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BytesInput.copy(BytesInput) should return a copy not a reference #3729

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BytesInput.copy(BytesInput) should return a copy not a reference #3729

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12 changes: 12 additions & 0 deletions parquet-column/src/test/java/org/apache/parquet/column/values/dictionary/TestDictionary.java
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Original file line number Diff line number Diff line change
Expand Up @@ -45,6 +45,7 @@
import org.apache.parquet.column.values.dictionary.DictionaryValuesWriter.PlainFloatDictionaryValuesWriter;
import org.apache.parquet.column.values.dictionary.DictionaryValuesWriter.PlainIntegerDictionaryValuesWriter;
import org.apache.parquet.column.values.dictionary.DictionaryValuesWriter.PlainLongDictionaryValuesWriter;
import org.apache.parquet.column.values.dictionary.PlainValuesDictionary.PlainBinaryDictionary;
import org.apache.parquet.column.values.dictionary.PlainValuesDictionary.PlainBooleanDictionary;
import org.apache.parquet.column.values.fallback.FallbackValuesWriter;
import org.apache.parquet.column.values.plain.BinaryPlainValuesReader;
Expand Down Expand Up @@ -803,6 +804,17 @@ public void testZeroValues() throws IOException {
}
}

@Test
public void testDictionaryPageCopyDoesNotAliasSourceBytes() throws IOException {
byte[] source = {1, 0, 0, 0, 'a'};
DictionaryPage copied = new DictionaryPage(BytesInput.from(source), 1, PLAIN).copy();

source[4] = 'b';

PlainBinaryDictionary dictionary = new PlainBinaryDictionary(copied);
assertThat(dictionary.decodeToBinary(0).toStringUsingUTF8()).isEqualTo("a");
}

@Test
public void testBooleanDictionary() throws IOException {
// Create a dictionary page with boolean values (false, true)
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9 changes: 0 additions & 9 deletions parquet-common/src/main/java/org/apache/parquet/bytes/BytesInput.java
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Expand Up @@ -690,18 +690,9 @@ public ByteBuffer toByteBuffer() throws IOException {
return java.nio.ByteBuffer.wrap(in, offset, length);
}

/**
* Zero-copy override: returns the backing array directly when fully used,
* skipping the base-class BAOS allocation + copy on every decompressor call.
* Returning the mutable array is safe — the base class already exposes a
* mutable {@code BAOS.getBuf()}.

@dossett dossett Aug 17, 2026

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I think Returning the mutable array is safe is the key. The array was mutable before, but it was a mutable copy of the original array.

*/
@SuppressWarnings("deprecation")
@Override
public byte[] toByteArray() {
if (offset == 0 && length == in.length) {
return in;
}
return Arrays.copyOfRange(in, offset, offset + length);
}

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8 changes: 4 additions & 4 deletions parquet-common/src/test/java/org/apache/parquet/bytes/TestBytesInput.java
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Expand Up @@ -123,16 +123,16 @@ public void testFromByteArray(ByteBufferAllocator innerAllocator) throws IOExcep

@ParameterizedTest(name = "{0}")
@MethodSource("parameters")
public void testFromByteArrayToByteArrayZeroCopy(ByteBufferAllocator innerAllocator) throws IOException {
public void testFromByteArrayToByteArrayCopiesFullArray(ByteBufferAllocator innerAllocator) throws IOException {
initAllocator(innerAllocator);
// Full array (offset=0, length=array.length): toByteArray() returns the backing array directly
byte[] data = new byte[1000];
RANDOM.nextBytes(data);
BytesInput bi = BytesInput.from(data, 0, data.length);
byte[] result = bi.toByteArray();
assertThat(result)
.as("toByteArray() should return the backing array when offset=0 and length=full")
.isSameAs(data);
.as("toByteArray() should materialize a copy when offset=0 and length=full")
.isEqualTo(data)
.isNotSameAs(data);
}

@ParameterizedTest(name = "{0}")
Expand Down