/*
* Copyright 2012 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 com.facebook.presto.jdbc.internal.netty.handler.codec.protobuf;
import static com.facebook.presto.jdbc.internal.netty.buffer.ChannelBuffers.*;
import com.facebook.presto.jdbc.internal.netty.buffer.ChannelBuffer;
import com.facebook.presto.jdbc.internal.netty.buffer.ChannelBufferOutputStream;
import com.facebook.presto.jdbc.internal.netty.channel.Channel;
import com.facebook.presto.jdbc.internal.netty.channel.ChannelHandler.Sharable;
import com.facebook.presto.jdbc.internal.netty.channel.ChannelHandlerContext;
import com.facebook.presto.jdbc.internal.netty.handler.codec.oneone.OneToOneEncoder;
import com.google.protobuf.CodedOutputStream;
/**
* An encoder that prepends the the Google Protocol Buffers
* <a href="http://code.google.com/apis/protocolbuffers/docs/encoding.html#varints">Base
* 128 Varints</a> integer length field. For example:
* <pre>
* BEFORE DECODE (300 bytes) AFTER DECODE (302 bytes)
* +---------------+ +--------+---------------+
* | Protobuf Data |-------------->| Length | Protobuf Data |
* | (300 bytes) | | 0xAC02 | (300 bytes) |
* +---------------+ +--------+---------------+
* </pre> *
*
* @see CodedOutputStream
*/
@Sharable
public class ProtobufVarint32LengthFieldPrepender extends OneToOneEncoder {
@Override
protected Object encode(ChannelHandlerContext ctx, Channel channel,
Object msg) throws Exception {
if (!(msg instanceof ChannelBuffer)) {
return msg;
}
ChannelBuffer body = (ChannelBuffer) msg;
int length = body.readableBytes();
ChannelBuffer header =
channel.getConfig().getBufferFactory().getBuffer(
body.order(),
CodedOutputStream.computeRawVarint32Size(length));
CodedOutputStream codedOutputStream = CodedOutputStream
.newInstance(new ChannelBufferOutputStream(header));
codedOutputStream.writeRawVarint32(length);
codedOutputStream.flush();
return wrappedBuffer(header, body);
}
}