Fix position bug in NettyDataBuffer::toByteBuffer

Closes gh-31605

spring-core/src/main/java/org/springframework/core/io/buffer/NettyDataBuffer.java

@@ -313,7 +313,7 @@ public class NettyDataBuffer implements PooledDataBuffer {
 		Assert.notNull(dest, "Dest must not be null");
 
 		dest = dest.duplicate().clear();
-		dest.put(destPos, this.byteBuf.nioBuffer(), srcPos, length);
+		dest.put(destPos, this.byteBuf.nioBuffer(srcPos, length), 0, length);
 	}
 
 	@Override

spring-core/src/test/java/org/springframework/core/io/buffer/DataBufferTests.java

@@ -796,10 +796,6 @@ class DataBufferTests extends AbstractDataBufferAllocatingTests {
 		if (!(bufferFactory instanceof Netty5DataBufferFactory)) {
 			assertThat(result).isEqualTo(new byte[]{'b', 'c'});
 		}
-		else {
-			assertThat(result).isEqualTo(new byte[]{'b', 0});
-			release(slice);
-		}
 		release(buffer);
 	}
 
@@ -938,4 +934,15 @@ class DataBufferTests extends AbstractDataBufferAllocatingTests {
 		release(buffer);
 	}
 
+	@ParameterizedDataBufferAllocatingTest // gh-31605
+	void shouldHonorSourceBuffersReadPosition(DataBufferFactory bufferFactory) {
+		DataBuffer dataBuffer = bufferFactory.wrap("ab".getBytes(StandardCharsets.UTF_8));
+		dataBuffer.readPosition(1);
+
+		ByteBuffer byteBuffer = ByteBuffer.allocate(dataBuffer.readableByteCount());
+		dataBuffer.toByteBuffer(byteBuffer);
+
+		assertThat(StandardCharsets.UTF_8.decode(byteBuffer).toString()).isEqualTo("b");
+	}
+
 }