io.ContentReference;
+import com.fasterxml.jackson.core.json.DupDetector;
 
 /**
  * Extension of {@link JsonStreamContext}, which implements
@@ -23,6 +24,14 @@ public final class XmlReadContext
 
     protected final XmlReadContext _parent;
 
+    /**
+     * Object used for checking for duplicate field names, if enabled
+     * (null if not enabled)
+     *
+     * @since 2.21
+     */
+    protected final DupDetector _dups;
+
     // // // Location information (minus source reference)
 
     protected int _lineNr;
@@ -59,28 +68,26 @@ public final class XmlReadContext
      */
 
     /**
-     * @since 2.18
+     * @since 2.21
      */
-    public XmlReadContext(XmlReadContext parent, int nestingDepth,
+    public XmlReadContext(XmlReadContext parent, DupDetector dups,
+            int nestingDepth,
             int type, int lineNr, int colNr)
     {
         super();
         _type = type;
         _parent = parent;
+        _dups = dups;
         _lineNr = lineNr;
         _columnNr = colNr;
         _index = -1;
         _nestingDepth = nestingDepth;
     }
 
-    /**
-     * @deprecated Since 2.18
-     */
-    @Deprecated // since 2.18
-    public XmlReadContext(XmlReadContext parent, int type, int lineNr, int colNr)
-    {
-        this(parent, (parent == null) ? 0 : parent._nestingDepth + 1,
-                type, lineNr, colNr);
+    @Deprecated // @since 2.21
+    public XmlReadContext(XmlReadContext parent, int nestingDepth,
+            int type, int lineNr, int colNr) {
+        this(parent, null, nestingDepth, type, lineNr, colNr);
     }
 
     protected final void reset(int type, int lineNr, int colNr)
@@ -92,7 +99,10 @@ protected final void reset(int type, int lineNr, int colNr)
         _currentName = null;
         _currentValue = null;
         _namesToWrap = null;
-        // _nestingDepth fine as is, same level for reuse
+        if (_dups != null) {
+            _dups.reset();
+        }
+        // _nestingDepth fine as-is, same level for reuse
     }
 
     @Override
@@ -111,20 +121,28 @@ public void setCurrentValue(Object v) {
     /**********************************************************************
      */
 
+    public static XmlReadContext createRootContext(DupDetector dups, int lineNr, int colNr) {
+        return new XmlReadContext(null, dups, 0, TYPE_ROOT, lineNr, colNr);
+    }
+
+    @Deprecated // @since 2.21
     public static XmlReadContext createRootContext(int lineNr, int colNr) {
-        return new XmlReadContext(null, 0, TYPE_ROOT, lineNr, colNr);
+        return createRootContext(null, lineNr, colNr);
     }
 
+    @Deprecated // @since 2.21
     public static XmlReadContext createRootContext() {
-        return new XmlReadContext(null, 0, TYPE_ROOT, 1, 0);
+        return createRootContext(null, 1, 0);
     }
-    
+
     public final XmlReadContext createChildArrayContext(int lineNr, int colNr)
     {
         ++_index; // not needed for Object, but does not hurt so no need to check curr type
         XmlReadContext ctxt = _child;
         if (ctxt == null) {
-            _child = ctxt = new XmlReadContext(this, _nestingDepth+1, TYPE_ARRAY, lineNr, colNr);
+            _child = ctxt = new XmlReadContext(this,
+                    (_dups == null) ? null : _dups.child(),
+                            _nestingDepth+1, TYPE_ARRAY, lineNr, colNr);
             return ctxt;
         }
         ctxt.reset(TYPE_ARRAY, lineNr, colNr);
@@ -136,10 +154,12 @@ public final XmlReadContext createChildObjectContext(int lineNr, int colNr)
         ++_index; // not needed for Object, but does not hurt so no need to check curr type
         XmlReadContext ctxt = _child;
         if (ctxt == null) {
-            _child = ctxt = new XmlReadContext(this, TYPE_OBJECT, lineNr, colNr);
-            return ctxt;
+            _child = ctxt = new XmlReadContext(this,
+                    (_dups == null) ? null : _dups.child(),
+                            _nestingDepth+1, TYPE_OBJECT, lineNr, colNr);
+        } else {
+            ctxt.reset(TYPE_OBJECT, lineNr, colNr);
         }
-        ctxt.reset(TYPE_OBJECT, lineNr, colNr);
         return ctxt;
     }
 
@@ -186,10 +206,22 @@ public final void valueStarted() {
         ++_index;
     }
 
-    public void setCurrentName(String name) {
+    public void setCurrentName(String name) throws JsonProcessingException {
         _currentName = name;
+        if (_dups != null) {
+            _checkDup(_dups, name);
+        }
     }
 
+    // @since 2.21
+    private static void _checkDup(DupDetector dd, String name) throws JsonProcessingException
+    {
+        if (dd.isDup(name)) {
+            throw new JsonParseException(null,
+                    "Duplicate field '"+name+"'", dd.findLocation());
+        }
+    }
+
     public void setNamesToWrap(Set<String> namesToWrap) {
         _namesToWrap = namesToWrap;
     }

src/test/java/com/fasterxml/jackson/dataformat/xml/deser/StrictDuplicateDetection114Test.java

@@ -0,0 +1,65 @@
+package com.fasterxml.jackson.dataformat.xml.deser;
+
+import org.junit.jupiter.api.Test;
+
+import com.fasterxml.jackson.core.JsonParser;
+import com.fasterxml.jackson.core.exc.StreamReadException;
+import com.fasterxml.jackson.dataformat.xml.XmlMapper;
+import com.fasterxml.jackson.dataformat.xml.XmlTestUtil;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * Tests for [dataformat-xml#114]: Support for STRICT_DUPLICATE_DETECTION
+ *
+ * @since 2.21
+ */
+public class StrictDuplicateDetection114Test extends XmlTestUtil
+{
+    static class TestBean114 {
+        public String field1;
+        public String field2;
+    }
+
+    private final XmlMapper STRICT_MAPPER = XmlMapper.builder()
+            .enable(JsonParser.Feature.STRICT_DUPLICATE_DETECTION)
+            .build();
+
+    // [dataformat-xml#114]
+    @Test
+    public void testStrictDuplicateDetectionWithPOJO() throws Exception
+    {
+        // Test XML mapper should also reject duplicates
+        final String xmlWithDup = "<TestBean><field1>value1</field1><field1>value2</field1></TestBean>";
+
+        StreamReadException e = assertThrows(StreamReadException.class, () -> {
+            STRICT_MAPPER.readValue(xmlWithDup, TestBean114.class);
+        });
+        assertTrue(e.getMessage().contains("Duplicate field"),
+                "Expected 'Duplicate field' error, got: " + e.getMessage());
+    }
+
+    @Test
+    public void testNoDuplicatesShouldWork() throws Exception
+    {
+        final String xml = "<TestBean><field1>value1</field1><field2>value2</field2></TestBean>";
+
+        TestBean114 bean = STRICT_MAPPER.readValue(xml, TestBean114.class);
+        assertNotNull(bean);
+        assertEquals("value1", bean.field1);
+        assertEquals("value2", bean.field2);
+    }
+
+    @Test
+    public void testDuplicateDetectionDisabledByDefault() throws Exception
+    {
+        XmlMapper mapper = newMapper(); // default mapper without strict duplicate detection
+
+        // Should allow duplicates by default (last value wins)
+        final String xmlWithDup = "<TestBean><field1>value1</field1><field1>value2</field1></TestBean>";
+
+        TestBean114 bean = mapper.readValue(xmlWithDup, TestBean114.class);
+        assertNotNull(bean);
+        assertEquals("value2", bean.field1); // last value wins
+    }
+}