fix: exception when write replace return itself

src/main/java/com/caucho/hessian/io/JavaSerializer.java

@@ -146,14 +146,16 @@ public void writeObject(Object obj, AbstractHessianOutput out)
         try {
             if (_writeReplace != null) {
                 Object repl = _writeReplace.invoke(obj, new Object[0]);
+                // for those writeReplaces that might return obj itself, no need to replace repl with obj
+                if (repl != obj) {
 
-                out.removeRef(obj);
+                    out.removeRef(obj);
 
-                out.writeObject(repl);
+                    out.writeObject(repl);
 
-                out.replaceRef(repl, obj);
-
-                return;
+                    out.replaceRef(repl, obj);
+                    return;
+                }
             }
         } catch (Exception e) {
             log.log(Level.FINE, e.toString(), e);

src/test/java/com/caucho/hessian/io/WriteReplaceTest.java

@@ -0,0 +1,140 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.caucho.hessian.io;
+
+import org.junit.Assert;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.Serializable;
+
+/**
+ *
+ * @author junyuan
+ * @version WriteReplaceTest.java, v 0.1 2024-03-20 10:34 junyuan Exp $
+ */
+public class WriteReplaceTest {
+    private static SerializerFactory     factory;
+    private static ByteArrayOutputStream os;
+
+    @BeforeClass
+    public static void setUp() {
+        factory = new SerializerFactory();
+        os = new ByteArrayOutputStream();
+    }
+
+    @Test
+    public void TestWriteReplace() throws IOException {
+        TestObject origin = new TestObject();
+        origin.setName("testWR");
+
+        os.reset();
+        Hessian2Output output = new Hessian2Output(os);
+
+        output.setSerializerFactory(factory);
+        try {
+            output.writeObject(origin);
+        } catch (Exception e) {
+            Assert.fail("should be no exception");
+        }
+        output.flush();
+
+        ByteArrayInputStream is = new ByteArrayInputStream(os.toByteArray());
+        Hessian2Input input = new Hessian2Input(is);
+        input.setSerializerFactory(factory);
+        TestObject actual = (TestObject) input.readObject();
+        Assert.assertEquals(actual.name, origin.name);
+    }
+
+    @Test
+    public void TestWrappedWriteReplace() throws IOException {
+        WrappedTestObject origin = new WrappedTestObject();
+        TestObject testObject = new TestObject();
+        testObject.setName("testWR");
+        origin.setTestObject(testObject);
+
+        os.reset();
+        Hessian2Output output = new Hessian2Output(os);
+
+        output.setSerializerFactory(factory);
+        try {
+            output.writeObject(origin);
+        } catch (Exception e) {
+            Assert.fail("should be no exception");
+        }
+        output.flush();
+
+        ByteArrayInputStream is = new ByteArrayInputStream(os.toByteArray());
+        Hessian2Input input = new Hessian2Input(is);
+        input.setSerializerFactory(factory);
+        WrappedTestObject actual = (WrappedTestObject) input.readObject();
+        Assert.assertEquals(actual.testObject.name, origin.testObject.name);
+    }
+
+    private static class WrappedTestObject implements Serializable {
+        private TestObject testObject;
+
+        /**
+         * Getter method for property <tt>testObject</tt>.
+         *
+         * @return property value of testObject
+         */
+        public TestObject getTestObject() {
+            return testObject;
+        }
+
+        /**
+         * Setter method for property <tt>testObject</tt>.
+         *
+         * @param testObject  value to be assigned to property testObject
+         */
+        public void setTestObject(TestObject testObject) {
+            this.testObject = testObject;
+        }
+    }
+
+    private static class TestObject implements Serializable {
+        private static final long serialVersionUID = -452701306050912437L;
+
+        String                    name;
+
+        Object writeReplace() {
+            return this;
+        }
+
+        /**
+         * Getter method for property <tt>name</tt>.
+         *
+         * @return property value of name
+         */
+        public String getName() {
+            return name;
+        }
+
+        /**
+         * Setter method for property <tt>name</tt>.
+         *
+         * @param name  value to be assigned to property name
+         */
+        public void setName(String name) {
+            this.name = name;
+        }
+    }
+}