openflow/ctl/src/main/java/org/onlab/onos/openflow/controller/impl/OFMessageDecoder.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF 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 org.onlab.onos.openflow.controller.impl;


import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.handler.codec.frame.FrameDecoder;
import org.projectfloodlight.openflow.protocol.OFFactories;
import org.projectfloodlight.openflow.protocol.OFMessage;
import org.projectfloodlight.openflow.protocol.OFMessageReader;

/**
 * Decode an openflow message from a Channel, for use in a netty pipeline.
 */
public class OFMessageDecoder extends FrameDecoder {

    @Override
    protected Object decode(ChannelHandlerContext ctx, Channel channel,
            ChannelBuffer buffer) throws Exception {
        if (!channel.isConnected()) {
            // In testing, I see decode being called AFTER decode last.
            // This check avoids that from reading corrupted frames
            return null;
        }

        // Note that a single call to decode results in reading a single
        // OFMessage from the channel buffer, which is passed on to, and processed
        // by, the controller (in OFChannelHandler).
        // This is different from earlier behavior (with the original openflowj),
        // where we parsed all the messages in the buffer, before passing on
        // a list of the parsed messages to the controller.
        // The performance *may or may not* not be as good as before.
        OFMessageReader<OFMessage> reader = OFFactories.getGenericReader();
        OFMessage message = reader.readFrom(buffer);

        return message;
    }

}