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
    • Constructor Detail

      • XmlFrameDecoder

        public XmlFrameDecoder​(int maxFrameLength)
    • Method Detail

      • 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
      • isCommentBlockStart

        private static boolean isCommentBlockStart​(ByteBuf in,
                                                   int i)
      • isCDATABlockStart

        private static boolean isCDATABlockStart​(ByteBuf in,
                                                 int i)