[GitHub] [flink] gaoyunhaii commented on a change in pull request #7368: [FLINK-10742][network] Let Netty use Flink's buffers directly in credit-based mode

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gaoyunhaii commented on a change in pull request #7368: [FLINK-10742][network] 
Let Netty use Flink's buffers directly in credit-based mode
URL: https://github.com/apache/flink/pull/7368#discussion_r380292049
 
 

 ##########
 File path: 
flink-runtime/src/main/java/org/apache/flink/runtime/io/network/netty/NettyMessageParser.java
 ##########
 @@ -0,0 +1,84 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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 org.apache.flink.runtime.io.network.netty;
+
+import org.apache.flink.shaded.netty4.io.netty.buffer.ByteBuf;
+import org.apache.flink.shaded.netty4.io.netty.buffer.ByteBufAllocator;
+
+import javax.annotation.Nullable;
+
+/**
+ * Parsers for specified netty messages.
+ */
+public interface NettyMessageParser {
+
+       /**
+        * The result of message parsing with the provided data.
+        */
+       class ParseResult {
+               private final static ParseResult NOT_FINISHED = new 
ParseResult(false, null);
+
+               static ParseResult notFinished() {
+                       return NOT_FINISHED;
+               }
+
+               static ParseResult finishedWith(@Nullable NettyMessage message) 
{
+                       return new ParseResult(true, message);
+               }
+
+               final boolean finished;
+
+               @Nullable
+               final NettyMessage message;
+
+               private ParseResult(boolean finished, NettyMessage message) {
+                       this.finished = finished;
+                       this.message = message;
+               }
+       }
+
+       /**
+        * Notifies the underlying channel become active.
+        *
+        * @param alloc The netty buffer allocator.
+        */
+       void onChannelActive(ByteBufAllocator alloc);
+
+       /**
+        * Notifies a new message is to be parsed.
+        *
+        * @param msgId The type of the message to be parsed.
+        * @param messageLength The length of the message to be parsed.
+        */
+       void startParsingMessage(int msgId, int messageLength);
 
 Review comment:
   I tried to remove the `startParsingMessage` but I found some problem: the 
logic of the `onChannelRead` method has been complicated since it has carefully 
manage the state and find suitable place to clear the state for new message. 
   
   The logic of `NonBufferResponseDecoderDelegate` would be as following after 
changing:
   
   <pre>
   @Override
   public ParseResult onChannelRead(ByteBuf data, int msgId, int messageLength) 
throws Exception {
        if (messageCumulationBuffer.writerIndex() == 0 && 
messageCumulationBuffer.capacity() < messageLength) {
                messageCumulationBuffer.capacity(messageLength);
        }
   
        ByteBuf toDecode = ByteBufUtils.cumulate(messageCumulationBuffer, data, 
messageLength);
   
        if (toDecode == null) {
                return ParseResult.notFinished();
        }
   
        NettyMessage message;
        switch (msgId) {
                case NettyMessage.ErrorResponse.ID:
                        message = NettyMessage.ErrorResponse.readFrom(toDecode);
                        break;
                default:
                        throw new ProtocolException("Received unknown message 
from producer: " + msgId);
        }
   
        messageCumulationBuffer.clear();
   
        return ParseResult.finishedWith(message);
   }
   </pre>
   
   And for `BufferResponseDecoderDelegate`, the situation get worse since it 
has multiple `return` statement. Before each `return` statement it has to clear 
state for processing the next message. 
   
   With `startParsingMessage` notification we will be able to reset the state 
uniformly.

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