Respect ByteBuffer position and limits in ByteUtils.getBytes(ByteBuffer).

We now properly extract the byte array from a ByteBuffer by copying its content respecting the read position and limits.

Closes #2204
Original Pull Request: #2213

src/test/java/org/springframework/data/redis/util/ByteUtilsUnitTests.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2021 the original author or authors.
+ *
+ * Licensed 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
+ *
+ *      https://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.springframework.data.redis.util;
+
+import static org.assertj.core.api.Assertions.*;
+
+import java.nio.ByteBuffer;
+import java.nio.charset.StandardCharsets;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for {@link ByteUtils}.
+ *
+ * @author Mark Paluch
+ */
+class ByteUtilsUnitTests {
+
+	@Test // GH-2204
+	void getBytesShouldUseCorrectHeapBufferSpace() {
+
+		ByteBuffer buffer = ByteBuffer.allocate(16);
+		buffer.put("hello".getBytes(StandardCharsets.US_ASCII));
+		buffer.flip();
+
+		byte[] bytes = ByteUtils.getBytes(buffer);
+
+		assertThat(bytes).hasSize(5);
+	}
+
+	@Test // GH-2204
+	void getBytesShouldUseCorrectDirectBufferSpace() {
+
+		ByteBuffer buffer = ByteBuffer.allocateDirect(16);
+		buffer.put("hello".getBytes(StandardCharsets.US_ASCII));
+		buffer.flip();
+
+		byte[] bytes = ByteUtils.getBytes(buffer);
+
+		assertThat(bytes).hasSize(5);
+	}
+}