io.netty.handler.codec.xml.XmlFrameDecoder Maven / Gradle / Ivy

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/*
 * Copyright 2013 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:
 *
 *   https://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.xml;

import static io.netty.util.internal.ObjectUtil.checkPositive;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ByteToMessageDecoder;
import io.netty.handler.codec.CorruptedFrameException;
import io.netty.handler.codec.TooLongFrameException;

import java.util.List;

/**
 * A frame decoder for single separate XML based message streams.
 * 
 * A couple examples will better help illustrate
 * what this decoder actually does.
 * 

 * Given an input array of bytes split over 3 frames like this:
 * 
 * +-----+-----+-----------+
 * | <an | Xml | Element/> |
 * +-----+-----+-----------+
 * 
 * 
 * this decoder would output a single frame:
 * 

 * 
 * +-----------------+
 * | <anXmlElement/> |
 * +-----------------+
 * 
 *
 * Given an input array of bytes split over 5 frames like this:
 *  * +-----+-----+-----------+-----+----------------------------------+
 * | <an | Xml | Element/> | <ro | ot><child>content</child></root> |
 * +-----+-----+-----------+-----+----------------------------------+
 * 
 * 
 * this decoder would output two frames:
 * 

 * 
 * +-----------------+-------------------------------------+
 * | <anXmlElement/> | <root><child>content</child></root> |
 * +-----------------+-------------------------------------+
 * 
 *
 * 
 * The byte stream is expected to be in UTF-8 character encoding or ASCII. The current implementation
 * uses direct {@code byte} to {@code char} cast and then compares that {@code char} to a few low range
 * ASCII characters like {@code '<'}, {@code '>'} or {@code '/'}. UTF-8 is not using low range [0..0x7F]
 * byte values for multibyte codepoint representations therefore fully supported by this implementation.
 * 

 * Please note that this decoder is not suitable for
 * xml streaming protocols such as
 * XMPP,
 * where an initial xml element opens the stream and only
 * gets closed at the end of the session, although this class
 * could probably allow for such type of message flow with
 * minor modifications.
 */
public class XmlFrameDecoder extends ByteToMessageDecoder {

    private final int maxFrameLength;

    public XmlFrameDecoder(int maxFrameLength) {
        this.maxFrameLength = checkPositive(maxFrameLength, "maxFrameLength");
    }

    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List