Fix #10261 stomp can be chunked, so implement StompWebSocketFrameEncoder (#10274)

Motivation:

Current implementation `StompSubframeEncoder` can encode `StompFrame` into several separate chunks or encode separately `StompHeadersSubframe` and `StompContentSubframe`. But some client libraries (e.g. stomp.js) do not support aggregation.

Modification:

Add StompWebSocketFrameEncoder for integration between origin stomp suframe encoder and `ContinuationWebSocketFrame` to support  chunks on transport level.

Result:

Fixes #10261

example/src/main/java/io/netty/example/stomp/websocket/StompWebSocketFrameEncoder.java

@@ -0,0 +1,68 @@
+/*
+ * Copyright 2020 The Netty Project
+ *
+ * The Netty Project licenses this file to you 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
+ *
+ * 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. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+package io.netty.example.stomp.websocket;
+
+import io.netty.buffer.ByteBuf;
+import io.netty.buffer.CompositeByteBuf;
+import io.netty.channel.ChannelHandlerContext;
+import io.netty.handler.codec.http.websocketx.ContinuationWebSocketFrame;
+import io.netty.handler.codec.http.websocketx.TextWebSocketFrame;
+import io.netty.handler.codec.http.websocketx.WebSocketFrame;
+import io.netty.handler.codec.stomp.LastStompContentSubframe;
+import io.netty.handler.codec.stomp.StompFrame;
+import io.netty.handler.codec.stomp.StompHeadersSubframe;
+import io.netty.handler.codec.stomp.StompSubframe;
+import io.netty.handler.codec.stomp.StompSubframeEncoder;
+
+import java.util.List;
+
+public class StompWebSocketFrameEncoder extends StompSubframeEncoder {
+
+    @Override
+    public void encode(ChannelHandlerContext ctx, StompSubframe msg, List<Object> out) throws Exception {
+        super.encode(ctx, msg, out);
+
+        if (out.isEmpty()) {
+            return;
+        }
+
+        final WebSocketFrame webSocketFrame;
+        if (msg instanceof StompFrame) {
+            if (out.size() == 1) {
+                webSocketFrame = new TextWebSocketFrame(getFirst(out));
+            } else {
+                CompositeByteBuf content = ctx.alloc().compositeBuffer(out.size());
+                for (Object byteBuf : out) {
+                    content.addComponent(true, (ByteBuf) byteBuf);
+                }
+                webSocketFrame = new TextWebSocketFrame(content);
+            }
+        } else if (msg instanceof StompHeadersSubframe) {
+            webSocketFrame = new TextWebSocketFrame(false, 0, getFirst(out));
+        } else if (msg instanceof LastStompContentSubframe) {
+            webSocketFrame = new ContinuationWebSocketFrame(true, 0, getFirst(out));
+        } else {
+            webSocketFrame = new ContinuationWebSocketFrame(false, 0, getFirst(out));
+        }
+
+        out.clear();
+        out.add(webSocketFrame);
+    }
+
+    private static ByteBuf getFirst(List<Object> container) {
+        return (ByteBuf) container.get(0);
+    }
+}

example/src/main/java/io/netty/example/stomp/websocket/StompWebSocketProtocolCodec.java

@@ -15,24 +15,25 @@
  */
 package io.netty.example.stomp.websocket;
 
-import io.netty.buffer.ByteBuf;
 import io.netty.channel.ChannelHandler.Sharable;
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.handler.codec.MessageToMessageCodec;
 import io.netty.handler.codec.http.websocketx.TextWebSocketFrame;
 import io.netty.handler.codec.http.websocketx.WebSocketFrame;
+import io.netty.handler.codec.http.websocketx.WebSocketFrameAggregator;
 import io.netty.handler.codec.http.websocketx.WebSocketServerProtocolHandler;
 import io.netty.handler.codec.http.websocketx.WebSocketServerProtocolHandler.HandshakeComplete;
+import io.netty.handler.codec.stomp.StompSubframe;
 import io.netty.handler.codec.stomp.StompSubframeAggregator;
 import io.netty.handler.codec.stomp.StompSubframeDecoder;
-import io.netty.handler.codec.stomp.StompSubframeEncoder;
 
 import java.util.List;
 
 @Sharable
-public class StompWebSocketProtocolCodec extends MessageToMessageCodec<WebSocketFrame, ByteBuf> {
+public class StompWebSocketProtocolCodec extends MessageToMessageCodec<WebSocketFrame, StompSubframe> {
 
     private final StompChatHandler stompChatHandler = new StompChatHandler();
+    private final StompWebSocketFrameEncoder stompWebSocketFrameEncoder = new StompWebSocketFrameEncoder();
 
     @Override
     public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
@@ -40,8 +41,8 @@ public class StompWebSocketProtocolCodec extends MessageToMessageCodec<WebSocket
             StompVersion stompVersion = StompVersion.findBySubProtocol(((HandshakeComplete) evt).selectedSubprotocol());
             ctx.channel().attr(StompVersion.CHANNEL_ATTRIBUTE_KEY).set(stompVersion);
             ctx.pipeline()
+               .addLast(new WebSocketFrameAggregator(65536))
                .addLast(new StompSubframeDecoder())
-               .addLast(new StompSubframeEncoder())
                .addLast(new StompSubframeAggregator(65536))
                .addLast(stompChatHandler)
                .remove(StompWebSocketClientPageHandler.INSTANCE);
@@ -51,8 +52,8 @@ public class StompWebSocketProtocolCodec extends MessageToMessageCodec<WebSocket
     }
 
     @Override
-    protected void encode(ChannelHandlerContext ctx, ByteBuf stompFrame, List<Object> out) {
+    protected void encode(ChannelHandlerContext ctx, StompSubframe stompFrame, List<Object> out) throws Exception {
-        out.add(new TextWebSocketFrame(stompFrame.retain()));
+        stompWebSocketFrameEncoder.encode(ctx, stompFrame, out);
     }
 
     @Override