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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 out) throws Exception { boolean openingBracketFound = false; boolean atLeastOneXmlElementFound = false; boolean inCDATASection = false; long openBracketsCount = 0; int length = 0; int leadingWhiteSpaceCount = 0; final int bufferLength = in.writerIndex(); if (bufferLength > maxFrameLength) { // bufferLength exceeded maxFrameLength; dropping frame in.skipBytes(in.readableBytes()); fail(bufferLength); return; } for (int i = in.readerIndex(); i < bufferLength; i++) { final byte readByte = in.getByte(i); if (!openingBracketFound && Character.isWhitespace(readByte)) { // xml has not started and whitespace char found leadingWhiteSpaceCount++; } else if (!openingBracketFound && readByte != '<') { // garbage found before xml start fail(ctx); in.skipBytes(in.readableBytes()); return; } else if (!inCDATASection && readByte == '<') { openingBracketFound = true; if (i < bufferLength - 1) { final byte peekAheadByte = in.getByte(i + 1); if (peekAheadByte == '/') { // found we can decrement openBracketsCount if (in.getByte(peekFurtherAheadIndex) == '>') { openBracketsCount--; break; } peekFurtherAheadIndex++; } } else if (isValidStartCharForXmlElement(peekAheadByte)) { atLeastOneXmlElementFound = true; // char after < is a valid xml element start char, // incrementing openBracketsCount openBracketsCount++; } else if (peekAheadByte == '!') { if (isCommentBlockStart(in, i)) { // start found openBracketsCount++; } else if (isCDATABlockStart(in, i)) { // start found openBracketsCount++; } } } else if (!inCDATASection && readByte == '/') { if (i < bufferLength - 1 && in.getByte(i + 1) == '>') { // found />, decrementing openBracketsCount openBracketsCount--; } } else if (readByte == '>') { length = i + 1; if (i - 1 > -1) { final byte peekBehindByte = in.getByte(i - 1); if (!inCDATASection) { if (peekBehindByte == '?') { // an tag was closed openBracketsCount--; } else if (peekBehindByte == '-' && i - 2 > -1 && in.getByte(i - 2) == '-') { // a was closed openBracketsCount--; } } else if (peekBehindByte == ']' && i - 2 > -1 && in.getByte(i - 2) == ']') { // a block was closed openBracketsCount--; inCDATASection = false; } } if (atLeastOneXmlElementFound && openBracketsCount == 0) { // xml is balanced, bailing out break; } } } final int readerIndex = in.readerIndex(); int xmlElementLength = length - readerIndex; if (openBracketsCount == 0 && xmlElementLength > 0) { if (readerIndex + xmlElementLength >= bufferLength) { xmlElementLength = in.readableBytes(); } final ByteBuf frame = extractFrame(in, readerIndex + leadingWhiteSpaceCount, xmlElementLength - leadingWhiteSpaceCount); in.skipBytes(xmlElementLength); out.add(frame); } } private void fail(long frameLength) { if (frameLength > 0) { throw new TooLongFrameException( "frame length exceeds " + maxFrameLength + ": " + frameLength + " - discarded"); } else { throw new TooLongFrameException( "frame length exceeds " + maxFrameLength + " - discarding"); } } private static void fail(ChannelHandlerContext ctx) { ctx.fireExceptionCaught(new CorruptedFrameException("frame contains content before the xml starts")); } private static ByteBuf extractFrame(ByteBuf buffer, int index, int length) { return buffer.copy(index, length); } /** * Asks whether the given byte is a valid * start char for an xml element name. *

* Please refer to the * NameStartChar * formal definition in the W3C XML spec for further info. * * @param b the input char * @return true if the char is a valid start char */ private static boolean isValidStartCharForXmlElement(final byte b) { return b >= 'a' && b <= 'z' || b >= 'A' && b <= 'Z' || b == ':' || b == '_'; } private static boolean isCommentBlockStart(final ByteBuf in, final int i) { return i < in.writerIndex() - 3 && in.getByte(i + 2) == '-' && in.getByte(i + 3) == '-'; } private static boolean isCDATABlockStart(final ByteBuf in, final int i) { return i < in.writerIndex() - 8 && in.getByte(i + 2) == '[' && in.getByte(i + 3) == 'C' && in.getByte(i + 4) == 'D' && in.getByte(i + 5) == 'A' && in.getByte(i + 6) == 'T' && in.getByte(i + 7) == 'A' && in.getByte(i + 8) == '['; } }