XOM API for Processing XML with Java

[Wolfgang Hoschek <wolfgang.hoschek AT mac.com>]

On Oct 20, 2006, at 12:42 PM, Steve Loughran wrote:

> On 20/10/06, Wolfgang Hoschek <wolfgang.hoschek AT mac.com> wrote:
> > XML does not specify an end-of-document marker. Instead, such framing
> > issues are left to a higher level protocol (e.g. HTTP).
> >
> > A generic XML parser has no knowledge of the higher level protocol in
> > use, thus will parse until it hits end-of-stream (EOS). For example,
> > HTTP/MIME knows where the end of a response occurs, so an InputStream
> > containing the XML payload derived from a servlet will indicate EOS
> > at the correct spot. If you're not using a protocol that has framing
> > built-in, you'll have to roll your own. Here's a simple example:
> >
> > msg := length payload
> > length := 4 byte integer (big endian)
> > payload := sequence of <length> bytes
> >
> > For are more thorough discussion of framing issues, see [1] and [2].
>
> You could also stick a version number/magic number at the start of the
> communication. If the receipient does this it piggybacks on the TCP
> ack packet and costs you nothing.
>
> Also, ASCII 0 is a forbidden character in an XML document. So you
> could write something that streams out a document and sticks a NUL at
> the end.  The reciepient relays everything to an XML parser (via a
> special Reader), until that NUL gets received, at which point an
> end-of-file should be signalled. Result: no need to determine the size
> of the message.

Might be a non-issue, but to be precise: NUL may occur for encodings  
other than ASCII and UTF-8.
In contrast, Consistent Overhead Byte Stuffing (COBS) provides  
efficient, reliable, unambigous packet framing regardless of packet  
content.

Wolfgang.