Offer restricted access to DataBuffer's ByteBuffer

This commit introduces DataBuffer::readableByteBuffers and
DataBuffer::writableByteBuffers, allowing restricted access to the
ByteBuffer used internally by DataBuffer implementations.

Closes gh-29943

spring-core/src/main/java/org/springframework/core/codec/ByteBufferDecoder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -51,9 +51,11 @@ public class ByteBufferDecoder extends AbstractDataBufferDecoder<ByteBuffer> {
 	public ByteBuffer decode(DataBuffer dataBuffer, ResolvableType elementType,
 			@Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {
 
-		ByteBuffer result = dataBuffer.toByteBuffer();
+		int len = dataBuffer.readableByteCount();
+		ByteBuffer result = ByteBuffer.allocate(len);
+		dataBuffer.toByteBuffer(result);
 		if (logger.isDebugEnabled()) {
-			logger.debug(Hints.getLogPrefix(hints) + "Read " + dataBuffer.readableByteCount() + " bytes");
+			logger.debug(Hints.getLogPrefix(hints) + "Read " + len + " bytes");
 		}
 		DataBufferUtils.release(dataBuffer);
 		return result;

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -16,14 +16,18 @@
 
 package org.springframework.core.io.buffer;
 
+import java.io.Closeable;
 import java.io.InputStream;
 import java.io.OutputStream;
+import java.io.UncheckedIOException;
 import java.nio.ByteBuffer;
 import java.nio.CharBuffer;
+import java.nio.charset.CharacterCodingException;
 import java.nio.charset.Charset;
 import java.nio.charset.CharsetEncoder;
 import java.nio.charset.CoderResult;
 import java.nio.charset.CodingErrorAction;
+import java.util.Iterator;
 import java.util.function.IntPredicate;
 
 import org.springframework.util.Assert;
@@ -265,27 +269,28 @@ public interface DataBuffer {
 			CharsetEncoder charsetEncoder = charset.newEncoder()
 					.onMalformedInput(CodingErrorAction.REPLACE)
 					.onUnmappableCharacter(CodingErrorAction.REPLACE);
-			CharBuffer inBuffer = CharBuffer.wrap(charSequence);
-			int estimatedSize = (int) (inBuffer.remaining() * charsetEncoder.averageBytesPerChar());
-			ByteBuffer outBuffer = ensureCapacity(estimatedSize)
-					.asByteBuffer(writePosition(), writableByteCount());
-			while (true) {
-				CoderResult cr = (inBuffer.hasRemaining() ?
-						charsetEncoder.encode(inBuffer, outBuffer, true) : CoderResult.UNDERFLOW);
-				if (cr.isUnderflow()) {
-					cr = charsetEncoder.flush(outBuffer);
+			CharBuffer src = CharBuffer.wrap(charSequence);
+			int length = (int) (src.remaining() * charsetEncoder.maxBytesPerChar());
+			ensureWritable(length);
+			try (ByteBufferIterator iterator = writableByteBuffers()) {
+				Assert.state(iterator.hasNext(), "No ByteBuffer available");
+				ByteBuffer dest = iterator.next();
+				int pos = dest.position();
+				CoderResult cr = charsetEncoder.encode(src, dest, true);
+				if (!cr.isUnderflow()) {
+					cr.throwException();
 				}
-				if (cr.isUnderflow()) {
-					break;
-				}
-				if (cr.isOverflow()) {
-					writePosition(writePosition() + outBuffer.position());
-					int maximumSize = (int) (inBuffer.remaining() * charsetEncoder.maxBytesPerChar());
-					ensureCapacity(maximumSize);
-					outBuffer = asByteBuffer(writePosition(), writableByteCount());
+				cr = charsetEncoder.flush(dest);
+				if (!cr.isUnderflow()) {
+					cr.throwException();
 				}
+				length = dest.position() - pos;
 			}
-			writePosition(writePosition() + outBuffer.position());
+			catch (CharacterCodingException ex) {
+				// should not happen, because the encoder uses action REPLACE
+				throw new UncheckedIOException(ex);
+			}
+			writePosition(writePosition() + length);
 		}
 		return this;
 	}
@@ -353,8 +358,8 @@ public interface DataBuffer {
 	 * changes in the returned buffer's {@linkplain ByteBuffer#position() position}
 	 * will not be reflected in the reading nor writing position of this data buffer.
 	 * @return this data buffer as a byte buffer
-	 * @deprecated as of 6.0, in favor of {@link #toByteBuffer()}, which does
-	 * <strong>not</strong> share data and returns a copy.
+	 * @deprecated as of 6.0, in favor of {@link #toByteBuffer(ByteBuffer)},
+	 * {@link #readableByteBuffers()}, or {@link #writableByteBuffers()}.
 	 */
 	@Deprecated(since = "6.0")
 	ByteBuffer asByteBuffer();
@@ -368,8 +373,8 @@ public interface DataBuffer {
 	 * @param length the length of the returned byte buffer
 	 * @return this data buffer as a byte buffer
 	 * @since 5.0.1
-	 * @deprecated as of 6.0, in favor of {@link #toByteBuffer(int, int)}, which
-	 * does <strong>not</strong> share data and returns a copy.
+	 * @deprecated as of 6.0, in favor of {@link #toByteBuffer(int, ByteBuffer, int, int)},
+	 * {@link #readableByteBuffers()}, or {@link #writableByteBuffers()}.
 	 */
 	@Deprecated(since = "6.0")
 	ByteBuffer asByteBuffer(int index, int length);
@@ -380,7 +385,11 @@ public interface DataBuffer {
 	 * <strong>not</strong> shared.
 	 * @return this data buffer as a byte buffer
 	 * @since 6.0
+	 * @see #readableByteBuffers()
+	 * @see #writableByteBuffers()
+	 * @deprecated as of 6.0.5, in favor of {@link #toByteBuffer(ByteBuffer)}
 	 */
+	@Deprecated(since = "6.0.5")
 	default ByteBuffer toByteBuffer() {
 		return toByteBuffer(readPosition(), readableByteCount());
 	}
@@ -391,9 +400,67 @@ public interface DataBuffer {
 	 * {@code ByteBuffer} is <strong>not</strong> shared.
 	 * @return this data buffer as a byte buffer
 	 * @since 6.0
+	 * @see #readableByteBuffers()
+	 * @see #writableByteBuffers()
+	 * @deprecated as of 6.0.5, in favor of
+	 * {@link #toByteBuffer(int, ByteBuffer, int, int)}
 	 */
+	@Deprecated(since = "6.0.5")
 	ByteBuffer toByteBuffer(int index, int length);
 
+	/**
+	 * Copies this entire data buffer into the given destination
+	 * {@code ByteBuffer}, beginning at the current
+	 * {@linkplain #readPosition() reading position}, and the current
+	 * {@linkplain ByteBuffer#position() position} of destination byte buffer.
+	 * @param dest the destination byte buffer
+	 * @since 6.0.5
+	 */
+	default void toByteBuffer(ByteBuffer dest) {
+		toByteBuffer(readPosition(), dest, dest.position(), readableByteCount());
+	}
+
+	/**
+	 * Copies the given length from this data buffer into the given destination
+	 * {@code ByteBuffer}, beginning at the given source position, and the
+	 * given destination position in the destination byte buffer.
+	 * @param srcPos the position of this data buffer from where copying should
+	 * start
+	 * @param dest the destination byte buffer
+	 * @param destPos the position in {@code dest} to where copying should
+	 * start
+	 * @param length the amount of data to copy
+	 * @since 6.0.5
+	 */
+	void toByteBuffer(int srcPos, ByteBuffer dest, int destPos, int length);
+
+	/**
+	 * Returns a closeable iterator over each {@link ByteBuffer} in this data
+	 * buffer that can be read. Calling this method is more efficient than
+	 * {@link #toByteBuffer()}, as no data is copied. However, the byte buffers
+	 * provided can only be used during the iteration.
+	 *
+	 * <p><b>Note</b> that the returned iterator must be used in a
+	 * try-with-resources clause or explicitly
+	 * {@linkplain ByteBufferIterator#close() closed}.
+	 * @return a closeable iterator over the readable byte buffers contained in this data buffer
+	 * @since 6.0.5
+	 */
+	ByteBufferIterator readableByteBuffers();
+
+	/**
+	 * Returns a closeable iterator over each {@link ByteBuffer} in this data
+	 * buffer that can be written to. The byte buffers provided can only be used
+	 * during the iteration.
+	 *
+	 * <p><b>Note</b> that the returned iterator must be used in a
+	 * try-with-resources clause or explicitly
+	 * {@linkplain ByteBufferIterator#close() closed}.
+	 * @return a closeable iterator over the writable byte buffers contained in this data buffer
+	 * @since 6.0.5
+	 */
+	ByteBufferIterator writableByteBuffers();
+
 	/**
 	 * Expose this buffer's data as an {@link InputStream}. Both data and read position are
 	 * shared between the returned stream and this data buffer. The underlying buffer will
@@ -450,4 +517,20 @@ public interface DataBuffer {
 	 */
 	String toString(int index, int length, Charset charset);
 
+
+	/**
+	 * A dedicated iterator type that ensures the lifecycle of iterated
+	 * {@link ByteBuffer} elements. This iterator must be used in a
+	 * try-with-resources clause or explicitly {@linkplain #close() closed}.
+	 *
+	 * @see DataBuffer#readableByteBuffers()
+	 * @see DataBuffer#writableByteBuffers()
+	 */
+	interface ByteBufferIterator extends Iterator<ByteBuffer>, Closeable {
+
+		@Override
+		void close();
+
+	}
+
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -906,13 +906,16 @@ public abstract class DataBufferUtils {
 
 		@Override
 		public void accept(SynchronousSink<DataBuffer> sink) {
-			ByteBuffer byteBuffer = this.dataBufferFactory.isDirect() ?
-					ByteBuffer.allocateDirect(this.bufferSize) :
-					ByteBuffer.allocate(this.bufferSize);
+			int read = -1;
+			DataBuffer dataBuffer = this.dataBufferFactory.allocateBuffer(this.bufferSize);
 			try {
-				if (this.channel.read(byteBuffer) >= 0) {
-					byteBuffer.flip();
-					DataBuffer dataBuffer = this.dataBufferFactory.wrap(byteBuffer);
+				try (DataBuffer.ByteBufferIterator iterator = dataBuffer.writableByteBuffers()) {
+					Assert.state(iterator.hasNext(), "No ByteBuffer available");
+					ByteBuffer byteBuffer = iterator.next();
+					read = this.channel.read(byteBuffer);
+				}
+				if (read >= 0) {
+					dataBuffer.writePosition(read);
 					sink.next(dataBuffer);
 				}
 				else {
@@ -922,11 +925,16 @@ public abstract class DataBufferUtils {
 			catch (IOException ex) {
 				sink.error(ex);
 			}
+			finally {
+				if (read == -1) {
+					release(dataBuffer);
+				}
+			}
 		}
 	}
 
 
-	private static class ReadCompletionHandler implements CompletionHandler<Integer, ByteBuffer> {
+	private static class ReadCompletionHandler implements CompletionHandler<Integer, ReadCompletionHandler.Attachment> {
 
 		private final AsynchronousFileChannel channel;
 
@@ -978,20 +986,27 @@ public abstract class DataBufferUtils {
 		}
 
 		private void read() {
-			ByteBuffer byteBuffer = this.dataBufferFactory.isDirect() ?
-					ByteBuffer.allocateDirect(this.bufferSize) :
-					ByteBuffer.allocate(this.bufferSize);
-			this.channel.read(byteBuffer, this.position.get(), byteBuffer, this);
+			DataBuffer dataBuffer = this.dataBufferFactory.allocateBuffer(this.bufferSize);
+			DataBuffer.ByteBufferIterator iterator = dataBuffer.writableByteBuffers();
+			Assert.state(iterator.hasNext(), "No ByteBuffer available");
+			ByteBuffer byteBuffer = iterator.next();
+			Attachment attachment = new Attachment(dataBuffer,  iterator);
+			this.channel.read(byteBuffer, this.position.get(), attachment, this);
 		}
 
 		@Override
-		public void completed(Integer read, ByteBuffer byteBuffer) {
+		public void completed(Integer read, Attachment attachment) {
+			attachment.iterator().close();
+			DataBuffer dataBuffer = attachment.dataBuffer();
+
 			if (this.state.get().equals(State.DISPOSED)) {
+				release(dataBuffer);
 				closeChannel(this.channel);
 				return;
 			}
 
 			if (read == -1) {
+				release(dataBuffer);
 				closeChannel(this.channel);
 				this.state.set(State.DISPOSED);
 				this.sink.complete();
@@ -999,9 +1014,7 @@ public abstract class DataBufferUtils {
 			}
 
 			this.position.addAndGet(read);
-
-			byteBuffer.flip();
-			DataBuffer dataBuffer = this.dataBufferFactory.wrap(byteBuffer);
+			dataBuffer.writePosition(read);
 			this.sink.next(dataBuffer);
 
 			// Stay in READING mode if there is demand
@@ -1017,7 +1030,10 @@ public abstract class DataBufferUtils {
 		}
 
 		@Override
-		public void failed(Throwable exc, ByteBuffer byteBuffer) {
+		public void failed(Throwable exc, Attachment attachment) {
+			attachment.iterator().close();
+			release(attachment.dataBuffer());
+
 			closeChannel(this.channel);
 			this.state.set(State.DISPOSED);
 			this.sink.error(exc);
@@ -1026,6 +1042,8 @@ public abstract class DataBufferUtils {
 		private enum State {
 			IDLE, READING, DISPOSED
 		}
+
+		private record Attachment(DataBuffer dataBuffer, DataBuffer.ByteBufferIterator iterator) {}
 	}
 
 
@@ -1048,9 +1066,11 @@ public abstract class DataBufferUtils {
 		@Override
 		protected void hookOnNext(DataBuffer dataBuffer) {
 			try {
-				ByteBuffer byteBuffer = dataBuffer.toByteBuffer();
-				while (byteBuffer.hasRemaining()) {
-					this.channel.write(byteBuffer);
+				try (DataBuffer.ByteBufferIterator iterator = dataBuffer.readableByteBuffers()) {
+					ByteBuffer byteBuffer = iterator.next();
+					while (byteBuffer.hasRemaining()) {
+						this.channel.write(byteBuffer);
+					}
 				}
 				this.sink.next(dataBuffer);
 				request(1);
@@ -1080,20 +1100,20 @@ public abstract class DataBufferUtils {
 
 
 	private static class WriteCompletionHandler extends BaseSubscriber<DataBuffer>
-			implements CompletionHandler<Integer, ByteBuffer> {
+			implements CompletionHandler<Integer, WriteCompletionHandler.Attachment> {
 
 		private final FluxSink<DataBuffer> sink;
 
 		private final AsynchronousFileChannel channel;
 
+		private final AtomicBoolean writing = new AtomicBoolean();
+
 		private final AtomicBoolean completed = new AtomicBoolean();
 
 		private final AtomicReference<Throwable> error = new AtomicReference<>();
 
 		private final AtomicLong position;
 
-		private final AtomicReference<DataBuffer> dataBuffer = new AtomicReference<>();
-
 		public WriteCompletionHandler(
 				FluxSink<DataBuffer> sink, AsynchronousFileChannel channel, long position) {
 
@@ -1108,19 +1128,22 @@ public abstract class DataBufferUtils {
 		}
 
 		@Override
-		protected void hookOnNext(DataBuffer value) {
-			if (!this.dataBuffer.compareAndSet(null, value)) {
-				throw new IllegalStateException();
+		protected void hookOnNext(DataBuffer dataBuffer) {
+			DataBuffer.ByteBufferIterator iterator = dataBuffer.readableByteBuffers();
+			if (iterator.hasNext()) {
+				ByteBuffer byteBuffer = iterator.next();
+				long pos = this.position.get();
+				Attachment attachment = new Attachment(byteBuffer, dataBuffer, iterator);
+				this.writing.set(true);
+				this.channel.write(byteBuffer, pos, attachment, this);
 			}
-			ByteBuffer byteBuffer = value.toByteBuffer();
-			this.channel.write(byteBuffer, this.position.get(), byteBuffer, this);
 		}
 
 		@Override
 		protected void hookOnError(Throwable throwable) {
 			this.error.set(throwable);
 
-			if (this.dataBuffer.get() == null) {
+			if (!this.writing.get()) {
 				this.sink.error(throwable);
 			}
 		}
@@ -1129,43 +1152,55 @@ public abstract class DataBufferUtils {
 		protected void hookOnComplete() {
 			this.completed.set(true);
 
-			if (this.dataBuffer.get() == null) {
+			if (!this.writing.get()) {
 				this.sink.complete();
 			}
 		}
 
 		@Override
-		public void completed(Integer written, ByteBuffer byteBuffer) {
-			long pos = this.position.addAndGet(written);
-			if (byteBuffer.hasRemaining()) {
-				this.channel.write(byteBuffer, pos, byteBuffer, this);
-				return;
-			}
-			sinkDataBuffer();
+		public void completed(Integer written, Attachment attachment) {
+			this.writing.set(false);
+			attachment.iterator().close();
 
-			Throwable throwable = this.error.get();
-			if (throwable != null) {
-				this.sink.error(throwable);
+			long pos = this.position.addAndGet(written);
+			ByteBuffer byteBuffer = attachment.byteBuffer();
+			DataBuffer.ByteBufferIterator iterator = attachment.iterator();
+			if (byteBuffer.hasRemaining()) {
+				this.writing.set(true);
+				this.channel.write(byteBuffer, pos, attachment, this);
 			}
-			else if (this.completed.get()) {
-				this.sink.complete();
+			else if (iterator.hasNext()) {
+				ByteBuffer next = iterator.next();
+				this.writing.set(true);
+				this.channel.write(next, pos, attachment, this);
 			}
 			else {
-				request(1);
+				sinkDataBuffer(attachment.dataBuffer());
+
+				Throwable throwable = this.error.get();
+				if (throwable != null) {
+					this.sink.error(throwable);
+				}
+				else if (this.completed.get()) {
+					this.sink.complete();
+				}
+				else {
+					request(1);
+				}
 			}
 		}
 
 		@Override
-		public void failed(Throwable exc, ByteBuffer byteBuffer) {
-			sinkDataBuffer();
+		public void failed(Throwable exc, Attachment attachment) {
+			this.writing.set(false);
+			attachment.iterator().close();
+
+			sinkDataBuffer(attachment.dataBuffer());
 			this.sink.error(exc);
 		}
 
-		private void sinkDataBuffer() {
-			DataBuffer dataBuffer = this.dataBuffer.get();
-			Assert.state(dataBuffer != null, "DataBuffer should not be null");
+		private void sinkDataBuffer(DataBuffer dataBuffer) {
 			this.sink.next(dataBuffer);
-			this.dataBuffer.set(null);
 		}
 
 		@Override
@@ -1173,6 +1208,10 @@ public abstract class DataBufferUtils {
 			return Context.of(this.sink.contextView());
 		}
 
+		private record Attachment(ByteBuffer byteBuffer, DataBuffer dataBuffer, DataBuffer.ByteBufferIterator iterator) {}
+
+
 	}
 
+
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -202,15 +202,37 @@ public class DataBufferWrapper implements DataBuffer {
 	}
 
 	@Override
+	@Deprecated
 	public ByteBuffer toByteBuffer() {
 		return this.delegate.toByteBuffer();
 	}
 
 	@Override
+	@Deprecated
 	public ByteBuffer toByteBuffer(int index, int length) {
 		return this.delegate.toByteBuffer(index, length);
 	}
 
+	@Override
+	public void toByteBuffer(ByteBuffer dest) {
+		this.delegate.toByteBuffer(dest);
+	}
+
+	@Override
+	public void toByteBuffer(int srcPos, ByteBuffer dest, int destPos, int length) {
+		this.delegate.toByteBuffer(srcPos, dest, destPos, length);
+	}
+
+	@Override
+	public ByteBufferIterator readableByteBuffers() {
+		return this.delegate.readableByteBuffers();
+	}
+
+	@Override
+	public ByteBufferIterator writableByteBuffers() {
+		return this.delegate.writableByteBuffers();
+	}
+
 	@Override
 	public InputStream asInputStream() {
 		return this.delegate.asInputStream();

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -19,6 +19,7 @@ package org.springframework.core.io.buffer;
 import java.nio.ByteBuffer;
 import java.nio.charset.Charset;
 import java.util.Arrays;
+import java.util.NoSuchElementException;
 import java.util.function.IntPredicate;
 
 import org.springframework.lang.Nullable;
@@ -304,9 +305,14 @@ public class DefaultDataBuffer implements DataBuffer {
 	}
 
 	@Override
-	public DefaultDataBuffer write(DataBuffer... buffers) {
-		if (!ObjectUtils.isEmpty(buffers)) {
-			write(Arrays.stream(buffers).map(DataBuffer::toByteBuffer).toArray(ByteBuffer[]::new));
+	public DefaultDataBuffer write(DataBuffer... dataBuffers) {
+		if (!ObjectUtils.isEmpty(dataBuffers)) {
+			ByteBuffer[] byteBuffers = new ByteBuffer[dataBuffers.length];
+			for (int i = 0; i < dataBuffers.length; i++) {
+				byteBuffers[i] = ByteBuffer.allocate(dataBuffers[i].readableByteCount());
+				dataBuffers[i].toByteBuffer(byteBuffers[i]);
+			}
+			write(byteBuffers);
 		}
 		return this;
 	}
@@ -388,6 +394,7 @@ public class DefaultDataBuffer implements DataBuffer {
 	}
 
 	@Override
+	@Deprecated
 	public ByteBuffer toByteBuffer(int index, int length) {
 		checkIndex(index, length);
 
@@ -398,6 +405,29 @@ public class DefaultDataBuffer implements DataBuffer {
 		return copy.flip();
 	}
 
+	@Override
+	public void toByteBuffer(int srcPos, ByteBuffer dest, int destPos, int length) {
+		checkIndex(srcPos, length);
+		Assert.notNull(dest, "Dest must not be null");
+
+		dest = dest.duplicate().clear();
+		dest.put(destPos, this.byteBuffer, srcPos, length);
+	}
+
+	@Override
+	public DataBuffer.ByteBufferIterator readableByteBuffers() {
+		ByteBuffer readOnly = this.byteBuffer.asReadOnlyBuffer();
+		readOnly.clear().position(this.readPosition).limit(this.writePosition - this.readPosition);
+		return new ByteBufferIterator(readOnly);
+	}
+
+	@Override
+	public DataBuffer.ByteBufferIterator writableByteBuffers() {
+		ByteBuffer duplicate = this.byteBuffer.duplicate();
+		duplicate.clear().position(this.writePosition).limit(this.capacity - this.writePosition);
+		return new ByteBufferIterator(duplicate);
+	}
+
 	@Override
 	public String toString(int index, int length, Charset charset) {
 		checkIndex(index, length);
@@ -512,4 +542,37 @@ public class DefaultDataBuffer implements DataBuffer {
 		}
 	}
 
+
+	private static final class ByteBufferIterator implements DataBuffer.ByteBufferIterator {
+
+		private final ByteBuffer buffer;
+
+		private boolean hasNext = true;
+
+
+		public ByteBufferIterator(ByteBuffer buffer) {
+			this.buffer = buffer;
+		}
+
+		@Override
+		public boolean hasNext() {
+			return this.hasNext;
+		}
+
+		@Override
+		public ByteBuffer next() {
+			if (!this.hasNext) {
+				throw new NoSuchElementException();
+			}
+			else {
+				this.hasNext = false;
+				return this.buffer;
+			}
+		}
+
+		@Override
+		public void close() {
+		}
+	}
+
 }

spring-core/src/main/java/org/springframework/core/io/buffer/Netty5DataBuffer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -18,11 +18,12 @@ package org.springframework.core.io.buffer;
 
 import java.nio.ByteBuffer;
 import java.nio.charset.Charset;
-import java.nio.charset.StandardCharsets;
+import java.util.NoSuchElementException;
 import java.util.function.IntPredicate;
 
 import io.netty5.buffer.Buffer;
-import io.netty5.util.AsciiString;
+import io.netty5.buffer.BufferComponent;
+import io.netty5.buffer.ComponentIterator;
 
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
@@ -188,20 +189,20 @@ public final class Netty5DataBuffer implements CloseableDataBuffer, TouchableDat
 	}
 
 	@Override
-	public Netty5DataBuffer write(DataBuffer... buffers) {
-		if (!ObjectUtils.isEmpty(buffers)) {
-			if (hasNetty5DataBuffers(buffers)) {
-				Buffer[] nativeBuffers = new Buffer[buffers.length];
-				for (int i = 0; i < buffers.length; i++) {
-					nativeBuffers[i] = ((Netty5DataBuffer) buffers[i]).getNativeBuffer();
+	public Netty5DataBuffer write(DataBuffer... dataBuffers) {
+		if (!ObjectUtils.isEmpty(dataBuffers)) {
+			if (hasNetty5DataBuffers(dataBuffers)) {
+				Buffer[] nativeBuffers = new Buffer[dataBuffers.length];
+				for (int i = 0; i < dataBuffers.length; i++) {
+					nativeBuffers[i] = ((Netty5DataBuffer) dataBuffers[i]).getNativeBuffer();
 				}
 				return write(nativeBuffers);
 			}
 			else {
-				ByteBuffer[] byteBuffers = new ByteBuffer[buffers.length];
-				for (int i = 0; i < buffers.length; i++) {
-					byteBuffers[i] = buffers[i].toByteBuffer();
-
+				ByteBuffer[] byteBuffers = new ByteBuffer[dataBuffers.length];
+				for (int i = 0; i < dataBuffers.length; i++) {
+					byteBuffers[i] = ByteBuffer.allocate(dataBuffers[i].readableByteCount());
+					dataBuffers[i].toByteBuffer(byteBuffers[i]);
 				}
 				return write(byteBuffers);
 			}
@@ -248,13 +249,7 @@ public final class Netty5DataBuffer implements CloseableDataBuffer, TouchableDat
 		Assert.notNull(charSequence, "CharSequence must not be null");
 		Assert.notNull(charset, "Charset must not be null");
 
-		if (StandardCharsets.US_ASCII.equals(charset) && charSequence instanceof AsciiString asciiString) {
-			this.buffer.writeBytes(asciiString.array(), asciiString.arrayOffset(), asciiString.length());
-		}
-		else {
-			byte[] bytes = charSequence.toString().getBytes(charset);
-			this.buffer.writeBytes(bytes);
-		}
+		this.buffer.writeCharSequence(charSequence, charset);
 		return this;
 	}
 
@@ -300,6 +295,21 @@ public final class Netty5DataBuffer implements CloseableDataBuffer, TouchableDat
 		return copy;
 	}
 
+	@Override
+	public void toByteBuffer(int srcPos, ByteBuffer dest, int destPos, int length) {
+		this.buffer.copyInto(srcPos, dest, destPos, length);
+	}
+
+	@Override
+	public ByteBufferIterator readableByteBuffers() {
+		return new BufferComponentIterator<>(this.buffer.forEachComponent(), true);
+	}
+
+	@Override
+	public ByteBufferIterator writableByteBuffers() {
+		return new BufferComponentIterator<>(this.buffer.forEachComponent(), false);
+	}
+
 	@Override
 	public String toString(Charset charset) {
 		Assert.notNull(charset, "Charset must not be null");
@@ -342,4 +352,53 @@ public final class Netty5DataBuffer implements CloseableDataBuffer, TouchableDat
 		return this.buffer.toString();
 	}
 
+
+	private static final class BufferComponentIterator<T extends BufferComponent & ComponentIterator.Next>
+			implements ByteBufferIterator {
+
+		private final ComponentIterator<T> delegate;
+
+		private final boolean readable;
+
+		@Nullable
+		private T next;
+
+
+		public BufferComponentIterator(ComponentIterator<T> delegate, boolean readable) {
+			Assert.notNull(delegate, "Delegate must not be null");
+			this.delegate = delegate;
+			this.readable = readable;
+			this.next = readable ? this.delegate.firstReadable() : this.delegate.firstWritable();
+		}
+
+		@Override
+		public boolean hasNext() {
+			return this.next != null;
+		}
+
+		@Override
+		public ByteBuffer next() {
+			if (this.next != null) {
+				ByteBuffer result;
+				if (this.readable) {
+					result = this.next.readableBuffer();
+					this.next = this.next.nextReadable();
+				}
+				else {
+					result = this.next.writableBuffer();
+					this.next = this.next.nextWritable();
+				}
+				return result;
+			}
+			else {
+				throw new NoSuchElementException();
+			}
+		}
+
+		@Override
+		public void close() {
+			this.delegate.close();
+		}
+	}
+
 }

spring-core/src/main/java/org/springframework/core/io/buffer/Netty5DataBufferFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -127,7 +127,9 @@ public class Netty5DataBufferFactory implements DataBufferFactory {
 			return netty5DataBuffer.getNativeBuffer();
 		}
 		else {
-			return DefaultBufferAllocators.preferredAllocator().copyOf(buffer.toByteBuffer());
+			ByteBuffer byteBuffer = ByteBuffer.allocate(buffer.readableByteCount());
+			buffer.toByteBuffer(byteBuffer);
+			return DefaultBufferAllocators.preferredAllocator().copyOf(byteBuffer);
 		}
 	}
 

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -19,6 +19,7 @@ package org.springframework.core.io.buffer;
 import java.nio.ByteBuffer;
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
+import java.util.NoSuchElementException;
 import java.util.function.IntPredicate;
 
 import io.netty.buffer.ByteBuf;
@@ -182,19 +183,20 @@ public class NettyDataBuffer implements PooledDataBuffer {
 	}
 
 	@Override
-	public NettyDataBuffer write(DataBuffer... buffers) {
-		if (!ObjectUtils.isEmpty(buffers)) {
-			if (hasNettyDataBuffers(buffers)) {
-				ByteBuf[] nativeBuffers = new ByteBuf[buffers.length];
-				for (int i = 0; i < buffers.length; i++) {
-					nativeBuffers[i] = ((NettyDataBuffer) buffers[i]).getNativeBuffer();
+	public NettyDataBuffer write(DataBuffer... dataBuffers) {
+		if (!ObjectUtils.isEmpty(dataBuffers)) {
+			if (hasNettyDataBuffers(dataBuffers)) {
+				ByteBuf[] nativeBuffers = new ByteBuf[dataBuffers.length];
+				for (int i = 0; i < dataBuffers.length; i++) {
+					nativeBuffers[i] = ((NettyDataBuffer) dataBuffers[i]).getNativeBuffer();
 				}
 				write(nativeBuffers);
 			}
 			else {
-				ByteBuffer[] byteBuffers = new ByteBuffer[buffers.length];
-				for (int i = 0; i < buffers.length; i++) {
-					byteBuffers[i] = buffers[i].toByteBuffer();
+				ByteBuffer[] byteBuffers = new ByteBuffer[dataBuffers.length];
+				for (int i = 0; i < dataBuffers.length; i++) {
+					byteBuffers[i] = ByteBuffer.allocate(dataBuffers[i].readableByteCount());
+					dataBuffers[i].toByteBuffer(byteBuffers[i]);
 				}
 				write(byteBuffers);
 			}
@@ -295,6 +297,7 @@ public class NettyDataBuffer implements PooledDataBuffer {
 	}
 
 	@Override
+	@Deprecated
 	public ByteBuffer toByteBuffer(int index, int length) {
 		ByteBuffer result = this.byteBuf.isDirect() ?
 				ByteBuffer.allocateDirect(length) :
@@ -305,6 +308,26 @@ public class NettyDataBuffer implements PooledDataBuffer {
 		return result.flip();
 	}
 
+	@Override
+	public void toByteBuffer(int srcPos, ByteBuffer dest, int destPos, int length) {
+		Assert.notNull(dest, "Dest must not be null");
+
+		dest = dest.duplicate().clear();
+		dest.put(destPos, this.byteBuf.nioBuffer(), srcPos, length);
+	}
+
+	@Override
+	public DataBuffer.ByteBufferIterator readableByteBuffers() {
+		ByteBuffer[] readable = this.byteBuf.nioBuffers(this.byteBuf.readerIndex(), this.byteBuf.readableBytes());
+		return new ByteBufferIterator(readable, true);
+	}
+
+	@Override
+	public DataBuffer.ByteBufferIterator writableByteBuffers() {
+		ByteBuffer[] writable = this.byteBuf.nioBuffers(this.byteBuf.writerIndex(), this.byteBuf.writableBytes());
+		return new ByteBufferIterator(writable, false);
+	}
+
 	@Override
 	public String toString(Charset charset) {
 		Assert.notNull(charset, "Charset must not be null");
@@ -355,4 +378,42 @@ public class NettyDataBuffer implements PooledDataBuffer {
 		return this.byteBuf.toString();
 	}
 
+
+	private static final class ByteBufferIterator implements DataBuffer.ByteBufferIterator {
+
+		private final ByteBuffer[] byteBuffers;
+
+		private final boolean readOnly;
+
+		private int cursor = 0;
+
+
+		public ByteBufferIterator(ByteBuffer[] byteBuffers, boolean readOnly) {
+			this.byteBuffers = byteBuffers;
+			this.readOnly = readOnly;
+		}
+
+		@Override
+		public boolean hasNext() {
+			return this.cursor < this.byteBuffers.length;
+		}
+
+		@Override
+		public ByteBuffer next() {
+			int index = this.cursor;
+			if (index < this.byteBuffers.length) {
+				this.cursor = index + 1;
+				ByteBuffer next = this.byteBuffers[index];
+				return this.readOnly ? next.asReadOnlyBuffer() : next;
+			}
+			else {
+				throw new NoSuchElementException();
+			}
+		}
+
+		@Override
+		public void close() {
+		}
+	}
+
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -122,17 +122,19 @@ public class NettyDataBufferFactory implements DataBufferFactory {
 	/**
 	 * Return the given Netty {@link DataBuffer} as a {@link ByteBuf}.
 	 * <p>Returns the {@linkplain NettyDataBuffer#getNativeBuffer() native buffer}
-	 * if {@code buffer} is a {@link NettyDataBuffer}; returns
+	 * if {@code dataBuffer} is a {@link NettyDataBuffer}; returns
 	 * {@link Unpooled#wrappedBuffer(ByteBuffer)} otherwise.
-	 * @param buffer the {@code DataBuffer} to return a {@code ByteBuf} for
+	 * @param dataBuffer the {@code DataBuffer} to return a {@code ByteBuf} for
 	 * @return the netty {@code ByteBuf}
 	 */
-	public static ByteBuf toByteBuf(DataBuffer buffer) {
-		if (buffer instanceof NettyDataBuffer nettyDataBuffer) {
+	public static ByteBuf toByteBuf(DataBuffer dataBuffer) {
+		if (dataBuffer instanceof NettyDataBuffer nettyDataBuffer) {
 			return nettyDataBuffer.getNativeBuffer();
 		}
 		else {
-			return Unpooled.wrappedBuffer(buffer.toByteBuffer());
+			ByteBuffer byteBuffer = ByteBuffer.allocate(dataBuffer.readableByteCount());
+			dataBuffer.toByteBuffer(byteBuffer);
+			return Unpooled.wrappedBuffer(byteBuffer);
 		}
 	}