[ISSUE #7757] Use CompositeByteBuf to prevent memory copy. (#7694)

* Use CompositeByteBuf to prevent mem_copy.

* Fix code

* Add tests

* Remove useless UTs

* Remove unused imports.

---------

Co-authored-by: RongtongJin <jinrongtong16@mails.ucas.ac.cn>

remoting/src/main/java/org/apache/rocketmq/remoting/netty/FileRegionEncoder.java

@@ -18,6 +18,9 @@
 package org.apache.rocketmq.remoting.netty;
 
 import io.netty.buffer.ByteBuf;
+import io.netty.buffer.ByteBufAllocator;
+import io.netty.buffer.CompositeByteBuf;
+import io.netty.buffer.Unpooled;
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.channel.FileRegion;
 import io.netty.handler.codec.MessageToByteEncoder;
@@ -51,9 +54,12 @@ public class FileRegionEncoder extends MessageToByteEncoder<FileRegion> {
         WritableByteChannel writableByteChannel = new WritableByteChannel() {
             @Override
             public int write(ByteBuffer src) {
-                int prev = out.writerIndex();
-                out.writeBytes(src);
-                return out.writerIndex() - prev;
+                // To prevent mem_copy.
+                CompositeByteBuf b = (CompositeByteBuf) out;
+                // Have to increase writerIndex manually.
+                ByteBuf unpooled = Unpooled.wrappedBuffer(src);
+                b.addComponent(true, unpooled);
+                return unpooled.readableBytes();
             }
 
             @Override
@@ -76,4 +82,10 @@ public class FileRegionEncoder extends MessageToByteEncoder<FileRegion> {
             msg.transferTo(writableByteChannel, transferred);
         }
     }
-}
+
+    @Override
+    protected ByteBuf allocateBuffer(ChannelHandlerContext ctx, FileRegion msg, boolean preferDirect) throws Exception {
+        ByteBufAllocator allocator = ctx.alloc();
+        return preferDirect ? allocator.compositeDirectBuffer() : allocator.compositeHeapBuffer();
+    }
+}

remoting/src/test/java/org/apache/rocketmq/remoting/netty/FileRegionEncoderTest.java

@@ -21,14 +21,15 @@ import io.netty.buffer.ByteBuf;
 import io.netty.channel.DefaultFileRegion;
 import io.netty.channel.FileRegion;
 import io.netty.channel.embedded.EmbeddedChannel;
+import org.junit.Assert;
+import org.junit.Test;
+
 import java.io.BufferedOutputStream;
 import java.io.File;
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.util.Random;
 import java.util.UUID;
-import org.junit.Assert;
-import org.junit.Test;
 
 public class FileRegionEncoderTest {