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/*
 * 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 io.netty.handler.codec;

import io.netty.channel.ChannelDuplexHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelPromise;
import io.netty.util.ReferenceCounted;
import io.netty.util.internal.TypeParameterMatcher;

import java.util.List;

/**
 * A Codec for on-the-fly encoding/decoding of message.
 *
 * This can be thought of as a combination of {@link MessageToMessageDecoder} and {@link MessageToMessageEncoder}.
 *
 * Here is an example of a {@link MessageToMessageCodec} which just decode from {@link Integer} to {@link Long}
 * and encode from {@link Long} to {@link Integer}.
 *
 * 
 *     public class NumberCodec extends
 *             {@link MessageToMessageCodec}<{@link Integer}, {@link Long}> {
 *         {@code @Override}
 *         public {@link Long} decode({@link ChannelHandlerContext} ctx, {@link Integer} msg, List<Object> out)
 *                 throws {@link Exception} {
 *             out.add(msg.longValue());
 *         }
 *
 *         {@code @Override}
 *         public {@link Integer} encode({@link ChannelHandlerContext} ctx, {@link Long} msg, List<Object> out)
 *                 throws {@link Exception} {
 *             out.add(msg.intValue());
 *         }
 *     }
 * 
* * Be aware that you need to call {@link ReferenceCounted#retain()} on messages that are just passed through if they * are of type {@link ReferenceCounted}. This is needed as the {@link MessageToMessageCodec} will call * {@link ReferenceCounted#release()} on encoded / decoded messages. */ public abstract class MessageToMessageCodec extends ChannelDuplexHandler { private final MessageToMessageEncoder encoder = new MessageToMessageEncoder() { @Override public boolean acceptOutboundMessage(Object msg) throws Exception { return MessageToMessageCodec.this.acceptOutboundMessage(msg); } @Override @SuppressWarnings("unchecked") protected void encode(ChannelHandlerContext ctx, Object msg, List out) throws Exception { MessageToMessageCodec.this.encode(ctx, (OUTBOUND_IN) msg, out); } }; private final MessageToMessageDecoder decoder = new MessageToMessageDecoder() { @Override public boolean acceptInboundMessage(Object msg) throws Exception { return MessageToMessageCodec.this.acceptInboundMessage(msg); } @Override @SuppressWarnings("unchecked") protected void decode(ChannelHandlerContext ctx, Object msg, List out) throws Exception { MessageToMessageCodec.this.decode(ctx, (INBOUND_IN) msg, out); } }; private final TypeParameterMatcher inboundMsgMatcher; private final TypeParameterMatcher outboundMsgMatcher; /** * Create a new instance which will try to detect the types to decode and encode out of the type parameter * of the class. */ protected MessageToMessageCodec() { inboundMsgMatcher = TypeParameterMatcher.find(this, MessageToMessageCodec.class, "INBOUND_IN"); outboundMsgMatcher = TypeParameterMatcher.find(this, MessageToMessageCodec.class, "OUTBOUND_IN"); } /** * Create a new instance. * * @param inboundMessageType The type of messages to decode * @param outboundMessageType The type of messages to encode */ protected MessageToMessageCodec( Class inboundMessageType, Class outboundMessageType) { inboundMsgMatcher = TypeParameterMatcher.get(inboundMessageType); outboundMsgMatcher = TypeParameterMatcher.get(outboundMessageType); } @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { decoder.channelRead(ctx, msg); } @Override public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception { encoder.write(ctx, msg, promise); } /** * Returns {@code true} if and only if the specified message can be decoded by this codec. * * @param msg the message */ public boolean acceptInboundMessage(Object msg) throws Exception { return inboundMsgMatcher.match(msg); } /** * Returns {@code true} if and only if the specified message can be encoded by this codec. * * @param msg the message */ public boolean acceptOutboundMessage(Object msg) throws Exception { return outboundMsgMatcher.match(msg); } /** * @see MessageToMessageEncoder#encode(ChannelHandlerContext, Object, List) */ protected abstract void encode(ChannelHandlerContext ctx, OUTBOUND_IN msg, List out) throws Exception; /** * @see MessageToMessageDecoder#decode(ChannelHandlerContext, Object, List) */ protected abstract void decode(ChannelHandlerContext ctx, INBOUND_IN msg, List out) throws Exception; }