From 35c7f66c4805427fa7c779d789a0cd225c55eebf Mon Sep 17 00:00:00 2001
From: Norman Maurer <nmaurer@redhat.com>
Date: Mon, 23 Jun 2014 07:01:05 +0200
Subject: [PATCH] MessageToByteEncoder always starts with ByteBuf that use
 initalCapacity == 0

Motivation:

MessageToByteEncoder always starts with ByteBuf that use initalCapacity == 0 when preferDirect is used. This is really wasteful in terms of performance as every first write into the buffer will cause an expand of the buffer itself.

Modifications:

 - Change ByteBufAllocator.ioBuffer() use the same default initialCapacity as heapBuffer() and directBuffer()
 - Add new allocateBuffer method to MessageToByteEncoder that allow the user to do some smarter allocation based on the message that will be encoded.

Result:

Less expanding of buffer and more flexibilty when allocate the buffer for encoding.
---
 .../buffer/AbstractByteBufAllocator.java      |  4 ++--
 .../io/netty/buffer/ByteBufAllocator.java     |  2 +-
 .../handler/codec/MessageToByteEncoder.java   | 19 ++++++++++++++-----
 3 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/buffer/src/main/java/io/netty/buffer/AbstractByteBufAllocator.java b/buffer/src/main/java/io/netty/buffer/AbstractByteBufAllocator.java
index e94d2e51d0..7eda9d97bb 100644
--- a/buffer/src/main/java/io/netty/buffer/AbstractByteBufAllocator.java
+++ b/buffer/src/main/java/io/netty/buffer/AbstractByteBufAllocator.java
@@ -96,9 +96,9 @@ public abstract class AbstractByteBufAllocator implements ByteBufAllocator {
     @Override
     public ByteBuf ioBuffer() {
         if (PlatformDependent.hasUnsafe()) {
-            return directBuffer(0);
+            return directBuffer(DEFAULT_INITIAL_CAPACITY);
         }
-        return heapBuffer(0);
+        return heapBuffer(DEFAULT_INITIAL_CAPACITY);
     }
 
     @Override
diff --git a/buffer/src/main/java/io/netty/buffer/ByteBufAllocator.java b/buffer/src/main/java/io/netty/buffer/ByteBufAllocator.java
index 9c33af88d8..c30d962046 100644
--- a/buffer/src/main/java/io/netty/buffer/ByteBufAllocator.java
+++ b/buffer/src/main/java/io/netty/buffer/ByteBufAllocator.java
@@ -43,7 +43,7 @@ public interface ByteBufAllocator {
     ByteBuf buffer(int initialCapacity, int maxCapacity);
 
     /**
-     * Allocate a {@link ByteBuf} whose initial capacity is 0, preferably a direct buffer which is suitable for I/O.
+     * Allocate a {@link ByteBuf}, preferably a direct buffer which is suitable for I/O.
      */
     ByteBuf ioBuffer();
 
diff --git a/codec/src/main/java/io/netty/handler/codec/MessageToByteEncoder.java b/codec/src/main/java/io/netty/handler/codec/MessageToByteEncoder.java
index 3cf0719215..1dbbb94998 100644
--- a/codec/src/main/java/io/netty/handler/codec/MessageToByteEncoder.java
+++ b/codec/src/main/java/io/netty/handler/codec/MessageToByteEncoder.java
@@ -102,11 +102,7 @@ public abstract class MessageToByteEncoder<I> extends ChannelHandlerAdapter {
             if (acceptOutboundMessage(msg)) {
                 @SuppressWarnings("unchecked")
                 I cast = (I) msg;
-                if (preferDirect) {
-                    buf = ctx.alloc().ioBuffer();
-                } else {
-                    buf = ctx.alloc().heapBuffer();
-                }
+                buf = allocateBuffer(ctx, cast, preferDirect);
                 try {
                     encode(ctx, cast, buf);
                 } finally {
@@ -134,6 +130,19 @@ public abstract class MessageToByteEncoder<I> extends ChannelHandlerAdapter {
         }
     }
 
+    /**
+     * Allocate a {@link ByteBuf} which will be used as argument of {@link #encode(ChannelHandlerContext, I, ByteBuf)}.
+     * Sub-classes may override this method to returna {@link ByteBuf} with a perfect matching {@code initialCapacity}.
+     */
+    protected ByteBuf allocateBuffer(ChannelHandlerContext ctx, @SuppressWarnings("unused") I msg,
+                               boolean preferDirect) throws Exception {
+        if (preferDirect) {
+            return ctx.alloc().ioBuffer();
+        } else {
+            return ctx.alloc().heapBuffer();
+        }
+    }
+
     /**
      * Encode a message into a {@link ByteBuf}. This method will be called for each written message that can be handled
      * by this encoder.