JSONDecoder.java

/*
 * Copyright (c) 2013 Big Switch Networks, Inc.
 *
 * Licensed under the Eclipse Public License, Version 1.0 (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.eclipse.org/legal/epl-v10.html
 *
 * 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.sdnplatform.ovsdb.internal;

import java.io.ByteArrayOutputStream;
import java.io.EOFException;

import org.codehaus.jackson.JsonNode;
import org.codehaus.jackson.JsonParser;
import org.codehaus.jackson.JsonProcessingException;
import org.codehaus.jackson.map.MappingJsonFactory;
import org.codehaus.jackson.map.ObjectMapper;
import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.buffer.ChannelBufferInputStream;
import org.jboss.netty.buffer.ChannelBuffers;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.handler.codec.frame.FrameDecoder;

/**
 * FrameDecoder for using Jackson to read JSON-RPC as used by
 * the OVS DB.
 * @author readams
 *
 */
public class JSONDecoder extends FrameDecoder {
    // remainderBytes is used to save any bytes left over from
    // the previous frame, since Jackson will aggressively read
    // ahead in the buffer
    byte[] remainderBytes = null;
    ObjectMapper mapper = new ObjectMapper();
    MappingJsonFactory mjf = new MappingJsonFactory(mapper);
    int ctr = -1;
    
    @Override
    protected Object decode(ChannelHandlerContext chc, Channel channel,
                            ChannelBuffer cb) throws Exception {
        ctr++;
        cb.markReaderIndex();
        ChannelBuffer compositeBuffer = cb;
        if (remainderBytes != null) {

            ChannelBuffer remainderBuffer =
                    ChannelBuffers.wrappedBuffer(remainderBytes);
            compositeBuffer = 
                    ChannelBuffers.wrappedBuffer(remainderBuffer, cb);

            remainderBytes = null;
        }
        
        ChannelBufferInputStream cbis =
                new ChannelBufferInputStream(compositeBuffer);
        JsonParser jp = mjf.createJsonParser(cbis);
        JsonNode node = null;
        try {
            node = jp.readValueAsTree();
        } catch (EOFException e) {

            return null;
        } catch (JsonProcessingException e) {
            // This is pretty inefficient but seems to be the only way
            // to deal with this.
            if (e.getMessage().contains("end-of-input")) {
                cb.resetReaderIndex();

                return null;
            } else {
                throw e;
            }
        }
        
        ByteArrayOutputStream os = new ByteArrayOutputStream();
        jp.releaseBuffered(os);
        if (os.size() > 0) {
            remainderBytes = os.toByteArray();
        } 
        return node;
    }

}