Fixed DataBufferUtils.join leak for error in source

This commit fixes an issue where DataBufferUtils.join() would not
release databuffers that preceded an error signal.

Issue: SPR-17025

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

@@ -32,6 +32,7 @@ import java.util.concurrent.Callable;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.function.Consumer;
+import java.util.function.IntPredicate;
 
 import org.reactivestreams.Publisher;
 import org.reactivestreams.Subscription;
@@ -473,6 +474,9 @@ public abstract class DataBufferUtils {
 	 * Depending on the {@link DataBuffer} implementation, the returned buffer may be a single
 	 * buffer containing all data of the provided buffers, or it may be a true composite that
 	 * contains references to the buffers.
+	 * <p>If {@code dataBuffers} contains an error signal, then all buffers that preceded the error
+	 * will be {@linkplain #release(DataBuffer) released}, and the error is stored in the
+	 * returned {@code Mono}.
 	 * @param dataBuffers the data buffers that are to be composed
 	 * @return a buffer that is composed from the {@code dataBuffers} argument
 	 * @since 5.0.3
@@ -481,14 +485,26 @@ public abstract class DataBufferUtils {
 		Assert.notNull(dataBuffers, "'dataBuffers' must not be null");
 
 		return Flux.from(dataBuffers)
+				.onErrorResume(DataBufferUtils::exceptionDataBuffer)
 				.collectList()
 				.filter(list -> !list.isEmpty())
-				.map(list -> {
+				.flatMap(list -> {
+					for (int i = 0; i < list.size(); i++) {
+						DataBuffer dataBuffer = list.get(i);
+						if (dataBuffer instanceof ExceptionDataBuffer) {
+							list.subList(0, i).forEach(DataBufferUtils::release);
+							return Mono.error(((ExceptionDataBuffer) dataBuffer).throwable());
+						}
+					}
 					DataBufferFactory bufferFactory = list.get(0).factory();
-					return bufferFactory.join(list);
+					return Mono.just(bufferFactory.join(list));
 				});
 	}
 
+	private static Mono<DataBuffer> exceptionDataBuffer(Throwable throwable) {
+		return Mono.just(new ExceptionDataBuffer(throwable));
+	}
+
 
 	private static class ReadableByteChannelGenerator implements Consumer<SynchronousSink<DataBuffer>> {
 
@@ -658,4 +674,153 @@ public abstract class DataBufferUtils {
 		}
 	}
 
+	/**
+	 * DataBuffer implementation that holds a {@link Throwable}, used in {@link #join(Publisher)}.
+	 */
+	private static final class ExceptionDataBuffer implements DataBuffer {
+
+		private final Throwable throwable;
+
+
+		public ExceptionDataBuffer(Throwable throwable) {
+			this.throwable = throwable;
+		}
+
+		public Throwable throwable() {
+			return this.throwable;
+		}
+
+		// Unsupported
+
+		@Override
+		public DataBufferFactory factory() {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public int indexOf(IntPredicate predicate, int fromIndex) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public int lastIndexOf(IntPredicate predicate, int fromIndex) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public int readableByteCount() {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public int writableByteCount() {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public int capacity() {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public DataBuffer capacity(int capacity) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public int readPosition() {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public DataBuffer readPosition(int readPosition) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public int writePosition() {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public DataBuffer writePosition(int writePosition) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public byte getByte(int index) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public byte read() {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public DataBuffer read(byte[] destination) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public DataBuffer read(byte[] destination, int offset, int length) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public DataBuffer write(byte b) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public DataBuffer write(byte[] source) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public DataBuffer write(byte[] source, int offset, int length) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public DataBuffer write(DataBuffer... buffers) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public DataBuffer write(ByteBuffer... buffers) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public DataBuffer slice(int index, int length) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public ByteBuffer asByteBuffer() {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public ByteBuffer asByteBuffer(int index, int length) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public InputStream asInputStream() {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public InputStream asInputStream(boolean releaseOnClose) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public OutputStream asOutputStream() {
+			throw new UnsupportedOperationException();
+		}
+	}
+
 }