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Fix bug in Path.toString() method with Unicode surrogate pairs handling\n\nFixed an issue where the wrong loop variable 'i' was used instead of 'j' when processing Unicode surrogate pairs in JSON field names. This caused ArrayIndexOutOfBoundsException or incorrect results when serializing JSON with emoji keys or other Unicode characters represented by surrogate pairs.\n\nAdded test cases to verify the fix works correctly with various Unicode characters including emojis.
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3 files changed

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‎core/src/main/java/com/alibaba/fastjson2/JSONWriter.java

Lines changed: 4 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -2489,10 +2489,10 @@ public String toString() {
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ascii = false;
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final int uc;
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if (ch < '\uDBFF' + 1) { // Character.isHighSurrogate(c)
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if (name.length() - i < 2) {
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if (name.length() - j < 2) {
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uc = -1;
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} else {
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char d = name.charAt(i + 1);
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char d = name.charAt(j + 1);
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// d >= '\uDC00' && d < ('\uDFFF' + 1)
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if (d >= '\uDC00' && d < ('\uDFFF' + 1)) { // Character.isLowSurrogate(d)
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uc = ((ch << 10) + d) + (0x010000 - ('\uD800' << 10) - '\uDC00'); // Character.toCodePoint(c, d)
@@ -2603,10 +2603,10 @@ public String toString() {
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ascii = false;
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final int uc;
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if (ch < '\uDBFF' + 1) { // Character.isHighSurrogate(c)
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if (name.length() - i < 2) {
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if (name.length() - j < 2) {
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uc = -1;
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} else {
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char d = name.charAt(i + 1);
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char d = name.charAt(j + 1);
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// d >= '\uDC00' && d < ('\uDFFF' + 1)
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if (d >= '\uDC00' && d < ('\uDFFF' + 1)) { // Character.isLowSurrogate(d)
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uc = ((ch << 10) + d) + (0x010000 - ('\uD800' << 10) - '\uDC00'); // Character.toCodePoint(c, d)

‎core/src/test/java/com/alibaba/fastjson2/JSONWriterPathBugDemoTest.java

Lines changed: 80 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,80 @@
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package com.alibaba.fastjson2;
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import org.junit.jupiter.api.Test;
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import java.util.HashMap;
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import java.util.Map;
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import static org.junit.jupiter.api.Assertions.*;
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public class JSONWriterPathBugDemoTest {
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/**
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* This test demonstrates the bug that was fixed.
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* Before the fix, this test would fail with an ArrayIndexOutOfBoundsException
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* or produce incorrect results when processing JSON field names with Unicode surrogate pairs.
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*
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* The bug was in the Path.toString() method where the wrong loop variable 'i' was used
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* instead of 'j' when processing characters in a string containing surrogate pairs.
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*/
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@Test
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public void testUnicodeSurrogatePairsPathBug() {
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// Create a map with keys that contain Unicode surrogate pairs
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Map<String, Object> map = new HashMap<>();
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// These emojis are represented by surrogate pairs:
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// 😀 (grinning face) = \uD83D\uDE00
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// 🌍 (earth globe) = \uD83C\uDF0D
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// 👍 (thumbs up) = \uD83D\uDC4D
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map.put("key😀", "value1");
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map.put("key🌍", "value2");
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map.put("key👍", "value3");
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// Create nested objects to trigger reference path handling
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Map<String, Object> nested1 = new HashMap<>();
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Map<String, Object> nested2 = new HashMap<>();
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nested1.put("nested😀", nested2); // Emoji in nested key
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nested2.put("deepValue", "deepValue");
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map.put("nested", nested1);
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try {
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// Serialize with reference detection enabled to trigger Path.toString()
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String json = JSON.toJSONString(map, JSONWriter.Feature.ReferenceDetection);
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System.out.println("Serialized JSON: " + json);
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// Verify that the JSON contains our values
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assertTrue(json.contains("value1"), "JSON should contain value1");
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assertTrue(json.contains("value2"), "JSON should contain value2");
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assertTrue(json.contains("value3"), "JSON should contain value3");
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System.out.println("Test passed - no exception thrown during serialization");
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} catch (Exception e) {
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fail("Exception thrown during JSON serialization with Unicode surrogate pairs: " + e.getMessage(), e);
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}
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}
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/**
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* Additional test with circular references to further stress the Path.toString() method.
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*/
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@Test
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public void testUnicodeSurrogatePairsWithCircularReference() {
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// Create objects with circular references and Unicode surrogate pairs in keys
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Map<String, Object> parent = new HashMap<>();
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Map<String, Object> child = new HashMap<>();
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// Use keys with surrogate pairs
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parent.put("parent😀", child);
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child.put("child👍", parent); // Circular reference with emoji
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try {
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// Serialize with reference detection enabled
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String json = JSON.toJSONString(parent, JSONWriter.Feature.ReferenceDetection);
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System.out.println("Serialized JSON with circular reference: " + json);
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// Should not throw any exception
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System.out.println("Test passed - no exception thrown during serialization with circular reference");
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} catch (Exception e) {
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fail("Exception thrown during JSON serialization with surrogate pairs and circular reference: " + e.getMessage(), e);
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}
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}
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}

‎core/src/test/java/com/alibaba/fastjson2/JSONWriterPathTest.java

Lines changed: 98 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,98 @@
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package com.alibaba.fastjson2;
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import org.junit.jupiter.api.Test;
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import java.util.HashMap;
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import java.util.Map;
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import static org.junit.jupiter.api.Assertions.*;
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public class JSONWriterPathTest {
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/**
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* Test for reproducing the bug with Unicode surrogate pairs in JSON field names.
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*/
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@Test
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public void testUnicodeSurrogatePairsInPath() {
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// Create a map with a key that contains Unicode surrogate pairs
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Map<String, Object> map = new HashMap<>();
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// This emoji is represented by surrogate pairs: \uD83D\uDE00 (grinning face)
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String keyWithSurrogatePairs = "key" + "\uD83D\uDE00"; // "key😀"
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map.put(keyWithSurrogatePairs, "value");
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// Also add a nested object to trigger reference path handling
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Map<String, Object> nested = new HashMap<>();
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nested.put("nestedKey", "nestedValue");
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map.put("nested", nested);
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// Enable reference detection to trigger the Path.toString() code path
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try (JSONWriter writer = JSONWriter.of(JSONWriter.Feature.ReferenceDetection)) {
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// Use JSONObjectWriter directly instead of ObjectWriterCreator
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writer.write(map);
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String json = writer.toString();
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System.out.println("Generated JSON: " + json);
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assertNotNull(json);
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// The test passes if no exception is thrown during serialization
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// Check that the value is present in the output
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assertTrue(json.contains("value"), "JSON should contain the value 'value'");
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} catch (Exception e) {
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fail("Exception thrown during JSON serialization with Unicode surrogate pairs: " + e.getMessage(), e);
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}
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}
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/**
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* Additional test with more complex Unicode surrogate pairs.
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*/
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@Test
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public void testComplexUnicodeSurrogatePairsInPath() {
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Map<String, Object> map = new HashMap<>();
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// Using various emojis that are represented with surrogate pairs
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map.put("key😀", "value1"); // Grinning face
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map.put("key🌍", "value2"); // Earth globe
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map.put("key👍", "value3"); // Thumbs up
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try (JSONWriter writer = JSONWriter.of(JSONWriter.Feature.ReferenceDetection, JSONWriter.Feature.PrettyFormat)) {
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// Use JSONObjectWriter directly instead of ObjectWriterCreator
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writer.write(map);
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String json = writer.toString();
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System.out.println("Generated JSON: " + json);
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assertNotNull(json);
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// The test passes if no exception is thrown during serialization
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// Check that the values are present in the output
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assertTrue(json.contains("value1"), "JSON should contain the value 'value1'");
64+
assertTrue(json.contains("value2"), "JSON should contain the value 'value2'");
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assertTrue(json.contains("value3"), "JSON should contain the value 'value3'");
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} catch (Exception e) {
67+
fail("Exception thrown during JSON serialization with complex Unicode surrogate pairs: " + e.getMessage(), e);
68+
}
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}
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/**
72+
* Test that specifically targets the bug with surrogate pairs in path handling.
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* This test creates a circular reference to force the Path.toString() method to be called.
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*/
75+
@Test
76+
public void testSurrogatePairsInPathWithCircularReference() {
77+
// Create objects with circular references
78+
Map<String, Object> parent = new HashMap<>();
79+
Map<String, Object> child = new HashMap<>();
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// Use keys with surrogate pairs
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parent.put("parent😀", child);
83+
child.put("child😀", parent); // Circular reference
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// Enable reference detection to trigger the Path.toString() code path
86+
try (JSONWriter writer = JSONWriter.of(JSONWriter.Feature.ReferenceDetection)) {
87+
// Use JSONObjectWriter directly instead of ObjectWriterCreator
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writer.write(parent);
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String json = writer.toString();
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System.out.println("Generated JSON with circular reference: " + json);
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assertNotNull(json);
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// Should not throw any exception
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} catch (Exception e) {
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fail("Exception thrown during JSON serialization with surrogate pairs and circular reference: " + e.getMessage(), e);
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}
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}
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}

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