Package io.netty.handler.codec.xml

Class XmlFrameDecoder

  • All Implemented Interfaces:
    ChannelHandler, ChannelInboundHandler
    public class XmlFrameDecoder
extends ByteToMessageDecoder
    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 byte to char cast and then compares that char to a few low range ASCII characters like '<', '>' or '/'. 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.

    • Field Detail

      • maxFrameLength

        private final int maxFrameLength

      • openingBracketFound

        private boolean openingBracketFound

      • atLeastOneXmlElementFound

        private boolean atLeastOneXmlElementFound

      • inCDATASection

        private boolean inCDATASection

      • inCommentBlock

        private boolean inCommentBlock

      • inProcessingInstruction

        private boolean inProcessingInstruction

      • inClosingTag

        private boolean inClosingTag

      • openBracketsCount

        private long openBracketsCount

      • length

        private int length
        Index, relative to the current reader index, of the byte right after the last '>' seen so far. Netty's cumulation buffer may be compacted (rebasing both the reader index and the bytes) in between two decode(ChannelHandlerContext, ByteBuf, List) invocations, which would silently invalidate an absolute buffer index stored across calls; storing this relative to the reader index keeps it valid across such compactions, just like scanOffset.

      • leadingWhiteSpaceCount

        private int leadingWhiteSpaceCount

      • scanOffset

        private int scanOffset
        Index, relative to the current reader index, of the next byte that still needs to be scanned. This lets decode(ChannelHandlerContext, ByteBuf, List) resume scanning where the previous invocation left off instead of rescanning the whole accumulated buffer every time, which would otherwise make a slowly trickled, never-balanced element run in quadratic time.

      • CDATA_START_SUFFIX

        private static final byte[] CDATA_START_SUFFIX

    • Constructor Detail

      • XmlFrameDecoder

        public XmlFrameDecoder​(int maxFrameLength)

    • Method Detail

      • resetState

        private void resetState()

      • fail

        private void fail​(long frameLength)

      • extractFrame

        private static ByteBuf extractFrame​(ByteBuf buffer,
                                    int index,
                                    int length)

      • isValidStartCharForXmlElement

        private static boolean isValidStartCharForXmlElement​(byte b)
        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.

        Parameters:
        b - the input char
        Returns:
        true if the char is a valid start char

      • classifyBangMarkup

        private static XmlFrameDecoder.BangMarkupKind classifyBangMarkup​(ByteBuf in,
                                                                 int i,
                                                                 int bufferLength)
        Classifies the markup declaration starting at in.getByte(i) == '<' followed by '!', matching it incrementally against the <!-- and <![CDATA[ prefixes so a genuinely different declaration (e.g. <!DOCTYPE ...> or an unknown <!x>) is recognised as such immediately, without waiting for bytes that would only be needed to confirm a comment or CDATA start.