JsonFrameDecoder.java

/**
 * Copyright 2010 CosmoCode GmbH
 *
 * Licensed 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 de.cosmocode.palava.ipc.json;

import javax.annotation.concurrent.NotThreadSafe;

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;

/**
 * A {@link FrameDecoder} which frames json arrays/objects.
 * 
 * @since 1.0
 * @author Willi Schoenborn
 * @author Tobias Sarnowski
 */
@NotThreadSafe
public final class JsonFrameDecoder extends FrameDecoder {

    private char open;
    
    private char close;
    
    private int counter;
    
    private int index;
    
    private boolean string;
    
    private boolean escaped;
    
    @Override
    protected Object decode(ChannelHandlerContext ctx, Channel channel, ChannelBuffer buffer) throws Exception {
        if (buffer.readable()) {
            readFirst(buffer);
            count(buffer);
            if (counter == 0) {
                final ChannelBuffer result = buffer.readBytes(index);
                // reset for next iteration
                index = 0;
                open = 0;
                close = 0;
                return result;
            }
        }
        return null;
    }
    
    private void readFirst(ChannelBuffer buffer) {
        if (open == 0 || close == 0) {
            final byte b = buffer.getByte(0);
            if (b == '[') {
                open = '[';
                close = ']';
            } else if (b == '{') {
                open = '{';
                close = '}';
            } else {
                throw new IllegalArgumentException(String.format("Unknown starting character %s", (char) b));
            }
        }
    }
    
    private void count(ChannelBuffer buffer) {
        int i = buffer.readerIndex() + index;

        while (i < buffer.writerIndex()) {
            if (string) {
                inString(buffer.getByte(i));
            } else {
                outsideOfString(buffer.getByte(i));
            }
            
            i++;

            if (counter == 0) break;
        }
        index = i - buffer.readerIndex();
    }
    
    private void inString(byte current) {
        if (current == '"' && !escaped) {
            string = false;
        } else if (current == '\\' && !escaped) {
            escaped = true;
        } else if (escaped) {
            escaped = false;
        }
    }
    
    private void outsideOfString(byte current) {
        if (current == open) {
            ++counter;
        } else if (current == close) {
            --counter;
        } else if (current == '"') {
            string = true;
        }
    }

    int getCounter() {
        return counter;
    }
    
}