diff --git a/src/main/java/com/corundumstudio/socketio/BroadcastOperations.java b/src/main/java/com/corundumstudio/socketio/BroadcastOperations.java
index 7866d991..bd9468ab 100644
--- a/src/main/java/com/corundumstudio/socketio/BroadcastOperations.java
+++ b/src/main/java/com/corundumstudio/socketio/BroadcastOperations.java
@@ -1,12 +1,12 @@
 /**
  * Copyright (c) 2012-2019 Nikita Koksharov
- *
+ * <p>
  * 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
- *
- *    http://www.apache.org/licenses/LICENSE-2.0
- *
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
  * 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.
@@ -21,12 +21,23 @@
 
 /**
  * broadcast interface
- *
  */
 public interface BroadcastOperations extends ClientOperations {
 
     Collection<SocketIOClient> getClients();
 
+    /**
+     * {@link Packet#attachments} needs to be filled when sending byte[].
+     * Using {@link io.netty.buffer.Unpooled#wrappedBuffer(byte[])} to
+     * fill byte[] into {@link Packet#attachments} is the recommended way.
+     * Before using {@link Packet#addAttachment(io.netty.buffer.ByteBuf)},
+     * be sure to initialize the number of attachments with
+     * {@link Packet#initAttachments(int)})}
+     *
+     * @param packet
+     * @param ackCallback
+     * @param <T>
+     */
     <T> void send(Packet packet, BroadcastAckCallback<T> ackCallback);
 
     void sendEvent(String name, SocketIOClient excludedClient, Object... data);
diff --git a/src/main/java/com/corundumstudio/socketio/ClientOperations.java b/src/main/java/com/corundumstudio/socketio/ClientOperations.java
index dc576608..79a9bb4b 100644
--- a/src/main/java/com/corundumstudio/socketio/ClientOperations.java
+++ b/src/main/java/com/corundumstudio/socketio/ClientOperations.java
@@ -27,6 +27,13 @@ public interface ClientOperations {
      * Send custom packet.
      * But {@link ClientOperations#sendEvent} method
      * usage is enough for most cases.
+     * If the Packet is sent by BroadcastOperations,
+     * {@link Packet#attachments} needs to be filled when sending byte[].
+     * Using {@link io.netty.buffer.Unpooled#wrappedBuffer(byte[])} to
+     * fill byte[] into {@link Packet#attachments} is the recommended way.
+     * Before using {@link Packet#addAttachment(io.netty.buffer.ByteBuf)},
+     * be sure to initialize the number of attachments with
+     * {@link Packet#initAttachments(int)})}
      *
      * @param packet - packet to send
      */
diff --git a/src/main/java/com/corundumstudio/socketio/SingleRoomBroadcastOperations.java b/src/main/java/com/corundumstudio/socketio/SingleRoomBroadcastOperations.java
index 8957c5df..6d5f6c17 100644
--- a/src/main/java/com/corundumstudio/socketio/SingleRoomBroadcastOperations.java
+++ b/src/main/java/com/corundumstudio/socketio/SingleRoomBroadcastOperations.java
@@ -1,12 +1,12 @@
 /**
  * Copyright (c) 2012-2019 Nikita Koksharov
- *
+ * <p>
  * 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
- *
- *    http://www.apache.org/licenses/LICENSE-2.0
- *
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
  * 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.
@@ -22,9 +22,14 @@
 import com.corundumstudio.socketio.store.StoreFactory;
 import com.corundumstudio.socketio.store.pubsub.DispatchMessage;
 import com.corundumstudio.socketio.store.pubsub.PubSubType;
+import io.netty.buffer.Unpooled;
+import org.springframework.lang.NonNull;
+import org.springframework.util.CollectionUtils;
 
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.List;
+import java.util.stream.Collectors;
 
 /**
  * Author: liangjiaqi
@@ -80,12 +85,15 @@ public void disconnect() {
     }
 
     @Override
-    public void sendEvent(String name, SocketIOClient excludedClient, Object... data) {
+    public void sendEvent(String name, SocketIOClient excludedClient, @NonNull Object... data) {
         Packet packet = new Packet(PacketType.MESSAGE, EngineIOVersion.UNKNOWN);
         packet.setSubType(PacketType.EVENT);
         packet.setName(name);
         packet.setData(Arrays.asList(data));
 
+        // handle byte[] data
+        handleBytes(packet, data);
+
         for (SocketIOClient client : clients) {
             packet.setEngineIOVersion(client.getEngineIOVersion());
             if (client.getSessionId().equals(excludedClient.getSessionId())) {
@@ -97,14 +105,31 @@ public void sendEvent(String name, SocketIOClient excludedClient, Object... data
     }
 
     @Override
-    public void sendEvent(String name, Object... data) {
+    public void sendEvent(String name, @NonNull Object... data) {
         Packet packet = new Packet(PacketType.MESSAGE, EngineIOVersion.UNKNOWN);
         packet.setSubType(PacketType.EVENT);
         packet.setName(name);
         packet.setData(Arrays.asList(data));
+
+        // handle byte[] data
+        handleBytes(packet, data);
+
         send(packet);
     }
 
+    private static void handleBytes(Packet packet, Object[] data) {
+        List<byte[]> bytes = Arrays.stream(data)
+                .filter(o -> o instanceof byte[])
+                .map(b -> (byte[]) b)
+                .filter(b -> b.length > 0)
+                .collect(Collectors.toList());
+
+        if (!CollectionUtils.isEmpty(bytes)) {
+            packet.initAttachments(bytes.size());
+            bytes.stream().peek(b -> packet.addAttachment(Unpooled.wrappedBuffer(b)));
+        }
+    }
+
     @Override
     public <T> void sendEvent(String name, Object data, BroadcastAckCallback<T> ackCallback) {
         for (SocketIOClient client : clients) {
diff --git a/src/main/java/com/corundumstudio/socketio/handler/EncoderHandler.java b/src/main/java/com/corundumstudio/socketio/handler/EncoderHandler.java
index b26ad866..5a1322e0 100644
--- a/src/main/java/com/corundumstudio/socketio/handler/EncoderHandler.java
+++ b/src/main/java/com/corundumstudio/socketio/handler/EncoderHandler.java
@@ -259,7 +259,7 @@ private void handleWebsocket(final OutPacketMessage msg, ChannelHandlerContext c
             for (ByteBuf buf : packet.getAttachments()) {
                 ByteBuf outBuf = encoder.allocateBuffer(ctx.alloc());
                 outBuf.writeByte(4);
-                outBuf.writeBytes(buf);
+                outBuf.writeBytes(buf, 0, buf.readableBytes());
                 if (log.isTraceEnabled()) {
                     log.trace("Out attachment: {} sessionId: {}", ByteBufUtil.hexDump(outBuf), msg.getSessionId());
                 }
diff --git a/src/main/java/com/corundumstudio/socketio/protocol/Packet.java b/src/main/java/com/corundumstudio/socketio/protocol/Packet.java
index dfc8a994..1609f5a9 100644
--- a/src/main/java/com/corundumstudio/socketio/protocol/Packet.java
+++ b/src/main/java/com/corundumstudio/socketio/protocol/Packet.java
@@ -15,6 +15,7 @@
  */
 package com.corundumstudio.socketio.protocol;
 
+import com.corundumstudio.socketio.namespace.Namespace;
 import io.netty.buffer.ByteBuf;
 
 import java.io.Serializable;
@@ -22,8 +23,6 @@
 import java.util.Collections;
 import java.util.List;
 
-import com.corundumstudio.socketio.namespace.Namespace;
-
 public class Packet implements Serializable {
 
     private static final long serialVersionUID = 4560159536486711426L;
@@ -71,9 +70,9 @@ public void setData(Object data) {
 
     /**
      * Get packet data
-     * 
+     *
      * @param <T> the type data
-     * 
+     *
      * <pre>
      * @return <b>json object</b> for PacketType.JSON type
      * <b>message</b> for PacketType.MESSAGE type
@@ -145,6 +144,16 @@ public void initAttachments(int attachmentsCount) {
         this.attachmentsCount = attachmentsCount;
         this.attachments = new ArrayList<ByteBuf>(attachmentsCount);
     }
+
+    /**
+     *
+     * It needs to be called when transferring the byte[].
+     * Recommended Use{@link io.netty.buffer.Unpooled#wrappedBuffer(byte[])}.
+     * Before using {@link #addAttachment(ByteBuf)},
+     * be sure to initialize the number of attachments with {@link #initAttachments(int)})}
+     *
+     * @param attachment
+     */
     public void addAttachment(ByteBuf attachment) {
         if (this.attachments.size() < attachmentsCount) {
             this.attachments.add(attachment);
diff --git a/src/main/java/com/corundumstudio/socketio/protocol/PacketEncoder.java b/src/main/java/com/corundumstudio/socketio/protocol/PacketEncoder.java
index 73a3fa15..ce40a686 100644
--- a/src/main/java/com/corundumstudio/socketio/protocol/PacketEncoder.java
+++ b/src/main/java/com/corundumstudio/socketio/protocol/PacketEncoder.java
@@ -15,7 +15,7 @@
  */
 package com.corundumstudio.socketio.protocol;
 
-import com.corundumstudio.socketio.handler.ClientHead;
+import com.corundumstudio.socketio.Configuration;
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.ByteBufAllocator;
 import io.netty.buffer.ByteBufOutputStream;
@@ -29,8 +29,6 @@
 import java.util.List;
 import java.util.Queue;
 
-import com.corundumstudio.socketio.Configuration;
-
 public class PacketEncoder {
 
     private static final byte[] BINARY_HEADER = "b4".getBytes(CharsetUtil.UTF_8);
@@ -254,18 +252,20 @@ public void encodePacket(Packet packet, ByteBuf buffer, ByteBufAllocator allocat
 
                     ByteBuf encBuf = null;
 
-                    if (packet.getSubType() == PacketType.ERROR) {
+                    PacketType subType = packet.getSubType();
+                    if (subType == PacketType.ERROR) {
                         encBuf = allocateBuffer(allocator);
 
                         ByteBufOutputStream out = new ByteBufOutputStream(encBuf);
                         jsonSupport.writeValue(out, packet.getData());
                     }
 
-                    if (packet.getSubType() == PacketType.EVENT
-                            || packet.getSubType() == PacketType.ACK) {
+                    PacketType tmpSubType = subType;
+                    if (subType == PacketType.EVENT
+                            || subType == PacketType.ACK) {
 
                         List<Object> values = new ArrayList<Object>();
-                        if (packet.getSubType() == PacketType.EVENT) {
+                        if (subType == PacketType.EVENT) {
                             values.add(packet.getName());
                         }
 
@@ -277,17 +277,22 @@ public void encodePacket(Packet packet, ByteBuf buffer, ByteBufAllocator allocat
                         jsonSupport.writeValue(out, values);
 
                         if (!jsonSupport.getArrays().isEmpty()) {
-                            packet.initAttachments(jsonSupport.getArrays().size());
-                            for (byte[] array : jsonSupport.getArrays()) {
-                                packet.addAttachment(Unpooled.wrappedBuffer(array));
+                            // If the Packet is sent by BroadcastOperations,
+                            // there is a problem of concurrent initialization for the same Packet.
+                            // Please initAttachment when creating the Packet to avoid this problem.
+                            if (!packet.hasAttachments()) {
+                                packet.initAttachments(jsonSupport.getArrays().size());
+                                for (byte[] array : jsonSupport.getArrays()) {
+                                    packet.addAttachment(Unpooled.wrappedBuffer(array));
+                                }
                             }
-                            packet.setSubType(packet.getSubType() == PacketType.ACK
+                            tmpSubType = (subType == PacketType.ACK
                                     ? PacketType.BINARY_ACK : PacketType.BINARY_EVENT);
                         }
                     }
 
-                    byte subType = toChar(packet.getSubType().getValue());
-                    buf.writeByte(subType);
+                    byte subTypeByte = toChar(tmpSubType.getValue());
+                    buf.writeByte(subTypeByte);
 
                     if (packet.hasAttachments()) {
                         byte[] ackId = toChars(packet.getAttachments().size());
@@ -295,7 +300,7 @@ public void encodePacket(Packet packet, ByteBuf buffer, ByteBufAllocator allocat
                         buf.writeByte('-');
                     }
 
-                    if (packet.getSubType() == PacketType.CONNECT) {
+                    if (subType == PacketType.CONNECT) {
                         if (!packet.getNsp().isEmpty()) {
                             buf.writeBytes(packet.getNsp().getBytes(CharsetUtil.UTF_8));
                         }