Implement #1441: Add StreamReadFeature.CLEAR_CURRENT_TOKEN_ON_CLOSE (#1442)

Author: cowtowncoder

release-notes/VERSION-2.x

@@ -17,6 +17,7 @@ a pure JSON library.
 2.20.0 (not yet released)
 
 #1438: `ParserBase.close()` does not clear `_currToken`
+#1441: Add `StreamReadFeature.CLEAR_CURRENT_TOKEN_ON_CLOSE` (default: true)
 - Generate SBOMs [JSTEP-14]
 
 2.19.1 (not yet released)

src/main/java/com/fasterxml/jackson/core/JsonParser.java

@@ -405,9 +405,15 @@ public enum Feature {
           *
           * @since 2.15
           */
-          USE_FAST_BIG_NUMBER_PARSER(false)
+         USE_FAST_BIG_NUMBER_PARSER(false),
 
-         ;
+         /**
+          * See {@link StreamReadFeature#CLEAR_CURRENT_TOKEN_ON_CLOSE}.
+          *
+          * @since 2.20
+          */
+         CLEAR_CURRENT_TOKEN_ON_CLOSE(true)
+        ;
 
         /**
          * Whether feature is enabled or disabled by default.

src/main/java/com/fasterxml/jackson/core/StreamReadFeature.java

@@ -111,8 +111,19 @@ public enum StreamReadFeature
      *
      * @since 2.15
      */
-    USE_FAST_BIG_NUMBER_PARSER(JsonParser.Feature.USE_FAST_BIG_NUMBER_PARSER)
+    USE_FAST_BIG_NUMBER_PARSER(JsonParser.Feature.USE_FAST_BIG_NUMBER_PARSER),
 
+    /**
+     * Feature that determines whether parser will clear "current token"
+     * (accessible via JsonParser#currentToken()) when it is closed (via
+     * {@link JsonParser#close()}).
+     *<p>
+     * Feature is enabled by default.
+     *
+     * @since 2.20
+     */
+    CLEAR_CURRENT_TOKEN_ON_CLOSE(JsonParser.Feature.CLEAR_CURRENT_TOKEN_ON_CLOSE),
+    
     ;
 
     /**

src/main/java/com/fasterxml/jackson/core/base/ParserBase.java

@@ -404,7 +404,9 @@ public void overrideCurrentName(String name) {
             _inputPtr = Math.max(_inputPtr, _inputEnd);
             _closed = true;
             // 30-May-2025, tatu: was missing before 2.20
-            _currToken = null;
+            if (JsonParser.Feature.CLEAR_CURRENT_TOKEN_ON_CLOSE.enabledIn(_features)) {
+                _currToken = null;
+            }
             try {
                 _closeInput();
             } finally {

src/test/java/com/fasterxml/jackson/core/json/JsonFactoryTest.java

@@ -354,9 +354,9 @@ private void verifyCanonicalizationTestResult(JsonParser parser, boolean canonic
         if (canonicalize) {
             assertSame(field1, field2);
         } else {
-            // n.b. It's possible that this may flake if a garbage collector with string deduplication
+            // n.b. It's possible that this may flake if a garbage collector with string de-duplication
             // enabled is used. Such a failure is unlikely because younger GC generations are typically
-            // not considered for deduplication due to high churn, but under heavy memory pressure it
+            // not considered for de-duplication due to high churn, but under heavy memory pressure it
             // may be possible. I've left this comment in an attempt to simplify investigation in the
             // off-chance that such flakes eventually occur.
             assertNotSame(field1, field2);

src/test/java/com/fasterxml/jackson/core/json/JsonParserClosedCaseTest.java

@@ -5,11 +5,15 @@
 import java.util.Collection;
 import java.util.List;
 
+import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 
+import com.fasterxml.jackson.core.JUnit5TestBase;
 import com.fasterxml.jackson.core.JsonFactory;
 import com.fasterxml.jackson.core.JsonParser;
+import com.fasterxml.jackson.core.JsonToken;
+import com.fasterxml.jackson.core.StreamReadFeature;
 import com.fasterxml.jackson.core.io.SerializedString;
 import com.fasterxml.jackson.core.testsupport.MockDataInput;
 
@@ -20,7 +24,9 @@
  * Tests asserts that using closed `JsonParser` doesn't cause ArrayIndexOutOfBoundsException
  * with `nextXxx()` methods but returns `null` as expected.
  */
-public class JsonParserClosedCaseTest {
+public class JsonParserClosedCaseTest
+    extends JUnit5TestBase
+{
     private static final JsonFactory JSON_F = new JsonFactory();
 
     JsonParser parser;
@@ -73,6 +79,49 @@ void nullReturnedOnClosedParserOnNextValue(String parserName, JsonParser parser)
         assertNull(parser.nextValue());
     }
 
+    // [core#1441]: StreamReadFeature.CLEAR_CURRENT_TOKEN_ON_CLOSE
+    @Test
+    void clearCurrentTokenOnCloseEnabled() throws Exception {
+         JsonFactory f = JsonFactory.builder()
+                 .enable(StreamReadFeature.CLEAR_CURRENT_TOKEN_ON_CLOSE)
+                 .build();
+         _clearCurrentTokenOnCloseEnabled(f, MODE_INPUT_STREAM);
+         _clearCurrentTokenOnCloseEnabled(f, MODE_INPUT_STREAM_THROTTLED);
+         _clearCurrentTokenOnCloseEnabled(f, MODE_READER);
+         _clearCurrentTokenOnCloseEnabled(f, MODE_DATA_INPUT);
+                 
+    }
+
+    @Test
+    void clearCurrentTokenOnCloseDisabled() throws Exception {
+         JsonFactory f = JsonFactory.builder()
+                 .disable(StreamReadFeature.CLEAR_CURRENT_TOKEN_ON_CLOSE)
+                 .build();
+         _clearCurrentTokenOnCloseDisabled(f, MODE_INPUT_STREAM);
+         _clearCurrentTokenOnCloseDisabled(f, MODE_INPUT_STREAM_THROTTLED);
+         _clearCurrentTokenOnCloseDisabled(f, MODE_READER);
+         _clearCurrentTokenOnCloseDisabled(f, MODE_DATA_INPUT);
+                 
+    }
+
+    private void _clearCurrentTokenOnCloseEnabled(JsonFactory f, int mode) throws Exception
+    {
+        try (JsonParser p = f.createParser("[ 1 ]")) {
+            assertToken(JsonToken.START_ARRAY, p.nextToken());
+            p.close();
+            assertNull(p.currentToken());
+        }
+    }
+    
+    private void _clearCurrentTokenOnCloseDisabled(JsonFactory f, int mode) throws Exception
+    {
+        try (JsonParser p = f.createParser("[ 1 ]")) {
+            assertToken(JsonToken.START_ARRAY, p.nextToken());
+            p.close();
+            assertToken(JsonToken.START_ARRAY, p.currentToken());
+        }
+    }
+
     private static Collection<Object[]> closeParsers(JsonParser... parsersToClose) throws IOException {
         List<Object[]> list = new ArrayList<>();
         for (JsonParser p : parsersToClose) {