/*
* 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.oneone;
import static com.facebook.presto.jdbc.internal.netty.channel.Channels.*;
import com.facebook.presto.jdbc.internal.netty.channel.Channel;
import com.facebook.presto.jdbc.internal.netty.channel.ChannelEvent;
import com.facebook.presto.jdbc.internal.netty.channel.ChannelHandlerContext;
import com.facebook.presto.jdbc.internal.netty.channel.ChannelPipeline;
import com.facebook.presto.jdbc.internal.netty.channel.ChannelUpstreamHandler;
import com.facebook.presto.jdbc.internal.netty.channel.MessageEvent;
import com.facebook.presto.jdbc.internal.netty.handler.codec.frame.DelimiterBasedFrameDecoder;
import com.facebook.presto.jdbc.internal.netty.handler.codec.frame.Delimiters;
import com.facebook.presto.jdbc.internal.netty.handler.codec.frame.FrameDecoder;
/**
* Transforms a received message into another message. Please note that this
* decoder must be used with a proper {@link FrameDecoder} such as
* {@link DelimiterBasedFrameDecoder} or you must implement proper framing
* mechanism by yourself if you are using a stream-based transport such as
* TCP/IP. A typical setup for TCP/IP would be:
* <pre>
* {@link ChannelPipeline} pipeline = ...;
*
* // Decoders
* pipeline.addLast("frameDecoder", new {@link DelimiterBasedFrameDecoder}(80, {@link Delimiters#nulDelimiter()}));
* pipeline.addLast("customDecoder", new {@link OneToOneDecoder}() { ... });
*
* // Encoder
* pipeline.addLast("customEncoder", new {@link OneToOneEncoder}() { ... });
* </pre>
*
* @apiviz.landmark
*/
public abstract class OneToOneDecoder implements ChannelUpstreamHandler {
/**
* Creates a new instance with the current system character set.
*/
protected OneToOneDecoder() {
}
public void handleUpstream(
ChannelHandlerContext ctx, ChannelEvent evt) throws Exception {
if (!(evt instanceof MessageEvent)) {
ctx.sendUpstream(evt);
return;
}
MessageEvent e = (MessageEvent) evt;
Object originalMessage = e.getMessage();
Object decodedMessage = decode(ctx, e.getChannel(), originalMessage);
if (originalMessage == decodedMessage) {
ctx.sendUpstream(evt);
} else if (decodedMessage != null) {
fireMessageReceived(ctx, decodedMessage, e.getRemoteAddress());
}
}
/**
* Transforms the specified received message into another message and return
* the transformed message. Return {@code null} if the received message
* is supposed to be discarded.
*/
protected abstract Object decode(
ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception;
}