Support ByteBuffer payload for basic.publish

pom.xml

@@ -784,6 +784,7 @@
             <includes>
               <include>src/main/java/com/rabbitmq/client/ConnectionFactory.java</include>
               <include>src/main/java/com/rabbitmq/client/PemReader.java</include>
+              <include>src/main/java/com/rabbitmq/client/WriteListener.java</include>
               <include>src/main/java/com/rabbitmq/client/impl/NettyFrameHandlerFactory.java</include>
               <include>src/main/java/com/rabbitmq/client/impl/Environment.java</include>
               <include>src/main/java/com/rabbitmq/client/observation/**/*.java</include>
@@ -797,6 +798,8 @@
               <include>src/test/java/com/rabbitmq/client/test/ProtocolVersionMismatch.java</include>
               <include>src/test/java/com/rabbitmq/client/test/TestUtils.java</include>
               <include>src/test/java/com/rabbitmq/client/test/RpcTopologyRecordingTest.java</include>
+              <include>src/test/java/com/rabbitmq/client/test/PublishWithByteBufferTest.java</include>
+              <include>src/test/java/com/rabbitmq/client/test/ByteBufferPublishTest.java</include>
             </includes>
             <googleJavaFormat>
               <version>${google-java-format.version}</version>

src/main/java/com/rabbitmq/client/Channel.java

@@ -19,6 +19,7 @@
 import com.rabbitmq.client.AMQP.*;
 
 import java.io.IOException;
+import java.nio.ByteBuffer;
 import java.util.Map;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.TimeoutException;
@@ -299,6 +300,48 @@ void basicPublish(String exchange, String routingKey, boolean mandatory, BasicPr
     void basicPublish(String exchange, String routingKey, boolean mandatory, boolean immediate, BasicProperties props, byte[] body)
             throws IOException;
 
+    /**
+     * Publish a message with a {@link ByteBuffer} body and a {@link WriteListener} for
+     * write completion notification.
+     *
+     * <p>The buffer's content between its current position and its limit will be sent.
+     *
+     * <p>The listener is called when the network layer has finished writing the body to the
+     * socket. This is useful for off-heap buffers that must be released after the write completes.
+     *
+     * <p>Using this method will only benefit workloads using off-heap {@link ByteBuffer}s and the Netty
+     * IO layer. Other workloads can stick to the basicPublish variants that use an array of bytes
+     * for message payloads.
+     *
+     * <p><strong>Threading:</strong> the listener may be called on the Netty event loop thread.
+     * It must not perform blocking operations.
+     *
+     * <p>This API is experimental and is susceptible to change at any time.
+     *
+     * @param exchange the exchange to publish the message to
+     * @param routingKey the routing key
+     * @param mandatory true if the 'mandatory' flag is to be set
+     * @param immediate true if the 'immediate' flag is to be
+     * set. Note that the RabbitMQ server does not support this flag.
+     * @param props other properties for the message - routing headers etc
+     * @param body the message body
+     * @param listener called when the write completes, may be {@code null}
+     * @throws java.io.IOException if an error is encountered
+     * @since 5.30.0
+     */
+    default void basicPublish(String exchange, String routingKey, boolean mandatory, boolean immediate, BasicProperties props, ByteBuffer body, WriteListener listener)
+            throws IOException {
+        byte[] bytes = null;
+        if (body != null) {
+            bytes = new byte[body.remaining()];
+            body.get(bytes);
+        }
+        basicPublish(exchange, routingKey, mandatory, immediate, props, bytes);
+        if (listener != null) {
+            listener.done(true, null);
+        }
+    }
+
     /**
      * Actively declare a non-autodelete, non-durable exchange with no extra arguments
      * @see com.rabbitmq.client.AMQP.Exchange.Declare

src/main/java/com/rabbitmq/client/WriteListener.java

@@ -0,0 +1,44 @@
+// Copyright (c) 2007-2026 Broadcom. All Rights Reserved.
+// The term "Broadcom" refers to Broadcom Inc. and/or its subsidiaries.
+//
+// This software, the RabbitMQ Java client library, is triple-licensed under the
+// Mozilla Public License 2.0 ("MPL"), the GNU General Public License version 2
+// ("GPL") and the Apache License version 2 ("ASL"). For the MPL, please see
+// LICENSE-MPL-RabbitMQ. For the GPL, please see LICENSE-GPL2.  For the ASL,
+// please see LICENSE-APACHE2.
+//
+// This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND,
+// either express or implied. See the LICENSE file for specific language governing
+// rights and limitations of this software.
+//
+// If you have any questions regarding licensing, please contact us at
+// info@rabbitmq.com.
+package com.rabbitmq.client;
+
+/**
+ * Listener notified when the network layer has finished writing a message body.
+ *
+ * <p>This is primarily useful when publishing with an off-heap {@link java.nio.ByteBuffer}: the
+ * callback tells the caller when the buffer is no longer in use and can be safely released.
+ *
+ * <p>This only applies when using Netty as the IO layer and is unnecessary when using the blocking
+ * IO layer.
+ *
+ * <p><strong>Threading:</strong> the callback may be invoked on the Netty event loop thread.
+ * Implementations must not perform blocking operations.
+ *
+ * <p>This API is experimental and is susceptible to change at any time.
+ *
+ * @since 5.30.0
+ */
+@FunctionalInterface
+public interface WriteListener {
+
+  /**
+   * Called when the write operation completes.
+   *
+   * @param success {@code true} if the data was written to the socket successfully
+   * @param cause the exception if the write failed, {@code null} on success
+   */
+  void done(boolean success, Throwable cause);
+}

src/main/java/com/rabbitmq/client/impl/AMQCommand.java

@@ -18,11 +18,13 @@
 import java.io.ByteArrayOutputStream;
 import java.io.DataOutputStream;
 import java.io.IOException;
+import java.nio.ByteBuffer;
 import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
 
 import com.rabbitmq.client.AMQP;
 import com.rabbitmq.client.Command;
+import com.rabbitmq.client.WriteListener;
 
 /**
  * AMQP 0-9-1-specific implementation of {@link Command} which accumulates
@@ -46,44 +48,49 @@ public class AMQCommand implements Command {
     /** The assembler for this command - synchronised on - contains all the state */
     private final CommandAssembler assembler;
     private final Lock assemblerLock = new ReentrantLock();
+    private final WriteListener writeListener;
 
+    /** Construct a command for inbound frame assembly with a max body length. */
     AMQCommand(int maxBodyLength) {
-        this(null, null, null, maxBodyLength);
+        this.assembler = new CommandAssembler(null, null, maxBodyLength);
+        this.writeListener = null;
     }
 
-    /** Construct a command ready to fill in by reading frames */
+    /** Construct a command ready to fill in by reading frames. */
     public AMQCommand() {
-        this(null, null, null, Integer.MAX_VALUE);
+        this(Integer.MAX_VALUE);
     }
 
     /**
      * Construct a command with just a method, and without header or body.
      * @param method the wrapped method
      */
     public AMQCommand(com.rabbitmq.client.Method method) {
-        this(method, null, null, Integer.MAX_VALUE);
+        this.assembler = new CommandAssembler((Method) method, null, Integer.MAX_VALUE);
+        this.writeListener = null;
     }
 
     /**
-     * Construct a command with a specified method, header and body.
+     * Construct a command with a ByteBuffer body for transmission.
      * @param method the wrapped method
      * @param contentHeader the wrapped content header
-     * @param body the message body data
+     * @param body the message body as a ByteBuffer
      */
-    public AMQCommand(com.rabbitmq.client.Method method, AMQContentHeader contentHeader, byte[] body) {
-        this.assembler = new CommandAssembler((Method) method, contentHeader, body, Integer.MAX_VALUE);
+    public AMQCommand(com.rabbitmq.client.Method method, AMQContentHeader contentHeader, ByteBuffer body) {
+        this(method, contentHeader, body, null);
     }
 
     /**
-     * Construct a command with a specified method, header and body.
+     * Construct a command with a ByteBuffer body and a write completion listener.
      * @param method the wrapped method
      * @param contentHeader the wrapped content header
-     * @param body the message body data
-     * @param maxBodyLength the maximum size for an inbound message body
+     * @param body the message body as a ByteBuffer
+     * @param writeListener called when the network layer finishes writing, may be {@code null}
      */
-    public AMQCommand(com.rabbitmq.client.Method method, AMQContentHeader contentHeader, byte[] body,
-                      int maxBodyLength) {
-        this.assembler = new CommandAssembler((Method) method, contentHeader, body, maxBodyLength);
+    public AMQCommand(com.rabbitmq.client.Method method, AMQContentHeader contentHeader, ByteBuffer body,
+                      WriteListener writeListener) {
+        this.assembler = new CommandAssembler((Method) method, contentHeader, body);
+        this.writeListener = writeListener;
     }
 
     /** Public API - {@inheritDoc} */
@@ -122,13 +129,13 @@ public void transmit(AMQChannel channel) throws IOException {
         try {
             Method m = this.assembler.getMethod();
             if (m.hasContent()) {
-                byte[] body = this.assembler.getContentBody();
-
-                Frame headerFrame = this.assembler.getContentHeader().toFrame(channelNumber, body.length);
+                ByteBuffer body = this.assembler.getByteBufferBody();
+                int bodySize = body == null ? 0 : body.remaining();
+                Frame headerFrame = this.assembler.getContentHeader().toFrame(channelNumber, bodySize);
 
                 int frameMax = connection.getFrameMax();
                 boolean cappedFrameMax = frameMax > 0;
-                int bodyPayloadMax = cappedFrameMax ? frameMax - EMPTY_FRAME_SIZE : body.length;
+                int bodyPayloadMax = cappedFrameMax ? frameMax - EMPTY_FRAME_SIZE : bodySize;
 
                 if (cappedFrameMax && headerFrame.size() > frameMax) {
                     String msg = String.format("Content headers exceeded max frame size: %d > %d", headerFrame.size(), frameMax);
@@ -137,14 +144,14 @@ public void transmit(AMQChannel channel) throws IOException {
                 connection.writeFrame(m.toFrame(channelNumber));
                 connection.writeFrame(headerFrame);
 
-                for (int offset = 0; offset < body.length; offset += bodyPayloadMax) {
-                    int remaining = body.length - offset;
-
-                    int fragmentLength = (remaining < bodyPayloadMax) ? remaining
-                            : bodyPayloadMax;
-                    Frame frame = Frame.fromBodyFragment(channelNumber, body,
-                            offset, fragmentLength);
-                    connection.writeFrame(frame);
+                if (body != null) {
+                    int bodyPosition = body.position();
+                    for (int offset = 0; offset < bodySize; offset += bodyPayloadMax) {
+                        int remaining = bodySize - offset;
+                        int fragmentLength = (remaining < bodyPayloadMax) ? remaining : bodyPayloadMax;
+                        Frame frame = Frame.fromBodyFragment(channelNumber, body, bodyPosition + offset, fragmentLength);
+                        connection.writeFrame(frame);
+                    }
                 }
             } else {
                 connection.writeFrame(m.toFrame(channelNumber));
@@ -153,7 +160,7 @@ public void transmit(AMQChannel channel) throws IOException {
             assemblerLock.unlock();
         }
 
-        connection.flush();
+        connection.flush(this.writeListener);
     }
 
     @Override public String toString() {
@@ -200,7 +207,7 @@ public static void checkPreconditions() {
      * code in Frame.
      */
     private static void checkEmptyFrameSize() {
-        Frame f = new Frame(AMQP.FRAME_BODY, 0, new byte[0]);
+        Frame f = new Frame(AMQP.FRAME_BODY, 0, ByteBuffer.wrap(new byte[0]));
         ByteArrayOutputStream s = new ByteArrayOutputStream();
         try {
             f.writeTo(new DataOutputStream(s));

src/main/java/com/rabbitmq/client/impl/AMQConnection.java

@@ -655,8 +655,12 @@ void writeFrame(Frame f) throws IOException {
      * Public API - flush the output buffers
      */
     public void flush() throws IOException {
+        flush(null);
+    }
+
+    void flush(WriteListener listener) throws IOException {
         try {
-            _frameHandler.flush();
+            _frameHandler.flush(listener);
         } catch (IOException ioe) {
             this.errorOnWriteListener.handle(this, ioe);
         }

src/main/java/com/rabbitmq/client/impl/ChannelN.java

@@ -28,6 +28,7 @@
 import org.slf4j.LoggerFactory;
 
 import java.io.IOException;
+import java.nio.ByteBuffer;
 import java.util.*;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.CopyOnWriteArrayList;
@@ -714,6 +715,18 @@ public void basicPublish(String exchange, String routingKey,
                              boolean mandatory, boolean immediate,
                              BasicProperties props, byte[] body)
         throws IOException
+    {
+        basicPublish(exchange, routingKey, mandatory, immediate, props,
+                body == null ? null : ByteBuffer.wrap(body), null);
+    }
+
+    /** Public API - {@inheritDoc} */
+    @Override
+    public void basicPublish(String exchange, String routingKey,
+                             boolean mandatory, boolean immediate,
+                             BasicProperties props, ByteBuffer body,
+                             WriteListener listener)
+        throws IOException
     {
         final long deliveryTag;
         if (nextPublishSeqNo > 0) {
@@ -734,7 +747,7 @@ public void basicPublish(String exchange, String routingKey,
                 .build();
         try {
             ObservationCollector.PublishCall publishCall = properties -> {
-                AMQCommand command = new AMQCommand(publish, properties, body);
+                AMQCommand command = new AMQCommand(publish, properties, body, listener);
                 transmit(command);
             };
             observationCollector.publish(publishCall, publish, props, body, this.connectionInfo());

src/main/java/com/rabbitmq/client/impl/CommandAssembler.java

@@ -16,6 +16,7 @@
 package com.rabbitmq.client.impl;
 
 import java.io.IOException;
+import java.nio.ByteBuffer;
 import java.util.ArrayList;
 import java.util.List;
 
@@ -50,20 +51,41 @@ private enum CAState {
     /** sum of the lengths of all fragments */
     private int bodyLength;
 
+    /** Zero-copy body buffer, mutually exclusive with bodyN usage on the outbound path */
+    private final ByteBuffer byteBufferBody;
+
     /** No bytes of content body not yet accumulated */
     private long remainingBodyBytes;
 
     private final int maxBodyLength;
 
-    public CommandAssembler(Method method, AMQContentHeader contentHeader, byte[] body,
+    public CommandAssembler(Method method, AMQContentHeader contentHeader,
                             int maxBodyLength) {
         this.method = method;
         this.contentHeader = contentHeader;
         this.bodyN = new ArrayList<>(2);
         this.bodyLength = 0;
+        this.byteBufferBody = null;
         this.remainingBodyBytes = 0;
         this.maxBodyLength = maxBodyLength;
-        appendBodyFragment(body);
+        if (method == null) {
+            this.state = CAState.EXPECTING_METHOD;
+        } else if (contentHeader == null) {
+            this.state = method.hasContent() ? CAState.EXPECTING_CONTENT_HEADER : CAState.COMPLETE;
+        } else {
+            this.remainingBodyBytes = contentHeader.getBodySize() - this.bodyLength;
+            updateContentBodyState();
+        }
+    }
+
+    public CommandAssembler(Method method, AMQContentHeader contentHeader, ByteBuffer body) {
+        this.method = method;
+        this.contentHeader = contentHeader;
+        this.bodyN = new ArrayList<>(0);
+        this.bodyLength = body == null ? 0 : body.remaining();
+        this.byteBufferBody = body;
+        this.remainingBodyBytes = 0;
+        this.maxBodyLength = Integer.MAX_VALUE;
         if (method == null) {
             this.state = CAState.EXPECTING_METHOD;
         } else if (contentHeader == null) {
@@ -151,9 +173,19 @@ private byte[] coalesceContentBody() {
     }
 
     public synchronized byte[] getContentBody() {
+        if (byteBufferBody != null) {
+            ByteBuffer dup = byteBufferBody.duplicate();
+            byte[] result = new byte[dup.remaining()];
+            dup.get(result);
+            return result;
+        }
         return coalesceContentBody();
     }
 
+    public ByteBuffer getByteBufferBody() {
+        return this.byteBufferBody;
+    }
+
     private void appendBodyFragment(byte[] fragment) {
         if (fragment == null || fragment.length == 0) return;
         bodyN.add(fragment);

src/main/java/com/rabbitmq/client/impl/DefaultHeartbeatSender.java

@@ -137,7 +137,7 @@ public void run() {
 
                 if (now > (lastActivityTime + this.heartbeatNanos)) {
                     frameHandler.writeFrame(new Frame(AMQP.FRAME_HEARTBEAT, 0));
-                    frameHandler.flush();
+                    frameHandler.flush(null);
                 }
             } catch (IOException e) {
                 // ignore