From 6f9fad556185467f2000156a4e27e76159423ac5 Mon Sep 17 00:00:00 2001
From: yangjie01 <yangjie01@baidu.com>
Date: Tue, 1 Sep 2026 15:39:49 +0800
Subject: [PATCH] [common] Fix double position advance in
 DataOutputSerializer.writeBytes

writeBytes(String) wrote each byte through writeByte, which goes to write(int)
and advances position itself, and then advanced position by the string length a
second time. After the call length() reported twice the bytes written and the
next write landed past a gap of untouched bytes. The sibling writeChars has the
same shape and never had that line.

Nothing in the repository calls this overload; it is part of the java.io.DataOutput
contract that DataOutputView exposes, so the defect is visible to callers outside
the repository.

Assisted-by: GLM-5.3
---
 .../paimon/io/DataOutputSerializer.java       |  1 -
 .../paimon/io/DataOutputSerializerTest.java   | 56 +++++++++++++++++++
 2 files changed, 56 insertions(+), 1 deletion(-)
 create mode 100644 paimon-common/src/test/java/org/apache/paimon/io/DataOutputSerializerTest.java

diff --git a/paimon-common/src/main/java/org/apache/paimon/io/DataOutputSerializer.java b/paimon-common/src/main/java/org/apache/paimon/io/DataOutputSerializer.java
index 33f2a8f0bf06..ee87cdbedbfc 100644
--- a/paimon-common/src/main/java/org/apache/paimon/io/DataOutputSerializer.java
+++ b/paimon-common/src/main/java/org/apache/paimon/io/DataOutputSerializer.java
@@ -153,7 +153,6 @@ public void writeBytes(String s) throws IOException {
         for (int i = 0; i < sLen; i++) {
             writeByte(s.charAt(i));
         }
-        this.position += sLen;
     }
 
     @Override
diff --git a/paimon-common/src/test/java/org/apache/paimon/io/DataOutputSerializerTest.java b/paimon-common/src/test/java/org/apache/paimon/io/DataOutputSerializerTest.java
new file mode 100644
index 000000000000..ac6d99573c16
--- /dev/null
+++ b/paimon-common/src/test/java/org/apache/paimon/io/DataOutputSerializerTest.java
@@ -0,0 +1,56 @@
+/*
+ * 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 org.apache.paimon.io;
+
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/** Test for {@link DataOutputSerializer}. */
+public class DataOutputSerializerTest {
+
+    @Test
+    public void testWriteBytesAdvancesPositionOnce() throws IOException {
+        DataOutputSerializer out = new DataOutputSerializer(16);
+        out.writeBytes("abc");
+
+        assertThat(out.length()).isEqualTo(3);
+        assertThat(out.getCopyOfBuffer()).containsExactly('a', 'b', 'c');
+    }
+
+    @Test
+    public void testWriteBytesLeavesTheNextWriteInPlace() throws IOException {
+        DataOutputSerializer out = new DataOutputSerializer(16);
+        out.writeBytes("abc");
+        out.writeInt(42);
+
+        // "abc" and then 42 as a big-endian int, with no gap of untouched bytes in between.
+        assertThat(out.getCopyOfBuffer()).containsExactly('a', 'b', 'c', 0, 0, 0, 42);
+    }
+
+    @Test
+    public void testWriteBytesAcrossAResize() throws IOException {
+        DataOutputSerializer out = new DataOutputSerializer(2);
+        out.writeBytes("abcdef");
+
+        assertThat(out.getCopyOfBuffer()).containsExactly('a', 'b', 'c', 'd', 'e', 'f');
+    }
+}